Mississippi State University Department of Electrical and Computer Engineering Theremi n THEREMIN

Douglas Beard Micah Caudle Jeffrey Jun-Fey Wong Way Beng Koay Dr. Raymond Winton Faculty Advisor Theremin Theremin Team

Theremi n Responsibilities Douglas Beard:  Analog to Digital  Digital to Analog  Microprocessor Micah Caudle:  Oscillators.  Beat frequency extractor.  Voltage to Frequency Way Beng Koay:  Frequency to Voltage Conversion  Voltage to Frequency Jeffrey Jun-Fey Wong:  Output Stage  Footswitch Circuit  Tuner Out

Theremi n  Quality theremins are too expensive. $350-3,500  Theremins are hard to play because they are continuous frequency instruments like violin or trombone. Motivation  Limited playing style currently prevents broad use. A more versatile theremin will expand use.

Theremin Lack of Reference : Since the thereminist does not actually touch the theremin, the thereminist has no point of reference for notes and nothing to steady his or her hand. Problems Continuous Pitch : The theremin is a continuous pitch instrument like trombone or violin which makes staying in tune difficult. This fact makes theremin difficult to learn, but it also produces some desired effects. Continuous Volume : Staccato playing or quick stops and starts are difficult with the theremin because of continuous volume.

Theremin Discrete Frequency Accuracy –Switchable between playing the traditional continuous range and playing only distinct frequencies in selectable scales with error < 0.1%. Precise Articulation –A footswitch will connect to the theremin to enable the performer to quickly and easily articulate notes. Frequency Range –A frequency range of four octaves with a center frequency at 440Hz. Design Requirements

Theremin Tuning –A small amplitude signal will always be present at the 1/4" tuner out jack to enable the performer to locate starting pitches and for pitch verification during practice. Design Requirements Cost –The theremin will not cost over $ If sold for a 33% profit margin at $106.40, our theremin will still provide considerable savings relative to comparable theremins. This will greatly enhance the marketability of the unit.

Theremin Modular Design Variable Oscillator Fixed Oscillator Detector Pitch Control Variable Oscillator Volume Tuning Volume Control VCA Processor Voltage Controlled Amplifier Output Control Freq Switch Theremin Tuner Out Signal Footswitch Amplifier Signal Freq-Voltage Converter PIC controller with A/D Discrete Frequency Controller 14-bit D/A V/F Converter

Theremi n Comfortable Range of Motion Capacitance Test 2 pF to 6 pF Range

Theremin VPO and FPO Circuits

Theremi n Detector Circuit

Theremin Beat Frequency Output Range f = 1 / T = Hz T = msec C MAX = 6 pF gives f MAX of Hz C MIN = 2 pF gives f MIN of Hz f = 1 / T = Hz T = 9.1 msec

Theremi n Discrete Mode Overview Frequency/Voltage Converter PIC controller with 10 bit A/D 14 bit D/A Converter Voltage/Frequency Converter Hz continuous beat frequency from detector V continuous voltage range Binary representation of selected output level Resulting discrete voltage level Desired note within 0.045% error

Theremi n Percentage Error Calculation Frequency level Ideal Note Frequency D/A Voltage/ Frequency Converter Voltage level x = MIDI note number A = reference note frequency (440Hz) Percentage Error

Theremi n Percentage Error Tuner Requirement Design Requirement Max. Error = 0.045%

Frequency from VFC Voltage level Output Frequency Theremi n Output Note Four Octaves 110 Hz – 1760 Hz A BbBb B C DbDb D EbEb E F GbGb G AbAb A

Theremi n Component Cost Analysis Design Requirement = $80.00 Leaves $80.00 – $41.61 = $38.39 for packaging costs.

Theremin Conclusions and Future Work Our.1% pitch error limit may be more stringent than needed. Some common tuners accept up to.2% pitch error. The discrete frequency output may have a different timbre than the continuous frequency output. A wave-shaping circuit could be added to give them similar quality. To get the desired discrete frequency accuracy within a four octave range, we need 14 bits, and accurately converting this to analog is expensive in relation to other operations. Lastly, build it!

Mississippi State University Department of Electrical and Computer Engineering Theremi n Questions?