Transcript PDR Slides - School of Electrical and Computer Engineering at

Analog Theremin Using Vacuum
Tubes and Frequency Detection
via Band-pass Filters
Matt Britt, Ryan Adams, William Findley Jr., Yuri
Yelizarov, James Lewis
Georgia Institute of Technology
School of Electrical and Computer Engineering
March 4, 2008 and March 6, 2008
Team Theremin
1
Analog Theremin and Frequency
Detector
• The Theremin is an electronic musical
instrument controlled by interaction with volume
and pitch antennae.
• The frequency detector is designed to assist
new players in playing on the musical scale.
• The target customers are musicians.
• The projected cost of the Theremin is $550.
• The projected cost of the frequency detector is
$145.
Team Theremin
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Theremin: Technical Objectives
• Designed using vacuum tubes in order to suit the
preference of musicians.
• Safe to use.
• Dynamic pitch and volume ranges to provide
sufficient playability.
• Tuning controls to allow adjustments in player
stance.
• Compatible with standard audio equipment.
• Finished case design in a form suitable for a final
product.
Team Theremin
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Theremin: Block Diagram
Team Theremin
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Theremin: Technical Specifications
• Output of the pitch circuit will cover a 30 Hz to
1 kHz range of sound.
• Volume circuit will produce a control voltage for
the voltage-controlled amplifier.
• Power supply circuit will provide two power rails:
6.3 VAC at 2.5 A and 75 VDC at 10 mA.
• The output will use a standard audio equipment
line-out, max 1.4 Vrms.
Team Theremin
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Pitch Control Overview
• RF signals generated by Colpitts oscillators at
~500 kHz
• Mixer is a triode biased in non-linear region
• Low-pass filter is a two-pole RC cascade
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Pitch Control Circuit
Pitch Reference Oscillator
Low-pass Filter
Mixer
Pitch Variable Oscillator
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Pitch Control Performance
• First versions
– High harmonic output
– Unable to produce tones
below 500 Hz
– Smaller effective pitch
range
• Current version
– Near-sinusoidal output
from oscillators
– Able to produce low
frequencies
– Strong RF signal difficult to
isolate
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Volume Control Overview
•
•
•
•
Uses another RF oscillator at 480 kHz
High-Q band-pass filter using ceramic resonator
Peak detector circuit via level shifter and rectifier
Voltage controlled amplifier in form of a differential
amplifier
Team Theremin
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Theremin Design Approach
• Research possible
circuits
• Hand design using
published and
simulated I-V
curves
• Simulation using
phenomenological
triode SPICE
model
– Imperfect
– Model better for
“high” plate current
Linear
amplifier
Nonlinear
mixer
Published plate characteristics for 12AU7A
twin triode. Circa 1956.
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Frequency Detector Overview
• Objective:
– Indicate to the user which output is being used by the Theremin.
• Problem:
– The Theremin produces a wide range, continuous signal.
– With most instruments, a user knows exactly what pitch is
produced.
– The Theremin relies on the musician’s ear and muscle memory.
• Solution:
– An external system that lights up an LED corresponding to an
output frequency produced by the Theremin.
– An LED is provided for each pitch of a chromatic scale.
Team Theremin
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Frequency Detector Block Diagram
Team Theremin
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Frequency Detector Building Blocks
• Gain = (Z1 + Z2)/Z1
• Increasing the
impedance Z2 or
decreasing the
impedance Z1 will
increase the gain.
• Increasing the
impedance Z1 or
decreasing the
impedance Z2 will
decrease the gain.
Team Theremin
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Frequency Detector Notch Filter Simulation
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Frequency Detector: Combining Elements
R1 = 10 kΩ
RL = 1 kΩ
L1 = 3 mH
C1 = 43.6 µF
Op Amp Gain: 1000 V/V
Input Signal: 1 Vrms
Signal Range: 400 Hz – 500 Hz
Number of Points: 500
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Frequency Detector Simulation
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Demonstration Plan
• Measure DC voltage of the antennae,
should be less than a few millivolts.
• Demonstrate pitch range, straight antenna.
– Keep volume hand steady and change
position of pitch hand.
• Demonstrate volume range, loop antenna.
– Keep pitch hand steady and change position
of volume hand.
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Problems: RF Propagation
• RF propagation issue:
– High power, 5 Vpp, signal coming out of the
oscillators may cause coupling and
propagation along power rails.
• Alleviation:
– Careful routing of traces and wiring on PCB
and placement of decoupling capacitors.
– Reduced signal on DC power rail from 1 V to
10 mV.
Team Theremin
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Problems: Mixer Design
• Nonlinear design issue:
– Nonlinear mixer behavior is difficult to predict.
– The practical results differ greatly from
simulation.
• Alleviation:
– Trial and error used to get current result.
– A curve tracer may be used later.
Team Theremin
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Project Schedule
Task
Owner
Status
Evaluation and ordering of tubes
Matt Britt
Completed
Building prototype board
Ryan Adams
Completed
Oscillator design and testing
Matt Britt
Completed
Antenna design
Will Findley
Completed
Frequency detector design
Yuri Yelizarov
In progress
Mixer design
Matt Britt
In progress
Voltage controlled amplifier
design and testing
James Lewis
In progress
Power supply design and testing
James Lewis
Not started
PCB board design and layout
Will Findley
Not started
Final construction
Ryan Adams
Not started
Team Theremin
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Theremin Cost Analysis
• Projected sales volume of
10,000 over a four year
period.
• Three group members
working on Theremin
portion of project.
• The cost of each
Theremin unit is $550.
Description
Unit Cost
Overall Cost
Type
Development Personnel
$36,000
Non-recurring
Development Capital
Equipment
$10,000
Non-recurring
Development Overhead
200 %
$92,000
Non-recurring
Total Development Cost
Parts
$200
Production
$50
Market and Sales
$138,000
$2,000,000
Recurring
$100,000
Recurring
$100,000
Recurring
Total Recurring Cost
$2,200,000
Recurring Cost Overhead, 150%
$3,300,000
Adjusted Recurring Cost
$5,500,000
Team Theremin
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Frequency Detector Cost Analysis
• Projected sales volume of
20,000 over a four year
period.
• Two group members
working on frequency
detector portion of
project.
• The cost of each
frequency detector unit is
$145.
Description
Unit Cost
Overall Cost
Type
Development Personnel
$24,000
Non-recurring
Development Capital
Equipment
$10,000
Non-recurring
Development Overhead
200 %
$68,000
Non-recurring
Total Development Cost
$102,000
Parts
$50
$1,000,000
Recurring
Production
$30
$60,000
Recurring
$100,000
Recurring
Market and Sales
Total Recurring Cost
$1,160,000
Recurring Cost Overhead, 150%
$1,740,000
Adjusted Recurring Cost
$2,900,000
Team Theremin
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Current Status
• Circuit built on tube
“breadboard”.
• Pitch control circuit
works up to the lowpass filter.
• Band-pass filter, for
volume control circuit,
is designed.
• Antennae material is
decided on.
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Questions?
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