Lab 2 Critical Design Review:
Optical Theremin
Michelle Donzé
Michael Ladesic
Jeffery Chen
EE 300, Section 4
Blue Barracudas (#3)
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Table of Contents
I.
Abstract ......................................................................................................................... 3
II. Introduction ................................................................................................................... 3
III. Value Statement ............................................................................................................. 3
IV. Theory ............................................................................................................................ 4
V. Implementation .............................................................................................................. 4
VI. Conclusion ...................................................................................................................... 4
VII.
Appendices ............................................................................................................. 5
a) Gantt Chart ...........................................................................................................................5
b) Bill of Materials .....................................................................................................................5
c) Financial Costs .......................................................................................................................6
d) Reasoning Behind Using the TL074 Op-Amp ........................................................................6
e) Block Diagrams ......................................................................................................................6
Initial Block Diagram............................................................................................................................ 6
Final Block Diagram ............................................................................................................................. 7
f) How to Improve Design Performance .....................................................................................7
g) Light Detector Circuit ............................................................................................................8
Schematic .............................................................................................................................................. 8
Circuit Built on Bread Board ................................................................................................................ 8
h) DAQ Assistant Settings ...........................................................................................................8
DAQ Assistant In .................................................................................................................................. 8
DAQ Assistant Out ............................................................................................................................... 9
Simulate Signal ..................................................................................................................................... 9
Observations ......................................................................................................................................... 9
i) LabVIEW Analysis .................................................................................................................9
j) LabVIEW Block Diagram Schematics .................................................................................. 10
Main Block Diagram........................................................................................................................... 10
Auto Tune Block Diagram (Sub VI) ................................................................................................... 10
k) LabVIEW Front Panel Schematic........................................................................................ 11
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I.
Abstract
This project is to create an Optical Theremin, which is a device that can play sound
without physical contact. The Theremin will be constructed by the amount of light that
reaches the photodiodes used in the circuit and will control the frequency and amplitude.
The frequency and amplitude results will be displayed in a LabVIEW VI after running
the frequency through an auto tuner to make the sound improved.
II.
Introduction
In this project, the team is to create an optical Theremin using a photo sensing circuit and
LabVIEW. A Theremin is a musical instrument that can be played without physical
contact, this means pitch and volume are both controlled without actually touching the
instrument. The design requirements call for the frequency and amplitude to be adjusted
based on light intensity. Photodiodes are implemented in this design for their low cost
and their simplicity in analysis. The light will be measured using photodiodes with the
current to be analyzed using LabVIEW. After sufficient signal processing a sinusoidal
audio tone will be outputted by the myDAQ. The user will be able to control pitch and
volume by regulating the amount of light that reaches the photodiodes. The user will also
be able to configure the intensity range seen by each sensor.
Through a LabVIEW virtual circuit, the user will be able to control the maximum and
minimum light intensity levels along with the range of frequencies that the Theremin will
produce. The front panel is to display the normalized waveforms that control pitch and
volume. It is also to display numeric indicators of light intensities as detected by both
photodiodes. LabVIEW is used in the design for its simplicity and easy programmability;
it provides multiple ways to implement a circuit without uses any physical parts.
The second part of this lab calls for the implementation of an auto-tune feature to the
existing optical Theremin design. This feature will tune the pitch to the nearest half tone.
The auto-tune feature is to implemented using LabVIEW virtual circuitry with the
functionality being able to be turned on or off by the user using the front panel.
LabVIEW is being used to for this feature as it allows the designer to nearly seamlessly
add to an existing design.
III.
Value Statement
This project has value for our team by the process we used to get to the critical design
review. We learned important lessons in teamwork and cooperation, as well as setting
goals for the next week to accomplish. Learning how to work together and write a critical
design review is an experience and skill we can take with us to our Capstone Project next
semester and beyond. This assignment was one of the first projects we had in a group
setting to design a product from beginning to end. Working with a team can be difficult,
but we each found our strengths that we brought to the design process.
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IV.
Theory
A design was created to satisfy the Optical Theremin project through a light sensing
circuit, an amplifier/buffer, an intensity/time range control, and current to frequency
converter. The light sensing circuit should be able to read in the light intensity and then
output that to the LabVIEW VI. The LabVIEW VI will then read the signals (amplitude
and frequency) and amplify them to be able to read at the output. Before the signals reach
the output, the frequency will be put through an auto tuner to match it to the closest note
to improve the sound. Finally, the signal will be heard with the varying amplitude and
frequency that the light intensity captured by the photodiodes produce.
V.
Implementation
The Optical Theremin design is broken down into many components designed to work
separately as well as together. For this design, the bottom-up approach was used because
it was known what subsystems were needed to create an overall functioning system.
 Light Sensing Circuit –
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


VI.
Photodiodes will be used to interpret user interaction through an op amp circuit.
Users will change the intensity of the light delivered to the circuit. The photodiodes
will then output a current proportional to the light intensity.
Amplifier/Buffer –
Since the output of the photodiode will be low level, it will be necessary to amplify
the signal to a usable level. This will be accomplished with an op amp
amplifier/buffer that will interface with a LabVIEW VI through the NI myDAQ.
Intensity/Time Range Control –
The user will be able to control the range of light intensities seen by each sensor
and the tone range output from a LabVIEW front panel interface.
Current to Frequency Converter –
Because the photodiodes output a current of varying amplitude, it will be necessary
to convert it into a frequency in order to output an audio signal. The converter will
convert the current into a sine wave of varying frequency that can be outputted
through the myDAQ TRS connector.
Auto Tune –
The auto tune rounds the frequency to the closet note after being amplified. This
addition to the LabVIEW VI will improve the sound at the output.
Conclusion
The project of an Optical Theremin will meet the requirements of the assignment by
having a functional light sensing circuit and a successful LabVIEW VI that reads the
frequency and amplitude from the circuit. Using a combination of knowledge from
previous electrical engineering classes, an op-amp circuit design was created with the
photodiodes and then being able to use LabVIEW to amplify and auto tune the signal; a
successful Optical Theremin was created.
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VII.
Appendices
a) Gantt Chart
Number
1
2
3
4
5
6
7
8
Task
Design circuit
Build circuit
Initial LabVIEW Code
Testing/Fixing Code
and Interface
Add Auto Tune to Code
Create Bill of Materials
Design Modifications
Critical Design Review
Document
Start Date
Sept. 18
Sept. 25
Sept. 25
Oct. 2
End State
Sept. 25
Sept. 25
Oct. 2
Oct. 2
Duration
7 days
1 day
7 days
1 day
Oct. 2
Oct. 9
Oct. 10
Oct. 10
Oct. 9
Oct. 9
Oct. 10
Oct. 15
7 days
1 day
1 day
5 days
b) Bill of Materials
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2 photo diodes: $1.00
TL074 Op Amp: $2.26
myDAQ Kit: $312.52
Breadboard: $40.00
Pack of ten 1 Mega-Ohm Resistors: $0.15
Total Cost of Materials: $355.93
**Cost of materials on the date of October 9, 2013.
**Subject to change.
Assumptions for what is provided:
The student has access to an oscilloscope with the necessary cables to connect to
the circuit, speakers, and a computer with LabVIEW installed or the capabilities
to have LabVIEW installed (myDAQ kit comes with LabVIEW).
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c) Financial Costs
Cost of Labor:
Hourly
Number of
Rate
Employees
$35/hour
3
Hourly Rate
(all)
$105/hour
Hours
Worked
16
Total Labor
Cost
$1680.00
Fringe (15% of Labor): $252.00
Overheard (40% of Labor + Fringe): $772.80
Grand Total Cost of Project: $3060.73
d) Reasoning Behind Using the TL074 Op-Amp
The TL074 Op-Amp has low input bias and offset currents that are important
because of the photodiode’s low output current. Even a small amount of offset
current will negatively affect the signal. The high slew will allow user input to affect
the output of the Theremin with little to no lag time. There is not another op-amp
better for the application because this one is provided at no cost, which makes the
performance/price ratio infinite.
e) Block Diagrams
Initial Block Diagram
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Final Block Diagram
Inputs
 Light intensity as controlled by the user
 User settings (frequency and amplitude limits)
Output
 Amplified, auto tuned sound
f) How to Improve Design Performance
There are three ways we would like to alter our circuit design after testing and
debugging. The first problem was the noise factor created by the power source.
Adding a filter to remove the noise will help fix this problem. Another way to
improve our design is to have more accurate resistors because the resistors we are
using have a 5% tolerance. Having resistors with a 1% tolerance will make our
circuit more precise. Finally, we can improve our design by having matched
photodiodes. In our circuit the two photodiodes do not register the same light
intensity because the sensitivity of photodiodes vary from one to the other.
Therefore, having matched photodiodes, our circuit will perform better.
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g) Light Detector Circuit
Schematic
Circuit Built on Bread Board
h) DAQ Assistant Settings
DAQ Assistant In
 Voltage_0:
Max = 10 V
Min = -10 V
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
Voltage_1:
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
Acquisition Mode: N Samples
Samples to Read: 2k Hz
Rate: 80k Hz
DAQ Assistant Out
 VoltageOut_0:
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
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Max = 10 V
Min = -10 V
Max = 2 V
Min = -2 V
Acquisition Mode: Continuous Samples
Samples to Read: 20k
Rate: 80k Hz
Simulate Signal
 Samples per Second: 80k Hz
 Number of Samples: 20k Hz
Observations
The DAQ Assistant writer and reader had to be configured so that it produces a
smooth audio signal. Without a proper configuration the outputted audio signal can
potential sound choppy meaning a low quality signal. IN our attempts to avoid this
we found that for the reader a high sampling rate with a low number of samples
produced a smooth signal. For the writer configuration it was the sampling rate that
needed to be adjusted as it was sampling continuously.
i) LabVIEW Analysis
Our original block diagram only accounted for the N=1 level of operation. Our
breadboard implementation and LabVIEW code detail the N=2 subsystems and
beyond while still conforming to the original block diagram. The original idea has
only changed in the details in order to meet the specific project requirements.
Our LabVIEW block diagram creates and outputs a sinusoidal voltage signal based
on the input. To begin, the input signal is split into an average frequency and
amplitude number. These two numbers are normalized to the light intensity limits
specified in the front panel.
Input Signal - Min Preset
Normalized Signal =
Max Preset - Min Preset
The frequency is then scaled to the frequency limits specified in the front panel and
passed through a switch that dictates the presence of auto-tuning. The result is
combined with the amplitude to simulate a sine wave that is sent to the DAQ
Assistant for output.
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Our auto-tune sub-vi is named T-Pain in the diagram. The vi works by looking for
the nearest musical note on the scale given and coercing the input to that note. This
task is accomplished by comparing the input with every element in a variable array
in the inner while loop. The array contains the base frequencies for notes and is
multiplied by two, each iteration of the loop, in order to raise every note by an
octave.
j) LabVIEW Block Diagram Schematics
Main Block Diagram
Auto Tune Block Diagram (Sub VI)
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k) LabVIEW Front Panel Schematic
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