Theremi n Design Review II

Douglas Beard Micah Caudle u 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 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. Theremi n 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

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

Theremin Pitch Control Variable Oscillator Fixed Oscillator 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. Variable Oscillator Fixed Oscillator Detector 290 – 288 kHz 292 – 288 kHz Audio: 110 – 1760Hz

Theremin Oscillators VPO and FPO schematic

Theremin Variable Pitch Oscillator Simulation result VPO MAX 291 kHzVPO MIN 288kHz

Theremin Fixed Pitch Oscillator FPO MIN 288kHz Simulation result FPO MAX 292 kHz

Theremin Detector Requirement: Extract beat frequency from variable and fixed oscillators (heterodyning)

Theremin Detector Simulation Simulation resultCircuit output Beat frequency range70 Hz – 1850 Hz Sensitivity104.5 Hz/inch (from 1 – 17 inches)

Theremin Volume Control Functioning on breadboard circuit Not working in box Needs more testing and debugging

Theremin Oscillator Drift 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

Theremin Discrete Frequency Controller 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 0.1% 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 741Integrated circuits comparator – LM 239

Theremin Frequency-Voltage Converter Requirement Sensitivity (to allow PIC control) 2.5mV/Hz ± 1mV/Hz Achieved sensitivity1.6mV/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 123 Discrete Frequency Controller Debug Micro-code Testing 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: Hz/V ± 25Hz/V Linearity: ± 0.11Hz worst-case

Theremin Voltage-Frequency Converter Required Sensitivity Hz/V ± 25Hz/V Achieved sensitivity 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 frequencyHighest frequency

Theremi n Tuner Out Circuit Requirement: Provide signal for common tuner (frequency discriminator) Gain = -RF / R1 = -46k / 13k = 3.54 V/V To Tuner Detector

Theremi n Tuner Out Results Simulation Circuit Output Actual Gain = Vo / Vin = / 0.4 = 3.54 V/V The output signal meets the requirement for common tuners

Theremin Footswitch Tip Ring Amplified Audio Out Audio In Control Signal Normally Open Requirements:(1) Stepping on footswitch enables Audio Out. (2) Releasing footswitch disables Audio Out.

Theremin Cost Analysis PartQuantityCost Inductors11$16.50 AD75381$10.92 Resistors/Capacitors81$3.66 LM3312$3.02 PIC16F8701$2.74 Pitch Antenna1$2.00 Transistors8$0.72 Volume Antenna1$0.30 Diodes5$0.10 LM2391$0.25 LM137001$0.53 Voltage Regulator2$2.30 Box1$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 RequirementObjectiveAchieved Frequency Range110 – 1760 Hz Automatic scales < 0.1%No FootswitchStaccato articulation Tuner SignalAlways active Cost< $80.00$54.10 Size18” x 6” x 4”22” x 7” x 3” Weight< 8 lbs7.5 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.

Theremi n 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.

Theremi n Demonstration