THEREMIN

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THEREMIN
Theremin

• Department of Electrical and Computer Engineering

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Theremin Team
Theremin
Douglas Beard dtb4_at_ra.msstate.edu
Way Beng Koay wk4_at_ece.msstate.edu
Dr. Raymond Winton Faculty Advisor
Jeffrey Jun-Fey Wong jw5_at_ra.msstate.edu
Micah Caudle Msc1_at_ece.msstate.edu
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Responsibilities
Theremin

• Micah Caudle
• Oscillators.
• Beat frequency detector.
• Volume Circuit

• Way Beng Koay
• Frequency to Voltage Conversion
• Voltage to Frequency

• Douglas Beard
• Analog to Digital
• Digital to Analog
• Microprocessor

• Jeffrey Jun-Fey Wong
• Output Stage
• Footswitch Circuit
• Tuner Out

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Motivation
Theremin

• Theremins are hard to play because they are
  continuous frequency instruments like violin or
  trombone.

• Limited playing style currently prevents broad
  use. A more versatile theremin will expand use.

• Quality theremins can be pricy.
• 350-3,500

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Problems
Theremin

• 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.

• 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.

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Design Requirements
Theremin

• Discrete Frequency Accuracy
• Switchable between playing the traditional
  continuous range and playing only distinct
  frequencies in selectable scales with error lt
  0.1.

• Frequency Range
• A frequency range of four octaves with a center
  frequency at 440Hz.

• Precise Articulation
• A footswitch will connect to the theremin to
  enable the performer to quickly and easily
  articulate notes.

• 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.

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Theremin Modular Design
Theremin
V/F Converter
Freq Switch
Audio Out
Tuner Out Signal
Footswitch
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VPO and FPO Circuits
Theremin
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VPO and FPO Outputs
Theremin
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Detector Circuit
Theremin
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Beat Frequency Output Range
Theremin
CMAX 6 pF gives fMAX of 1765.4 Hz
f 1 / T 1765.4 Hz T 0.566 msec
CMIN 2 pF gives fMIN of 109.9 Hz
f 1 / T 109.9 Hz T 9.1 msec
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Lab Results
Theremin
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Beat Frequency Oscillator
Theremin

• Beat frequency oscillator functions fairly well.
• Audio range falls short of design requirement.

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Plan of Action
Theremin
Step 1

• 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.

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Footswitch
Theremin
Footswitch
Ring
Normally Open
Tip
Control Signal
AmplifiedAudio Out
Audio In

• Stepping on footswitch enables Audio Out.
• Releasing footswitch disables Audio Out.

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Discrete Mode Overview
Theremin
110-1760 Hz continuous beat frequency from
detector
0.3-5 V continuous voltage range
Voltage/Frequency Converter
Binary representation of selected output level
Resulting discrete voltage level
Desired note within 0.1 error
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Frequency-to-Voltage Converter
Theremin
Problem solved --- A comparator circuit was
implemented to convert the audio signal into a
pulse wave for proper detection by the V/F
converter. Problems --- Output voltage range
does not swing across the whole range of
5V. Possible solutions --- Apply amplification
to the output before microcontroller.
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Percentage Error
Theremin
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Digital to Analog
Theremin
In a test of chromatic scale intervals, the
largest error was 0.17 which needs to be worked
back within our desired error of lt.1 .
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Voltage-to-Frequency Converter
Theremin
Problems Solved (1) Capacitance value of CT
(control chip trigger time) has increased by
factor of 10 to make trigger time of the chip
increase by factor of 10. Response range
increase.
Problems (1) The lowest frequency reachable is
around 160 Hz. (2) Frequency outputs from voltage
are not totally linear in relation to voltage.
Possible solution Change CT to higher value
(10x) to increase the trigger time. Test run, but
5.0-7.4V swing across 110-1760Hz. Again, the
circuit is too sensitive to the input voltage..
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Voltage-to-Frequency Output
Theremin
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Voltage-to-Frequency ConverterOutput Waveform
Theremin
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Summary
Theremin

• Beat Frequency Oscillator
• Functions well
• Need to increase audio frequency range

• Frequency/Voltage Converter
• Functions but needed pulse wave input
• Addition of comparator fixed the problem

• Volume Control Circuit
• Debugging
• Hardwiring control presently

• Micro Controller
• Programming not complete

• D/A Converter
• Functioning linearly and accurately

• Footswitch Circuit
• Works properly

• Voltage/Frequency Converter
• Functioning but gives pulse wave output

• Tuner Out Circuit
• Not yet implemented

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Conclusions and Future Work
Theremin

• 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.

• 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.

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Questions?
Theremin

• Mississippi State University
• Department of Electrical and Computer Engineering