Dedicated to my father.
This is my Mona Lisa, built in Lithuania around 1992. It could have been the USSR of the late 1980s.
One does not often get to see unique things that have a purpose. Here is one:
| A Home-Made Digital K155 Clock |
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It was based on the Soviet TTL K155-series microchips, with gas discharge displays. The whole thing consumed electricity like a heater.
The electric circuit diagram seems to be lost. ChatGPT does provide some strong clues where to look for, which is surprising considering old Soviet books which do not exist online.
Personal computers were very rare at the time in Lithuania. My secondary school "information technology" class taught us how to use ChiWriter which must have run on Robotron, a DOS-compatible East Germany-made personal computer. Computers were an optional once-a-week matter. We did not have access to the design of PCBs with say, P-CAD and automated printers.
We used a single copper (Cu) plated board, the routes were drawn with a nail polish followed by the board immersion into some chemical liquid compound. This was very rough and tedious, needless to say.
At first, we applied ferric chloride (Fe2Cl3) to etch the circuit routes, but our solution was not effective and we would wait for days if not weeks for the irrelevant Cu-parts to disappear from the board's surface. A slight warming or periodic movement would not speed a chemical reaction much. The designs were flawed in that there was so much copper to remove.
Once, after losing patience of watching over a never ending reaction, I decided to pour hydrochloric acid HCl on some metal shavings in a big plastic can used for sardines, to get a "stronger ferric chloride". Do not do this at home. I nearly lost my lungs.
Cupric sulfate CuSO4 was applied too. The etching got faster, but not by much. Years later I would also see my uncle use cupric sulfate to paint the trunks of the apple trees...
We also resorted to electrolysis. The painted board is immersed into a salted water inside an iron can. The cathode is attached to the can and the anode is immersed into the water in an isolated manner (by sticking it into a hole drilled in a plastic cover on top of the can to avoid a short-circuit). This would remove copper so rapidly, but the nail polish would not protect the routes well. The printed routes were never of high quality.
At the time it was common to build voltage transformers manually. We had a lot of varnished copper wire of old circuit relays floating around. The formula was surprisingly simple:
** # windings/volt = 50/S,**
where S was an effective area of a ferrite core entering the transformer's casing, in squared centimeters.
This would work for a vast range of transformer and wire sizes.
Consider an exercise to derive this formula from Maxwell's equations...
The process of hand rolling a transformer was an exercise of patience as thousands of windings were needed and a ferrite core consisted of many sheets that had to be assembled one by one. I would place some markings on paper in order not to get lost at counting the windings. This was so tiresome that once I even confused primary and secondary windings when connecting the transformer to the voltage source after an assembly. Puff, an evening's work was gone.
This magic was insufficient for small transformers. A small transformer size would demand a very thin copper wire due to size limitations, and often the electric current would come out too weak. It would not drive, say, a neighbour's portable cassette Sony Walkman used as a stationary desktop cassette player ;).
| Inside the Box |
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| Circuit Board: Top |
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| Circuit Board: Bottom |
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| Voltage Transformer |
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| Gas Discharge Displays |
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