Tim Alex Jacobs' Hardware Reverse Oscilloscope 2 Turns Waveforms Into Audio
Rather than turning a signal into a shape, this synth turns a shape into a signal — using no fewer than three microcontrollers.
Musical maker Tim Alex Jacobs has built a synthesizer which turns a common piece of lab equipment on its head: the Hardware Reverse Oscilloscope 2, which gives you the option to design a waveform through slider switches.
"The original hardware reverse oscilloscope was an analog multiplexer, driven by a binary counter, driven by one of my tiny square-wave midi synths," Jacobs explains of the project's history. "I liked very much how it was just simple hardware – and the design meant it was completely free of aliasing. I wanted this to be all hardware too, despite the fact that I wanted it to have a lot more features."
2015's Hardware Reverse Oscilloscope served as the basis, but 2023's project reboot is a major upgrade. At the board's heart are no fewer than three microcontrollers: a Raspberry Pi Pico, a Teensy 4.0, and a Microchip ATmega328P. These, in turn, handle a 16-bit analog to digital converter as a pitch input, 16 sliders and the same number of jobs and jacks through a pair of 16-channel analog multiplexers, and 16 LEDs — plus an audio output courtesy of a PT8211 digital-to-analog converter (DAC) connected over I2S.
The idea is simple enough: the 16 sliders are used to control the shape of the resulting audio waveform, performing exactly the opposite task to an oscilloscope by generating a signal from a shape rather than generating a shape from a signal.
"We could trivially turn this into a MIDI controller," Jacobs notes of the design. "Either by augmenting the [Raspberry Pi] Pico firmware or adding another microcontroller to listen in on that serial data. I'm not sure there's much need to do that though."
The full project write-up is available on Jacobs' website, though neither design files nor source code have been published. "At some point in the future, I will publish the source code for the microcontrollers in this project," Jacobs promises. "If you think the wiring's a mess, well, the less said about the source code the better."