Theremin

Theremin

Design Review II

Douglas Bearddtb4@ra.msstate.edu

Micah CaudleMsc1@ece.msstate.edu

Jeffrey Jun-Fey Wongjw5@ra.msstate.edu

Way Beng Koaywk4@ece.msstate.edu

Dr. Raymond Winton Faculty Advisor

Theremin

Theremin Team

Theremin

Responsibilities

Douglas Beard:

Analog to Digital

Digital to Analog

Microprocessor

Micah Caudle:

Oscillators.

Beat frequency detector.

Volume Circuit

Way Beng Koay:

Frequency to Voltage Conversion

Voltage to Frequency Conversion

Jeffrey Jun-Fey Wong:

Output Stage

Footswitch Circuit

Tuner Out

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.

Continuous Volume: Staccato playing or quick stops and starts are difficult with the theremin because of continuous volume control.

Theremin

Continuous Pitch: The theremin is a continuous pitch instrument like trombone or violin which makes playing in tune difficult, especially for beginners.

Motivation

Theremin

Tuning: A reference for tuning will be provided for silently locating starting pitches and pitch verification during practice. Theremin will interface with common tuners.

Solutions

Foot Pedal: A foot pedal will allow instantaneous mute and unmute in order to produce easier staccato.

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.

Theremin

•Footswitch for staccato articulation

Design Requirements

•Tuner signal independent of volume control

•Box dimensions of 18”x6”x4” and weight under 8 lbs.

•Four octave frequency range: 110 Hz to 1760 Hz

•Automatic scales with error < 0.1%

•Parts cost less than $80

VariableOscillator

FixedOscillator

Detector

Pitch Control

VariableOscillator

VolumeTuning

Volume Control

FreqSwitch

Theremin

Tuner Out Signal

Footswitch

Audio Out

Freq-VoltageConverter

PIC controllerwith A/D

Discrete Frequency Controller

14-bit D/AV/F

Converter

VCAProcessor

Voltage ControlledAmplifier

Output Control

Theremin Modular Design

ThereminTheremin

Pitch ControlVariableOscillator

FixedOscillator

Detector

Pitch Control

Requirements:

(1) Output an audible sinusoidal frequency between 110Hz and 1760Hz.

(2) Achieve the change in frequency with 1 to 17 inches hand distance from antenna.

VariableOscillator

FixedOscillator

Detector

290 – 288 kHz

292 – 288 kHz

Audio:110 – 1760Hz

Theremin

Oscillators

VPO and FPO schematic

Theremin

Variable Pitch OscillatorSimulation result

VPOMAX 291 kHz VPOMIN 288kHz

Theremin

Fixed Pitch Oscillator

FPOMIN 288kHz

Simulation result

FPOMAX 292 kHz

Theremin

Detector

Requirement:

Extract beat frequency from variable and fixed oscillators

(heterodyning)

Theremin

Detector

Simulation

Simulation result Circuit output

Beat frequency range 70 Hz – 1850 Hz

Sensitivity 104.5 Hz/inch (from 1 – 17 inches)

Theremin

Volume Control

•Functioning on breadboard circuit

•Not working in box

•Needs more testing and debugging

Volume vs. Distance

0

0.20.4

0.6

0.8

11.2

1.4

1.6

0 2 4 6 8 10 12 14 16

Distance (inches)

Au

dio

(p

k-p

k)

Theremin

Oscillator DriftProblem: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

Theremin

Discrete Frequency Controller

Frequency/Voltage

Converter

PIC controller with 10 bit A/D

14 bit

D/A Converter

Voltage/Frequency

Converter

110-1760 Hz continuous beat frequency from detector

0.3-5 V continuous voltage range

Binary representation of selected output level

Resulting discrete voltage level

Desired note within 0.1% error

Theremin

Frequency-Voltage Converter

Requirements:

(1) Take input of sinusoidal frequency between 110Hz and 1760 Hz and output DC voltage between 0.3V and 5 V

(2) Sensitivity 2.5mV/Hz ± 1mV/Hz.

(3) Convert the sinusoidal signal to pulse signal to meet the requirement of the LM331, slew rate < 0.05V/us.

Theremin

Frequency-Voltage Converter

Problem: Slew rate of the opamp comparator > 0.05V/us

Design factor: time, space and cost

Solution: LM 239 comparator

General purpose opamp – LM 741 Integrated circuits comparator – LM 239

Theremin

Frequency-Voltage Converter

Requirement Sensitivity(to allow PIC control)

2.5mV/Hz ± 1mV/Hz

Achieved sensitivity 1.6mV/Hz

Theremin

PIC controller and A/D

• Correct table values still need to added to code

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

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

Weeks 1 2 3

Discrete Frequency Controller Debug

Micro-codeTesting

Assemble on Board

Projected timeline for meeting all requirements

Theremin

Microchip Program

Flow Chart of the Microchip Program

Theremin

Voltage-Frequency Converter

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

Theremin

Voltage-Frequency Converter

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)

Theremin

Voltage-Frequency Converter

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

Lowest frequency Highest frequency

Theremin

Tuner Out Circuit

Requirement:

Provide signal for common tuner (frequency discriminator)

Gain = -RF / R1 = -46k / 13k = 3.54 V/V

To

Tuner

Detector

Theremin

Tuner Out ResultsSimulation Circuit Output

Actual Gain = Vo / Vin = 1.4154 / 0.4 = 3.54 V/V

The output signal meets the requirement for common tuners

Theremin

Footswitch

Footswitch

Tip

Ring

Amplified Audio Out

Audio InControl Signal

Normally Open

Requirements: (1) Stepping on footswitch enables Audio Out.

(2) Releasing footswitch disables Audio Out.

Theremin

Cost AnalysisPart 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: cost< $80.00

Actual cost = $54.10

Retail price = labor + manufacturer + marketing

= 400% of part cost

= $216.40

Theremin

Design Summary

Requirement Objective Achieved

Frequency Range 110 – 1760 Hz 110 – 1760Hz

Automatic scales < 0.1% No

Footswitch Staccato articulation

Tuner Signal Always active

Cost < $80.00 $54.10

Size 18” x 6” x 4” 22” x 7” x 3”

Weight < 8 lbs 7.5 lbs

Theremin

Market Possibility• Currently, the cheapest quality theremin is the Big Briar Etherwave Theremin. (cost US$369.00)

• 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.

Theremin

Senior Design II

• divide and conquer (solve the requirement by breaking it to a smaller requirement)

• importance of staying on schedule

• work in team

• presentation practice

Theremin

Future Work

• 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.

• 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.

Theremin

Acknowledgements

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.

Theremin

Demonstration