■■■

D 71683

-date electronics for lab and leisure

104

December 1983
85 p.

IR 130p. ( incl.VAT)

$2.75

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selektor 12-20

64-way 2-dimensional bus board 12-22

A new, perfectly symmetrical, extension bus with no less than 7 connec-
tors for those who feel that their present bus is becoming inadequate.

MF/HF USB marine receiver 12-24

Simple and inexpensive to build, this receiver is intended for the many
thousands who are interested in what's going on in the 1600 . . . 4000
kHz marine band.

LED ornaments 12-30

Some decorative, colourful, electronic 'ornaments' suitable for hanging
on the Christmas tree or as a unique Christmas gift.

symmetrical power supply 12-32

Many electronic applications require a symmetrical power supply: this
one provides two precise identical voltages of 0 to ± 18 V with adjust-
able current-limiting.

video amplifier . . 12-36

Suitable for use anywhere in a video chain, this amplifier provides three
identical outputs. Input and output impedances are, of course, 75 ohms.

missing link 12-39

PC board pages 12-40

cumulative index 1983 12-41

locomotive headlamp reverser 12-44

The high frequency generator for lighting model railway coaches (Elektor
— November 1982) can also be used for changing over locomotive head-
lamps according to the direction of travel.

frost warning device 12-47

With winter approaching fast, this circuit should prove useful for anyone
who has to know if and when the outside temperature is getting near
freezing point.

Our graphical department
seem to have got into the
'Christmas spirit' cabinet a
bit early this year, but at least
they managed to get the pic-
ture of our video distribution
amplifier straight. This is also
in keeping with the seasonal
cheer that is likely to be
abundant at this time as it
can have you seeing not
double but treble. And what
about a two-dimensional bus
board, or a Siamese power
supply! As you may gather
from this, it is not only the
graphical department who
have been at the 'Christmas
spirit' a bit early!

disco phaser 12-50

Studio quality phasers can be very complex and therefore very expensive,
but simpler methods do exist as this circuit proves.

banking program 12-56

A useful and instructive program for DOS Junior Computer owners:
it helps you control your finances and is also a good introduction to
indirect files.

NOVRAM: data storage without batteries 12-58

A very interesting new memory 1C will shortly become available in
Britain: the NOVRAM (NOn-Volatile RAM). It combines the access-
ibility of a RAM with the power-down storage of an EPROM.

bus extension 12-62

An extension which can be used with any personal computer provided
this has a buffered output bus.

market . . .
switchboard

12-64 A selection from

next month's issue:
12-69 • universal active filter

• digital cassette recording

12-80 • how accurate is your

watch?

12-82 • wind direction indicator

• address decoding

• fault finding in audio
equipment

• EPROM programmer

12-03

elektor december 1983

HOME LIGHTING KITS

Thase kill contain a" ngtnM' y compornnl! and K>'
instruction* A aft designed lo replete a Mandard we*
Mitdi and control up to 300w o' lighting

TDA300K Remote Control £14.30
WK8 T . » .»* :r.r (O' Ibov. £ 4.20/^

ov. £ 4 20/

TD300K Touchdimmer £7.00 L

TS300K Touch»w.tcH £7.00

T0€’X Extension kit lo< 2-way _ _ A
switching for TD300K 12.90

ELECTRONIC LOCK KIT XK101

This KIT contains a purpose designed lock 1C,
10-way keyboard, PCBs and all components
to construct a Digital Lock, requiring a 4-key
sequence to open and providing over 5000
different combinations. The open sequence
may be easily changed by means of a pre-
wired plug. Size: 7x6x3 cms. Supply: 5V to
15 V d.c. at 40uA. Ouput: 750mA max
Hundreds of uses for doors and garages, car
anti-theft device, electronic equipment, etc
Will drive most relays direct. Full instructions
supplied. ONLY £10.50

Electric lock machaniam for use with latch
locks and above kit £1 3 5 Q

"OPEN-SESAME"

The XK 103 >s a gene'ai ou'oote infra red transmitter
•eceiver with one momentary (normally ooeni relay
contact and two latched transistor outputs
Designed primarily for controlling motorised ga'age
doors and two auxilary outputs *or drive garage
lights at a r*nge of up to 40 tt The unit a'so has
numerous applications n the home fo' switching
lights. Tv ciosmg curtams. etc ideal fo» aged 0'
disabled persons

The Kn comprises a mams powered receiver a tour
button transmitter complete with pre d'-ned bo*
requiring a 9v battery and one opto isolated so id
state switch k<t for inter facing the receive' to mams
appliances As with an ou' kits fuH instructions a>e

DISCO LIGHTING KITS

DL IOOOK

This va*ue for money » 1 ‘aa
tures a b« direction* ee
quence. speed of seq^e*;*
and frequency of direc? o'

Change, being veneb'e b» : • -

t-ometers and inco'DO's-es s -»> 1
dimming control £ T 4

0LZ1000K

A lower cost version Of the aoc-e w. ;
undirectional channel seo-e-'ie - — «•*:
variable by means of a P's ee* ;c- :... 1
sw.tchedoniyatmamsie'c c-see*-* >1 — s
to reduce radio interference te • —

Optional opto input OlA!
Allowing audio I beat jr-
response
PL3000K

This 3 channel sound to ©~ «
zero voltage switching
control and built m mic No com
speaker or amp required No knot
simply connect to mams l
lamps ( IK w channel IfN « i

Only £1195

BEGINNERS
STARTER PACKS

Containing selection of electronic components including transistors. LEDs, diodes,
capacitors. ICs etc together with a descriptive booklet with 10 easy to-buikj projects plus
a solderless circuit board enabling the components to be re-used Requires 9V battery
Discreet component pack Ino ICs) €5.00 Integrated circuit pack £ 6 . 00

STOCKING FILLERS All full spec, branded devices.

PACK (1) 650 Resistors 47 ohm to lOMohm - 10 per value £4.00

PACK (2) 40 x 16V Electrolytic Capacitors 10pF to lOOOpF - 5 per value £3.25

PACK (3) 60 Polyester Capacitors 0.01 to 1pF/250V - 5 per value £5.55

PACK (4) 45 Sub-miniature Presets 100 ohm to 1 Mohm - 5 per value £2.90

PACK (5) 30 Low Profile 1C Sockets 8, 14. and 16 pin — 10 of each £2.40

PACK (6) 25 Red LEDs (5mm dia.) £1.25

NoSofSi- COMPUTER rl
SHOWROOM

Hours Mon-Fri 10am 6pm Sat 10am <

ONLY £23.75

Have you got our

FREE GREEN CATALOGUE v e»1

NO >l Se.»ilS A E 6 9 TODAY"

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of SEMICONDUCTORS mcluiSmq CMOS IS TTl
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Answering service evngs &wnds

MICROPROCESSOR CONTROLLED
MULTI-PURPOSE TIMER

Now you can run your central heat-ng, lighting, hi-fi system and lots
more with just one programmable timer At your selection it is
designed lo control four mams outputs independently, switching on
and off at pre set times over a 7 day cycle, e g to control your central
heating (including different switching times for weekends I. |usl
connect it to your system programme end set it and forget it —the
clock will do the rest a •

FEATURES INCLUDE •/*?>■[

HOME CONTROL CENTRE

Th.s kit enables you to control uo to ’€ : "e-r
appliances anywhere »n the house '-on u
comfort of you' armchair The !■»**“ ■!
miects coded ouises mt© the ma 's «** t- a
decoded by 'active' modules connec*ec •;
seme mams SuPO'v and used to s* •:*
appliance addressed ’he fens— » i
mciudesaCOMPuTER interface so vb. :e" :
gramme you' favounte m.cro leg Z*6‘
switch lights heatmg electric bia«»e - -*>
your mommg coffee, etc auto-e* ;a
Without rewirmg you' house JUST THINK C
THE POSSIBILITIES The k-t mciudes a 9 Cf
and components *or one transmiiter a'd tv
receivers o'us a pre drilled bo* »o- tt
transmitter

Order as XK112. £42.00

. Additional Receivers XK111 £10 00

REMOTE CONTROL KITS

FOP A DETAILED BOOKLET ON REMOTE CONTROL
send 30p - « • 9 S A E

MK6 SIMPLE INFRA RED TRANSMITTER

Supplied wiin nend ne-d plastic bo* Reaves 9v
iFH»3)bette-, £4 20

MK7 INFRA RED RECEIVER

Main* powered w th r- sc Output to switch up to
500W at 2*0v sc “s'g# appro* 20 ft on otf o'
momentary contre £9 00

iRC 500K - spec a o- ee *0' MK6MK7

MK9 4 WAY KEYBOARD C 12 SOI

We also stock peripherals and
accessories disc drives, printers,
joy sticks etc together with a
wide range of books and the latest I
software for all the above
computers including ZX81
SEND S A E FOR LIST TODAY!

Outputs (O' switching
MK18 cased on tn« Sl490
components to mass a coded
PR3baneiy endkevbos'd it*

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MK13 ’’ wav kevbos'3 *o- .»

ALL PRICES EXCLUDE VAT

Now only £ 39.00

(Kit includes all components PCS.
box assembly and programming
instructions)

Order as CT6000

24 HOUR CLOCK/
APPLIANCE TIMER KIT

Switches any appliance up to ikW on end off at
preset limes once per day K<t contains
Av 5 1230 lC 0 5" LED display mams Supply
display dnva's switches LEDs macs PCBs

and lull matroctrons

CTIOOOKBeeicK.1 €14 90

56 131 ■ 7lmml C17 40 V
Ready Bu.m €22 50

DVM/ULTRA SENSITIVE
THERMOMETER KIT

This new design is based on ■ .

the ICL7126 la lower power
version of the ICL7106 ehtpi l-r qua]

and a 3’^ digit liquid cry*!* 1 * *

dispay This kit will form the
basis of a digital multimeter
(only a few additional resistors and switches
are required — details supplied I, or a sensitive
digital thermometer 1-50*0 to *t50*C)
reeding to 0.1*C The basic kit has a
sensitivity of 200mV for a full scale reeding,
automatic polarity indication and an ultra
low power requirement— giving a 2 year
typical binary Ma from a standard 9V PP3
when used 8 hours a day. 7 days a weak

Price £15.50

Add 65p postage & packing * 15% VAT to
total Overseas Customers.

Add £2 50 (Europe). £6 00 (elsewhere! for

D&P

Send S A E for further STOCK DETAILS
Goods by return subject to availability

/vr*CM 9a m to 5pm (Mon to Fri)
vJr tIM 10am to 4pm (Sat)

ELECTRONICS

11-13 Boston Road
London W7 3SJ

TEL 01 567 8910 ORDERS

01 579 9794 ENQUIRIES
01-579 2842 TECHNICAL after jpm ,

12-10

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elektor december 1983

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THE NEW MARSHALL'S 1984 CATALOGUE is now available - one of

the biggest and best catalogues ever produced by MARSHALL'S.

56 pages crammed from cover to cover with components, accessories
and testgear.

New products include I.D.C. Plugs & Sockets, 'D' Plugs & Sockets, DIL
Headers, Ribbon Cable, Kits, Toroidal Transformers, I.C.'s, Capacitors,
Test Probes, and lots more — something for everyone.

TRADE, EXPORT, RETAIL AND MAIL ORDER SUPPLIED.

75p to callers, £1.00 post paid — Europe, £1.50 rest of the world.

Junior-

Paperware

(in 2 vols.)

The floppy disk is probably the most significant
mass storage medium for microcomputers. It seems
incredible that so much data can be stored on a
simple plastic disk at such speed and with such
precision.

Unfortunately, it is not enough to just connect a
floppy disk drive to a microcomputer. Without
software the hardware is useless! Where can you
get all the necessary source listings, hex-dumps,
and EPROM modifications? In the Elektor Junior
paperware, of course!

Junior paperware 1 contains the modifications of
the PM/PME EPROM and the source listings and
hex-dump of the software cruncher and puncher;
Junior paperware 2 gives the source listing of the
bootstrap loader for Ohio Scientific Floppys and
the hex-dump of the EPROM.

Elektor
Publishers Ltd
Canterbury

Price £ 2.00 + 50p postage &
packing per volume (outside U.K.
£ 1 . 00 ).

To order, please use the prepaid
order card at the end of this issue.

The K5000 Metal Detector Kit combines the challenge of Dl Y
electronics assembly with the reward and excitement of
discovering Britain's buried past.

As a Metal Detector-the K5000 boasts the proven
pedigree of C-Scope, Europe's leading detector manufacturer.

As a Kit— simplified assembly techniques require little technical
knowledge, and no complex electronic test equipment. All stages
of assembly are covered in a finely-detailed 36 page manual.
Detector Features Analytical Discrimination AGround Exclusion
Ask at your local Hobby/ Electronics shop or use the coupon and
send with your remittance to:-

C-Scope International Ltd., PO Box 36, Ashford, Kent TN23 2LN

Please send me K5000 Kits @ £1 19.99(+£3.00 p+p) each.

(M

A. Marshall (London) Ltd.
Electronic Component Distributors
85 WEST REGENT STREET
GLASGOW G2 2AW
TELEPHONE: 041 332 4133

MARSHALL (LONDON) LTD

1984 CATALOGUE
NOW OUT!

12-11

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elektor december 1983

The NUMBER 1 cataloguefortheelectronics,
computing, communications, audio and
video engineering enthusiasts

GET YOURS NOW!!

ambit

INTERNATIONAL

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Brentwood, Essex CM144SG

12-13

Telephone: (0277) 230909 Telex: 9951 94 Ambit G
200, North Service Road, Brentwood, Essex CM14

Use the voucher alongside and deduct £ 1 from a prepaid
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★ Alternatively — use it to obtain a FREE COPY
of the Ambit Catalogue (minus the discount vouchers
supplied to purchasers paying the RRPof 80p)

elektor december 1983

Universal logic:

more potential in the chip

Inputs

All possible output functions f (xj, Xj )

x i x i

fo

ft

f 2

fa

<4

fs

ft

fl

fs

f 9

f 10

fll

M2

f 13 f 14 f 15

0 0

0

0

0

0

0

0

0

0

1

1

1

1

1

1 1 1

0 1

0

0

0

0

1

1

1

1

0

0

0

0

1

1 1 1

1 0

0

0

1

1

0

0

1

1

0

0

1

1

0

0 1 1

1 1

0

1

0

1

0

1

0

1

0

1

0

1

0

1 0 1

Functions which can be obtained from various gates with two inputs. For three input
variables there are 256 possible output functions.

Most silicon chips are cheap because
they embody conventional circuits
of the sort generally needed in
electronic equipment and are mass-
produced. Many others are needed
for special applications, but making
small batches of chips designed to
do specific, less common-place jobs
is complicated and expensive. A new
approach to this problem, based on
what is called universal logic, is a
design for a chip with the potential
of virtually any kind of computer-
logic circuit and which can be used
as a 'universal' building block in
electronic systems.

A new and highly original line of
development in microelectronics was
pioneered by Dr Stanley Hurst, a
senior lecturer in the school of
electrical engineering at the University
of Bath, in the West of England some
time ago.

Microprocessors, computer control
processors on tiny slivers of silicon,
are cheap and plentiful; but they are
so only because of immense sales.
The range available from the world's
manufacturers is relatively inflexible,
which means that users have to sur-
round the microprocessor with other
integrated-circuit devices to get the
operation they require. So there is
already a market, one which will
increase in the mid 1980s and
onwards, where makers of equipment
need specific digital microelectronics
devices designed to their individual
needs. The difficulty here is that the
cost of designing a silicon-chip device
is enormous, involving many highly-
skilled scientists and engineers over a
very long time, even with computer-
aided design, and needing very
complex and expensive equipment.
This huge cost is quickly recovered
when there are large, world-wide
sales; but such a project cannot be
considered by an equipment manu-
facturer who needs but one or at
most a few types of special digital
devices designed for his particular
application.

Dr Hurst is not the only one to see
this. Indeed, one British firm has
already won a Queen's Award for
technology for what it calls its
uncommitted logic array, based on
blocks of conventional circuits
already incorporated in each chip
but not connected to each other
until the customer's needs are
known.

Dr Hurst's approach is quite different.
Though, as he says, there has been
and will continue to be tremendous
development in design and manu-

facturing techniques, there has not
been much 'evolution or revolution
at the fundamental level'. If there
were a general-purpose basic design,
needing only the final masking
procedure for arranging the inter-
connecting links to make a device
to suit a specific purpose, the small-
quantity market could be satisfied
economically. So he has researched
what the calls his Universal Logic.

In this context, logic is the appli-
cation of Boolean algebra to a digital
process using binary arithmetic.
Boole was an English logician and
mathematician who wrote a paper on
the mathematical analysis of deduct-
ive reasoning in 1847, a paper re-
discovered in 1938 and applied first
to relays and switches. It was seized
on in the mid-1940s for electronic
computing. A computer and any
similar digital device is an immense
multiplicity of electronic switches,
known as 'gates', which pass on
binary information (that is, a 0 for
'off' and a 1 for 'on') from one or
more input signals.

Lacking Power

From the evidence of digital com-
puting it must be agreed that standard
gates have been very successful, but
analytically they do not satisfy
Dr Hurst. In his words, they lack
logical power. It is easy to see that
there is an ambiguity in each gate.
With an AND gate, for example,
accepting inputs A and B, we can say
that when one input is in the off
state and the other in the on state
the output is 0, but it does not
indicate which one of A and B is
off or on. With three input things
are even more ambiguous. To put
it another way, the output of NOR
gate is unity only when all inputs
are 0, and of a NAND gate only
when all inputs are 1 .

The practical outcome of this lack
of logical power is that quite a
number of gates have to be com-
bined to give a specified result. For
example, in one simple device adding
numbers there are 16 gates. A

straightforward decoder (which trans-
lates from binary to ordinary decimal
numbers, among other tasks) needs
50 gates to do its basic job. A circuit
to compare one number with another
has 33 gates. (These figures are taken
from a random look at some pub-
lished circuits.) In a microprocessor
there may be at least 3000 gates.

The inefficient way orthodox gates
operate Boolean logic has set more
than one microelectronics engineer
or scientist thinking of possible
better circuits. But large manu-
facturers have had such enormous
success in getting thousands of
gates on a silicon chip, making it
a cheap device, that they are in-
terested only in competitive techno-
logical improvements in getting more
and more on less and less. There is
no reason why they should be
interested in fundamental changes
in logic. In the market for small-
quantity, custom-built chips things
are different.

Mathematical

The approach of Dr Hurst and his
colleagues is fundamental yet uncon-
ventional. In trying to find out
whether one could get a basic circuit
that would do whatever logical step
was needed, according to the connec-
tions and the programming, their
thinking was primarily mathematical:
it made use of esoteric techniques
such as set theory, Walsh functions
and so on. They were able to show
that a universal logic gate was indeed
a possibility. With two input variables
there are 16 possible output func-
tions (see table 1, which is an exer-
cise to see what functions could be
obtained from various gates). For
three input variables there are 256
possible output functions. Could a
single circuit cope?

Calling the circuits ULG2 (universal-
logic gate for two input variables)
and ULG3, Dr Hurst has shown that
an array of ULG2 gates will do all
the logical steps possible even for
three input variables and that one
ULG3 will be capable of realising all

12-20

elektor december 1 983

1

■J- v«

SR3

f(xi, x,)

869 S

Figure 1. Basic circuit of a ULG2, com-
prising two transistors, two diodes and
three resistors. Although only two input
variables are applied, three input connec-
tions Is, t and rl are provided. This is to do
with the set-theory mathematics of the
device.

256 outputs — not all at once, of
course, for the result depends on
which input terminals are used and
how the circuit internal wiring is
connected.

The number of ULG2 cells needed
to realise all the 256 functions of
three input variables has been calcu-
lated and compared with the equiv-
alent figure for orthodox gates. The
results are shown in table 2.

We can see that the ULG2 is roughly
twice as powerful as a NANO or a
NOR. Incidentally, it should be
noted that although a ULG2 may
have only two independent variables
as input, there may be three or four
physical connections. Figure 1 shows
a circuit for a ULG2. It has two
transistors, two diodes, and three
resistors. Though there are but two
input variables, there are three input
connections. This is to do with the
set-theory mathematics of the device
and need not concern us.

The circuit shown brings in elec-
tronics, which has so far not been
discussed and need not be considered
in detail. A gate is made of transis-
tors, diodes, resistors and, some-
times, capacitors. Up to now most
logic gates have depended on bipolar
technology, that is, transistors with
two possible states. This is the one
represented in the diagram. A newer

technique is based on MOS (metal-
oxide-semiconductor) devices, which
involve far fewer stages in manufac-
ture and avoid the 'cross-talk' be-
tween adjacent conductors. Dr Hurst
considers that bipolar methods will
die out in the next decade and be
replaced by MOS circuitry.

The practical problem is concerned
with how big an area of silicon is
used up in a U LG as compared with
orthodox gates. It is easily seen that
a ULG3 would occupy much more
space. So is it better to use an array
of identical ULG2s or rely on a
ULG3? When such matters are de-
cided there will be available a set of
universal-logic gates which can be
supplied as units. All that the de-
signer then has to do is produce a
suitable mask, a task made simple by
computer-aided design, which will
deposit the appropriate interconnec-
tions on the chip. The cost of design
for a custom-made device will there-
fore be drastically reduced, even if
the ULGs are themselves more ex-
pensive than orthodox gates —
another question being researched.
Furthermore, as Dr Hurst has said, a
considerable amount of special logic
design in ULG form can be under-
taken and a library of standard inter-
connection details built up, ready for
individual customer requirements.

It is a long-term research develop-
ment programme for which full-
time staff will be recruited. It could
lead to a commanding position in the
ever-growing use of silicon chips for
specific purposes.

C.L. Boltz SPECTRUM 171

Taking the heat out of
electronics

Air cooling was traditionally used to
cool electronic units but as com-
ponent densities are continually in-
creased in new designs of equipment
so the problem of cooling has grown
to the point where liquid cooling is
having to be adopted. This is because

Table 2.

ULG2

1 NAND

NOR

Total number of cells or gates to realise all 256 functions

683

!

1118

1124

Average number per function

2.67

4.36

4.39

Maximum number per function

4

7

7

Average number of cell /gate connections per function 1

i 10.68

17.44

17.56

Comparison between the capabilities of ULG2 cells and that of orthodox gates. The
table shows that the ULG2 is roughly twice as powerful as a NAND or a NOR gate.

of its ability to offer higher heat
removal rates.

However, liquid cooling has brought |
its own constraints because its pipe-
work, pumps and fluids make it
much more difficult for service
engineers to get to the electronic
components.

Now the dynamics group of British
Aerospace claims to have solved the
problems with what it describes as
a 'new concept' in liquid cooling sys-
tems. Known as Flexiwall, the BAe
system is subject to a provisional
patent application and, at an inter-
national design engineering exhibition
recently held at Birmingham in the
English Midlands, has been chosen as
a good example of British inno-
vation.

A BAe spokesman said: 'The major
benefit of Flexiwall is that un-
interrupted access can be obtained
to electronic units for servicing or
replacement without the need to
drain or disconnect the cooling sys-
tem, which is entirely separate and
self-contained. Other attributes are
that it is a low-pressure system,
silent in operation, and is inexpensive
to manufacture and install. In terms
of volume occupied by a Flexiwall
system, it is significantly more
effective in removing a given quan-
tity of heat than air cooling systems
of comparable capacity.

Tests with a prototype system have
shown that an electronic unit con-
taining a large number of com-
ponents tightly packed together and
dissipating four kilowatts of heat can
be maintained at component tem-
peratures below 70 degrees C.

This is achieved by circulating a
cooling fluid such as water glycol
through a convoluted chamber which
expands like a bellows to allow a
flexible face to move forward until
it touches the electronics equipment.

It will then mould itself to the shape
of the component and the cooling
fluid rapidly removes heat being
conducted from inside the elec-
tronics unit. When the pressure on
the cooling fluid is switched off the
F lexiwall face retracts elastically clear
of the equipment being cooled.

This ability to retract when not
being used to cool the unit means
that components can be freely re-
moved from their racks for servicing
or replacement. When maintenance
work is completed the Flexiwall
system is simply switched on and
the stainless steel foil face of the
cooling chamber advances to regain
contact.

Made in Britain/John. F. Webb

(895 S)

12-21

64-way bus board
elektor december 1983

The first time a microprocessor bus system is used it seems enormous, but
before long it begins to seem a bit limited, and then cramped, and finally
completely inadequate. So after our first bus with 3 connectors, and the
second with 5, we now introduce the new extension bus with no less than 7
connectors, which, unlike its predecessors, is perfectly symmetrical.

64 -way bus board

and service aid in jjP systems

a new two-
dimensional
extension
bus with
7 + 2 con-
nectors

Parts list

The new Elektor universal bus differs from
its predecessors in that it has seven 64- way
female connectors, plus a male connector
at one end (the ‘input’) and a female con-
nector at the other end (the ‘output’). In
addition to this, its upper side (connector
side) is copper-clad and acts as a screen.
The layout of the board also allows easy
interconnection between lines.

An extension for testing

As can be seen from figure 2, the bus board
is in eurocard format. This is neither luck
nor simply the consequence of the number
of connectors used. It was, in fact, a delib-
erate choice to allow us to use the new
board as a service aid. Imagine a micro
computer constructed of eurocard-format
boards mounted on a bus board that is
hidden somewhere at the back of a 19
inch rack. What happens if one of these
cards has to be tested and repaired? With-
out removing everything from the case the
cards are inaccessible.

This is where the new bus comes in. The

extension board can be plugged in in place
of the suspect one which is, in turn, plugged
into the female connector on the bus board.
This leaves the board to be tested com-
pletely outside the case of the computer
and thus perfectly accessible. Obviously
this makes childs play of something that
would otherwise be quite difficult. This
method of using the extension bus to
counter the problems of testing in tight
spaces can also serve as an aid for checking
signals on the bus itself, with an oscilloscope
or logic analyer for example.

576 pins to solder

As we have already said there are 64 lines
and there is no interconnection between
any pin in an ‘a’ row and a neighbouring
‘c’ pin. At least, that is the idea. Careless
soldering could inadvertently change this.
Bear in mind that the vertical (1 ... 7)
connectors are polarized and therefore must
be mounted the right way round. Connector
0 (the input) is a male right angle connector
(note that the ‘a’ and ‘c’ rows are inter-

Seven 64-way straight
female connectors
(a + c rows). DIN 41612
One 64-way right-angled
male connector (a + c
rows). DIN 4161 2
One 64-way right-angled
female connector (a + b
or a + c rows) DIN 4161 2
Two metal brackets (for
mounting connector
no. 8)

Mounting hardware and
ideally guide rails

1

Figure 1. This is how the
connectors are mounted.
Particular care must be
taken with the two outside
connectors.

12-22

2

64 -way bus board
elektor december 1983

««««««««

® ® ® ® ^ _1

changed).

As there are two types of angled female
connectors available, one with 2.5 mm
between the rows and the other with 5 mm,
we have made the printed circuit board
compatible with both ‘a + b’ and ‘a + c’
types.

Remember to connect the earth plane on
the upper side of the board to the ‘0 V’
pins of connectors 0 and 8! N

This bus can easily be used for the Junior
Computer, but in this case connector no. 8
should be omitted. In its place, the output
connector of the interface card should be
connected by means of crossed wires, so •
that the 'a' row of the interface card is
linked to the 'c' row of the bus, and vice
versa.

Figure 2. The copper-clad
side of the board acts as
an earth plane. Connectors
0 and 8 mount parallel
to the board whereas all
the remaining (polarised)
connectors mount verti-
cally. If cards are to be
fitted and removed fre-
quently the female con-
connectors should be
provided with guide rails.

12-23

MF/HF USB marine
receiver

elektor december 1 983

For some time now, a number of our readers, fervent DXers, have been asking
for a follow-up to our short-wave SSB receiver (June 1982). DX literally
means 'distance X' or 'distance unknown' and DXers are therefore hobbyists
interested in long-distance radio communication (transmission and/or
reception). Apart from these enthusiasts there are thousands of other people
interested in listening to what goes on at sea and it was with them in mind
that we thought it would be a good idea to design an inexpensive receiver
for operation in the 1600 . . . 4000 kHz band.

MF/HF USB
marine receiver

Radio traffic in the 1600 . . . 4000 kHz
band comprises CW (ICW and MCW, often
just called ‘morse’), RTTY (radio teletype),
radio facsimile, and plain telephony. For
most DXers, morse and telephony are, of
course, the most interesting and it is these
that the receiver described in this article
is designed to process.

In principle, most of the 1600 . . . 4000 kHz
band is intended for medium range marine
communications: longer distances are served
by maritime bands on higher frequencies.

A substantial part of the traffic in this band
is concerned with

■ weather reports

■ warnings to shipping

■ storm and gale warnings

■ traffic lists

These are all services supplied free to
shipping by the various national administra-
tions and which can therefore be listened to
by anyone. It is as well to point out now

that it is NOT allowed to listen in to private
telephone conversations and like traffic:
if you do by accident, NEVER repeat it
to third parties.

The services mentioned above are invariably
preceded by an announcement on 2182 kHz,
the international distress and call frequency
in this band. This is therefore the frequency
to which DXers tune in. Although not so
pleasant for those at sea, the worse the
weather, the more lively things become for
the DXer. The number of weather reports
and warnings to shipping is approximately
directly proportional to the wind force!
However, even when the weather at sea is
good, there is much of interest going on . . .
Traffic lists are lists of names of ships for
which a particular coast station has messages.
Such lists are transmitted regularly through-
out the day, always preceded by an announce-
ment on 2182 kHz. The announcement
includes the information at which fre-

12-24

1

MF/HF USB marine
receiver

elektor december 1983

Figure 1. Coast stations
which can be received
in Europe. Frequencies
cannot be given, but
these can be ascertained
by listening diligently
on the international distress
and call frequency of
2182 kHz.

quency the coast station is about to transmit
the lists. If a ship finds that its name is in-
cluded on the list, it will call the coast
station - again on 2182 kHz - to arrange
the frequencies on which the messages will
be transmitted and received.

A simple chart of the most important
European coast stations is shown in figure 1.
It should be possible to receive most of these
stations when conditions are good. Unfor-
tunately, frequencies in the 1600 . . . 4000
kHz band are affected by the so-called D-
layer which, in contrast to other layers
such as the E and F, absorbs rather than
reflects them. As long-distance radio com-
munication depends heavily on reflected
waves, it is therefore badly curtailed in the
presence of the D-layer. However, after
sunset this layer disappears and reception
over much longer distances than during
daytime becomes possible. The evening
hours are therefore best for DXing in this

particular band.

So much for a short introduction to the
why, where, and how? Now for the actual
receiver . . .

Direct conversion

As we wanted the receiver to give good
performance and yet be relatively simple
and inexpensive to build, we opted for a
direct-conversion design. For those who
have forgotten (or never read) our June
1982 articles ‘the principles behind an
SSB receiver’ and 'compact short-wave
SSB receiver’, here is a short resume.
The basic principle of a direct-conver-
sion receiver is that the radio signal is
converted into an audio signal without
the use of intermediate frequencies.
The layout of such a receiver is strongly
reminiscent of that of a superheterodyne
but the oscillator frequency is equal to the

12-25

MF/HF USB marine
receiver

elektor december 1983

Figure 2. The receiver
described operates on the
direct conversion principle.
Apart from the tuned-
oscillator circuit, the
mixer and oscillator are
contained in one type
S041P 1C. The input and
oscillator circuits are
ganged.

received frequency. This makes it possible
for the oscillator to operate as BFO (beat-
frequency oscillator) and thus function
as the demodulator for SSB and DSB signals.
The resulting advantages are that the circuit
is much more straight forward than that of
a superhet SSB receiver, the construction,
operation, and calibration are noticeably
simpler, and, last but not least, the cost
is lower. Of course, there are disadvantages,
such as susceptibility to a.f. image reception,
and the operational frequency range being
somewhat smaller than in superhets but as
we set out to keep the design simple and
inexpensive, these do not negate the ad-
vantages.

It should be noted that the receiver is
designed for processing the upper sideband
(USB) as this is the mode of modulation
internationally agreed to be used for maritime
communications in the 1600 . . . 4000 kHz
band.

The block schematic

Our design consists of a tuned input circuit,
a buffer, oscillator, mixer, low-pass filter,
a.f. amplifier, and sound transducer as can
be seen in figure 2. Input and oscillator
circuit tuning are, of course, ‘ganged’. For
those who want a little more than a ‘mini-
mum receiver’, there are facilities for con-
necting an additional low-pass filter (to give
improved selectivity), and a frequency
counter (to provide a precise frequency
read-out).

The circuit diagram

The various blocks of figure 2 can be readily
recognized in the circuit diagram in figure 3.
The tuned input circuit consists of LI, C24,
and D6; T1 funcions as the buffer, and IC1
contains the mixer and oscillator. The tuned
oscillator circuit comprises L2, C23, and
D7. The low-pass filter consists of just one
capacitor, C7, and the a.f. amplification is
provided by IC2.

The input and oscillator circuits are tuned
by means of varicaps D6 andD7 respectively.

These variable-capacitance diodes derive
their control voltage from a divider con-
sisting of PI, P2 and R1 . . . 4. The actual
tuning is carried out with PI (coarse) and
P2 (fine). Both these potentiometers are
10-turn types. Preset P3 ensures correct
tracking of the two tuned circuits.

The aerial can be connected directly to the
aerial input on the printed-circuit board,
or inductively by a secondary winding on
LI. The buffer (Tl) between the input
circuit and the mixer is a FET source-
follower which, because of its high input
impedance and low gate-source capacitance,
ensures that damping of the input circuit
is kept low. Because of that, input selec-
tivity is quite good and the risk of spurious
mixing products is small.

The signal at the source of Tl is fed to pin 7
of IC1, which is one of the inputs of the
quadrature multiplier (that is, mixer) con-
tained in that IC. The amplifier in the
S041P (outputs at pin 6 and pin 10) which
is internally coupled to the mixer, is used
as the active part of the oscillator. The tuned
oscillator circuit is connected to the input
(pin 14) of the internal amplifier via C9.

The a.f. output of the mixer is taken to the
audio amplifier, IC2, via a simple low-pass
filter (C7) and volume control P4. The a.f.
amplifier can drive high or low impedance
loudspeakers or headphones.

The power supply consists of the usual
bridge rectifier, D1 . . . D4, a smoothing
capacitor, C21, and a voltage regulator,
IC3. Resistors Rll, R12 and capacitors
Cl 7 . . . 20 ensure minimal interference
from the mains supply. The LED, D5,
functions as the on/off indicator.

Construction

The receiver is constructed on a double-sided
printed-circuit board as shown in figure 4.
As you probably know, double-sided means
that the component side of the board is
provided with a copper layer which functions
as an earth plane. All components connected
to earth must therefore be soldered at both
sides of the board.

12-26

An accidental advantage of the copper layer
is that it serves as a heat sink for IC3 which
can thus be mounted directly onto the board
(with the aid of some heat-sink compound).
Assuming that neither the mounting of the
components nor the connecting of the
potentiometers, power supply, and so on
will give you any problems, we turn to
some specifics and hints. First of all, the
coils: these will have to be wound by hand.
Fortunately, neither of them is bifilar,
nor do they have taps or coupling coils
(but see under aerial!). Coil LI consists of
25 turns enamelled copper wire SWG 30 on
a ferrite rod of 100 x 10 mm. The coil
should be wound so that it can be shifted
along the rod which can, for instance, be
achieved by laying the turns onto a tube
of thin cardboard around the rod. The
whole is then mounted onto the board
by means of two spacers and some string:
holes for securing the string are provided.
Coil L2 consists of 50 turns of the same
wire wound evenly onto a T50-2 toroid.
The whole assembly is mounted onto the
board with a nylon screw, nut, and washer.

Potentiometers PI and P2 must be 10-turn
types. We know there will be some of you
who, on cost considerations, will try to use
standard types: we must, however, strongly
advise against this, because tuning will
become almost impossible and certainly
will lead to very disappointing performance.
If you must economize, use a 10- turn
for PI and replace P2 by a wire bridge.
Tuning will then be a little more difficult
than it should be, but it will be possible.

The varicaps D6 and D7 also present a little
problem: they are manufactured as a pair
and must therefore be split into two (elec-
trically only!). Often they carry no indica-
tion as to cathode and anode, and these
have thus to be ascertained with the aid
of a multimeter. This can be done by com-
parison with a known diode.

To ensure good stability, it is advisable to
house the entire receiver in a closed metal
case. It is also advisable to screen the input
stages from the remainder by fitting a tin
or brass partition where indicated by a
dotted line in figures 3 and 4.

MF/HF USB marine
receiver

elektor december 1 983

Figure 3. The circuit
diagram is conspicuous by
its simplicity: one FET,
two ICs, a stabilizer, and
some passive components.
Tuning is effected by
means of varicaps D6
and D7.

3

12-27

MF/HF USB marine
receiver

elektor december 1983

Parts List

Resistors:

R1 , R13 = 1 k
R2, R3 = 22 k
R4 = 1 00 k
R5, R8, R9 = 220 k
R6 - 820 fi
R7 = 3k9

rio= ion

R11, R12 - 220 n
R 14 = 330 n

Capacitors:

Cl = 4p7

C2, C4, C5, CIO, C16 -
100 n
C3 = 1 n

C6. Cl 2, C22 = 1 p/16 V

C7, C11 - 22 n

C8 = 1 p/10 V

C9 = 3p3

C13 = 10 p/6 V

C14 = 1 n

Cl 5 = 470 p/10 V

Cl 7 . . . C20 = 47 n

C21 = 1 000 p/35 V

C23, C24 = 40 p trimmer

Semiconductors:

T1 = BF 256C
D1 . . . D4 « 1N4001
D5 * LED
D6, D7 = KV 1 236
IC1 - S041P
IC2 = LM 386
IC3 = 7812

Miscellaneous:

P1.P2 = 10 k 10-turn
potentiometer
P3 = 1 00 k preset
P4 = 10 k log potentio-
meter

LI - 25 turns enamelled
copper wire SWG 30 on
1 00 x 10 mm ferrite rod
L2 = 50 turns enamelled
copper wire SWG 30 on
T50-2 toroid
Trl = mains transformer
18 V/250 mA
SI m mains on/off switch

Figure 4. The printed-
circuit board is double -
sided. The copper layer
at the component side
functions as an earth plane.

12-28

MF/HF USB marine
receiver

elektor december 1983

Figure 5. The selectivity
can be improved by
fitting this low-pass
filter between C8 and
volume control P4.

Figure 6. Spectrum
analyzer photograph
of the filter in figure 5.
The horizontal scale is
1 kHz per division: the
vertical 10 dB per divi-
sion.

5

Calibration

The receiver can be calibrated without the
use of expensive test instruments.

■ Use a length of wire of not less than three
metres as a test antenna and connect this

to the aerial terminal on the printed circuit
board.

■ Set C23, C24, and P3 to their mid-
position.

■ Turn PI to the lowest frequency (lowest
tuning voltage) and then seek a broad-
casting station or interference whistle in
that region (of about 1600 kHz).

■ Shift LI along the ferrite rod until the
received signal is strongest.

■ Turn PI to the highest frequency band
(3500 . . . 4000 kHz), seek a station, and

6

adjust C24 for maximum signal strength.

■ The receiver should amply cover the 80
metre amateur band (3500 . . . 3800 kHz).

If it does not, adjust C23 until it does.

■ Once the range has been achieved, the
tracking of the input and oscillator

circuits must be set. Tune the receiver
to about the middle of the range (say,
2500 kHz), seek a station, and adjust P3
for maximum signal strength. If this means
a substantial adjustment of P3, it is wise
to repeat the entire calibration procedure.
When the receiver has been calibrated
correctly, its sensitivity is of the order of
1 pV, which is quite good. However, because
the transmitter power of most vessels is not
high, it pays to have a good aerial. This
should be at least 3 metres, but the longer,
the better! If the length goes above, say,
twenty metres, it is advisable to use inductive
aerial coupling as already stated. The coup-
ling winding should consist of 1 ... 3 turns
enamelled copper wire SWG 30 wound
around the ‘earthy’ end of LI.

Extensions

Connect a frequency counter to terminal
G on the printed-circuit board (where
the oscillator voltage of about 250 mV is
present) to obtain a precise frequency
read-out. Connecting a counter may, how-
ever, cause the oscillator frequency to
shift. If the sensitivity of the counter is
good, this shift may be reduced by fitting
a large capacitor between the counter out-
put and earth. This capacitor should be
so large that the counter just remains stable.
Better selectivity can be achieved by fitting
the low-pass filter shown in figure 5 be-
tween C8 and P4. This filter can be readily
constructed on a small piece of prototyping
(vero) board. Its pass band shown in figure 6
was obtained from a spectrum analyzer:

65 dB additional attenuation at 6 kHz
off -tune is not bad for a receiver intended
for beginners! M

12-29

LED ornaments
elektor december 1983

Around this time of the year even the most hardened of electronic hobbyists
is likely to be thinking of a completely different type of circuit than the
usual ones. Now a circuit does not necessarily have to do anything, except
maybe play a game or simply look decorative. Of course, electronics is totally
suited to this sort of task and, as we have always known, electronics can just
be good fun.

LED ornaments

seasonal

electronics

Figure 1 . Here we show
just a few of the countless
designs that can be made
with a few LEDs. Use your
imagination. Unfortunately
it is not possible to show
the colours here, but
almost all the colours in
the spectrum are available.

The purpose of this article is to give any
‘not entirely sane’ handymen among you a
few ideas. What we have in mind is making
decorative, colourful 'LED ornaments',
suitable for hanging on the Christmas tree,
or as an exclusive brooch (with a battery
in an inside pocket) or something similar.
To anyone not familiar with electronics,
especially children, it could be something
totally fascinating, and it is also an idea
for a unique Christmas present.

What we really mean is simple figures, such
as those shown in figure 1. They consist of
nothing more than a group of LEDs arranged
in a certain pattern. Exactly how it is made
and how big it is is a matter for each to
decide for himself. It could be anything
from a simple brooch to a fully fledged
star with all the options. We opted for a
star, cut from a piece of plywood with
holes drilled for the LEDs and with a good
coat of a suitable colour paint. We ended
up with something like that shown in
figure 2. This is only intended as an example
as it could be constructed in any number of
ways.

Flashing electronics

Simply having a display of LEDs is all very
well, but as an electronics hobbyist you are
more or less obliged to make the LEDs flash.
Only then can it really be called ‘eye-
catching’. It is not at all difficult, but there
are a few basic elements required. In its

simplest form the electronics needed consist
of an oscillator for the flash timing, a div-
ider, and the LED driver. A few suggestions
are shown in figure 3.

If there is not very much room to play with
then one of the four oscillators from figure
3a, the divider (figure 3c) and a few of the
driver stages drawn in figure 3d are all
that are strictly essential. If there is more
space available, taking a bit more time and a
few more components, the circuit can be
expanded.

Instead of using one oscillator, for example,
four switchable oscillators could be substi-
tuted, as figure 3a shows, so that differ-
ent rhythms can be chosen. The clock
frequencies used is a question of taste.

Cl . . . C4 can have any value from 100 n
to 1 00 ju and R 1 . . . R4 can be any resist-
ance from 10 k to 10 M. That gives a range
of speeds from very slow to very fast. The
wiper of the four-way switch is connected
to the clock input (CL) of the divider IC
(figure 3c).

The oscillator of figure 3b is also a nice
possibility. This automatically supplies dif-
ferent rhythms of its own accord, without
any need for switching. When SI is open the
CL output alternately supplies high and low
frequency clock pulses. If SI is closed the
high and low frequency pulses follow each
other at random.

The divider circuit of figure 3c requires little
comment. This is a straightforward appli-

1

disco (tar

Christmas star

shoot irvg target

12-30

cation of a well known decade counter IC.

If all ten outputs are to be used, then the
reset input (pin 15) must be connected to
ground. Otherwise this pin should be con-
nected to one of the 0 ... 9 outputs, so that
whenever this output is reached the counter
goes back to ‘O’.

The LEDs

Now the LED drivers. As the decade counter
of figure 3c cannot drive the LEDs directly,
each output must be followed by a transistor
stage. The simplest version is shown in
figure 3d. Each transistor can drive a number
of LEDs connected in series. The value of
the series resistor can be calculated by
subtracting the total voltage drop across the
LEDs from the supply voltage and then
dividing this by the current that is to flow
in the LEDs:

Ub-(n-ULED)

Both Uled ^ ILED depend on the type
used. The voltage drop across red LEDs is

*

* *

generally 1.6 V; for yellow it is approxi-
mately 1.9 V and for green the norm is
about 2.2 V. The current required can vary
between 10 and 50 mA.

An expanded LED driver stage is shown in
figure 3e. In this case transistor T1 is pro-
tected by the current limiting components,
T2 and R2. Given a supply of 15 V, this
stage can drive a maximum of six and a
minimum of three LEDs in series. Fewer
LEDs cannot be used here or T1 will have
to dissipate too much current. The LED
current is determined by the choice of R2.
The value of this resistor is easily calculated
by dividing the voltage drop across this
resistor (= the base/emitter voltage of
T1 = 0.6 V) by the current required:

0 .
ILED

From theory to practice
By now you should have all the information
you need to start making your own original
LED ornaments (except maybe which end of
a fret saw is the sharp end).

The power supply can in principle be kept
very simple, but it should not be underrated.
The oscillator and divider certainly require
little current, but the LEDs need quite a bit
more. If a voltage of 15 V and the full ten
channels are to be used, then for a LED
current of 10 mA the supply must be able
to provide at least 100 mA. If the LEDs
draw even more current the total consump-
tion can rise to as much as 0.5 A (if ILED * s
50 mA). The final design of the power
supply therefore depends on the number and
type of LEDs used.

Finally . . . while we are on the subject of
LEDs. There seems to be an ever-increasing
number and variety of LEDs available today
and you may be wondering which to use.
The majority are perfectly suitable for our
purposes here, but the best are the diffused
coloured types. These have a wide viewing
angle and remain visible from a distance
even if you are not standing straight in front
of them. M

Figure 2. Our 'prototype'
shown here actually
involves more carpentry
than electronic ability.

Figure 3. Driving the
LEDs. Figures a and b
show two variations for the
oscillator. The output (CL)
goes to the decade counter
of figure c, each of the out-
puts (0 ... 9) of which can
be followed by a transistor
stage (d or e) driving one
or more LEDs.

12-31

symmetrical power supply
elektor december 1983

Anyone with some knowledge of electronics knows that to be able to
experiment with operational amplifiers, or to check circuits using them, a
symmetrical power supply is virtually indispensable. The power supply
described here provides two precise INDENTICAL voltages which are set by
ONE potentiometer and ADJUSTABLE current-limiting.

symmetrical

power supply

The specification of a symmetrical mains
power supply must include the provision of
two precise, identical voltages (one positive,
the other negative) which can be set with
ONE potentiometer. It must be possible to
set the lowest voltage to 0 V. And, perhaps
most important of all, the unit must have
adjustable current-limiting, which on over-
load reduces or switches off BOTH cur-
rents.

We have not often used the LM317 (posi-

tive) and LM337 (negative) adjustable
voltage regulators in our designs and a few
words about these devices may, therefore,
not come amiss. They are very easy to use
and require only two external resistors to
set the output voltage and an output ca-
pacitor for frequency compensation. In
addition to higher performance than fixed
regulators, they offer thermal and electrical
overload protection, current limiting, and
safe-area protection. The overload pro-

Figure 1. The three-ter-
minal integrated, adjust-
able regulator type LM317
operates as a series regu-
lator. The required output
voltage is obtained by
adding voltage divider
R1/R2. The minimum load
current is set to 10 mA
by means of R 1.

Table 1

Output voltage
(LM 317) 1.2

(LM 337) -1.2

Line regulation, typically
Load regulation, typically
Reference voltage
Adjustment pin current
Minimum load current
Temperature stability
Current limiting
(constant with temperature)
Ripple rejection (LM317)
(LM 337)

Thermal regulation
(LM 317)

(LM 337)

. . . 37 V
. . . -37 V
0.01%/V
0 . 1 %

1.2 V
50 nA

3.5 mA
0.01%/°C

2.2 A

OPAMP

0.04%/W

0.03%/W

83121 1

12-32

tection circuitry remains fully functional
even if the adjustment terminal is dis-
connected. The ‘K’ versions are packaged in
the standard TO-3 transistor housing. The
operating temperature range is 0 . . . 125°C.
Further features are shown in table 1.

For those who may have forgotten: a series
voltage regulator is a circuit in which a
‘ballast’ transistor, controlled by an ampli-
fier, is used as a preset resistor in series
with the load. This transistor absorbs any
superfluous voltage.

Principle of operation

The operation of a voltage regulator (in this
case the LM 317) may be described with the
aid of figure 1 in which an operational am-
plifier (opamp) drives a power darlington
transistor. The opamp and the circuit pro-
viding the d.c. bias for the regulator are
arranged so that the quiescent current flows
to the output of the regulator instead of to
earth (hence no earth connection!). The
reference voltage of 1 .2 V appears between
the non-inverting input of the opamp and
the ADJ(ustment) pin. The quiescent cur-
rent for the reference-voltage source is set
to 50 nA and emerges from the ADJ pin.
In actual operation, the output voltage of
the IC is equal to the voltage at the ADJ
pin plus 1.2 V. If you therefore connect
the ADJ pin to earth, the regulator func-
tions as a 1.2 V reference voltage source.
Higher voltages are arranged by means of
voltage divider R1/R2. As the reference
voltage appears across Rl, a current of
10 mA flows through the voltage divider.
This current also flows through R2 and thus
increases the voltage at the ADJ pin. The

real output voltage is therefore given by the
formula

U ou t= (12 (1 + R2/R1) + 50 x 10‘ 6 xR2]V

As we’re dealing with a series regulator, the
quiescent current is taken off the load cur-
rent. If the latter becomes very small, the
regulation is affected. It’s for that reason
that the minimum load current is set (by
means of Rl) at 10 mA.

The circuit

The complete circuit diagram in figure 2 is,
of course, more complex than that of the
regulator in figure 1. But remember what we
said at the beginning: it must be possible to
preset both the positive and the negative
voltage with one potentiometer, the output
voltage must go down to 0 V, and the cur-
rent limiting must be adjustable.

Regulation of the positive output voltage
is effected by an LM 317 and that of the
negative output by an LM337. Because of
the voltage drop across diodes D7 and D8,
the wiper of potentiometer P4 is at -1.2 V,
provided T1 does not conduct. Substituting
the minimum and maximum values of P4
in the formula

Uout = [1.2P4/120 + 50 x 10‘ 6 x P4] V
a range of output voltages of 0 ... 22 V is
obtained.

The setting of both output voltages to the
same numerical value is arranged by opamp
IC8. As the non-inverting input of this IC
is at earth potential, its output will closely
follow the voltage at its inverting input. This
ensures that, provided P5 is adjusted cor-
rectly, the values of the negative and positive

symmetrical power supply
elektor december 1983

Figure 2. The circuit of the
symmetrical power supply
which meets the require-
ments for one poten-
tiometer-setting of both
the positive and negative
output voltage, and for
adjustable current limiting.

2

12-33

symmetrical power supply
elektor december 1983

Figure 3. Component
layout and trackside of the
printed circuit board for
the power supply. The
two adjustable regulators
must be fitted with heat
sinks - DO NOT FORGET
ISOLATING WASHERS!

output are the same. Capacitor C12 slows
down the regulating action of IC8 to some
extent so that any tendency of IC7 to
oscillate is effectively suppressed.

It should be noted that the operating voltage
of IC8 is asymmetrical: +5 V and -25 V.
This gives, of course, the maximum operating
voltage of 30 V for this IC. The asymmetry
is necessary to ensure that the output of IC8
can go down to at least -18 V, otherwise it
would not be possible for the negative out-
put voltage to reach this value.

Voltage regulators IC1 ... 3 merely provide
the stabilized supply voltages for the op-
amps. The input voltages for the adjustable
regulators, IC6 and IC7, are provided by
capacitors Cl and C2 respectively. These

electrolytic capacitors are as large as possible
to ensure that the ripple voltage is kept to a
minimum and that the rectified voltage does
not drop below the required input level of
the regulators.

Last, but not least, the adjustable current
limiting. In the positive leg this is effected
as follows. A reference voltage derived from
voltage divider R5/R2 is applied to the non-
inverting input (pin 3) of opamp IC4. If the
ratio of voltage divider P3a-Pl-R6/Rl is the
same as that of R5/R2, the voltage at the
inverting input (pin 2) at maximum load
current will be smaller than that at pin 3
(because of the voltage drop across cur-
rent sensing resistor R9). The output of
the opamp becomes positive and switches on

12-34

transistor Tl. The resulting current through
T1 ensures that the output of both IC6
and IC7 is returned to the predetermined
reference level. The level at which current
limiting commences is set by potentiometer
P3a.

The current limiting action in the negative
leg is similar, but here the voltage level at
the non-inverting input (pin 3) of IC5
becomes greater than that at pin 2 at the
onset of current limiting. Again, the opamp
switches on transistor Tl and from then on
the action is as described for the positive leg
P3 is a stereo potentiometer so that the
current limiting can be set to commence at
the same level in both legs.

Construction and calibration

The use of the printed -circuit board shown
in figure 3 makes the mounting of most
components simplicity itself. The usual care
should be taken to observe polarity where
necessary and to avoid dry soldering joints.
The remainder is primarily a problem of
constructing a suitable housing for the
unit.

The front panel should be provided with
holes for P3 and P4, the output terminals,
and the mains on/off switch. The rear panel
must have holes for fitting the adjustable
regulator-ICs and their heat sinks, and mains
fuse. Once this work has been done, the
wiring between all these components and
the printed -circuit board can be completed.
When the wiring has been completed and
carefully checked, the unit can be calibrated.

■ Set presets PI and P2, and potentiometer
P3, to minimum resistance - check this

with an ohmmeter.

■ Connect a voltmeter to the positive-

symmetrical power supply
elektor december 1 983

RIO

a

831214

voltage output terminal; if a second one
is available, this may be connected to the
negative-voltage terminal. (Be careful to
observe polarity!)

■ Switch on the mains, and check that
adjusting P4 causes a change in both

output voltages. Adjust preset P5 to give
equal numerical values for these voltages.

■ Switch off the mains, and connect a

1 J2/5 W resistor to both the positive and
negative output terminals, in parallel with
the voltmeter(s).

■ Switch on the mains and adjust P4 for
maximum output voltage(s). Set P3 so

that the voltage across the 1 £1 resistors
increases; check that when P3 is turned
back, the voltage decreases.

■ Set P3 for maximum voltage across the
1 resistors and then adjust PI and P2

so that the voltage across these resistors is
exactly 1.000 V. The current will then, of
course, be exactly 1 A. In our laboratory
prototype, it was possible with P3 to set the
current limiting between 15 mA and 1 A.
Many of you will find it worthwhile to
build in the meters shown in figure 4. The
reading and setting of voltage and current
levels is then much easier. Do not, however,
calibrate these instruments until you are
sure that the supply unit is functioning
satisfactorily. M

Figure 4. Optional instru
ments for incorporating
in the power supply
enable direct reading of
output voltage and load
current.

Parts list

Resistors:

R1 . . . R4 = 8k2
R5,R7,R11,R12 = 27 k
R6,R8 = 22 k
R9.R10 = 0,82 H/3W
R13.R14 = 1 k
R15.R16 = 120 H
R17.R18 = 100 k
PI ,P2 = 10 k preset
P3 = 1 k linear stereo
potentiometer
P4 = 2k2 linear preset
P5 = 1 k preset

Capacitors:

C1,C2 = 4700 p/63 V
electrolytic
C3.C4.C5 = 10 p/16 V
tantalum

C6.C7 = 2n2 ceramic
C8.C9.C11,

C13 = 10 m/ 30 V
tantalum

CIO = 10 n ceramic
Cl 2 = 1n8 ceramic

Semiconductors:

D1 . . . D4 = IN 5408
D5.D6 = 1N4148
D7.D8 = 1N4001
Tl = BC 141
IC1 = 7812
IC2 = 79L12
IC3 = 7805
IC4.IC5.IC8 = LF 356
IC6 = LM317K
IC7 = LM 337K

Miscellaneous:

SI = double-pole mains
switch

FI = miniature fuse holder
and fuse 0.5 A
Trl = mains transformer
2 x 18V/1.5A
Heat sinks for two
TO-3 ICs

Printed circuit board
83121

Output terminals
Four 100 mA meters as
required

12-35

Extra amplification is desirable in almost every extended video chain. We are
talking about, for example, compensating for losses in cables, strengthening
the signal from a not very sensitive input, or other applications where signal
levels have to be tuned in to each other.

This simple amplifier is ideal for all these applications. Furthermore it also
acts as a distributor as it is equipped with three outputs as standard.

video amplifier

universal
amplifier and
distributor
for video
signals

A video amplifier rarely needs a high gain.
By ‘high' we mean a factor of 100 or more,
as is the norm for audio pre-amplifiers. For
adjusting video levels a gain factor of 2 or 3
times is generally called for - maybe a bit
more in a few cases.

In this circuit we have made the amplifi-
cation adjustable between 1 x and a good
4 x, so that the amplifier is suitable for
almost any situation where boosting is
needed. The maximum output voltage is
4 Vpp, and the input and output impedance
is, of course, set at 75 ohms.

As well as being a normal amplifier, this
circuit can also be used as a video signal
distributor, which is handy if more than
one channel in a video chain are to be
driven from one video signal. As we have
already said, the amplifier has three out-
puts. However, that is not to say that they
all have to be used. The circuit can also be
used with just one or two outputs.

Now the only data needed to complete the
technical specification of the amplifier is the
bandwidth. This is at least 5 MHz providing
the specified semiconductors are used.

The circuit diagram

A good video amplifier need not be very

complicated, as is shown by figure la.
The circuit contains a very ordinary two-
stage amplifier (T1/T2) followed by an
emitter follower. The transistors used are
simply normal BC and BD types because
these can quite easily fulfil the required
conditions for adequate bandwidth. A
nice side-effect is, of course, that these
transistors are relatively cheap, and in
this case expensive HF types are simply
not needed.

The input impedance is set to 75 ohms by
Rl. The signal travels from the input via C2
to the base of Tl. Because the content of
the video signal can change a lot, the d.c.
current setting of Tl is provided by a small
circuit (R3, PI, Cl, R2 and Dl). The maxi-
mum output voltage swing of the amplifier
can be set using PI. We will deal with
setting this potentiometer later. The base
of transistor T2 is connected directly to
the collector of Tl thus forming a direct
coupled amplifier, the amplification of
which can be varied with potentiometer
P2 in the feedback network. The amplifi-
cation factor is defined by the ratio between
R5 and the resistance of the R6/R7/P2/C3
network. With the values we have used, P2
covers a range of 1.95 x to 8.7 x. With the

12-36

Figure 1. The circuit is
very simple to construct
and contains very ordinary
components. The amplifi-
cation can be adjusted with
P2 between 1 x and 4 x.

1b

normal output load of 75 ohms the final
amplification is effectively halved, so that
the actual range is from 1 x to just over
4 x.

The T1/T2 stage is followed by a ‘bigger’
transistor (T3), which has to ensure the
desired low frequency output impedance.
This demands a very small emitter resistor
(R9) and an accordingly high collector
current. The amplified signal leaves the
circuit by three 75 ohm outputs, made up
of C5/C6/C7 and R10/R11/R12.

If only one or two of the three outputs are
needed, then obviously the power consump-
tion of the circuit will be correspondingly
less. The greatest part of the current con-
sumption is in R9. If three outputs are used
R9 must be 56 ohms, with two outputs it
can be increased to 82 ohms and with one
output 150 ohms is sufficient. The total
current consumption for the three con-
ditions is then 150 mA, 110 mA and 70 mA
respectively.

Adjustment

There are two ways of adjusting PI. The
‘normal’ method, which gives satisfactory
results 90% of the time, and an alternative
for setting it up 'by eye’. In the first case,
PI is simply adjusted so that there is about
1 V at the base of Tl. The voltage across

R8 should then be about 7.5 V (with no
signal).

The alternative method is somewhat more
involved. Start by setting PI to mid position
and with an input signal of about 1V PP,
reduce the amplification to minimum with
P2. Then a test image is fed into the input
(from a video recorder, for example),
and a TV set or monitor is connected
to the output. PI is now adjusted so that
all distortion is just eliminated.

Another point which may be of importance.
Although input signals a bit higher than the
nominal 1 Vpp are not a direct disadvan-
tage to the amplifier, they are actually of
little use. Significantly higher voltages can
therefore better be reduced. This can be
done by experimenting with R5 and using
a bigger resistor here (the maximum amplifi-
cation then decreases) or by placing an
extra resistor in series with the input, so that
it forms a voltage divider with R1 . Then the
value of R 1 is reduced so that the total
resistance of the extra resistor and R1 add
up to 75 ohms.

Construction

A simple power supply for the amplifier
is easily built, as figure lb shows. Both
amplifier and power supply are constructed
on the same printed circuit board, the layout

12-37

video amplifier
elektor december 1983

Figure 2. The printed
circuit board contains
both the amplifier and
power supply. Only the
mains transformer is not
mounted on the board.

Resistors:

R1.R10 . . . R12 = 75 a

R2 = 10k

R3 = 8k2

R4 = 1 k

R5.R7 = 180 a

R6 = 3k3

R8 = 470 a

R9 = 56 a/5 W # *

PI = 2k 5 preset
P2 = 2k2 linear
*75 a * 1 50 a ii 150 a
**see text

Very little needs be said about mechanical
construction for this project. Depending on
circumstances, it could be built into the
case of some existing equipment, or it could
be mounted in a case of its own. The only
important point is that the ‘amplification’
pot must be freely accessible. fr

of which is shown in figure 2.

‘Construction’ is really only a matter of
fitting everything correctly to the printed
circuit board and soldering it there. How-
ever, there are a few points to note. When
three outputs are in use voltage regulator
IC1 has to work reasonably hard and be-
cause of this it needs to be mounted on a
heatsink. The 75 ohm resistors (marked with
an asterisk) are not standard E12 values.
They actusdly consist of two 150 ohms
connected in parallel.

Capacitors:

Cl ,C4 = 100 n
C2,C3 = 10 m/16 V
C5 . . . C7 = 100 m/16 V
C8 = 470 m/35 V
C9 = 330 n

Semiconductors:

D1 = 1N4148
D2 . . . D5 = 1N4001
T1 = BC547B
T2 = BC557B
T3 = BD 137/139
IC1 = 7812

Miscellaneous:

SI = double pole mains
switch

FI =100 mA slow blow
fuse

Trl = 15 V, 0.8 A mains
transformer
Heatsink for IC1
Case, approximate dimen-
sions 1 20 x 65 x 65 mm

12-38

elektor december 1 983

Personal FM

(September 1983,
page 9-46)

The 0.22 pH Toko coils
for LI and L2 should
be of the small axial-leaded
type. Alternatively, they
can quite easily be wound.
The correct inductance can
be obtained by winding 13
turns of SWG 27 enamelled
copper wire on a 3.5 mm
'former' (we used the plas-
tic refill for a well-known
ballpoint pen). L3 is listed
as stock number 35-01144
in the Ambit catalogue
under the heading 'coil
style MC 120'.

Electronic voltage
regulator

(October 1983,
page 10-57)

The text for this article
states that this circuit will
work with a d.c. dynamo.
The theory behind the
regulator does apply for
d.c. dynamos, but this par-
ticular circuit will only
work with an alternator.

7-day timer/
controller

(April 1983,
page 4-42)

In a few cases difficulties
are encountered with the
storing of the switching
data. This is caused by an
incorrect trigger level at
IC5. The remedy consists
of reducing the value of C8
down to 1 nF (but not
lower), if necessary.

12-39

elektor december 1983

The following pages contain the
mirror images of the track layout of
the printed circuit boards (excluding
double-plated ones as these are very
tricky to make at home) relating to
projects featured in this issue to
enable you to etch your own boards.

■ To do this, you require: an
aerosol of ‘ISOdraft’ trans-

parentizer (available from your
local drawing office suppliers;
distributors for the UK: Cannon
& Wrin), an ultraviolet lamp,
etching sodium, ferric chloride,
positive photo-sensitive board
material (which can be either
bought or home made by applying
a film of photo-copying lacquer to
normal board material).

■ Wet the photo-sensitive (track)
side of the board thoroughly

with the transparent spray.

PC board pages

■ Lay the layout cut from the
relevant page of this magazine

with its printed side onto the wet
board. Remove any air bubbles by
carefully ‘ironing’ the cut-out with
some tissue paper.

■ The whole can now be exposed
to ultra-violet light. Use a glass

plate for holding the layout in place
only for long exposure times, as
normally the spray ensures that the
paper sticks to the board. Bear in
mind that normal plate glass (but
not crystal glass or perspex) absorbs
some of the ultra-violet light so that
the exposure time has to be in-
creased slightly.

■ The exposure time is dependent
upon the ultra-violet lamp used.

the distance of the lamp from the
board, and the photo-sensitive
board. If you use a 300 watt

UV lamp at a distance of about
40 cm from the board and a sheet
of perspex, an exposure time of
4 ... 8 minutes should normally
be sufficient.

■ After exposure, remove the
layout sheet (which can be

used again), and rinse the board
thoroughly under running water.

■ After the photo-sensitive film
has been developed in sodium

lye (about 9 grammes of etching
sodium to one litre of water), the
board can be etched in ferric chlo-
ride (500 grammes of FeCl 3 to
one litre of water). Then rinse the
board (and your hands! ) thoroughly
under running water.

■ Remove the photo-sensitive film
from the copper tracks with

wire wool and drill the holes.

disco

Phaser:

oscillator

board

12-40

elektor december 1983

itive index 1983 cumulative index !

Audio and sound generation

accessories for the Crescendo power amplifier .. 1-28

audio traffic light 3-56

common base mixer 7-84

Crescendo revisited 11-62

cricket simulator 7-63

disco phaser 12-50

electronic switch for audio signals 7-78

electronic tuning fork 7.34

electronic two-tone metronome 1 1-48

40 watt main amplifier 7-82

Interlude 4-36

logarithmic amplifier 7-37

machine gun sound generator 7-44

Maestro part 1 5-38

Maestro part 2 646

MC/MM phono preamp 4-26

microphone amplifier with preset tone control . . 7-93

music quantizer 10-30

(missing link) 11-41

mini compressor 7-89

personal FM 946

(missing link) 12-39

Prelude part 1 2-18

Prelude part 2 3-36

Prelude part 3 4-52

Prelude buffer 7-50

Prelude class A headphone amplifier 2-34

Prelude p.s 5.33

preset the hard (ware) way 7-88

pseudo stereo 11-52

RC equalizer 4-40

sea murmur simulator 7-77

simple PA system 7-91

spectrum display 6-38

ZN 41 5 — a complete AM radio tuner
(Applicator) 11-63

Car

autotest 9-22

car lights warning device (J. Glauser) 7-60

car PDM amplifier • 7-36

(missing link) 9-59

electronic voltage regulator 10-57

(missing link) 12-39

interior temperature control for cars 7-66

main beam dimmer 2-32

Domestic

alarm extension 9-51

anemometer 1040

anti burglar lights 7-55

code lock with door opener 7-60

constant light source 7-29

doorbell memory 7-33

doorbell — or telephone — operated flash-light . . 11-23

drill speed controller 7-85

electronics and plant physiology 7-52

energy meter 6-24

frost warning device 12-47

fuse protector (H. Dominic) 2-39

LED ornaments 12-30

low cost CMOS lock 7-75

(missing link) 10-47

low power digital thermometer (E. Schmidt) . . . 4-22

portable egg timer 7-62

7-day timer/controller 4-42

stay awake alarm 7-54

talking clock extension (E.A.J. Bogers) 4-60

thermometer (A. van Olderen) 7-30

wattmeter 5-22

Fun and games

dexterity game 7-81

double dice 2-51

electronic pocket pinball (H.J. Walter) 7-70

horse paces simulator (B. Darnton) 7-58

reaction tester (L. van Boven) 3-50

trick battery (L. van Boven) 1 1-60

'HF'

MF/HF USB marine receiver 12-24

morse converter (R. Unterricker) 5-52

morse decoding with the Z80A (P. von Berg) . . . 5-60

personal FM 9-46

pseudo stereo 11 -52

RTTY decoder 6-30

Hobby

action flash 7-68

darkroom computer tips (H. Fietta) 1-33

darkroom light 7-61

flashing running light 7-42

locomotive headlamp reverser 12-44

power controller for model railways 1 1-26

programmable darkroom timer 4-56

servo tester (G. Luber) 3-23

solid state darkroom lighting 10-36

switching channel for radio control 6-28

Informative articles
a (re)new(ed) eight bitter: the 65C02

(Applicator) 10-70

Basicode-2 10-27

Better way of depositing semiconductor compounds

(Selektor) 10-26

chips for digital audio (I) 1-36

chips for digital audio (I I) 2-54

coming soon 1-19

cutting costs with sparks (Selektor) 1-17

decoupling in digital circuits 11-30

discovering the infra-red universe (Selektor) .... 10-24

electrical language offish (Selektor) 5-19

fluorescent displays 3-18

Fourier synthesis (E. Muller) (Ejektor) 1-50

high speed CMOS 9-32

membrane switches . . . 4-34

morse and radio teletype (RTTY) 6-52

NOVRAM — data storage without batteries .... 12-58
0. 1C! 3-52

1241

elektor december 1983

983 cumulative index 1983 cumuli

raindrops and radar (Selektor) 6-21

readership survey results 10-21

R5620 ... a programmable universal filter with

switched capacitors 2-58

stereo TV sound (Selektor) 5-21

taking the heat out of electronics (Selektor) ... 12-21

talking to computers (Selektor) 2-16

the potential of the bucket brigade 4-20

tomorrow's music 1-53

universal logic: more potential in the chip

(Selektor) 12-20

videographics 9-18

what is power? . 5-47

when electromagnetic waves came to light
(Selektor) 11-21

Measuring/test equipment

capacitance meter 7-34

energy meter 6-24

5 V logic tester (C. Bajeux) 7-92

heatsink thermometer 7-72

h pe tester 7-49

high and low tester (R. Storn) 7-97

LCD luxmeter 3-24

low power digital thermometer 4-22

mains wiring tester (A. Scragg) 7-56

milliohmmeter 1-24

multitester (E. Osterwick) 5-36

optical voltage indicator 7-71

resistance comparator 7-28

simple MOSFET test 9-58

temperature indicator 7-69

thermal indicator for heat sinks 7-96

thermometer (A. van Olderen) 7-30

transistor selector 10-62

voltage monitor 7-89

wattmeter 5-22

Microprocessor

acoustic 'flag' for the RS232 interface 7-91

acoustic telephone modem (J.J.M. Habets and

C.A. Truijens) 2-42

(missing link) 1 0-46

ASCII keyboard 5-26

banking program 12-56

Basicode-2 interface for the Junior Computer .. 10-51

bus extension 12-62

busy indicator for the Junior Computer

(W. Schaaij) 7-77

Centronics interface 7-45

CPU card 11-32

EPROMmer using the Junior Computer 10-68

fault finder for ASCII keyboard 7-94

fluorescent display (Applicator) 6-58

FSKleaner 10-64

joystick interface 7-46

Junior program tester (P. Wild) 4-51

Junior synthesizer 9-56

microprocessor aid 7-80

/^Processor fault finder 7-95

microprocessor 'stethoscope' 7-31

morse converter (R. Unterricker) 5-52

(missing link) 9-59

morse decoding with the Z80A (P. von Berg) . . . 5-60

(missing link) 10-46

parallel-serial keyboard converter 5-50

(missing link) 10-46

RTTY decoder 6-30

simple baud rate generator 7-41

6809 DRAM controller (H. Fischer) 7-90

64 K on the 16 K Dynamic RAM card 9-29

(missing link) 11-41

64-way bus board 12-22

software RAM tester 749

traffic-light control system (D. Herzberg) 1-46

2650 single step 7-43

universal memory card 3-28

universal terminal 11-56

upper and lower case on the Elekterminal

(D. Paulsen) 1-56

(missing link) 11-41

VAM — video/audio modulator 2-27

VDU card 9-38

vector control for the Junior Computer
(N. Humphreys) 7-79

Miscellaneous

amplified triac drive 7-68

automatic display dimmer 3-46

auto trigger 7-46

battery economizer 7-51

capacitive switch 7-98

decimal-to-binary converter 11-40

distance meter for thunderstorms 7-84

economic LED 7-47

electronic aerial switch (C. Abegg) 6-36

electronic switch for audio signals 7-78

electronic tuning fork 7-34

four quadrant multiplier 7-79

frequency comparator 7-62

glitch suppressor 7-76

horse paces simulator (B. Darnton) 7-58

inexpensive 45 MHZ crystal filter 7-74

key bleep 8-00

LED amplifier 7-47

LED current source 7-39

lie detector 7-69

movement detector 1145

noise and vibration detector 7-35

on/off with a single push button 7-74

precision voltage divider 9-50

reproducible delay 7-38

signal purifier for SSB telegraphy receiver

(P. von Berg) 7-57

simple D/A converter 7-86

solar tracking system 740

S.P.T.S 7-85

stable zener 7-38

symmetrical voltages from a doorbell transformer

(R. Storn) 7-39

ultrasonic/infra-red barrier 11-58

universal AFC 7-99

useful tip . . . 2N3055 Super Darlington pair . . . 10-67

12-42

elektor december 1 983

itive index 1983 cumulative index

I

Missing link

acoustic telephone modem

(February 1983, page 2-42) 10-46

car PDM amplifier

(Summer circuits 1983, page 7-36) 9-59

Crescendo (December 1982, page 12-32) 1141

drum interface (November 1982, page 11-20) . . 11-41
electronic voltage regulator

(October 1983, page 10-57) 12-39

floppy disk interface for the Junior Computer

(December 1982, page 1248) 9-59,11-41

in-car ioniser (December 1982, page 1245) .... 1 141

infocard 55 9-59

infocard 70 9-59

Video

VAM — video/audio modulator . .

video amplifier

video effect generator (L. Heylen)
video pattern generator

2-27

12-36

6- 50

7- 58

variable zener 7-88

very narrow crystal filter 7-56

VFO with variable inductor (A.B. Bradshaw) . . . 7-67

window comparator (R. de Boer) 7-76

zero crossing detector (O.M. Kellogg) 7-83

Power supplies/generators

battery eliminator 10-60

current source for photodiodes 7-94

DC-DC converter (A. Bovee) 7-61

d.c. voltage doubler using a 4049 (G. Ramm) . . . 7-53

emergency mains cut-out 7-41

high-voltage regulator 10-38

LED current source 7-39

negative printhead supply 7-83

offset-less rectifier 7-64

180 watt DC/AC converter 8-00

1 MHz time-base without crystal 7-44

power back-up for CMOS ICs during mains failures 7-32

programmable power supply 1049

pulse/pulse train generator 7-64

RC generator (W. Meislinger) 7-65

78L voltage regulators . . . and 79L 5-59

simple baud rate generator 741

simple power supply regulator 7-98

simple regulated power supply 7-48

simple sawtooth generator (R. Oppelt) 7-71

simple stabilizer 7-78

stepped voltage generator 7-32

synchronous, constant amplitude,

sawtooth generator 7-87

symmetrical harmonic oscillator 7-31

symmetrical power supply 12-32

symmetrical voltages from a doorbell transformer

(R.Storn) 7-39

3 A computer power supply 1-43

video effect generator (L. Heylen) 6-50

video pattern generator 7-58

voltage booster regulator 7-54

low cost CMOS lock

(Summer circuits 1983, page 7-75) 1047

morse decoding with the Z80A

(May 1983, page 5-60) 10-46

morse converter (May 1983, page 5-52) 9-59

music quantisizer (October 1983, page 10-33) .. 1141

personal FM (September 1983, page 946) 12-39

parallel-serial keyboard converter

(May 1983, page 5-50) 10-46

7-day timer/controller (April 1983, page 4-42) . . 12-39
single channel infra-red remote control

(January 1982, page 1-52) 11-41

64 K on the 16 K dynamic RAM card

(September 1983, page 9-31 ) 11-41

upper and lower case on the Elekterminal
(January 1983, page 1-56) 1141

1243

The generator described in our November
1982 issue superimposes a high-frequency
alternating voltage (ul) onto the direct-
voltage output (Up) of the power controller.
Capacitors are used both at the output of
the generator and at the input to the coach
lamps to prevent the d.c. from the controller
interfering with the lighting system.

The composite voltage (uc) is applied to the
input (A, B) of the reversing circuit shown in
figure 1. This circuit ensures appropriate
control of the reed relay in accordance with

In our November 1982 issue we
published the design of a high-
frequency generator for the lighting of
model railway coaches independent of
the locomotive power supply. It
occurred to us that this generator
could also be used for changing the
headlamps to the direction of travel
on double-ended locomotives.

locomotive headlamp
reverse r

elektor december 1983

the direction of travel of the locomotive
(which can, of course, be detected from the
polarity of Up). As space in model railway
locomotives is restricted, all components
used are, of course, miniature or sub-minia-
ture types.

Depending upon the position of the relay
contact, either Laf or La r is connected
to the input voltage, uc, via capacitor
Cl,. The value of Cl is calculated from
Cl = 1/(2 n fXc) Farad, where f is the
frequency of the generator (19 kHz) and
Xc is the reactance of Cl. This reactance
should preferably be not more than 1/5
of the value of the lamp resistance. If
thus, for instance, a 12 V, 50 mA lamp
is used (resistance = 240 SI), Xc should
not exceed 48 S2 and
Cl = 1/(2 x 3.142 x 19 x 10 3 x 48)

= 175 x lO' 9 = 175 nF.

The nearest (higher) standard value of
220 nF should thus be used.

The operating voltage for the circuit is
derived from uc. The h.f. component is
rectified in diodes D1 and D2 and smoothed
by capacitors Cl and C2.

Opamp IC1 is used as a comparator: its
non-inverting input lies at the centre of
voltage divider R2-R3 which is connected
across Up. If 'B' is positive with respect to
‘A’, that is, when the locomotive is reversing,
capacitor C2 charges and the inverting input,
pin 2, of the opamp is more negative than
the non-inverting input, pin 3: the output
of the comparator is then positive. Transis-
tor T1 conducts, and the consequent voltage
across zener diode D4 and voltage regulator
IC2 actuates the relay. The relay operates
and connects La r to ul-
When the locomotive goes forward again
(and 'A' is positive with respect to ‘B’), the
voltage across Cl becomes greater than that
across C2, the output of the comparator
goes negative, T1 stops conducting, the relay
is no longer actuated, and Laf is again
connected across ul-

Zener diode D3 is included as a high-voltage
protection, but can be omitted if ul is
smaller than 35 Vpp-

The zener voltage, Uz, of diode D4 is calcu-
lated from Uz = ULpp - 20 V.

Miniature reed relays are available in DIL
package and these are ideal for our purpose.
If a relay with integral diode is used, D5 can,
of course, be omitted. However, take note
that the integral diode may be of either
polarity. This should be carefully checked
before wiring the relay. M

addition to
model train
lighting

Figure 1. The circuit dia-
gram of the locomotive
headlamp reverser. Ter
minals A and B are the
external connections
across which a composite
voltage (19 kHz super-
imposed onto the d.c.
control voltage) is applied.
The supply voltage for the
circuit is derived from the
a.c. component.

(A)XJ-

* IC2 V
78L05

Figure 2. The internal
construction and pin
layout of the reed relay.
In spite of their small
size, many miniature
relays have an integral
diode-

83136 -2

1244

elektor december 1983

PC board pages

Note: the PCBs for the 64-way bus board
(EPS 831021 and the marine receiver
(EPS 83024) are not included since these
are double-sided boards.

1 4 \ \

1

video amplifier

1 m-s

frost warning device

m

disco phaser: delay line board

OSrCB

frost warning device
elektor december 1983

in the

In spite of the
cold weather we have had
since the summer disappeared, winter has
just begun and the worst weather almost invariably comes
first few months of the year. Then the weather forecast is

nearly always the same: 'cold . . . possibility of sleet or snow . . . watch out for
ice . . .', and so on. However, meteorologists cannot give a detailed an accurate
weather forecast for the whole of the country, particularly considering the
effect that local geography has on the weather. All our efforts to design a
'weather controller' have so far been in vain, but we did come up with this

frost warning device which should be a bit less hazardous than the usual suck

it and see' method.

frost

warning

device

with

a memory

While Britain is normally spared the worst
extremes of weather, there are times when it
does not seem like that. This is particularly
so in winter when the cold seems to be able
to creep through any number of layers of
woolen clothing. It’s unpleasant, but we just
have to grumble and bear it. It would be
very convenient, however, if you knew
before stepping outside whether it is merely
‘cold’ or ‘very very cold’. If you have a
thermometer the problem is solved, except,
of course, that it has to be left outside -
which sort of defeats the purpose. What
is really needed is a temperature sensor
mounted outside giving an indication inside.
For motorists the problem is somewhat dif-

ferent as weather conditions can vary quite
considerably in the course of a journey.
Gardeners are often interested in one par-
ticular weather condition - frost. In this
case, of course, it would be invaluable to
know if the temperature has dropped below
freezing point overnight, for example.

These are the principle applications we
considered for this frost warning device
but, because the temperature to be detected
can be adjusted, the circuit here has many
more possible applications than a simple
freezing-point detector.

Operation

The circuit diagram for this frost wamer is
shown in figure 1. The temperature is sensed
by the LM 335Z which gives a specific value
(A) in mV proportional to the measured
temperature. This provides one of the inputs
to comparator Al. The second input (B) is a
reference voltage which can be adjusted with
PI. When the sensor voltage at point A be-
comes lower than the reference voltage at
point B the output of Al goes high. This
causes the oscillator around A2 to start and
LED D1 flashes about once per second.

At the same time the one-shot at A3 will
go high for almost two seconds and during
this time a second oscillator based on A4
drives the piezo buzzer at a frequency of
about 1 kHz.

As far as the user is concerned, this is what
happens: when the temperature first drops

12-47

frost warning device
elektor december 1983

max. 45 mA

Figure 1. This is the cir-
cuit diagram of the frost
warning device. When the
temperature sensed by the
LM 335Z falls below a
preset level, this is indi-
cated by the two LEDs
and the buzzer.

below the preset level the buzzer sounds
briefly. At the same time LED D1 begins
to flash and flashes until the temperature
rises above the preset level again.

The circuit around T2 and T3 acts as a mem-
ory. Whenever the temperature drops below
the preset level D2 lights and continues
to do so even if the temperature has sub-
sequently risen above the preset level.

Push button SI must be pressed to ex-
tinguish this LED and thus reset the mem-
ory.

Construction and adjustment

Construction should present no problems,
especially if the printed circuit board layout
as shown in figure 2 is used. The LM 335Z
should, however, be protected from the wet,
and this is quite easily done. After soldering
wires onto the appropriate two leads of this
sensor, the assembly can be slipped into a
length of heat shrinkable tubing about Vi"
from the end. Heating this empty Vi' will
then cause it to contract and provide a
waterproof seal over the device. Alterna-
tively, the sensor could simply be sealed
with two-component epoxy glue.

12-48

frost warning device
elektor december 1983

Parts list

Resistors:

R1 = 2k2

R2.R3.R5 . . R12,
R16 . . . R19 = 100 k
R4 = 120 k
R13.R21.R22 = 10 k
R14,R23 = 470 (1
R 15 = 560 k
R20- 10 n
PI = 10 k preset

Capacitors:

Cl - 10 p/16 V
C2 = 1 p/16 V
C3,C4 = 10 p/35 V
C5 = 10 n
C6 = 470 p/25 V

Semiconductors:

01, D2 = LED
D3,D4,D6 = 1N4148
D5 = 1N4001
T1.T3 = BC550C
T2 = BC 560C
IC1 = 78L05
IC2 = 324
IC3 = LM 335Z

Miscellaneous:

Bz = piezo buzzer (Toko
PB 2720)

SI = push to make
pushbutton
Case, dimensions
120 x 65 x 65

A mixture of crushed ice and water is
needed to adjust the circuit. Stirring the
mixture with the sensor for a minute or
two will cause the sensor to be at freezing
point. Potentiometer PI is then adjusted
until LED D1 just lights and the buzzer
sounds briefly. Some people may consider
this as a case of shutting the stable door
after the horse has bolted as freezing can
occur at any temperature below about
+3°C. However, if a thermometer is used
as a reference, this temperature could just
as easily be used as the preset value.

The maximum current consumption of the
circuit is about 45 mA, and with its supply
voltage of 12 . . . 15 V it can be powered
by a car battery. If it is to be used in the
home a suitable power supply will have
to be added, of course.

Even though this circuit may seem
eminently suitable for use in a car as
an ice warning device, there are a few
problems to be considered first. The
sensor would have to be mounted some-
where out of the air stream but where
it is not affected by engine (or cabin)
heat. Even if your car has a suitable
mounting location, this will still leave
the sensor several inches above the
road (which is where the sensor really
should be). Also temperature is not the
only factor affecting the formation of
ice and just measuring one parameter
cannot be considered as a reliable indi-
cation. It is rather doubtful, therefore,
whether any so-called frost warning
device is of any use in a car. However,
if you are going on a long journey the
weather (and road) conditions may
change a lot, so if your frost wamer
starts to flash before you are half way
to your destination then at least you
know you should be on your guard!

Figure 2. This is the
printed circuit board
layout for the circuit
showing where all the
components are mounted.

1249

Phasing is an effect well known to musicians. In electronic parlance it is, in fact, a comb filter so called
because the response is the attenution and amplification of a number of equally spaced frequencies in
the audio spectrum. It lends itself particularly well to sounds rich in harmonics and is therefore ideal
for use with recordings, musicassettes, or records containing much percussion. E-string guitar music, or
choral works; it is not really suitable for solo instruments.

comb fitter
with switched
resistors

The filter response which provides the
phasing effect is illustrated in figure 1. From
this it is easy to see why it is called a comb
filter. There are a number of ways in which
this can be achieved in practical terms.
Studio quality systems can be very complex
and therefore very expensive, but simpler
methods do exist and, while not giving hi-fi
performance, do give a reasonable sound
quality. The easiest method, which is inci-

dentally the method used by virtually all
low-cost commercial phasers, is to use a
string of wide-band filters. These form a
delay line with a delay which can normally
be varied between 1 and 15 ms. To be sure,
quite a number of electronic switches are
required, but the use of TL 084 JFET
opamps and 4066 quad bilateral switches
keeps the number of components to a
minimum. Moreover, the circuit needs no

Figure 1. Frequency
response of a phaser. The
typical comb shape is the
result of the amplification
or attenuation of certain
frequencies. By modulating
the clock output, the
'teeth' are stretched and
compressed like a concer-
tina.

12-50

calibration, it accepts all signals of which the
level lies between the two supply voltages,
it produces neither noise nor distortion, and
it requires no low-pass filters.

The circuit shown in figure 2 is one element
of the 16-stage delay line used in the phaser.
With the type of filter used, it is, perhaps,
better to speak of time shift rather than
phase shift. It is readily seen from figure 2
how this shift is achieved: the larger
capacitor C, the greater the time shift.
Unfortunately, there’s a limit to this,
because the frequency response of the
filter tends to narrow with increasing C.
The only way to reconcile these two incom-
patible factors is a compromise between
the number of switches (as few as possible!)
and the sound quality (good transfer charac-
teristic). We found that values of C = 4n7
and R1 . . . 3 = 10 k gave the best results.
The delay line is housed on a separate
printed-circuit board from the oscillator
and control stages. This arrangement makes
it possible for a number of delay lines to
be connected in series or for the delay line
to be used for purpose other than described
here.

Coupling capacitors C17 ... 19 are necess-
ary at the audio input and delay outputs 1
and 2 to prevent d.c. entering, or off-set
voltages produced by the many opamps
leaving, the delay line.

It is, of course, vital that the delay line is
adjustable and the various means by which
this can be achieved include OTAs (oper-
ational transconductance amplifiers), FETs
(field-effect transistors), and so on. It is,
however, much cheaper to switch resistors
by means of CMOS switches which open and
close (under the control of the clock gener-
ator, Nl) at a high frequency. When the
switch is open, the flow of current is inter-
rupted and the associated capacitor does
not charge. When the switch is closed, cur-
rent flows and the capacitor charges. The
switching frequency is of little concern in
this application: what is important is how
long the switch is open or closed as this
determines the length of pulses and pauses.
Ideally, the duty cycle (that is, the pulse/
pause ratio) should be continuously variable
between 0 and 100 per cent, and all switches
should be controlled by the same clock. The
clock frequency should preferably be more
than twice the highest audio frequency, say,
40 ... 50 kHz. Be careful when using tape
recorders, however, as the erase oscillator
may work at the about the same frequency.

Oscillator

As stated, we need a pulse-width (clock)
generator which produces square waves at a
frequency of about 40 ... 50 kHz: this is
Schmitt trigger Nl and associated com-
ponents (see figure 3b). The square-wave
pulses are converted by low-pass filter
R12-C6 into a triangular wave form which
is then fed to opamp IC5. This IC functions
as a comparator and its trigger level is
determined by the voltage at its non-
inverting input (pin 3). The pulse width at
the output (pin 6) of IC5 is also directly
dependent upon the voltage at pin 3. Schmitt
trigger N2 merely restores the output pulses
to square waves.

2

As we said before, it must be possible to
vary the pulse-width at the output of N2,
and this can be done in two ways: manually,
with P3, and by means of an LFO (low-
frequency oscillator) consisting of integrator
A1 and trigger A2.

As the phasing effect sounds better if the
pulse-width is modulated by a sine wave
rather than a triangular wave, buffer A3 and
limiting diodes D5 and D6 are connected in
series with the (triangular) output of the
LFO. The output level of the LFO is about
± 0.7 V which can be set to any value
within this range by means of P2. The out-
put of the LFO stages is taken across R 18 to
A4 (pin 13) where it is mixed with the
voltage from P3. The relation between these
two inputs is determined by the trigger level
of the mixer which is set by P3.

It may, unfortunately, happen that the
presetting range of P2 and P3 includes
an area where the output voltage of A4
is too low or too high. This results in IC5
clipping the triangular wave form at pin 2
(see figure 4), which causes a loud click in
the loudspeaker. This trouble is encountered
particularly when the pulse width is set too
narrow (duty cycle below about 2 or 3 per
cent).

A control stage is therefore needed to limit
the output of A4. A Schmitt trigger, N3,
is triggered by the output signal of IC5
(which has a variable duty cycle) and
functions as a secondary clock generator:
its output is inverted by N4. The outputs
of N3 and N4 are integrated and converted
into d.c. voltages which are compared with
a reference voltage by IC1 and IC2 respect-
ively. The reference voltages are preset by
P5 and P6 respectively. The d.c. levels
(which are thus proportional to the duty
cycle) are used to control A4 so that the
output of this stage cannot exceed a duty
cycle range of 10 ... 90 per cent (see
figure 4). An incidental advantage of this
arrangement is that the control stage is
independent of the clock generator and the
low-frequency oscillator. If necessary, it can
therefore be disconnected from A4 without
any ill effect.

Additional points

The delay time of the sixteen-element delay
line is 6 ms. The delay time can, of course,
be lengthened by connecting a number of
delay lines in series. However, we found that
when more than two lines are used, the
sound becomes increasingly distorted and
the overall effect is one of impairment
rather than improvement.

disco phaser
elektor december 1983

Figure 2. Basic circuit of
a wide band filter: the
delay is determined by C
and R1.

12-51

disco phaser
elektor december 1983

Figure 3a. The circuit
diagram of the sixteen
active filters and the
(electronically) switched
input resistors which form
the delay line.

disco phaser
elektor december 1983

X

x

7

©

©

©

a

IC1 IC2 IC3 IC4 IC5

lOOn s

©

©

©

a

^"16V

•4— —

.-I

X

X

X

N1 ... N4 = IC3 = 4093
A1 ... A4 = IC4 = TL084

Figure 3b. The circuit
diagram of the oscillator
and control stages.

break-through of clock trgnal

i \

Figure 4. The most likely
fault is the breaking
through of the clock signal
when the pulse/pause
ratio becomes too large
or too small. The control
stage limits the ratio.

disco phaser
elektor december 1983

Parts list - delay line

Resistors:

R1 . . . R49 = 10 k

R50 = 100 k

PI = 100 k linear preset

Capacitors:

Cl . . . C16 = 4n7 ceramic
Cl 7 . . . C19 = 470 n
ceramic

C20 * 100 n ceramic
C21.C22 = 10 jlx/ 16 V
electrolytic

Semiconductors:

IC1 . . . IC4 = TL 084
IC5 . . . IC8 = 4066
IC9 = 741

Miscellaneous:
printed-circuit board
83120-1

Parts list — oscillator
Resistors:

R1 ,R2,R9,R10,R12 = 10k
R3,R4,R13,R14 = 47 k
R5,R6,R15,R16,

R20 = 100 k
R7,R8 = 47 k
R11 = 27 k
R17 = 15 k
R 18 = 22 k
R19= 390k
PI = 1 M linear preset
P2,P3 = 100 k linear preset
P4 = 25 k preset
P5.P6 = 47 k preset

Capacitors:

C1.C2.C11 = 100 n
ceramic

C3 = 220 /i/16 V
electrolytic

C4.C9.C10 = 22 /i/16 V
electrolytic
C5.C6 = 1 n ceramic
C7.C8 = 2ju2/16 V
electrolytic
C12.C13 = 10 /i/16 V
electrolytic

Semiconductors:

D1 . . . D6 = 1N4148
IC1.IC2 = LF 356
IC3 = 4093
IC4 = TL 084
IC5 = 3140

Miscellaneous:

SI = SPST switch
Printed-circuit board
83120-2

The mixer output should not be used when
connecting delay lines in series: use output
delay 1 (eight filters) or delay 2 (sixteen
filters) only. The preset PI can be omitted
from all but the last in a series of delay
lines, but it must then be replaced by a

100 k resistor to earth as shown in dotted
lines in figure 3a.

The outputs of the delay lines are wired
to the input resistors, R51 . . . R54, of
mixer IC9. Four inputs are provided to
enable two delay lines to be wired in series.

12-54

disco phaser
elektor december 1983

Figure 5. Layout and
trackside of the printed-
circuit board for the delay
line: provision is made
for resistors R51 . . . 54.

This then forms a delay line of 8, 16, 24,
and 32 stages. The least delayed sound
should be connected to the highest resist-
ance. The resistors can be of the following
values: 1M (R51), 470 k (R52), 220 k
(R53), 100 k (R54). These values are, of

course, entirely arbitrary and you may
find other values more pleasing to you.
Furthermore, different phasing effects can
be found by switching the outputs of the
delay lines to the mixer. M

Figure 6. Layout and
trackside of the printed-
circuit board for the
oscillator and control
stages.

12-55

banking program
elektor december 1983

One of the most interesting characteristics of combining a BASIC compiler
with a Disk Operating System is the possibility of creating data files accessed
by one or more programs written in BASIC. For Junior Computer owners
the procedure is described briefly in the Ohio notes, but when this banking
program was sent in by a reader we saw it as an excellent opportunity to
delve a bit deeper into the operation of indirect files.

banking program

a financial
control pro-
gram using
indirect filing
on the Junior
Computer

L. Germain

Table 1. Program PRPDA3
is only used for entering
the (secret) security code
into file DATA3.

Before we start in earnest it is important
to note the difference between direct and
indirect files. If a programmer writes a
program with line numbers, he has direct
access while he is editing, modifying and
listing it. When this same program generates
data due to calculations, compiles the
results and makes a new (‘data’) file saved
on disk under another name using the
OPEN, CLOSE, GET and PUT instructions,
this is known as indirect access. In effect,
the user cannot add to, remove from, or
even inspect the data directly in this file.

How to prepare indirect files

As a general rule the first task is to assign
names to the files. In our example, these
are ‘DATA2’ and ‘DATA3’, which are
the indirect files, ‘BANK’, which is the
main program and ‘PRPDA3’ (for ‘prepare
DATA3'). ‘DATA3’ is an indirect random
file which is only used to save the total of
the count, the number of the last operation
(these are both initialised automatically
by ‘PRPDA3’) and a security code to re-
fuse access to anybody who does not know
it (if the RUN at the end of line 45 of
‘BANK’ is replaced by NEW the program
automatically erases itself if the code is
wrong). The instruction POKE 741,10 could
also be included at the start of line 20 of
‘BANK’ to prevent the program from being
listed.

‘DATA2’ contains the financial operations
(amounts, date and nature) registered
by the program ‘BANK’. Before storing
the programs ‘BANK’ and ‘PRPDA3’ in
memory, buffer zones must be created
using option 7 of BEXEC*. Two buffers
are needed for ‘BANK’ (‘DATA2’ and
‘DATA3’) and a single one for ‘PRPDA3’.
Initially four tracks of diskette could be
reserved for ‘BANK’, one for ‘DATA3’,
one for ‘PRPDA3’ and at least ten for
‘DATA2’ (enough for about a year’s use).
When all of table 1 has been saved on
diskette, ‘PRPDA3’ must be run, a code
entered, and then ‘BANK’ run. When the
correct code has been entered, the screen
will then display the eight options available
to the user.

The routines used

At the start of each of the specific routines
the program will seek two fundamental data
values on the diskette: the remaining balance
(variable S) and the number of the last
operation specified (variable C). This is done
starting at line 500. The subroutine at line
525 reverses the procedure at the end of
each routine.

Input and output routines

The program first asks the number of credits
or debits to be processed. Then it requests
the amount of the first operation, its nature
(or category) and its date.

The date is always indicated by six figures,
first the day, then the month and finally
the year, with two numbers for each. The
category is registered as a string of charac-
ters, so it could consist of names (‘taxes’ for
example), numbers (such as cheques) or
abbreviations.

Request routine

It is possible to get a complete list of all
credits or debits, or a listing per month or
even of a certain operation (identified by
amount, category and date). If one or two
of the required parameters are not known
(amount/category/date) write ‘X’.

Balance routine

This routine displays the balance available.

Adding routines

As the name implies, these options are used
for compiling totals for the different types
of operations.

When the program is used for the first time,
option ‘1’ must be used to register at least
one credit, otherwise the program will refuse
all attempts to get it to work. As it would
take far too much space to deal with all the
various details of this program, we will have
to be content with the bare minimum, so we
will go no further. We are sure that any
interested readers will make short work of
sorting out this program and will use nothing
but indirect files from now on. M

Table 1

5 REM PRPDA3

10 PRINT: PRINT: INPUT”INPUT CODE " ;E$ : C=0 :S*0
20 DISK CPEN,6,”DATA3":DISK GET, 1
30 PRINTS6..1 DISK PUT:DISK GET, 2
40 PRINTS6 ,2 ; " , " ;C ; " , " ;S: DISK PUT: DISK CLOSE, 6

12-56

Table 2

banking program
elektor dec ember 1983

1 REM BANK

5 PRINT:PRINT: PRINT:POKE 2888 , 0 : P0KE8722 , 0

10 PRINTTABC 16 ) "‘FINANCIAL CONTROL PROGRAM*" : PRINT : PRINT

20 PRINTrPRINT: INPUT" CODE "; A$ : PRINT : PRINT

30 DISK OPEN ,6, "DATA 3" : DISK GET , 1

45 INPUT §6 , R , B$ : DISK CLOSE, 6 : IFA$OB$ THEN RUN

70 CLEAF:PRINT:PRINTTAB(3) m 1 = CREDITS"

80 PRINTTABC 3 )"2 = DEBITS"

* REQUESTS"

BALANCE"

MONTHLY TOTAL"

ANNUAL TOTAL-
TOTAL PER CATEGORY"

EXIT"

90 PRINTTAB( 3 ) " 3

95 PRINTTABC 3)"4 =

96 PRINTTABC 3 ) "5 =

97 PRINTTABC 3 ) "6 =

98 PRINTTABC 3)"7 =
100 PRINTTAEC 3 )"8

105 PRINT :INPUT"NUMBER SELECTED ";A

110 ON A GOTO 130,200,250,330,3^0,380,^30, 1000
120 G0T070
’2 * REM

130 G0SUB500 :PRINT:PRINT:PRINTT ABC 16) "CREDIT ROUTINE"

145 PRINT : PRINT : INPUT"NUMBER OF CREDITS" : D : PRINT : PRI NT
150 DISK OPEN , 6 , "DATA2"

155 FOR R = C«-1 TO C+D

160 INPUT" AMOUNT "; E : SsS«-E : PRINT : PRINT

'61 INPUT-OPERATION OR CATEGORY "; A$ : PRINT : PRINT

170 INPUT-DATE ( DA Y/MONTH/ YEAR ) "; b$ : S$= "C" : PR INT : PRINT : DISK GET

180 PRINT§6 , R ; " , " ; E ; " , " ; A$ ; " , " ; B$ ; " , " ; S$

185 DISK PUT:NEXTR:C=R-1 :GOSUB525:GOTO70

>R

186 REM

2 00 GOSUB500 : S$= "D" : PRINT : PRINT : PRINTTABC 16) "DEBIT ROUTINE" : PRINT: PRINT
205 DISK OPEN , 6 , "DATA2" : INPUT"NUMBER OF DEBITS B : PRINT : PRINT

215 FOR R=C+ 1 TO C+B

220 INPUT" AMOUNT E : PRINT : PRINT

221 IF(S-E)<0THEN PRINT"YOU ONLY HAVE ";S;" POUNDS !": PRINT : PRINT :G0T0220

225 S=S-E

226 I NPUT"OPERATION OR CATEGORY A| : PRINT : PRINT

227 INPUT"DATE (DAY/MONTH/YEAR) "; B$ : PRINT : PRINT
235 DISK GET,R:PRINT§6,R;",";E;",";A$;",";B$;",";S$

21*0 DISK PUT : NEXTR : DISK CLOSE , 6 : G0SUB525 : GOT070

241 REM

250 PRINT : PRINTTABC 16)"REQUEST ROUTINE" : PRINT : PRINT

255 PR I NT" DO YOU WANT TO LOOK AT ";

256 INPUT"CREDITS OR DEBITS (C/D) "; Z$ : PRINT : PRINT

260 INPUT"DO YOU WANT A LIST (Y/N) ";X$:IF X$<>"Y" THEN 265 : PRINT : PRINT

262 INPUT-DO YOU WANT A LIST PER MONTH ( Y/N )"; H$ : PRINT : PRINT : IF H$O"Y"THEN280

263 GOSUB 500 :GOSUB 7 10 : V$r Z$ :G0T0345

265 PRINTrPRINT: IN PUT" AMOUNT "; I $: PRINT : PRINT : IF I$<>"X" THEN 280

270 IN PUT" OPE RATI ON OR CATEGORY "; 1$ : PRINT : PRINT

271 IF I$<>"X" THEN 280

275 INPUT"DATE ";I$:IF I$="X" THENPRINT : PRINT" IMPOSSIBLE REQUEST !!":GOT070

276 REM

280 GOSUB 500 : DISK 0PEN,6,"DATA2"

285 FOR R= 1 TO C : DISK GET, R

290 IN PUT §6 ,R,E,A$,B$,S$:IF Z$OS$ THEN 320

295 IF X$= "Y" THEN GOSUB600 :GOTO 320

296 REM

300 IF I$=A$ OR I$=B$ OR EsVALC 1$ ) THEN GOSUB 600

320 IF Ws 15 THEN INPUT"CR TO CONTINUE ";W$:W=0

321 NEXTR: IF Y=0 THEN PRINT : PRINT"DATA NOT FOUND "

322 DISK CL0SE,6:Y=0

323 PRINT:PRINT: INPUT"CR TO CONTINUE ":W$:GOT070
321* REM

330 G0SUB500 : PRINT: PRI NT: PRINT" BA LANCE :":S:" POUNDS" :GOTO 323

331 REM

340 X$=" MONTH " :GOSUB700

345 PRINT : PRINT : INPUT"MONTH ";M:DISK OPEN , 6 , " DATA2"

355 FOR Rs 1 TO C:DISK GET , R
357 INPUT $6,R,E,A$,B$,S$

360 IF V$OS$ THEN 365

36 I L=VAL(MID$(B$,4,2)) :0= VALC RIGHTI ( B$ , 2 ) )

363 IF H$= " Y" AND Q=0 AND M=L THEN G0SUB600:IF W=18 THEN 320
36H if QsO AND M=L THEN LET T=T+E
365 NEXTR

370 PRINT : PRINT : PR INT" TOTAL OF ";V$;" FOR ";M:"/";Q;" : ":T:" POUNDS "

371 TsO : QsO

375 GOTO 323

376 REM

380 X$="YEAR " :G0SUB700:D1SK OPEN ,6,"DATA2"

1*00 FOR R= 1 TO C : DISK GET , R
1*10 INPUT S6,R,E,A$,B$,S$

415 IF V$OS$ THEN 425
420 0sVAL(RIGHT$(B$,2))

422 IF QsO THEN LET T = T4.E
425 NEXTR

427 PRINT : PRINT : PR I NT- TOTAL OF ";V$;" FOR ":Q:" : ":T:" POUNDS" :T=0:G0T0 323

428 REM

430 X$=" CATEGORY " :GOSUB700 : PRINT : PRINT : INPUT-CATEGORY ":I1
435 DISK OPEN , 6 , "DATA2"

440 FOR Rs 1 TO C:DISK GET, R : INPUT §6 , R , E , A$ , B$ , S$

442 IF V$OS$ THEN 450

444 L = VALC RIGHT$ ( B$ , 2) ) : IF Q=L AND A$=I$ THEN LET TsT-fE
450 NEXTR

455 PRINT: PRINT :PRINT"TOTAL OF ";I$;" FOR ";Q;" s ";T;" POUNDS" :Ts0 :G0T0323

456 REM

500 DISK OPEN , 6 , "DATA 3"

510 DISK GET , 2 : INPUT S6 , R , C , S : DISK CLOSE , 6 : RETURN
52.1 REM

525 CsR- 1 : DISK OPEN , 6 , "DATA3" : DISK GET , 2 : PRINTS6 , 2 : " , " : C : " " :S
540 DISK PUT: DISK CLOSE , 6 : RETURN
550 REM

600 IF LEN(STR$(E))=9 THEN SPsO:GOTO 620
602 KsLENCSTRICE)) :SP=(9-K)

620 PRINT R ;TAB( 4 ) "AMOUNT : " ;SPC( SP ) ; E ; "Pds /OPER. OR CAT. ";A$:

621 PRINTTABC 49 )" DATE :"; B$ ; " ";S$

630 W = W^1 : Y = Y+ 1 : RETURN

700 GOSUB 500: PRINT : PRINT" ADDING ROUTINE PER " ; \$

705 PRINT: PRINT: INPUT" CREDITS OR DEBITS (C/D) ";V$

710 PRINT : PRINT : IN PUT" YEAR " ;Q : RETURN
1000 END

Table 2. The banking
program proper (BANK)
works with two random
access files DATA2 and
DATA3 for which two
buffers must be created
after entering the instruc-
tions here.

12-57

NOVRAM: data
storage without batteries
elektor december 1983

NOVRAM:

data storage

without

batteries

Semiconductor manufacturers are at
present investing large amounts of
time (and money) into developing
non-volatile memories, whereby the
data is saved even in the case of the
power being removed. These devices
are finally about to hit the market,
and the manufacturer is very
confident about their success.

There is no questioning the need for
non-volatile memories. Every
computer user would like to be sure
that his memory storage is safe-
guarded if the power unexpectedly
fails. And how about the digital tuner
in some hi-fi systems which fail to
remember the transmitter frequencies
if the power supply is cut off for too
long? So NOVRAMs are definitely not
of the 'invent them first and find a use
for them later' school of electronics.

The CMOS RAM could be considered the
forerunner of the true non-volatile memory.
It is noted for its very low quiescent current
consumption, so that the data in the mem-
ory can be saved for months or even years
with batteries providing the power. This is
not a completely satisfactory solution, of
course, but it is handy as far as it goes.

In the last few years some proper non-
volatile memories have appeared, notably
the EAROM (Electrically Alterable ROM)
and the EEPROM (Electrically Erasable
PROM). These are ROMs whose contents
can be altered electrically, without the
device first having to be erased by exposure
to UV light, for example. An extra pro-
gramming voltage is often required, but in
the newest types even that is unnecessary
as a ‘high voltage’ generator is integrated in
the chip. A single voltage of 5 V is all that is
needed.

The biggest disadvantage of all these electri-
cally rewritable ROMs is the long time
needed to write to them. Normally it takes
about 10 ms per byte, which is very slow,
compared to the few hundred nanoseconds
for a normal RAM. This means that an
EAROM or EEPROM is no real substitute
for a RAM. A further point to remember is
that these ROMs can only be ‘rewritten’ a
certain number of times, normally about
10000. An EAROM or EEPROM is thus
entirely suitable as a transmitter memory in
a tuner, for example, but its application in
computers is limited.

The NOVRAM

The new NOVRAM (NOn-Volatile RAM)
from the Californian firm of Xicor is finally
a step in the right direction. This IC com-
bines the advantages of the normal RAM and
the electrically rewritable ROM. At the
moment the NOVRAM is available in three
versions: 1 K x 1 bit, 64 x 4 bit and 256 x
4 bit. The pin designations of the three types
are shown in figure 1 . All inputs and outputs
are fully TTL compatible and only one
supply voltage of 5 V is needed.

A block diagram of the NOVRAM is shown
in figure 2. From this it appears that the
layout is practically the same as a normal
static RAM. We see that it has normal ad-
dress and data lines plus a CS and WE input.
The actual memory is doubled: each RAM
memory location has an EEPROM counter-
part. This means that each IC contains not
one but two memory matrices laid one over
the other. Data transfer between the two
memories is contr olled usin g two extra in-
puts, S TORE and RECALL. Giving a pulse
at the STORE input causes the IC to dupli-
cate the total content of the RAM into the
EEPROM. The IC needs a maximum of
10 ms to complete this whole duplication!
If a pulse is given at the RECALL input the
contents of the EEPROM is written back to
RAM. The time taken for this operation is
about 1 ms.

This set up gives several important advan-
tages. For normal use (as RAM memory
in a computer system, for example) the
NOVRAM can simply act as a normal
memory and the computer does not have
to take long write-times into account. When

12-58

256 x 4

64 x 4

IK x 1

ps

83139 1

2

NOVRAM: data
storage without batteries
elektor december 1983

Figure 1. The pin desig-
nations of the three
NOVRAMs at present
available.

Figure 2. This block
diagram shows the layout
of the NOVRAM. The
memory section is
doubled, so it consists
of RAM and EEPROM
sections.

the power is switched off or fails, a single
pulse is enough to store all the data in the
EEPROM. In this way important data can
be saved for an indeterminate time without
the need for auxiliary supplies. Even though
the NOVRAM suffers partly from the
EPROM disadvantage of needing a certain
number of write cycles, this is rarely a
problem. The RAM section can be written
to and read from freely. The data only needs
to be written to the EEPROM section when
the power is to be switched off.

The technology

The Xicor NOVRAMs use FETs with
floating gates. A floating gate is an island of
polysilicon surrounded by oxides. A charge
can be induced on, or removed from, the
gate by applying a sufficiently strong electric
field to cause electron tunneling through the
oxides. Under normal conditions the charge
remains constant on the gates even when the
power is removed. The NOVRAM uses three
layers of polysilicon, the centre one being
the floating gate.

The diagram of figure 3 shows one single
data cell of a NOVRAM. The RAM section
consists of a conventional six transistor
structure, while the EEPROM section con-
sists of the three polysilicon layers and two
FETs to control the data transfer. The
floating gate (POLY 2) is only connected to
the rest of the circuit through capacitance.
POLY 2 is charged by transferring electrons
to it from POLY 1, and discharged by
transferring these electrons to POLY 3. The
key to the operation is in the ratios between
capacitances CC2, CC3, Ce and Cp. When
writing from RAM to EEPROM the sequence
is as follows. If node N1 is low, transistor Q7
is turned off so the junction between CC2
and CC3 floats. As the total capacitance of
CC2 + CC3 is larger than Cp the floating gate
follows the Internal Store Voltage node. If
the voltage on the floating gate is high
enough electrons are tunneled from POLY 1
to POLY 2 so that the floating gate is
negatively charged.

If node N1 is high, Q7 is turned on thus
grounding the junction between CC2 and

12-59

NOVRAM: data
storage without batteries
elektor december 1983

Figure 3. Here we see a
single memory cell. The
RAM section consists
of the upper part,
while the lower area
is the EEPROM cell.

Vcca

4

RAW DC O-

Figure 4. This circuit
is used to detect any
failure of the power
s upply an d it then gives
a STORE pulse to the
NOVRAM.

CC3. As CC2 is larger than Ce, it holds
the floating gate near ground when the
Internal Store Voltage node is pulled high.
This causes a sufficient field between POLY
2 and POLY 3 to tunnel electrons away
from the floating gate to leave it with a
positive charge.

The RECALL operation also takes advantage
of capacitance ratios, in particular that C2 is
larger than Cl. When the external RECALL
command is received, the internal power
supply, VcCA is first pulled low to make the
voltage at N1 and N2 equal. Then the supply
rises again and the node with the lesser
capacitance rises more rapidly than the
other, and is then latched high by the flip-
flop. If the floating gate has a positive
charge, N2 is connected to C2 via Q8 and
will latch low. If the floating gate has a
negative charge, Q8 is turned off and N1 will
thus latch low.

How a NOVRAM is used

Nothing needs to be said about connecting
up the NOVRAM as this is almost the same
as for a normal RAM. The only signals which
are different a re the STORE and RECALL.
The RECALL pulse can be taken care of by
the software in the computer. The STORE
signal on the other hand can better be
generated by a separate circuit. This circuit
watches for power failures and, if one is
detected, supplies a pulse to the NOVRAM

to ensure that the data is saved. An example
of such a circuit is shown in figure 4. If the
input voltage to the regulator drops, then at
a certain moment the voltage at the non-
inverting input of comparator A will be
lower than the reference voltage at the
inverting input. The output voltage then
drops from +5 V to zer o. This t ransition can
be used to trigger the STORE pulse. The
circuit reacts at an input voltage of about
8 V. It should be remembered that the
5 volts must remain present for at least
10 ms after the input voltage has dropped
below 8 V. This is the time needed by the
NOVRAM to transfer data from RAM to
EEPROM. The values of the supply ca-
pacitors should be made to suit this.

This NOVRAM is quite an interesting IC,
but, of course, every silver lining has a cloud,
and in this case it is the higher price than
‘normal’ memories and probably the dif-
ficulty of getting hold of them. However,
this is bound to change! M

Literature:

Xicor application notes AN 101 .. . 103
Xicor NOVRAM Memories data sheet.

Xicor 's U.K. suppliers are:

Micro Call Ltd.

Thame Park Road
Thame

Oxon 0X9 3XD
Telephone: 08442 15405

12-60

NOVRAM: data
storage without batteries
elektor december 1983

A.C. CHARACTERISTICS

T/\ = 0°C to 70°C, Vqq = +5 V ± 10%, unless otherwise specified.

READ CYCLE

Symbol

Parameter

tRC

Read Cycle Time

tA

Access Time

tco

Chip Select to Output Valid

tOH

Output Hold from Address Change

tLZ

Chip Select to Output in Low Z

tHZ

Chip Deselect to Output in High Z

WRITE CYCLE

Symbol

Parameter

twc

Write Cycle Time

tew

Chip Select to End of Write

tAS

Address Set-up Time

tWP

Write Pulse Width

tWR

Write Recovery Time

tow

Data Valid to End of Write

tOH

Data Hold Time

twz

Write Enable to Output in High Z

tow

Output Active from End of Write

LIMITS

Typ' 3 ' Max

LIMITS

Typ 0 * Max

Note: typical values are
stated for Ta - 25° C and
nominal supply voltages

STORE CYCLE

ARRAY RECALL CYCLE

ABSOLUTE MAXIMUM
RATINGS

Temperature Under Bias

-10°C to +85°C
Storage Temperature

-€5°C to +1 25°C
Voltage on Any Pin with
Respect to Ground

-1.0 V to +6 V
D.C. Output Current 5 mA

Table 1. The technical
specifications of the
NOVRAM.

12-61

f Si

. :

X 1

x iot |

What TRS-80, LNW80, Video Genie,
Atom, Junior Computer, Ohio owner
has never dreamed of being able to
connect some specialized circuit to his
computer? And what about a design
borrowed from another member of
his micro computer club? Just think
of the possibilities that opens up. That
would have to be very complicated,
you say. Not necessarily . . . read on
and find out more.

bus extension

for the
TRS-80 and
other
personal
computers

It is no secret to anybody that there is a
price war raging in the market for home
computers. Every manufacturer tries to
establish as wide a range as possible in order
to sell the maximum number of extensions
(their prices have fallen also, but not to the
same extent as the actual computers). This
can make it difficult to connect peripherals

to a computer without having to buy as
many connectors and cables as circuits.
When we came up against this problem we
decided it was time to see how the Elektor
bus board could be used with other (non-
Elektor) equipment.

Many specialized shops (and magazines)
supply all sorts of different equipment, and

T able 1

TRS80 Ml

SC/MP

(seen

SC/MP

TRS80MI

ACORN

LNW80/I

6809

<•’80

6502

INS 8060

from

INS 8060

6502

Z80

6809

LNW80/I

ACORN

ATOM

Vidfto Genie I/ll

INS 8070

below)

INS 8070

Vidfo Genie I/ll

ATOM

♦5 V

♦5 V

♦5 V

♦ 5 V

♦ 5 V

♦5 V

y • ■ t

♦5 V

♦5 V

♦ 5 V

♦5 V

♦5 V

♦5 V

NC

NC

NC

NC

NC

OMWflFFF'l

► • -7

06MV7FF '1

NC

NC

NC

NC

8u?0

(—12 V)

12 V

12 V

-12 V

12 V

1 - 1

12 V

12 V

12 V

-12 V

(-12 V)

(-12 V)

1

1

1

1

1

1

4 • 4

1

1

1

1

1

1

ROY

WAIT

MRDY

WAITE X

ROY

N HOLD

ft • S

NRST

RES

PWCl

RESET

SYSRES

NRST

NC

NC

NC

NC

NC

08«J«9Ff'I

I • 1

NBREO

NC

NC

CMAT&RTG

NC

NC

DO

DBOO

DBOO

OB00

DBOO

DBOO

7 • 7

OB01

DB01

0801

DB01

DB01

01

D2

DB02

OB02

OB02

D802

DB02

A • «

DB03

0803

0803

DB03

DB03

D3

04

DB04

OB04

OB04

0804

0804

• • f

DB05

DB05

D805

DB05

DB05

D5

06

DB06

DB06

OB06

DB06

OB06

l» • 10

DB0/

DB07

080/

DB07

DB07

D7

NC

NC

HALT

NC

NC

CONT'I

1 • v

NENIN

DD (OSD

BLfSRQ

NC

TEST

NC

NMI

NC

NMI

NMI

NMI

SA

* • i

SB

IRO

INT

IRQ

INT

IRQ

NC

IN

NC

NC/BB2.4 4 *

NC

SIN*

IX • 13

SOUT 1 )

NC

NC

NC

OUT

NC

SO

NC

NC

NC

SO

F0

14 • 14

FI

K 7

NC

NC

NC

NC

NC

NC

NC

NC

K6

F2

1» • IS

<muooi j ff 3 I

K5

NC

NC

NC

NC

1

1

1

1

L

1

ift • 16

i

1

1

i

1

NC

NC

NC

*12 V

M2 V

♦ 12 V

M2 V/NC

17 • 17

NC J >

K4

NC

8S I>3 >

NC

NC

NC

NC

BA

buSak

K3

NENOUT

NC/ -5 V

5 V

5 V

-5 V

(-5 V)

( -5 V)

A 14

AD 14

AD. 4

ADM

ADM

ADM

AD15

AD 15

AD15

AD15

AD15

A 1 5

A12

A012

A012

AD 1 2

AD12

AD12

AD13

AD 13

AD13

AD 13

AD 13

A13

A 10

A0 1 0

A0 10

AD10

AD10

AD 10

’ I

AD1 1

AD 1 1

AD1 1

AD1 1

AD1 1

All

A8

A DO 8

A 008

AD08

A 008

AD08

L ■ „

A 009

A 009

AD09

AD09

A 009

A9

A6

A 006

A 006

A 006

A 006

A 006

A 00 7

ADO 7

A DO 7

AD07

AD07

A7

A4

A 004

A 004

A 004

A 004

AD04

74 • - H

ADOb

ADOb

A DO 5

AD05

AD05

A5

A2

A 002

A 002

A DO 2

AD02

AD02

A 003

AD03

A 003

AD03

AD03

A3

AO

A 000

AO00

AO00

A 000

A 000

7ft • - 7f

AD0 1

AD0 1

AD0 1

AD0 1

AD01

A1

NC

NC

E

MREO

NC

NWDS*NRDS

XI

02

PHIEX

E

(O)

<t>2

NC

RAS

NC

RAS

K2

(lAWVBFF’l

-//♦5 V

NC

NC

NC

NC

NC

R /W

NC

NC

Ml

R/W

Cl RAM

7*- • rt

0C00 0DFF *>

K1

NC

NC

iwtsr

NC

NC

NR OS

NC

fu)

— a £_

F ’ R/W

IORQ

RD

EX

NC

CARDEN

NRDS

!, : 1

NADS 0

NWDS

4>1

RAM R/W

rERSR

WR

Q

R/W

NC

WR

SYNC

NWDS

» . w

1

1

c b a

-1

Notes.

)1 not used by INS 8070
)2 15a reserved for A1 7
17a reserved for A16

)3 subject to change

)4 88 2 4 battery back up » 2 4 V

These pm designations are the universally accepted

standards (taking note 3 into account, of course)

83135

12-62

bus extension
elektor december 1983

Figure 1. These are the
signals available at the
TRS-80 keyboard output
connector. The LNW80
has an extra signal, CAS,
at pin 3.

Figure 2. This shows an
example of how the bus
extension can be adapted
for a TRS-80. Some of
the a and c pins are con-
nected together in this
design to reduce resistance
in the power supply lines
(earth, +5 V and —12 V).

seen from above

♦5 V 39

aOc

Q-i-0

39 *5 V

X 29/37

□ 2D
0-3-a
cm-o

29/37 X

2

33

22

□ 60

30

26

□ so

32

28

o *□

18

20

o ion

24

23

□ " □

21

012 □

12

Ol3 □

19

X 29/37

0*0
□ isO
0160

29/37X

7

□ 170

□ 180
□ iso

10

6

□ 200

5

9

021 0

4

17

□ 220

11

36

0230

38

35

□ 24 0

31

34

□ 25 0

40

27

0260

25

□ 27 0

□ 280

1

14

□ 29 0

13

□ 300
0310

15

18

032-0

B1

o

83135.2

Table 1. Here we list the
relation between the pins
of a 64-way connector and
the signals available on
some microprocessor or
microcomputer buses.

64-way

connector

TRS-80

signals

TRS-80

signals

64 -way
connector

5a

SYSRES*

2

c

3

1

RAS*

28c

21c

A10

4

c

J

3

NC 1

NC

20a

A13

6

c

J

5

A 12

20c

32a. c

GND

8

c

J

7

A15

19a

19c

A14

10

c

□

9

All

21a

13a

OUT*

12

c

J

11

A8

22c

29a

INTAK*

14

L

J

13

WR*

31a

NC

NC

16

C

□

15

RD*

31c

9c

D4

18

L

J

17

A9

22a

10a

D7

20

c

J

19

IN*

13c

7a

D1

22

L

J

21

INT*

12a

10c

D6

24

L

J

23

TEST*

11a

8a

D3

26

L

J

25

A#

26c

9a

05

28

C.

J

27

A1

26a

7c

00

30

c

□

29

GND

4a,c/16a,c

8c

02

32

c

□

31

A4

24c

25a

A3

34

L

3

33

WAIT*

5c

23a

A7

36

c

J

35

A5

24a

23c

A6

38

c

J

37

GND

4a.c/16a,c

25c

A2

40

c

3

39

♦5 V

1a,c

Note:

• indicates negative logic (an input or output is
'true' at the low logic level)

1 CAS for the LNW80

83135-1

each circuit is more sophisticated than the
next. The very sight of them is enough to
bring out the ‘experimenter’ in every one of
us. To make proper experimentation feasible,
what is really needed is a bus board, which
has several connectors to accept one or a
number of cards, and preferably with its
own on-board supply.

What is a bus?

Obviously everybody could design their own
bus, to suit their own particular needs, but
this would almost certainly rule out the
possibility of borrowing a circuit from some-
body else with a similar computer.

This is why Elektor designed a bus board in
mid 1978 for the first microprocessor to
appear in any of our circuits, the SC/MP.
Gradually, as new micros started to appear
(the 6502, Z80 and 6809), the number of
lines needed began to increase. Originally
the bus was intended only for one computer,
the SC/MP. Eventually the Junior Computer
arrived and the bus was used for this also.
As the TRS-80 is still a very popular micro
we decided that some rationalization was in
order to make it compatible with the Elek-
tor bus. The same applies for several other
computers and the most recent addition to
our list is the Acorn Atom.

What we have in mind is more than simply
a modified and renewed bus. Since its incep-
tion, about five years ago, many micro com-
puter buffs have used the Elektor bus for
their computer system, whether that is
Elektor’s SC/MP or Junior Computer or
something completely different. The layout
suggested here has the advantage that it
allows almost all the cards published by Elek-
tor to be used without any modification;
cards published elsewhere will also fit the
format defined by the bus. Some of our
cards have proved very popular, among them
the universal memory card, the EPROM
programmer and the floppy disk interface.
Depending on what microprocessor the sys-
tem is based on, the various cards can be
used either without modification (6502), or
with a certain number of modifications for
some of them (Z80). Most of the Elektor
cards can very easily be adapted to almost
any system. Table 1 is a summary of the
conventions used by various systems.

Applications

This extension can be used with any
personal computer (possibly with some
modification with some of those we have
not mentioned), but it is absolutely im-
perative that the output bus of the com-
puter is buffered (with a 74LS367 in the
case of the TRS-80 model I).

It would be impossible to try to list all the
possible circuits that could be plugged into
the connectors of this bus extension. Some
of the more interesting are: a speech syn-
thesizer (SC01), sound synthesizer (1 ... 3
AY-5-8910), EPROM programmer, all sorts
of converters, real-time clock, circuit emu-
lator. Often these various circuits have a
large current consumption so it is a good
idea to give the bus extension its own supply
so that it can cope with these power -hungry
cards. Circumstances dictate the character-
istics of the supply (+ and —5 V, + and
-12 V).

If such a supply is added only the earth line
should be connected to the computer be-
cause the voltages supplied by the regulators
will probably be slightly different and this
could cause problems.

Nothing is more descriptive than an example,
and we chose the TRS-80 as our guinea-pig.
The signals available at the TRS-80 keyboard
output connector are given in figure 1 . The
corresponding connections on the bus exten-
sion are illustrated in the drawing of figure
2 .

Using this example you should be able to
adapt this extension to any computer with
a buffered output bus.

The simplest way of making this bus exten-
sion is to use a suitable printed circuit board,
either the one described in the article ‘new
bus board for microprocessors' (January
1980, page 1-31), or the one described else-
where in this issue. In the first case up to
five connectors can be used, in the second
this goes up to seven. In either case it is
important that the components should be
carefully located on the plug-in cards, to
ensure that they can all be fitted. H

12-63

Temperature controlled
soldering station

In new SA-3 series temperature controlled
solder station from OK Industries is ideal
for all soldering applications. Tip mounted
sensors and sophisticated control circuitry
ensure fast response and excellent stability
within 5% over 100-500°C.

Furthermore the mains powered unit
comes with a special 24 V 48 W low-
leakage iron and is earthed for MOS and
CMOS applications.

Ease of use is a feature and the tool has
power and heater indicators, proportional
temperature control and a temperature
indicator. A variety of tips is offered.
A solder spool holder, to accept any size
of solder spools up to 7 in (178 mm)
diameter is also available.

OK Industries UK Ltd,

Dutton Lane,

Eastleigh,

Hants, S05 4AA.

Telephone: 0703 610944

(2772 M)

Compact rotary encoder

Hero Electronics is now stocking the
Sharp range of incremental rotary enco-
ders and slotted discs.

The GP-1R04 series which is shown in
the photograph is a photointerruptor type
of rotary encoder with a built in light
level compensating circuit consisting pri-
marily of an infra red light emitting diode
and integrated type photodiode. Other
encoders include the GP-1 52 (rotary
shaft encoder) and the GP-1R11 a smaller
version of the GP-1 R04.

The GP-1 R04 provides 3 types of output
2-phase output — A — (approximate sine
wave), — B — (approximate cosine wave)
and — Z — Index output. The GP-1R04
series comprises 5 models with different
slotted discs. Their resolutions are 96,
100, 192, 200 and 360 pulses per rev-
olution.

The features of these encoders besides
their compact and lightweight design are
high accuracy in phase difference due to
laser trimming, high frequency response
because of the use of a laser diode and
very good thermal characteristics. The
encoders are excellent for detecting arc

elektor december 1983

angles the number of revolutions, ro-
tational speeds and directions.

Application are in typewriters and printers,
copiers, machine tools, robotics and in
various types of measuring instruments,
micrometers, venier calipers etc.

Hero Electronics Limited,

Dunstable Street,

Ampthill,

Bedfordshire, MK45 2JS
Telephone: 0525 405015

(2771 M)

The Zicon 701 logic analyser

The Zicon 701 is a new 40 channel logic
analyser from Zicon Instruments Ltd of
Norwich.

Designed for use with 8-bit and 16-bit
microprocessors, its 4 clock inputs permit
full analysis of multiclock and multiplexed
AiP'S (such as the Z80 and 8085), to
which it can be connected directly with-
out personality probes. Its ability to de-
multiplex makes possible the simultaneous
display of address, data and status infor-
mation. It records 1000 bits per channel at
speeds up to 10 MHz, using a separate
monitor or TV set as a display.

A succession of fully interactive menus,
with a flashing cursor to indicate the
relevant input field, makes setting-up
quick and trouble-free. Invalid data
entry is blocked, and messages on screen
identify the errors.

The trigger and trace capabilities of the
Zicon 701 result in very flexible and
precise data capture. Triggering is via a
24-bit trigger word with separate trigger
qualifier and trigger count of 1 to 999
events. The clock qualifier includes a
24-bit trace facility which filters and
selectively captures significant infor-
mation. A delay feature allows the last
trigger event to be positioned anywhere
in the 1000 line memory to give a com-
plete pre- and post-trigger analysis.

The data can be examined either (a)
'on screen' in normal listing format or
as data signatures, or (b) as hard copy
printout using the RS 232C output which
is fitted as standard. Transmission speeds
are selectable between 300 and 4800
baud.

Data listing offers a choice of six different
formats of hex and/or binary code, with
either 11 or 22 displayed lines depending
on the format selected. The instrument
accepts a full-width 40-bit search word,
and both trigger words and search words
are highlighted. Scrolling by line, page,
trigger word or search word greatly
facilitates data location.

The instrument is compact, light (5lbs)
and portable, and thus ideally suited to
field servicing and bench work alike. It
is 100% British in design and manufacture.
Zicon Instruments Ltd were established in
1978 as a company specializing in the
design and manufacture of logic analysers.
Two of their earlier models, the Zicon 620
(8 channel) and the Zicon 632 (16 chan-
nel) are still available for those users who
are looking for high performance linked
to low cost.

Zicon Instruments Ltd.,

23 Meteor Close,

Airport Industrial Estate,

Norwich NR6 6HQ.

Telephone: 0603 400083

(2774 M)

12-64

elektor december 1983

PCB terminal multipin capacitor

Axiom electronics limited, who already
carry in-depth stocks of Sprague type
705D aluminium electrolytic capacitors,
have added a multipin pcb terminal
version of the device to their inventory.

In common with the other components
in the range, the multipin terminal capaci-
tor features high ripple current, low ESR,
and good high frequency characteristics,
and has the additional advantage of
mounting straight onto the printed circuit
board.

The number of pins varies between three
and five, depending on the diameter of the
capacitor, to give total stability. The
705D multipin configuration conforms
to DIN specification.

Sprague type 705D capacitors are equiv-
alent to the Mullard 050 series. Excep-
tionally stable, they are ideal for use in
switch mode power supplies, instrumen-
tation, and telecommunications equip-
ment.

Axiom Electronics Limited ,

Turnpike Road,

Cressex Estate,

High Wycombe,

Bucks HP12 3NR.

Telephone: High Wycombe 442181

(2807 M)

and colour combinations, which include
red on aluminium, black on yellow, blue
on clear plastic and black on white plastic,
create smart, bright labels or signs for
every use.

With the kit it can take a mere five mi-
nutes to make a Photolabel — at around
4 pence per square inch.

19" terminal cases

New to OK Industries' Elrack enclosure
series of enclosures, a range of 19in
terminal cases has been designed for
industrial, electronic, communications en-
gineering and equipment monitor appli-
cations.

How it works

The original artwork, which should either
be a negative or a drawing on tracing
paper, is placed onto the emulsion side of
the selected sheet of Photolabel material,
and both are then exposed to ultra-
violet light. Next, the sheet of material is
processed by rubbing it gently with a pad
soaked in 3M developer. This entire
process may be carried out in daylight —
no darkroom is required.

Additional protection from damage may
be given to the label by either laminating
it with 3M gloss or matt laminating film.
With the Photolabel's reverse side being
coated with a pressure sensitive adhesive,
the completed label may be positioned
on any rigid surface by simple peeling off
the backing paper and pressing it into
place. The new Kit permits the user to
custom-make a wide range of attractive
labels. Typical applications include logos,
nameplates, prototype panels, wiring dia-
grams, charts, dial faces, control panels,
electrical boxes, switching information,
safety instructions, warning signs, art
layouts, and a host of other labelling/
signing projects.

Industrial Marking Systems Group,

3M United Kingdom PLC,

3M House,

P.O. Box 1,

Bracknell,

Berkshire RG 12 1JU.

Telephone: 0344 58457

(2803 M)

Photolabel introductory kit

The new 3M photolabel introductory
kit from the company's industrial marking
systems group allows anyone to produce
brightly coloured, self-adhesive metal and
plastic labels in minutes — at a fraction of
the cost of having them factory-made or
printed.

The kit is an ideal introduction for a
company or original equipement manufac-
turer wanting to make its own durable,
professional looking labels, signs or
markings for application to a smooth
surface. The only other additional item
required for their production is an ultra-
violet light source.

The kit's contents include 13 sheets of
photolabel material in assorted colours,
matt and gloss laminating film, reversal
film, developer solution and pads, an
exposure guide and full instructions.

The light-sensitive emulsions are coated
onto four types of base — heavy or stan-
dard guage aluminium, and transparent
or coloured polyester. The range of base

The design is modular, utilising six differ-
ent kits to enable virtually any require-
ment to be met. Moulded from tough
ABS the components include cases,
extension kits, with ventilated side panels,
keyboards and keyboard/displays. Compo-
nents can be supplied either complete or
in kit form for easy assembly.

Additionally the cases are available with
front panels to accept switches or instru-
mentation, front panel heights being
223.5, 312.5, 402 or 490.5 mm. The
standard colour is beige but other colours
are available on request.

OK Industries UK Ltd.,

Dutton Lane,

Eastleigh,

Hants S05 4AA.

Telephone: 0703 610944

(2801 M)

12-65

advertisement

elektor december 1983

Matching AKG Microphone to suit 'with speech and music
filter). Complete with lead ONLY £9 95 plus 75p p&p.

VHF STEREO TUNER KIT

STEREO CARTRIDGES

PHILIPS

Magnetic cartridge with diamond
Stylus Model No GP 397 III Output
2m V Separation 22dB Stylus 0 6mm

£3.95 each pi u , 60 P p&p

.ARRARD

Scrotone Garrard Ceramic cartridge.
'V«V. Wuh turnover Sapphire

£2.95 plus 60p p&p

diameter magnet

125W HIGH POWER AMP
MODULES finRn ni;.

£10.50 £14.25

♦ £1 .15 p&p < £1.1 5 p&p

The power amp kit is a module for high power applications
disco units, guitai amplifiers, public address systems and
even high power domestic systems The unit ■$ protected
aqamst short circuiting of the load and is safe in an open cir
curt condition A large safety margin exists by use of genei
ously rated components, result, a high powered rugged unit
The PC board is back printed, etched and ready to drill for
ease of construction and the aluminium chassis is preformed
and ready to use

Supplied with all parts, circuit diagrams and instructions.

ACCESSORY. Steieo/mono nioins power supply kd with
transformer £10.50 plus £2.00 p&p.

( . I F If' A T I ( )NS

Tper.it mq voltage (OC) 50 - 80 max
oads 4 16 ohms

-lequency lesponse measured (S> 100 watts 25H/ 20KH?,
icnsitivdy for 100 watts 400mV@47K
rypical T H D fy* 50 watts 4 ohms 0 1%

Dimensions: 205 * 90 ami 190 x 36 mnv

T.V. SOUND TUNER

BUILT AND
TESTED

PRACTICAL ELECTRONICS
STEREO CASSETTE
RECORDER
KIT

In the cut-throat world of consumer electronics, one of the
questions designers apparently ponder over is "Will anyone
notice if we save money by chopping this out?" In the
domestic TV set, one of the first casualties seems to be the
sound quality Small speakers and no tone controls are
common and ail this is really quite sad, as the TV compan-
ies do their best to transmit the highest quality sound.

Given this background a compact and independent TV
tuner that connects direct to your Hi-Fi is a must for quality
reproduction. The unit is mains operated.

This TV SOUND TUNER offers full UHF coverage with
5 pre selected tuning controls. It can also be used in conjunct
ion with your video recorder Dimensions: i 1 m " x 8y?"x 3%".
version of above without chassis, case and hardware. £12 95 plus Cl 50 p&p

MONO MIXER AMP

Ideal for Church o -

halls & Clubhouses lL^fD.UU * £2 00 p&p

50 WATT Six individually mixed inputs to: two pick ups
fCer. or mag ), two moving coil microphones and two
auxiliary for tape tuner, organs, etc Eight slider controls
six for level and two for master bass and treble, four
extra treble controls for mic and aux inputs. Si/e
13’*' *6 '/ - x3V app. Power output 50 watts RMS
Icont ) for use with 4 to 8 ohm speakers Attractive black
vmyl case with matching fascia and knobs. Ready to use.

Steieo cassette tape deck
transport with electronics
Manufac tuier s surplus
brand new and operational
sold without warranty

£11 95

plus £2 50 p&p

Just requires mams nans
former and input 'output
sockets and a volume
control to complete

L- includes tape transport mechanism, ready punched and
aac* printed quality circuit board and all electronic parts
r semiconductors, resistors capacitors, hardware top
s*tr, printed scale and mains transformer. You only supply
order and hook up wire. —

Featured .n April issue p E SPECIAL OFFER 1

forint 50p Free with kit £31 00 plus £2 75 p&p

5**f assembly simulated wood Complete with case

■mu £4 50 ‘£150 p&p

AUDAX 40W
FERRO-FLUID HI-FI

TWEETER

X/over on 5kH/

?2kH/ 60mm f5 50

square 8 ohm *60p p&p

£32.95 £2.75 p&p

NOISE REDUCTION SYSTEM • AUTO STOP • TAPE
CUNTER • SWITCHABLE E Q . INDEPENDENT
£ .EL CONTROLS • TWIN V.U METER • WOW &

. JTTER 0 1% . RECORD 'PLAYBACK I C WITH ELEC
"R0NIC SWITCHING • FULLY VARIABLE RECORDING
AS FOR ACCURATE MATCHING OF ALL TAPES

SPEAKER

t»ass mid range and 3 .
«eter Complete with screws
»e. crossover components
«a cabinet Cabinet comes m
r pre mitred 0 I Y form
n.*h chipboard covered
sod simulate. si*e 14 V*

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Impedance 8 ohms

i mail to

K HIGH STREET, ACTON W3 6NG.

re: Goods despatched to U K postal addresses only
rems subiect to availability. Prices correct at
9 83 and subject to change without notice
jse allow 14 working days from receipt of order
despatch RTVC Limited reserve the right to up-

date their products without notice All enquiries send
S A E

AI L CALLERS TO 323 EDGWARE ROAD,
LONDON W2. Telephone 01 723 8432

<5 minutes walk from Edgware Road Tube Station)
Now open 6 days a week 9 6. P> ices include VAT.

Telephone or mail orders by ACCESS welcome

spotlight on Elektor books

RESI & TRANSI

A series of strip cartoons in book form in
which two enterprising characters explore
the field of electronics in their own inimi-
table way. Their adventures are full of
tension, because they often go against the
current - whereby they encounter much
resistance - before they reach their goal.
These books familiarize the reader with
electronics in an unusual way: exciting,
playful, yet thorough. Part I comes com-
plete with a printed-circuit board and resi-
meter

Part I : Banish the Mysteries

of Electronics £ 5.75

Part II : Hands off my Bike! . . £4.50

TV GAMES COMPUTER

This book, provides a different - and. in
many ways, easier - approach to micro-
processors The TV games computer is
dedicated to one specific task, as the
name suggests. This provides an almost
unique opportunity to have fun while
learning!

Pnce £ 6.75

DIGIBOOK

Provides a simple step-by-step introduc-
tion to the basic theory and application
of digital electronics and gives dear
explanations of the fundamentals of
digital circuitry, backed up by exper
iments designed to reinforce this newly
acquired knowledge. Supplied with an
experimenter's PCB

Price £ 6.00

300 CIRCUITS

For the home constructor - 300 projects
ranging from the basic to the very sophis-
ticated.

Price £ 5.50

MICROPROCESSOR HARDWARE

This book describes a range of peripheral
ec^jipment that can be connected and
used with an assortment of personal
computers which use the 6502, 6809. Z80
or the 8080 CPU

Price £ 7.50

JUNIOR PAPERWARE 1

Modifications of the PM/PME EPROM:
Source listings. Hex dump of the Software
cruncher and puncher (Elektor 85, May
1982)

Price £2.00

JUNIOR PAPERWARE 2

Source listing of the bootstrap loader
for Ohio Scientific Floppys: Hex dump
of the EPROM (ESS 515)

p "ce £2.00

DATA SHEET BOOK

Here at last is the book that designers have
been waiting for: the Elektor Data Sheet
Book. In 240 pages it gives you a CMOS,
a Linear, Special Function and Audio Data
8ook: extensive information on 269 of
the most important IC’s. A very useful
and economical reference book!

Price £8.00

JUNIOR COMPUTER VIA 6522

This book deals with the well-known
Versatile Interface Adapter (VIA) type
6522 Although it is an indispensable ad-
dition to the four books already devoted
to the Junior Computer, it is not aimed
solely at Junior users, but at anybody who
has a system with one or more 6522s. It
affords a complete familiarization with
this flexible and effective component.

Price £3.25

JUNIOR COMPUTER BOOK 1

For anyone wishing to become familiar
with (micro)computers. this book gives
the opportunity to build and program a
personal computer at a very reasonable
cost.

Price £6.50

JUNIOR COMPUTER BOOK 2

Follows in a logical continuation of
Book 1. and contains a detailed appraisal
of the software. Three major programming
tools, the monitor, an assembler and an
editor, are discussed together with practi-
cal proposals for input and peripherals.
Price £ 6.50

JUNIOR COMPUTER BOOK 3

The next, transforming the basic, single-
board Junior Computer into a complete
personal computer system.

Pnce £ 6.50

JUNIOR COMPUTER BOOK 4

Book 4. the last in the series, describes all
the software required to operate the com-
plete system. A number of peripheral
devices, such as a printer and a video
terminal, may be 'hooked up' to the
computer. During the final stage in its
'growth', the machine is able to extend
its linguistic skills, for a special version of
BASIC is now available on cassette.

Price £ 6.50

301 CIRCUITS

The book is a continuation of our popular
and very successful 300 circuits publi-
cation. It is composed of 301 assorted
circuits ranging from simple to more
complex designs, described and explained
in straightforward language.

Price £ 5.50

SC/MPUTER (1)

Describes htyw to build and operate your

own mitrup&e-cssof system - the first
book of a side’s - further books will
show how the system may be extended to
meet various requirements,

Price £5.50

SC/MPUTER (2)

The second, book in series. An updated
version of the monitor program (Elbug II)
is introduced together with a number of
expansion possibilities. By adding the
Elekterminal to the system described in
Book 1 the microcomputer becomes even
more versatile.

Price £5.50

FORMANT

Complete constructional details of the
Elektor Formant Synthesiser comes

with a FREE cassette of sounds that
the Formant is capable of producing
together with advice on how to achieve
them.

Price £ 6.00

33 ELECTRONIC GAMES *

A selection of circuits which give as much
enjoyment in building them as actually
playing the games. The circuits are fasci-
nating although the electronics involved
aie not complex and therefore anyone
with a good soldering iron will find this
book satisfying. These are electronic games
that do not need a TV screen, and as a
result can be played just about anywhere.
Price . . £4.50

To order please use the postage paid order
card in this issue.

ADD 50p P 8. P U K. (OVERSEAS £ 1.00)

THE NEW AMPUN

CATALOGUE FOR 84!

nwpuni

PROJECTS FOR THE HOME CONSTRUCTOR

NEW MAPLIN STORE IN SOUTHAMPTON

Choose from our huge
range of value- for-
money projects. Projects
like our Modem, Mosfet j

Stereo Amplifier, Home
Security System, Fre- ^ * j

quency Counter and — 4

Home Computer add- ' — .

on kits. Full construction details in our Project Books and brief
specifications in our new catalogue. Dozens of fascinating new
projects coming soon including a Keyboard for the ZX
Spectrum with electronics to make all shifts, single- key
operations. Full details in Project Book 9 on sale 1 1th November
1983. Order As XA09K. Pfice 70p.

Opening on 1st November 1983, our new
south coast store is at 46-48 Bevois Valley
Road, Southampton (Tel: 0703 25831). You
will find our full range of components,
projects and computers on sale. We are within
easy reach of the city centre with good parking 5 V
close by. Call in and see us soon.

NOW WITH PRICES
ON THE PAGE

More data, more circuits, more
pictures, in the brand new 480 page Maplin
catalogue. Take a look at the completely
revised Semiconductor section or the new
Heathkit section with descriptions and
pictures of dozens of kits and educational
products from digital clocks to 16-bit business
computers. The much expanded computer
section itself, gives details of hundreds of
pieces of software for Atari, BBC, Commodore
64, Dragon, Spectrum and VIC20. In
addition to all this you’ll find hundreds of
fascinating new items spread through the rest
of the catalogue.

As always, the Maplin catalogue is
tremendous value for money and now has
prices on the page!

Pick up a copy at any branch of
W .H .Smith or in one of our shops for just
£1.35 or send £1.65 including postage to our
Rayleigh address. On sale from 1st Nov 198.

i ■

iiplflia

IS

■sun

is

,

Post this coupon now for your copy of the 1984 catalogue. ■

Price £1.35 + 30p post and packing. If you live outside the
U K. send £2.20 or 11 International Reply Coupons.

I enclose £1.65.

Name ■

Address •

I-

E 12/83

I

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ffMpun ksss.

Mail Order: P.O. Box 3. Rayleigh, Essex SS6 8LR. Tel: Southend
(0702) 552911 • Shops at: 159 161 King Street, Hammersmith.
London W6. Tel: 01 748 0926 • 8 Oxford Road, Manchester.
Tel: 061 236 0281 • Lynton Square, Perry Barr. Birmingham.
Tel: 021 356 7292 • 282 284 London Road. Westcliff on Sea
Essex. Tel: 0702 554000 • *46 --48 Bevois Valley Road,
Southampton. Tel: 0703 25831.

•Opens 1 st November 1983. All shops closed Mondays.

All prices include VAT and carriage. Please add 50p handling
charge to orders under £5 total value (except catalogue).