As I prepare to make a function mockup of the front panel, I've designed a utility board that can scan up to 48 potentiometers. The boards can be chained, allowing for a total of 288 potentiometers on six output pins.
The only input from the mcu is clock, reset, +V and GND.
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| Shown here: two input muxes (left), one per 10p connector. Only six of the eight inputs are used but all are adressed as the clock is sequential. The board has 8 input muxes in total. On the right is a single mux that selects one of the 8 input muxes for output to the MCU. Everything is clocked by a CD4520 six bit binary counter. Before scanning starts, clock is reset to make sure it is at 0. It can also be reset early if some of the input ports are not used. |
Testing shows that a single channel can be scanned at 50kSamples/second, the limitation is the speed of the ADC on the microcontroller. The analog output of the on board mux'es stabilize after approximately 2uS.
I've tested the circuit on a Teensy 4.0, and as it uses a single ADC for multiple channels, scanning six channels takes around 113uS. This means that we can do 185 samples/second per potentiometer when using all channels.
As I'm allergic to soldering, I have been looking for a way to connect the pots without solder. My best and simplest solution this far is to insert the potmeter directly into a 10p IDC connector. It stays fairly firmly in place, with the outer potentiometer pins at pin 1/2 and pin 9/10, and the center pin at pin 5/6.
If I connect +V to pin 1/2 and GND to pin 9/10, I can connect the pots at either the front or rear row of the connector, reading the value from pin 5/6.
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| Front row |
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| Rear row |
If I modify the cable a bit, crossing pin 3/4 to center and then 7/8 to center, I can connect six potentiometers to a single 10p ribbon cable!
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| Crossing two and two wires allows me to connect six potentiometers to one ribbon cable |
