This is a DIY variable resistor I created as an interface for live performance– like a stomp box. I designed it as a project my audio students could build with materials we already have in the classroom.
The result is a variable resistor that can be triggered with just a little pressure from hands or feet. Resistance ranges from 0 to about 18k ohms, and it’s very sensitive to slight changes in pressure. (With no pressure, resistance is infinite.)
With an Arduino, the clamshell’s big jumps in resistance can work as an on/off switch– perfect for foot-powered control! Depending on the code, you can use it as a toggle switch or a momentary switch. And as a stompbox, it’s flat and quiet(unlike metal stompswitches).
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Materials:
clamshell CD case
adhesive-backed copper foil
hot glue
solder
wire (22 AWG)
velostat
craft foam
plywood board (cardboard could also work)
Arduino
10k resistor (approximately)
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Tools:
glue gun
box cutter
hole punch (or use the box cutter)
drill (optional)
soldering work station (soldering iron, helping hands, goggles, etc.)
pen
ruler
multimeter
test leads
Step 1: The Clamshell Variable Resistor
Two holes punched on the same side of the case provide an exit for two wire leads, and prevent the case from crushing the wires.
The wire leads are soldered to two identical flag-shaped pieces of copper foil stuck to the insides of the case (on opposite sides). When the case is closed, the “tails” of foil extend up opposite sides, not touching (very important).
(I didn’t take pictures while modifying the clamshell case so I’m hoping you can follow from the photos of the finished piece. I’ve included a suggested order of steps, later on.)
Step 2:
One of the foils has a backing of craft foam between the foil and the plastic, which fills the air gap inside the case, so the rectangles of foil touch once the case is closed.
To create the variable resistance, I’ve taped a rectangle of velostat over each foil piece. The tape acts as a hinge– I can fold it back if I want to decrease the resistance.
With the case closed, the clamshell can take a fair amount of stomping, just stay off the wire and solder points. (Attaching it to the board in a later step provides protection for the wire and solder points.)
Read more: The Clamshell Stompbox