Difference between revisions of "Therething"

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(Merge the Theremin and Not-A-Theremin projects)
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* '''Completion date''': 30/10/2009
 
* '''Completion date''': 30/10/2009
  
We have been asked by Playgroup, local club promoters, to provide a 'sweetner' to perusade electronica djs [[http://www.evilnine.net/ 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).
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We have been asked by Playgroup, local club promoters, to provide a 'sweetner' to perusade electronica djs [[http://www.evilnine.net/ Evil Nine]] to take part in an event they are promoting.  This item is to be a [http://en.wikipedia.org/wiki/Theremin 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!
 
This is a lot of work to be done in a short amount of time, and the results must be professional. Volunteers wanted!
  
=== How a Theremin works ===
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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.
  
The theremin is unique among musical instruments in that it is played without physical contact. The musician stands in front of the instrument and moves his or her hands in the proximity of two metal antennas. The distance from one antenna determines frequency (pitch), and the distance from the other controls amplitude (volume).  Most frequently, the right hand controls the pitch and the left controls the volume, although some performers reverse this arrangement. Some low-cost theremins use a conventional, knob operated volume control and have only the pitch antenna.
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=== How the BuildBrighton Theremin will work ===
  
The theremin uses the [[Wikipedia:heterodyne|heterodyne]] principle to generate an audio signal. The instrument's pitch circuitry includes two [[Wikipedia:radio frequency|radio frequency]] [[Wikipedia:oscillator|oscillator]]s. One oscillator operates at a fixed frequency. The frequency of the other oscillator is controlled by the performer's distance from the pitch control antenna. The performer's hand acts as the [[Wikipedia:ground (electricity)|grounded]] plate (the performer's body being the connection to ground) of a [[Wikipedia:variable capacitor|variable capacitor]] in an L-C (inductance-capacitance) circuit. The difference between the frequencies of the two oscillators at each moment allows the creation of a difference tone in the [[Wikipedia:audio frequency|audio frequency]] range, resulting in audio signals that are amplified and sent to a loudspeaker.
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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.
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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.
  
To control volume, the performer's other hand acts as the grounded plate of another variable capacitor. In this case, the capacitor detunes another oscillator, which affects the amplifier circuit. The distance between the performer's hand and the volume control antenna determines the capacitor's value, which regulates the theremin's volume.
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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.
  
Modern circuit designs often simplify this circuit and avoid the complexity of two heterodyne oscillators by having a single pitch oscillator, akin to the original theremin's volume circuit. This approach is usually less stable and cannot generate the low frequencies that a heterodyne oscillator can. Better designs (e.g. Moog, Theremax) may use two pairs of heterodyne oscillators, for both pitch and volume.
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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.
 
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[http://en.wikipedia.org/wiki/Theremin From Wikipedia]
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=== Links to source materials/ideas ===
 
=== Links to source materials/ideas ===
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* [http://www.musiconmypc.co.uk/art_keyboard_connection.php http://www.musiconmypc.co.uk/art_keyboard_connection.php]
 
* [http://www.musiconmypc.co.uk/art_keyboard_connection.php http://www.musiconmypc.co.uk/art_keyboard_connection.php]
 
* [http://www.strangeapparatus.com/Theremin.html How to Build a Theremin] Circuit diagrams and discussion on building a true analogue theremin.
 
* [http://www.strangeapparatus.com/Theremin.html How to Build a Theremin] Circuit diagrams and discussion on building a true analogue theremin.
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* [http://www.8starshop.com/en/black-usb-to-midi-keyboard-interface-convertor-cable.html?language=en&currency=GBP USB-to-MIDI connection cable] You'll need these for testing on a PC if you don't have a gameport!
  
 
[[Category:Projects]]
 
[[Category:Projects]]

Revision as of 04:29, 8 October 2009

Theremin Project

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