What would the Russians do ?

A project log for Numitron Hexadecimal display module

Another hexadecimal display, this one is sans transistor for the extra vintage touch, and uses only Soviet-era parts

Yann Guidon / YGDESYann Guidon / YGDES 7 days ago3 Comments

At two points, a string of 3 coils in series is switched (by another relay) in the middle (that is not high-side or low-side). I expect a significant spike when the contact is released...

I don't want to waste 2×2 more diodes for the freewheel. They are not free, they use space and they might not stand the repetitive abuse. I prefer a passive approach, using dumb off-the-shelf parts that a Russian engineer might find, decades ago.

There is not much choice : a capacitor or a resistor...

A capacitor would be quite expensive, but a 100nF ceramic across the relay's contacts could reduce the dirty HF parasites. However I have no idea how high the voltages could go... And even though the Russians are known for their high-voltage capacitors, it might not be the cheapest approach, particularly if no electrical data is available. And increasing the capacitance will also increase the current spike when the relay closes again...

So I'm left with resistors. The prototype uses two vintage 1K 1W resistors from Russia. In theory, it would work, even though it adds a bit of quiescent current (6mA×2 ? that's as much as one incandescent segment). The bet is that as the voltage difference increases, the resistor will let more current flow. I should probably measure this on the scope....

Any advice ? @SHAOS ?


Yann Guidon / YGDES wrote 5 days ago point

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[skaarj] wrote 4 days ago point


Try old soviet 100nF, they might also contain a parasitic resistance so you will get both options in a single package.

How about any 155- or 555- IC series? they were available and they are still available, they even manufacture these and they have their own versions of reliable ARM microcontrollers - metalic capsule, strong connecting pins, original sockets without the need of permanent uctrl solder on the PCB, everything made in !(China). They even have their own versions of development boards - arduino style. But I do not know if they still use the Siberian snow to test them while still hot from the production line.

I have some catalogs with IC compatibility between western and soviet. /msg me if you need them. 

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Yann Guidon / YGDES wrote 4 days ago point

Here I'm dealing with "no transistors" circuits, made out of relays :-)

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