Schematic and PCB here - plan your build!!
Here for your planning purposes...the scheme and PCB layout will help you with your design. Build yourself a CCV style dual master gain channel.
The MIDI switcher implements switching logic that can be controlled by MIDI CC or PC messages, as well as momentary switches on the amps panel or footswitch. I have written the firmware in Arduino, and therefore runs to the Arduino standard 16Mhz clock/crystal.
If purchasing one of these boards from us, I will include a 28 pin socket and the atmega 168p chip pre-loaded with the headfirst firmware. The rest of the components required are readily available from local electronics stores (like Jaycar in Australia) or online (mouser etc).
Please refer to the BoM excel doc for the parts list.
The MIDI switcher needs a 5VDC supply, and the Ground can be set to chassis ground. If you want to implement a floating ground, you can do this but make sure your relay coils reference the same floating ground. I have used chassis ground many times without issue.
The 2020 Compact version of the board (pictured) relies on a readily available DC supply for the midi chip, which needs a 5v DC supply. This assumes that if you are already powering relays, then you probably have a DC supply line ready to go. It does include space for a 7805 regulator in case you have say a 12VDC line that needs to be dropped to 5V.
The 2019 board is more comprehensive and includes space for a 4 x diode bridge rectifier, and 7805 regulator. The 2019 board also includes buffering for running over long cable lengths for remote momentary footswitching.
See the Build Gallery page for further pictures of the two available PCB's
Compact board: 80mm x 40mm
Full board: 100mm x 40mm