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Circuit Playground multi-tool

Adafruit's round board has an accelerometer, light, sound and temperature sensors, eight touch pads, ten NeoPixels, a speaker, two buttons and a slide switch. One Arduino sketch puts one sensor at a time on MIDI duty. It ran the 2018 and 2019 Web MIDI workshops and the PCD 2026 one.

Source: github.com/georgemandis/circuit-playground-midi-multi-tool. What it sends, mode by mode, is on the device page. This page is about the firmware.

How it is built​

The MIDIUSB library gives three calls: sendMIDI with a four-byte packet, read for incoming, flush to push the buffer out. The sketch wraps them:

void noteOn(byte channel, byte pitch, byte velocity) {
  midiEventPacket_t noteOn = {0x09, 0x90 | channel, pitch, velocity};
  MidiUSB.sendMIDI(noteOn);
}

The first byte, 0x09, is USB-MIDI's own header: which jack and what kind of message. The other three are the MIDI bytes. channel here is zero-based and the sketch passes 1, so everything goes out as channel 2. That is the kind of thing a README has to say and this one did not, until now.

loop() is a switch on the mode. Each case reads one sensor and sends. The slide switch drops into a mode-picking loop where the buttons change the mode and the pixels show it. The buttons and the switch never send MIDI.

What the README got wrong​

Mode 7 is listed as "converts the accelerometer tap detection to a MIDI message". The tap interrupt is armed and it flashes the pixels, but the noteOn(2, 1, 127) that would send is commented out under "Accelerometer detect tap: TBD". No MIDI leaves the board on a tap. The fix is a proposed README in firmware/circuit-playground-midi-multi-tool/ with the full message map, the channel, and arduino-cli flash steps, as a patch against the repo. Uncomment the block if you want the note.

Flash​

arduino-cli core install arduino:avr
arduino-cli lib install MIDIUSB "Adafruit Circuit Playground"
git clone https://github.com/georgemandis/circuit-playground-midi-multi-tool
arduino-cli compile --fqbn arduino:avr:circuitplay32u4cat circuit-playground-midi-multi-tool
arduino-cli upload  --fqbn arduino:avr:circuitplay32u4cat -p /dev/cu.usbmodem14101 circuit-playground-midi-multi-tool

Express boards use adafruit:samd:adafruit_circuitplayground_m0 after installing the adafruit:samd core. The Classic is at 73% of its flash with this sketch, so there is room for a mode of your own.

Make it yours​

Change noteOn(1, ...) to noteOn(0, ...) and it is on channel 1 like everything else here. Add a case for a sensor combination you want, for instance light as CC 1 and the pads as notes in the same mode, since the one-sensor-at-a-time rule is a choice, not a limit. The starter is the same three functions with nothing else in the way.