CHEAPSYNTH – concept & safety info

how to use – how it soundshow to build (easy)how to fixhow to expand

NB: These pages are for the (previous) Arduino-based synth project – to use the keytar as a controller for Windows/Mac/Linux/Raspberry Pi and potentially Android, click here for code examples

2+ octave fully programmable open hardware 8-bit keyboard… for less than £30!

(above demo uses an early version of this Mozzi sketch, followed by this ‘sequencer’ one)

It was the start of 2013 – we were startled to find the acclaimed and versatile Rock Band MIDI keytar on sale for less than £15. We wondered: what’s the cheapest widely available MIDI sound module that you could connect it to, and also get decent sounds out of? (2014 update: of course another answer is “any MIDI-capable device that you already own” – here’s our demo code for using the Wii keytar wirelessly with Raspberry Pi, Windows PCs running Python, and Mac/Linux/other PCs.)

We thought the answer was a £10 Arduino Nano, running the versatile (and free) Mozzi sound synthesis library which has done most of the difficult audio stuff for you. You need a computer running Windows, Mac OS X, or Linux to download software to the Arduino, but you don’t need to be connected to the computer to make music – you also don’t need much electronics expertise to get one working, though programming experience or enthusiasm is handy for creating new sounds.

There are a few pages here showing how it sounds, plus the easy version of how to build one – though please also read the safety info below, and (of course) let us know how you get on. Cheers!

Advice for use – NB Arduino-based version

This is an experimental prototype audio project – due to the user-programmable and modifiable nature of the design, we can’t anticipate all its potential applications and risks. However, please bear in mind the following safety precautions:

  • The design is intended for use with cheap PC-style powered speakers that you’d be able to easily replace in the (unlikely) event that it shorts them out or something. In practice, most loudspeakers should work, though we’d advise against making extended use of headphones especially if you don’t have a reliable filter for the high-pitched 16kHz carrier tone.
  • If you don’t have a reliable 16kHz filter (or more than one), be aware that children, pets, tinnitus sufferers and maybe even hearing aid users may be annoyed by the carrier tone.
  • Don’t leave it unattended and switched on (running off batteries or USB power). Use of external USB power supplies is at your own risk.
  • It’s not intended for unsupervised use by under-14s.
  • Because it’s possible to program different frequency oscillations, avoid use in locations where there are risks of radio interference, eg hospitals, on board aircraft, or around people with pacemakers.
  • The external MIDI module can be played from MIDI instruments other than the Rock Band keytar, but you should remove the resistor connecting MIDI pin 4 to pin 5 before trying it.
  • Have fun!