Hall effect isomorphic keyboard synth on the ESP32-P4

Oct 20, 2026 Last reply: 1 day ago 3 Replies

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phil.harper 3 days ago

The detail that caught me off guard is the key sensing: each of the 80 keys is a magnetic switch read by a hall effect sensor sitting on the underside of the PCB. That gives per-key velocity, and polyphonic aftertouch comes through silicone gaskets. Eighty channels of magnetic sensing on one board is an ambitious amount of hardware for a keybed.

The playing surface is a 5x16 hexagonal grid with translucent keycaps, and every key carries two RGB LEDs. Under it all sits a custom black PCB holding surface-mount ICs, the sensor arrays and the encoders. Alongside the keys sit four rotary encoders for MIDI CC, a breath control sensor with an input tube, a 320x960 capacitive touch screen, MIDI in and out over 3.5mm TRS, a 1/4 inch pedal jack accepting switch or continuous pedals, stereo headphone plus L/R mono differential outputs, two line-level inputs, and USB-C carrying audio and MIDI.

The firmware runs a synth built on ESP32Synth plus a ROMpler that pulls sounds from 16 MB of onboard flash, with delay, reverb and distortion among the effects. There is also a drum machine, a sequencer and a touch strummer in the Omnichord style, plus a full I/O mixer. Layouts are programmable, the selector offers Wicki-Hayden, Janko and Tonnetz arrangements, and eight banks hold saveable patches. LovyanGFX and an FDN-reverb library round out the software stack.

Plenty is still in motion: the synth has no built-in patches yet, adding them is on the maker's list, and a few PCB details remain unfinished. The casing leaves little room inside, and that appears to rule out a tilting screen mechanism. A CrowdSupply crowdfunding round is planned with all code and files released as open-source, hopefully before summer though with no guarantees. The maker reports the LCD viewing angle is quite good, which I would call good news for a fixed panel.

Project by Xavier Dumont. Watch it on their YouTube channel:

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EmberShop_1969 3 days ago

Putting the hall sensors under the board rather than inside each switch seems a clever call to me. It leaves the keycaps free to be translucent while still delivering per-key velocity across all 80 pads. The trade-off I see is the aftertouch path: silicone gaskets will have their own feel, and getting that consistent over 80 keys sounds like serious tuning work.

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HeronMeadow_1972 2 days ago

With a sensor under every key, how are the sensor arrays laid out on the PCB to read all 80 switches at once? That many channels of magnetic sensing on a single custom board is the part I would most like to hear explained.

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wwalsh_1954 2 days ago

Since the ROMpler draws on 16 MB of flash and the synth still lacks patches, a concrete improvement would be a sample loading path, letting players fill the eight banks with their own sounds. That would give the banks real content from day one and open the door to custom samples too.

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