We have been asked by Playgroup, local club promoters, to provide a 'sweetner' to perusade electronica djs [Evil Nine] to take part in an event they are promoting. This item is to be a Theremin. We therefore need to design and build a theremin to be presented to Evil Nine on 30th October 2009 at The Komedia (where we will also be hosting the pre-party from 6-10pm).
This is a lot of work to be done in a short amount of time, and the results must be professional. Volunteers wanted!
A few group members have already worked on MIDI projects and have discussed the idea of building a theremin-type machine with midi output. The analogue signal used to drive the oscillator/speaker on the original could be sampled to give a digital value within a specific range, which in turn can be used to generate a midi "note on/off" signal. The idea of using ultrasonic range finders in place of the theremin's antenna has also been thrown around. This would mean that the end result would be an instrument that plays like a theremin (non-contact) but is actually a completely different beast altogether.
How the BuildBrighton Theremin will work
Ultrasonic sensors are used to return a distance value, from the sensor to the player's hand. This value is converted by an Arduino or other microcontroller into a MIDI key value and is output at the correct baud rate (31,250 bps) onto a serial pin. Since MIDI needs a signal to turn off a key pitch as well as a signal to turn it on, it is recommended that when the note changes, two MIDI signals are sent - one to turn off the previous note and one to activate the required note. It may be possible to program some sort of delay/sustain effect in here, so that the off signal is delayed. This would mean that note changes are not too abrupt as there could be a slight overlap between notes.
Volume can be controlled using a similar approach, using an ultrasonic transducer (or transmit/receive pair) that is away from the note-generating sensor (to avoid cross-talk or interference). Alternatively, a potentiometer, slider or rotary encoder could be used to control volume.
Additionally, optional "effects pedals" could be introduced - time permitting - to alter the MIDI output: instead of a single note, a chord could be played (a major or minor triad) by pressing a foot-switch or rocker pedal. Stress sensors or rotary encoders could be used to implement pitch bending. These are outside the original remit, and unlikely to be ready in time for the impending Oct 30th deadline, but offer food for thought for future development.
Links to source materials/ideas
- How to Build a Theremin Circuit diagrams and discussion on building a true analogue theremin.
- USB-to-MIDI connection cable You'll need these for testing on a PC if you don't have a gameport!