Dedicated to my father.
| A Home-Made Digital K155 Clock, circa 1992 |
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Soviet TTL K155-series microchips, gas discharge displays. The electric circuit diagram seems to be lost.
| 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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We used a single copper (Cu) plated board, the routes were drawn with a nail polish followed by the immersion into ferric chloride (Fe2Cl3) to etch the circuit routes, later replaced with Cupric sulfate CuSO4. The etching got faster, but not by much.
The fastest way is electrolysis, but the nail polish would not protect the routes well.
The printed routes were never of high quality.
This design is flawed in that there is too much copper to remove.
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, but extra-compact transformers would demand extremely thin copper wire which would not support enough power to drive a neighbour's portable cassette Sony Walkman used as a desktop cassette recorder ;).
Consider an exercise to derive this formula from Maxwell's equations...