Diode Array to turn Rotary Switch into Encoder

Joined 2023
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I'm honestly not sure if I used the right terms, but hey, ... maybe I'll learn even more.
Attached is a schematic that is hopefully self-explanatory. If not: For a Pro Audio-application I want to turn a Rotary Switch (1P23) into an encoder, to switch 5 "Bits" (Relays) in different combinations. The relays control simple attenuators in front of an inverted OP-Amp. The "Bits" 0.5dB, 1dB, 2dB, 4dB and 8dB, which would enable attenuation down to 15.5dB - more than enough for my case. I want a mechanically fixed amount of steps, 23 would be perfect, positions of the Steps/Attenuation-Values must be fixed for recall. I want to avoid any MCU/...
So far, I tested a small portion of the concept and it worked, yet I couldn't find much info on this, and maybe I'm just trying to re-invent the wheel. I'd very interested on input on this approach. Considerations, oversights, different approaches to the Rotary Switch-to-Binary-Encoder-topic. Better solutions, different solutions ... I thought about CMOS-ICs and even AD-converters, but this here was the most simplistic version, I could come up with. I'm aware of encoders, but most of them either have only 4bits (= 16 positions. I need more) and/or are endless, which is not suitable for my case (see above).
The concept is based on the RelaiXedPassive

For the diodes, I plan to use Diode Arrays (8 indpendent 1N4148 in 16-SOIC: S16-4148E3/TR7). Relays are Omron G6K, 5v. Voltage drop with 1N4148 seems to be in the tolerance of the G6K, worst case I beef up the Power Supply to compensate.

Thank you for your input!
Cheers. Tim


  • Binary Encoder through Diode Array_1.jpg
    Binary Encoder through Diode Array_1.jpg
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Seems fine, although there may be an ancient 74xx device that does this it probably only has 16 inputs and would be unobtainium now.

The other approach is a microcontroller. You'd string the switch contacts as a long resistor chain and feed the wiper to the on-chip ADC to figure out the code and drive the 5 outputs - only 6 I/O pins needed for the microcontroller so can be quite compact, and the switch can be remote from the PCB..
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Joined 2023
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Thank you Mark! That's actually great to hear. I felt a bit like re-inventing the wheel, knowing sth like this must have been done before microcontrollers and even CMOS. I never worked with logic ICs and diode matrices so far. So I was (and am) curious, how ancient my approach is ;)

I considered a microcontroller, but I would like to avoid to deal with programming that, if it doesn't have some greater benefits. Yet, I will keep it in mind, thanks for the input!
Joined 2023
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@Elvee, thank you, this looks very promising! I will get a couple of those and start to try them.

@benb, thank you as well for the input! I couldn't wrap my head around, how this would be implement in my case - but as a theoretical input it is highly interesting and appreciated. I'm learning a lot about encoding right now!