Transcript theremin - Courses - Mississippi State University

Theremi
n
THEREMIN
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Mississippi State University
Department of Electrical and Computer Engineering
Theremin
Theremin Team
Douglas Beard
[email protected]
Way Beng Koay
[email protected]
Dr. Raymond Winton
Faculty Advisor
Jeffrey Jun-Fey Wong
[email protected]
Micah Caudle
[email protected]
Theremi
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Responsibilities
Micah Caudle:
Way Beng Koay:
Oscillators.
Frequency to Voltage
Conversion
Beat frequency extractor.
Voltage to Frequency
Voltage to Frequency
Douglas Beard:
Jeffrey Jun-Fey Wong:
Analog to Digital
Output Stage
Digital to Analog
Footswitch Circuit
Microprocessor
Tuner Out
Theremi
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Motivation
Theremins are hard to play because they are
continuous frequency instruments like violin or
trombone.
Quality theremins are too expensive.
•$350-3,500
Limited playing style currently prevents broad use. A
more versatile theremin will expand use.
Theremin
Problems
• 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.
Theremin
Design Requirements
•Discrete Frequency Accuracy
–Switchable between playing the traditional continuous range and playing
only distinct frequencies in selectable scales with error < 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.
Theremin
Design Requirements
•Cost
–The theremin will not cost over $80.00. If sold for a 33% profit
margin at $106.40, our theremin will still provide considerable
savings relative to comparable theremins. This will greatly enhance
the marketability of the unit.
•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.
Theremin
Theremin Modular Design
Variable
Oscillator
Fixed
Oscillator
Freq-Voltage
Converter
PIC controller
with A/D
14-bit D/A
V/F
Converter
Detector
Discrete Frequency Controller
Pitch Control
Tuner Out Signal
Variable
Oscillator
Volume
Tuning
Volume
Control
Freq
Switch
Voltage Controlled
Amplifier
VCA
Processor
Footswitch
Output Control
Amplifier
Signal
Theremi
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Capacitance Test
Distance vs. Capacitance
7
6
Capacitance (pF)
5
2 pF to 6 pF Range
4
3
2
Comfortable Range of Motion
1
0
0
2
4
6
8
10
Distance (in)
12
14
16
18
Theremin
VPO and FPO Circuits
Theremi
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Detector Circuit
Theremin
Beat Frequency Output Range
CMAX = 6 pF gives
fMAX of 1765.4 Hz
f = 1 / T = 1765.4 Hz
T = 0.566 msec
CMIN = 2 pF gives
f = 1 / T = 109.9 Hz
fMIN of 109.9 Hz
T = 9.1 msec
Theremi
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Discrete Mode Overview
Frequency/Voltage
110-1760 Hz
continuous beat
frequency from
detector
Binary
representation of
selected output
level
PIC controller
with 10 bit A/D
Converter
0.3-5 V
continuous
voltage range
14 bit
D/A Converter
Voltage/Frequency
Resulting discrete
voltage level
Converter
Desired note
within 0.045%
error
Theremi
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Percentage Error Calculation
D/A
 A
Note : ( x)     2
 32 
  x 9  


 12 
x = MIDI note number
Voltage level
Voltage/
Frequency
Converter
Frequency level
A = reference note frequency (440Hz)
Ideal Note Frequency
Percentage Error
Theremi
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Percentage Error
Percentage Error of Output Frequency Compare to Desire
0.25
Tuner Requirement
Percentage Error %
0.2
0.15
Design Requirement
Max. Error = 0.045%
0.1
0.05
0
100
300
500
700
900
1100
Frequency (Hz)
1300
12 bits
1500
1700
14 bits
Design Requirement
Comman Tuner Acceptable Error
Theremi
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Output Note
Frequency
Frequencyfrom
fromVFC
VFC
A
1800
Ab
Output
Frequency
OutputFrequency
1700
1600
G
1600
1400
Gb
1500
1200
F
1400
1000
E
Eb
1300
800
D
1200
Db
600
C
1100
B
400
Four Octaves
Bb
1000
200
900
A
0
0
110 Hz – 1760 Hz
2.5
1
3
2
3.5
3
Voltage level
Voltage level
4
4
4.5
5
6
Theremi
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Component Cost Analysis
Part
Inductors
AD7538
Resistors/Capacitors
LM331
PIC16F870
Pitch Antenna
Transistors
Volume Antenna
Diodes
Opamp
Miscellaneous
Total
Quantity
11
1
81
2
1
1
8
1
5
1
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Cost
$16.50
$10.92
$3.66
$3.02
$2.74
$2.00
$0.72
$0.30
$0.10
$0.59
$1.06
$41.61
Design Requirement = $80.00
Leaves $80.00 – $41.61 = $38.39 for packaging costs.
Theremin
Conclusions and Future Work
• 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.
• Lastly, build it!
Theremi
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Questions?
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Mississippi State University
Department of Electrical and Computer Engineering