13. The Control Panel

Oct 23, 20013

  The mess of potentiometers and wires that I had been using to test stuff just wasn't cutting it anymore, and since the design features were pretty much set at this point, I decided it was time for the control panel.

  The question was, panel mounted and hand-wired or PCB mounted?  At something like 30 pots and switches, I suddenly didn't want to do all that hand-wiring.  I'd never done PCB mounted controls so I decided to give it a shot and see how it works out.

  At something like 14 inches long, this is the largest board I've etched my self by almost a factor of 2 and pushed the limits of my make-shift exposure setup.  The ends got less exposure than the middle and the whole thing ended up a little underexposed which made etching more difficult than it should have been.  Needed some touching up but in the end the thing works.

  It really needed to be two-sided, but as I was pushing my limits already I really didn't want to deal with trying to line up the two sides.  So there are a lot of jump wires to make the connections that would have been on the second side.

  The pots are all setup as voltage dividers providing 0-10V CV's (or -10 - +10V in some cases).  Each of these is then buffered with a simple non-inverting opamp buffer to drive the 8 voice boards with a nice strong stable CV.  Switches simply ground the control signal when on, the signal is pulled up with 5V though 100k resistor at the destination (DG41x series analog switches), so no buffering is necessary for the switches.

  The ribbon connectors make the connection to the voice board real nice clean and easy.  The two knobs with the wires are rotary switches, not potentiometers, and are too tall to mount on the PCB by the lugs.  I temporarily mounted them with the bushing but will eventually have to mount them directly to the front panel and put holes in the PCB to let the body of the switches through.

  The difference in height between the pots and switches is a bit more than I anticipated, but should be usable.  I may redo it at some point with different components that make for a nicer look and feel, but I think this will get me through the rest of the project.

  In the end, I don't think PCB mounted controls was any less effort than hand-wiring.  If making a number of them (and properly producing them with both sides) it would make sense to do it this way, but for a one-off it's probably simpler to just hand-wire it.  It was an interesting experience though so I'm glad I did it.

Next up, starting to think about an LFO....

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