CLOCK OSCILLATOR
1. IC Patchboard (1979)
I suppose I first become interested in electronics when as a young boy I wired up the electric points and lights in model houses on my UK-based crude (diecast metal with motor and rubber bands) Lone Star 000 scale and later, 9mm N-Gauge sophisticated (diecast plastic with direct driven and working overhead
pantographs), German Minitrix, Arnold Rapido, and less sophisticated UK-based Peco, model railway:
http://en.wikipedia.org/wiki/N_scale
http://en.wikipedia.org/wiki/Lone_Star_Toys
http://en.wikipedia.org/wiki/Trix_(company)
http://en.wikipedia.org/wiki/Arnold_(models)
http://en.wikipedia.org/wiki/Peco
At this time the UK manufacturing industry was still fairly bouyant and electronics was a common hobby with several monthly amateur publications, of which I remember Practical Electronics, Practical Wireless, Wireless World (which was a bit more serious), and later, Elektor, with a quirky layout. In those days they were full of adverts for surplus components and kits to build.
If I recall correctly, the modern day distributor Radio Spares (now RS Components) initially sold low cost reject parts, as did Maplin. I certainly remember buying identical parts from RS that didn't work to spec., and the same part from competitor Farnell (now Element 14) that did.
One of the first magazine circuits I built was an electronic die, which consisted of an oscillator, a counter and a decoder that drove 6 incandescent lamps (LEDs not invented yet) with the pattern you would expect on a die. It used Fairchild's RTL (Resistor Transistor Logic) µLogic series: the µL914 dual NOR gate and µL923 dual JK flipflop, datasheets below.
This site has some additional information on the µL923 and will even sell you one!
http://semiconductormuseum.com/MuseumStore/MuseumStore_Fairchild_923_Index.htm
(left)
(right)
The RTL chips were in 8-pin packages and fiddly to solder and I made my first PCB to accommodate them. This was my first introduction to digital logic chips.
Later I took an OND sandwich course in electrical and mechanical engineering, which combined 6 months of the year working at a local electronics company. They employed me as a trainee student in their Computer Systems dept where they built computer logic boards using [E65] Texas Instruments SN7400 series,
TTL (Transistor Transistor Logic) ICs; the SN stood for 'Semiconductor Network' and there were three temparature variants: -55°C to 125°C (Military), -40°C to +85C (Industrial), 0°C to 70°C (Commercial).
THE PATCHBOARD
Around 1979 as I became more familiar with the 7400 logic series I wanted to play with them myself but I was put off by the large amount of wiring needed to hook up multiple chips in the now familiar 14 and 16-pin DIP packages. It wasn't practical turning out large numbers of PCBs just to experiment with the odd chip so I decided to build my own logic IC patch board that could accommodate several experimental circuits at once.
It consisted of a huge PCB about 25" square, holding everything I could think of to make it easy to build and test multiple logic circuits, with a small built-in custom S-Dec for analogue circuits, and built-in power supplies.
FEATURES
Home made built-in +5V 10A PSU connected directly to the bulk-decoupled pcb power grid
Home made built-in -5V 1A, ±12V 1A, ±15V 1A regulated PSUs (added at a later date)
An 8-decade selectable, variable oscillator 0.1Hz - 10MHz with multiple buffered TTL outputs
A de-bounced pulse push button single shot with dedicated LED and buffered TTL output
110 x 16-pin IC sockets (I later regretted not fitting 20-pin sockets)
4 x 24-pin IC sockets
2 x 40-pin IC sockets
47nF decouplers connected diagonally opposite on sockets (usually the power pins on 7400 series logic)
4 x 7-segment LEDs (I programmed a PROM with HEX 0-F to drive them - the 7447 was only BCD 0-9)
2 rows of 16 x 5mm LEDs clumped in red/green coloured nibbles below the 7 segment display
A hexadecimal keypad (A - F customised from other keys) with latched and unlatched binary outputs
18 de-bounced paddle switches providing logic 0 or 1
18 5mm red LEDs with DIP switches to optionally link them to the switches
An SMA power connector for a custom logic pen I built in a biro body (green LED = 0, red LED = 1)
A DIY 480-hole custom S-DeC solderless breadboard with 0.1" spacing
A slot in the side of the box to accommodate an optional pcb.
CIRCUIT
I added circuitry (that actually includes an RTL µL923) to the pcb to provide all of the above features and wrote it up in a small notebook, several pages reproduced below:
THE PCB
Once I had finalised the circuitry I laid it out on a huge transparent plastic sheet using 1:1 scale Brady precision sticky-backed black tape and Circuitape DIL chip and eyelet symbol sheets, see photo of master negative below. I will add for commercial designs you would normally photographically reduce the layout to a small PCB, but mine was so big, this wasn't practical so the layout was 1:1, and roughly
four square feet in size!
More info here on manual PCB design before PCs and CAD:
CONSTRUCTION
By the time I got to university I had painstakingly laid out the PCB, and the Electronics Dept. kindly consented to make the PCB for me in their lab, the biggest they had ever attempted. After that I had the ominous task of drilling over 5000 holes in my campus bedroom using a small hand drill, followed by soldering in all sockets and two 1mm Veropins for each IC pin, and all of the remaining circuitry.
The PCB was only single-sided and it wasn't possible to connect all of the logic by PCB tracking, so next I had to add wiring to complete the circuitry.
PATCH LEADS
After this I began to make the patch leads themselves, consisting of a Molex Soldercon IC pin socket soldered to each end of an insulated wire. The sockets were not designed for 1mm Veropins but with the addition of heat-shrink tubing I was able to ensure they retained their shape and they have remained in use to this day.
Soldercon sockets - see page 16 of [D43] 1973 Molex catalog (they came on strips, Part No. 1938-4):
THE BOX!
Finally, my father got a nice wooden box made for it at his place of work and at my request, a removable hinged lid. The total weight of the unit is 30lbs.
SOLDERLESS BREADBOARD
The original S-DeC solderless breadboard [E43] was made in the 70s by UK company SDC Products. It had 0.2" spaced holes which meant it could not accommodate 7400 series ICs which have 0.1" spaced pins. They did make a µDec which had two dedicated 16-pin IC sockets, but could take very little extra circuitry and both DeCs were much more expensive than the modern day 0.1" solderless breadboards on ebay China that cost as little as $2. I already had IC sockets on my breadboard but I saw an advantage in an option to mount chips and discrete components close together, so I added my own 480-hole 0.1" spaced 3.0" x 1.6" breadboard into my patchboard design, together with custom supply rails.
The website below has some interesting information on solderless breadboards:
http://www.robotroom.com/Solderless-Breadboards.html
Below left: original S-Dec Below right: Modern breadboard
Left, DIY breadboard in need of a refit:
ALL white is Tippex typewriter correction fluid and the peeling plastic is Sellotape
Below, breaboard internal construction: every 2nd socket has heatshrink insulation
LED / SWITCH ROUTING
Above left, the 9-way DIP switches connect the LEDs to their adjacent switch, or allow the LED to be used as a separate indicator independent of the switch.
LOGIC PEN
The SMA RF connector to the right of the DIP switch is the 5V power supply to the 'Biro' logic pen I built, now sadly lost.
The logic pen contained a single 'flatpack' IC containing TTL logic inverters, that drove a red LED for logic 1 and a green LED for logic 0. At the time the gold-plated flatpack was a rarity and the forerunner to the common surface mount ICs of today.
KEYBOARD
Below left - Keyboard and 7-Seg displays Right - below the keyboard, oscillator caps top left
Above, the oscillator controls:
Range selection 0.1Hz - 10MHz Variable min - max, together with a latched pulse push button bottom right and its dedicated LED.
Right, the logic board for the PCB clock driver outputs and debounced switch outputs (µL923 to right).
The switch LEDs are driven by core store driver chips mounted adjacent to them on the pcb top.
POWER SUPPLIES
Above left: transformers & mains fan. Above right: the additional ±15V, ±12V and -5V 1A regulators
added much later, still insulated in their plastic bag - I never
got around to mounting them properly.
Despite being built in the late 70s, it still mostly works (a few switches have failed), and even sees occasional use when my modern solderless breadboard is too small. Its great size means I can explore several circuits simultaneously.