DIY ELECTRIC HANDPAN

Concept

In this version I'm going to fabricate the handpan 'chassis' from laser-cut MDF plates, install some piezo pick-ups, and use some electronics-and-code to turn percussive energy into sound.

I'm most interested in something that makes sound in a relatively stand-alone way (i.e. via on-board speakers), but will try to include some kind of MIDI output as well.

One nice advantage of an electric handpan is that the note scale will be configurable.

OnShape

As per usual, I'm doing my design work in OnShape. The design covers the chassis, plus several templates/jigs/guides to help put the chassis together.

I'm going to use 6mm-thick MDF for my chassis, and will route-out a 60mm-diameter/4mm-deep recess on the back of each note plate to bring the piezo pick-ups closer to the surface.

To explain a bit about the router jig (1st photo): the bits you see help locate the jig within the outermost ring (actually the handpan chassis base plate, not shown). The middle ring is then set aside. The inner ring slides around inside the (taped-down) outermost ring, limiting the cut to a 60mm-diameter circle.

Electronics

High-level design: 9 x piezo pick-ups (one per note plate); 9 x piezo-to-ADC mediators; 2 x ADCs (MCP3008); one Raspberry Pi; one Raspberry Pi DigiAMP+. I've split the electronics over several PCBs.

Each piezo sensor gets a small PCB that mediates between the piezo and the ADC that I'm using. The reason for the mediation is that the naked piezo can produce upwards of 25V, which can't be piped directly into the ADC (reference voltage 3V, as per the Raspberry Pi). In practise, the maximum voltage I was getting out of the piezo-bonded-to-MDF was around 10V, but you'll want to measure your own set-up, and adjust the voltage divider (R1) accordingly. As a backstop, the Zener diode should breakdown at 3V3 to protect the ADC from too high a voltage input. The other diode rectifies the output from the piezo.

The signals from each piezo-to-ADC PCB are fed into a pair of ADCs - each has eight inputs, so we need a pair to cover the nine inputs (the second of which is not doing much work). Given the spare inputs on the second ADC, I'm going to wire one up to a potentiometer to act as a master volume control.

Extended Gerber files for piezo-to-ADC PCB - suitable for submission to Elecrow.com, for example. If you get ten copies made, you'll have a spare to experiment with!