Theremin

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Theremin
Theremin

• Design Review II

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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
Micah Caudle Msc1_at_ece.msstate.edu
Jeffrey Jun-Fey Wong jw5_at_ra.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 Conversion

• 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
Continuous Pitch The theremin is a continuous
pitch instrument like trombone or violin which
makes playing in tune difficult, especially for
beginners.
Continuous Volume Staccato playing or quick
stops and starts are difficult with the theremin
because of continuous volume control.
Lack of Reference Since the thereminist does
not actually touch the theremin, he has no point
of reference for playing certain notes and
nothing to steady his hand.
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Solutions
Theremin
Dual Mode Theremin A more versatile theremin
will be able to switch from the original
continuous frequency mode and a new discrete
frequency mode that produces scales automatically.
Foot Pedal A foot pedal will allow
instantaneous mute and unmute in order to produce
easier staccato.
Tuning A reference for tuning will be provided
for silently locating starting pitches and pitch
verification during practice. Theremin will
interface with common tuners.
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Design Requirements
Theremin

• Four octave frequency range 110 Hz to 1760 Hz

• Automatic scales with error lt 0.1

• Footswitch for staccato articulation

• Tuner signal independent of volume control

• Parts cost less than 80

• Box dimensions of 18x6x4 and weight under 8
  lbs.

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Theremin Modular Design
Theremin
Freq Switch
Audio Out
Tuner Out Signal
Footswitch
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Pitch Control
Theremin
Theremin

• Requirements
• Output an audible sinusoidal frequency between
  110Hz and 1760Hz.
• Achieve the change in frequency with 1 to 17
  inches hand distance from antenna.

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Oscillators
Theremin
VPO and FPO schematic
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Variable Pitch Oscillator
Theremin
Simulation result
VPOMAX 291 kHz
VPOMIN 288kHz
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Fixed Pitch Oscillator
Theremin
Simulation result
FPOMAX 292 kHz
FPOMIN 288kHz
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Detector
Theremin
Requirement Extract beat frequency from variable
and fixed oscillators (heterodyning)
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Detector
Theremin
Simulation result
Circuit output
Simulation
Beat frequency range 70 Hz 1850 Hz
Sensitivity 104.5 Hz/inch (from 1 17 inches)
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Volume Control
Theremin
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Oscillator Drift
Theremin
Problem Temperature induced drift cause unstable
oscillator frequency Factor Temperature
sensitive components in the oscillator
circuit Solution (1) Adjust FPO on the fly with
potentiometer (2) Improve temperature stability
by up-grading temperature sensitive
components (3) Insert a feedback loop into
circuit to reduce drifting
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Discrete Frequency Controller
Theremin
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Frequency-Voltage Converter
Theremin

• Requirements
• Take input of sinusoidal frequency between 110Hz
  and 1760 Hz and output DC voltage between 0.3V
  and 5 V
• Sensitivity 2.5mV/Hz 1mV/Hz.
• Convert the sinusoidal signal to pulse signal to
  meet the requirement of the LM331, slew rate lt
  0.05V/us.

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Frequency-Voltage Converter
Theremin
General purpose opamp LM 741
Integrated circuits comparator LM 239
Problem Slew rate of the opamp comparator gt
0.05V/us Design factor time, space and
cost Solution LM 239 comparator
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Frequency-Voltage Converter
Theremin
Requirement Sensitivity (to allow PIC control) 2.5mV/Hz 1mV/Hz
Achieved sensitivity 1.6mV/Hz
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PIC controller and A/D
Theremin

• The microcontroller now takes in a voltage and
  outputs a corresponding stepped number.

• Correct table values still need to added to code

• Microcontroller then needs to be connected to the
  other portions of the Discrete Frequency
  Controller.

Projected timeline for meeting all requirements
Weeks 1 2 3
Discrete Frequency Controller
Debug Micro-code
Testing
Assemble on Board
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Microchip Program
Theremin
Flow Chart of the Microchip Program
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Voltage-Frequency Converter
Theremin
Requirement In order to achieve the 0.1
frequency error, the voltage-frequency converter
has to meet the following requirement. Sensitivity
146.67 Hz/V 25Hz/V Linearity 0.11Hz
worst-case
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Voltage-Frequency Converter
Theremin
Required Sensitivity 146.67 Hz/V 25Hz/V
Achieved sensitivity 160.31 Hz/V
Required linearity 0.11 Hz worst case (0.1 of 110 Hz)
Achieved linearity 20.7 Hz (std deviation)
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Voltage-Frequency Converter
Theremin
Lowest frequency
Highest frequency

• Problem Error exceeds 0.1 frequency accuracy
• Musical sinusoidal output
  signal
• Solution Re-design using a more accurate sine
  wave generator
• Voltage controlled oscillator
• Numerical controlled oscillator

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Tuner Out Circuit
Theremin
Detector
Requirement Provide signal for common tuner
(frequency discriminator) Gain -RF / R1 -46k
/ 13k 3.54 V/V
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Tuner Out Results
Theremin
Simulation
Circuit Output
Actual Gain Vo / Vin 1.4154 / 0.4 3.54
V/V The output signal meets the requirement for
common tuners
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Footswitch
Theremin
Requirements (1) Stepping on footswitch enables
Audio Out. (2) Releasing footswitch disables
Audio Out.
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Cost Analysis
Theremin
Part Quantity Cost
Inductors 11 16.50
AD7538 1 10.92
Resistors/Capacitors 81 3.66
LM331 2 3.02
PIC16F870 1 2.74
Pitch Antenna 1 2.00
Transistors 8 0.72
Volume Antenna 1 0.30
Diodes 5 0.10
LM239 1 0.25
LM13700 1 0.53
Voltage Regulator 2 2.30
Box 1 10.00
Miscellaneous --- 1.06
Total --- 54.10
Requirement costlt 80.00 Actual cost
54.10 Retail price labor manufacturer
marketing 400 of part cost
216.40
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Design Summary
Theremin
Requirement Objective Achieved
Frequency Range 110 1760 Hz 110 1760Hz
Automatic scales lt 0.1 No
Footswitch Staccato articulation
Tuner Signal Always active
Cost lt 80.00 54.10
Size 18 x 6 x 4 22 x 7 x 3
Weight lt 8 lbs 7.5 lbs
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Market Possibility
Theremin

• Currently, the cheapest quality theremin is the
• Big Briar Etherwave Theremin. (cost US369.00)
• Able to compete with this model. Extra features
• includes tuner out, footswitch and discrete
  mode.
• Has capability to match medium-range theremin in
• market with price.
• Currently there are no dealers in the state of
• Mississippi. Possibility of marketing it here.

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Senior Design II
Theremin

• divide and conquer (solve the requirement by
  breaking it to a smaller requirement)
• importance of staying on schedule
• work in team
• presentation practice

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Future Work
Theremin

• A switch can be added to enable/disable the
  footswitch
• option. This would prevent the player having to
  connect the
• footswitch every time he wants to play.

• 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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Acknowledgements
Theremin
We wish to acknowledge Dr. Ray Winton of
Mississippi State University for his assistance
and guidance with this project. We also would
like to acknowledge Dr. Joseph Picone for his
advice and providing access to many resources
necessary to complete this project.
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Demonstration
Theremin