Turi Scandurra's Picophonica Turns a Cheap Kid's Toy Into a Raspberry Pi Pico-Powered Synth
An RP2040-based upgrade turns this kid's noisemaker into a genuine musical instrument, complete with MIDI capabilities.
Creative designer Salvatore "Turi" Scandurra has given a children's toy keyboard a major overhaul to create the Picophonica, a fully-functional synth powered by a Raspberry Pi Pico and its dual-core RP2040 microcontroller.
"A friend gifted me a cheap toy musical keyboard," Scandurra explains of the origins of the Picophonica project. "The sound quality was atrocious, and it could only play one note at a time. So I removed its circuitry while keeping its enclosure, speaker, and keybed, and with some tinkering and a Raspberry Pi Pico I turned it into something usable."
Parents, as well as those with a personal interest in cheap plastic tat, will be familiar with the style of keyboard picked for the project. While technically functional, they're very much a single voice affair — playing back a pitch-shifted sample depending on key pressed, and typically set at a non-adjustable volume seemingly carefully chosen to drive any adults in the vicinity to despair.
The Picophonica is not one of these — at least, any more. Instead, the housing plays host to a Raspberry Pi Pico development board and its dual-core Arm Cortex-M0+ RP2040 microcontroller running a Scandurra's adaptation of a synth engine originally written by ISGK Instruments' Ryo Ishigaki.
"The new engine boasts two oscillators, featuring descending sawtooth and square waveforms, a customizable filter with resonance control, cut-off modulation, a decay-sustain amp envelope, and an LFO [Low-Frequency Oscillator] for added modulation possibilities," Scandurra explains. "In my build I managed to rewire a secondary keypad with fourteen keys, using it to recall the presets and change instrument parameters."
The matrix of the original keyboard is wired to the Raspberry Pi via its general-purpose input/output (GPIO) pins, with another used to provide analog audio output via pulse-width modulation (PWM). "The existing, rather pointless, 3.5mm microphone input found a new purpose as an audio output," Scandurra adds, an expansion which works alongside the on-board amplified speaker, "while a USB [Type]-C port exposed through a simple adapter enables MIDI-out functionality."
More information on Scandurra's build is available on his blog, while source code and a schematic for an amplifier should one be required can be found on GitHub under the permissive MIT license.