Roman Revzin's Crunch-E Puts an Espressif ESP32-Powered Music-Maker on Your Keychain

Designed to deliver maximum potential in a minimal footprint, this compact board brings the noise.

Gareth Halfacree
1 month agoMusic / HW101

Maker and musician Roman Revzin has designed a tiny multi-track synth, sampler, and tracker powered by an Espressif ESP32 microcontroller — and compact enough to dangle from your keychain: Crunch-E.

"Crunch-E is a keychain form factor music-making platform that is both limited and limitless," Revzin writes of his creation. "The current software supports four tracks, 10 synth instruments, and two drum machine banks, but who knows where developers will take the open-source software next?"

The Crunch-E turns an Espressif ESP32 into an ultra-compact multi-functional music-making marvel. (📹: Roman Revzin)

The heart of the project is an Espressif ESP32 microcontroller module, which communicates with an Analog Devices MAX98357A I2S amplifier to drive a 3.5mm analog audio output. The front of the surprisingly compact board features 16 push-button switches arranged in a 4×4 grid with four status LEDs above — plus two additional switches outside the main grid.

"[The] top four buttons are function buttons, the rest are note triggers/selection," Revzin explains. "For example, pressing F1 and then any of the buttons in the bottom three rows will switch instruments, F3 + any other function button will switch tracks, F4 will pause and resume playback."

The Crunch-E hardware itself can be built using discrete components, Revzin explains, including "any ESP32 dev board with enough pins," a MAX98357A breakout board, and an Arduino-compatible 16-switch keypad. The maker is also offering the device as a more polished fully-assembled single-board build — with both versions sharing the same open-source Arduino sketch firmware, dubbed "CrunchOS."

More information, including schematics, is available on Revzin's website; the source code is available on GitHub under an unspecified license.

Gareth Halfacree
Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire: freelance@halfacree.co.uk.
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