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

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 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.

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 Beat Frequency Oscillator Variable Oscillator Fixed Oscillator Detector 290 – 288 kHz 292 – 288 kHz Audio: 80 – 850 Hz Beat frequency oscillator functions fairly well. Audio range falls short of design requirement.

Theremi n Lab Results Variable Oscillator Fixed Oscillator Detector 290 – 288 kHz 292 – 288 kHz Audio: 80 – 850 Hz Left: VPOmax = 291 kHz Right: VPOmin = 288 kHz Left: FPOmax = 292 kHz Right: FPOmin = 288 kHz Detector Output Waveform

Theremi n Plan of Action Increase audio range by using larger antenna. Lab tests showed that a larger antenna gives increased hand capacitance. Greater hand capacitance should cause a greater change in VPO frequency and increase our audio range. Step 1: Step 2: Experiment with physical placement of the oscillator circuits on the breadboard to vary their tendency to synchronize.

Theremi n Footswitch Tip Ring Amplified Audio Out Audio In Control Signal Normally Open Stepping on footswitch enables Audio Out. Releasing footswitch disables Audio Out.

Theremi n Frequency-to-Voltage Converter Current StatusRequirementCurrent Status Input frequency110 – 1760 Hz110 – 1760 Output voltage0.3 – 5.0 V1.44 – 5.12 V Problems: (1)Output voltage range does not swing across the whole region of 5V. (2)Converter only detects pulse waveforms, not current pseudo-sinusoid Possible solutions: (1)Decrease R LOAD resistance to shift the voltage down. (2)Use comparator to convert to pulse waves

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

Theremi n Digital to Analog The maximum error from the digital to analog conversion is 82% of a bit. In a test of chromatic scale intervals, the largest error was 0.17% which needs to be worked back within our desired error of <.1%.

Theremi n Voltage-to-Frequency Converter Current StatusRequirementCurrent Status Input Voltage0 – 12 V0 – 2.04 V Output Frequency110 – 1760 Hz Hz Problems: (1)The lowest frequency can not reach 110 Hz. (2)The circuit response is too sensitive to input voltage. Possible solution: (1)Apply amp before the input. (2)Tweak the circuit resistance and capacitance and make it accept input voltage from 0-12V.

Theremi n Voltage-to-Frequency Converter Output Waveform Lower Range Upper Range

Theremi n Summary Beat Frequency Oscillator: Functions well Need to increase audio frequency range Volume Control Circuit: Debugging Hardwiring control presently D/A Converter: Functioning linearly and accurately Frequency/Voltage Converter: Functioning but needs pulse wave input Voltage/Frequency Converter: Functioning but gives pulse wave output Micro Controller: Not yet implemented Footswitch Circuit: Works properly Tuner Out Circuit: Not yet implemented

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