Electronics > Projects, Designs, and Technical Stuff
12-input BCD encoder circuit
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Lomax:
Hi all,

I'm repairing an old synthesizer which has a broken (as in clean off) 12-position C&K (or ITT, or Jeanrenaud) "RT-A" rotary BCD switch (RTA-P-3-ES12-M-25N-S). It turns out (of course) that these are basically impossible to get hold of - unless you want to order a minimum of 480pcs (which I don't). In contrast, physically identical 12-position single pole rotary switches (RTA-P-3-1S12-M-25N-S) are easy to find - indeed I have a couple lying around already. So I'm thinking a 16-input BCD encoder on a prototyping board could save the day, but it turns out that's not even a thing. Ok, fine, I can use two 8-input BCD encoders instead. But now I'm thinking... hmmm... there might be an easier way, e.g. "diode logic", or... something I'm not aware of. Yet. So, my fellow eevbloggers, I come here to ask: how would you deal with this conundrum?



Basically:

000000000001 > 0000
000000000010 > 0001
000000000100 > 0010
000000001000 > 0011
000000010000 > 0100
000000100000 > 0101
000001000000 > 0110
000010000000 > 0111
000100000000 > 1000
001000000000 > 1001
010000000000 > 1010
100000000000 > 1011
SiliconWizard:
As often these days, the probably lowest cost and lowest part count solution would be to use an ultra-cheap MCU for this.
Wimberleytech:
At first glance, looks like four OR gates which could be implemented with diode logic.
German_EE:
I'd use an EEPROM with your inputs going to the address lines and your outputs coming from the data pins. Programming only sixteen addresses will be quicker than writing code for an MCU
Lomax:

--- Quote from: Wimberleytech on January 05, 2020, 06:26:40 pm ---At first glance, looks like four OR gates which could be implemented with diode logic.

--- End quote ---

That's what I'm thinking, though a quick sketch indicates I would need twenty of them. Not a problem; there's plenty of room - just a little fiddly. That said, the transposition selector (which is what the switch is for) apparently uses negative logic; there are no meaningful voltages present between common and any of the bit outputs. So the synth detects the switch position by pins being pulled low.
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