Watch Sam Battle Use a Theremin to Control His Mini’s Throttle

The “classic” Mini (not to be confused with the BMW Mini Cooper) is arguably the most iconic British automobile of all time. They’re also still surprisingly affordable (similar to the VW Beetle in the US), because they were built in such large numbers for such a long time (1959-2000). Sam Battle, of the LOOK MUM NO COMPUTER YouTube channel, owns two Minis (with the theory that at least one of them will probably be working at any given time) and converted one to rev in response to a Theremin.

Many modern ICE (internal combustion engine) cars utilize some level of drive-by-wire with electronic throttles — and electric cars don’t need throttles at all. But older cars almost all used good ol’ fashioned throttle cables attached to the accelerator pedals. When the driver pushes the accelerator pedal, it pulls the cable that opens the spring-retracted throttle. That simple mechanical throttle is very easy to hijack, which is what Battle did here.

Battle started with a Teensy board, servo motor, and potentiometer knob. The Teensy runs the basic servo example code included in the Arduino IDE, which moves the servo arm according to the position of the potentiometer. The servo pulls the throttle cable, giving Battle electronic control over the Mini’s throttle. By twisting the potentiometer knob, he could control how open the throttle was. Theoretically, he could have driven around like that by using the potentiometer instead of the accelerator pedal—though he didn’t, for safety (and probably legal) reasons.

Next, Battle increased the stakes by replacing the potentiometer with a Theremin. If you’ve ever activated a capacitive button or touchscreen without actually touching it, then you’ve already experienced the operating principle of a Theremin. This strange instrument contains two “antennas,” which are actually capacitive sensors, and their analog output controls oscillators that alter pitch and amplitude. Some Theremin models omit the amplitude antenna in favor of a conventional volume knob, which was true for Battle’s instrument.

Battle fed the output from the Theremin to his Teensy, where it replaces the potentiometer in the chain. Simple digital signal processing (DSP) translates the Theremin signal’s frequency (the pitch) into a position for the servo. A higher pitch opens the throttle further, meaning Battle can wave his hand around the Theremin’s antenna to rev up his Mini’s engine.

Even though Battle could disengage the engine by simple pushing in the Mini’s clutch, driving the car with the Theremin controlling the throttle would have been a bad idea. It would have been distracting and likely would have broken several laws. But we’d be lying if we said that we didn’t want to see him do it.