Ideas for Areas to Explore

• Make a keyboard for the CPX MIDI controller:
  • "traditional" fruit: Circuit Playground Fruit Drums: Cirkey Cirkey,
  • crocodile clips only: Circuit Playground Fruit Drums: Tone Piano,
  • conductive paint: Bare Conductive: How to make a MIDI piano with the Touch Board (silk screen printed, may be harded to hand paint),
  • copper tape / aluminium foil: Wendian Jiang: Automatic Notation System with Capacitive Touch Piano (page 6).
• Enhance the note representation on the NeoPixels to include pitch bending.
• Change the synth waveform to a sine wave, a square wave or noise made from random values (audible result may surprise).
• Write a separate program to use the onboard microphone to record and process a very short sample for use in the synthesizer.
• Use the light sensor to modulate another MIDI cc.
• Implement MIDI "poly chaining" to send notes to the next CPX board when more than one note is played simultaneously.
• Explore the capabilities of the new audioio.Mixer class - this could be used for limited polyphony and smoother pitch bending.
• Emulate a Leslie speaker by mounting your CPX synth on a servo and wiggling it.

The boards based on the Cortex M0 processor (SAMD21) like the CPX have 32kB of memory. The M4 (SAMD51) boards with 192kB like the NeoTrellis M4 are likely to be a better choice for larger, more sophisticated programs using the adafruit_midi library. The NeoTrellis M4 also includes stereo 12bit DACs with 3.5mm audio output.

Related Projects

There are many projects using the NeoTrellis M4, the ones below are just a small selection.

MIDI

• Trellis M4 Expressive MIDI Controller - includes some useful background information on how MIDI works and how to use and connect iOS tablets.
• Grand Central USB MIDI Controller in CircuitPython.
• NeoTrellis M4 MIDI File Synthesizer.

Non-MIDI

• Make It Sound (CircuitPython and MakeCode examples).
• Circuit Playground Express: Piano in the Key of Lime.
• Touch Tone for Circuit Playground Express.
• Circuit Playground Express: Playground Drum Machine.
• Circuit Playground Fruit Drums - this uses the Circuit Playground Classic which has one extra touch-capable pad but has a smaller CPU and cannot run CircuitPython.
• Circuit Playground Musical Glove - this is inspired by the MINI.MU Glove Kit but uses MakeCode on the CPX.
• Matt Stanton's CPX Glove Synth code (C++/Arduino).

Further Reading and Listening

• Collin's Lab: MIDI (YouTube video with transcript).
• What is Web MIDI & BLE MIDI (BLE=Bluetooth Low Energy).
• Gizmodo: A Beginner's Guide to the Synth.
• Circuit Playground Analog Input: Analog vs. Digital.
• The Curious Cases of Rutherford & Fry: An Instrumental Case: Why do instruments sound different? (podcast, click on yellow Download button, main programme up to 00:21:30).
• The Synthesizer Academy (online guides).
• Kenny McAlpine: Bits and Pieces - A History of Chiptunes - a well researched book covering both the music and technology behind the Atari VCS, ZX Spectrum, Commodore 64, NES, Game Boy and more.
• Steve W. Smith: The Scientist and Engineer's Guide to
  Digital Signal Processing - an in-depth book available for free online.
• R code used to generate graphs on the Waveforms page.

Selected Music

• Music From Mathematics album (music made with IBM 7090 in 1962).
• Pixelh8 (Matthew Applegate) - Obsolete? (bandcamp) -  commissioned by The National Museum of Computing (UK).
• Tristan Perich - 1-Bit symphony (bandcamp).