Potentiometers are a great way to adjust the MIDI CC values on the synthesizer. By connecting a potentiometer to ground, voltage, and an analog input on the Feather, the varying positions of the potentiometer’s shaft as it is turned will be read as different voltage levels. These levels can then be mapped to a range of 0-127 values to send messages to the DSP-G1’s MIDI input leg.
We’ll start by connecting six potentiometers to the Feather. But why not connect more, since there are nineteen possible CC numbers to control on this synth? The limitation here is the number of available analog input pins on the Feather, there are six of them.
There are a few ways around this limitation — one would be to add IO expanders with more ADC (analog-to-digital) pins, such as this one. This is a great solution, particularly if you want one knob per parameter.
Another way to do it is to add a selector switch to allow each potentiometer to serve multiple functions. We’ll do this, and by using four different positions on the rotary selector switch, our six pots can serve as 24 different functions! This will introduce some complexity to the software, particularly around the issue of absolute knob position vs. previous parameter value when switching between bank positions. We’ll take a closer look at that in the main coding section.
To connect our potentiometers to the board, we’ll make a wiring interconnect. This will allow us to easily connect and disconnect the set of pots, which can make it easier later to assemble the synth in a case.
Additionally we can reduce the amount of wiring by connecting the power and ground to the first pot and then running those in series to the remaining five. Only the middle wiper pins with the varying voltage from each of those five pot need to run all the way back to the board.
Peel of a nine wire section of raw female/female jumper wires with the colors shown. Also grab a ten position single row housing and a ten pin section of right angle male header pins.
- Arrange the wires as shown. Note how the brown wire is flipped over the red wire to put it at the far left
- Also note the gap between the red wire and black wire
- Insert the wires into the housing as shown until they click into place snugly
Right Angle Header Pins
- Insert the long ends of right angle header pin section into the cable housing as shown
- Place the short ends of the right angle header pin section into the Perma-Proto PCB so they line up with row E columns 1-10 as seen here
- Solder the header pins into place
Now we can neatly connect or disconnect the wiring from the board!
- Start by sliding the black, white, and red wires onto the left, middle, and right legs of the first pot as shown and then solder them in place
- Then solder the middle leg of each of the remaining potentiometers to the gray, purple, blue, green, and yellow wires (ignore the brown wire, we'll use that later for the system reset button)
Now we'll share the ground connection from the first potentiometer to the other five.
- Cut five 6" lengths each of black and red silicone cover stranded wire
- Solder a black wire to the first pot's ground leg (it already has an incoming black wire from the cable connected to the board)
- Now, solder the other end of this wire to the ground leg of the second potentiometer
- Run three more lengths like this between the ground legs of the remaining potentiometers to create a continuous series
- Repeat the procedure with red wires for the power connections
Your potentiometers are wired up and ready to go! Next up, the selector switch.