Auto-Chromatic Instrument Tuner

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Auto-Chromatic Instrument Tuner

• Erin Smith
• Advisor Dr. James Irwin
• Date November 20th, 2000

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Presentation Overview

• Project Summary
• Milestones Critical Problems
• Future Work

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Project Summary

• Brief Overview of Operation
• State of Received Tuner
• Proposed Modifications

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Overview of Operation

• The auto-chromatic tuner is a self contained tool
  that is used to determine the pitch and
  intonation of a musical instrument in real time

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Functional Description

• Inputs
• Microphone
• Pitch selector
• Power/Mode Switch
• Outputs
• Pitch indicator
• Digital tuning indicator
• Speaker
• 8031 Microcontroller

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Auto-Chromatic Tuner
LED Display
Octave Up
Pitch Up
E b 6
Pitch Down
Octave Down
G
Y
Y
R
R
Auto
Manual
Tuning
Tuning
Off
Audible Pitch
Pitches G Green LED 5 cents Y Yellow
LED 5-15 cents R Red LED 15-50 cents
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Threshold Detector
Timer/ Counter
Audio In
Amplifier
Microphone
Automatic Gain Control
Clock
Divide By 2 Tree
Switched DC Power to all sub- systems
- Parts which do not work, or have not been
included yet
Bus
Overflow
Power/ Mode Switch
Mode
Bus
Microprocessor
Display Control
Bus
Analog Meter
DC Power
Bus
Bus
Bus
Tuning LEDs
Function Generator
Pitch Selector
Pitch Indicator
Pitch Indicator
Frequency Look-Up Table
Speaker Driver
Selected Pitch Out
Speaker
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Threshold Detector
Timer/ Counter
Audio In
Amplifier
Microphone
Automatic Gain Control
Clock
Divide By 2 Tree
Switched DC Power to all sub- systems
- Parts which were modified
Bus
Overflow
Power/ Mode Switch
Mode
Bus
Microprocessor
Display Control
Bus
Analog Meter
DC Power
Bus
Bus
Bus
Tuning LEDs
Function Generator
Pitch Selector
Pitch Indicator
Pitch Indicator
Frequency Look-Up Table
Speaker Driver
Selected Pitch Out
Speaker
9
Start
Initialization Mode
Read Mode/ Power Switch
Auto Tune
Audible Reference Pitch
Display Pitch
Manual Tune
Setup and Start Counter
Adjust Frequency Driver
Counter Overflow
Yes
No
Read Counter
Tuning Mode
Display Results
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State of Received Tuner

• Auto-tune worked with pre-selected octave only
• Manual tune supposedly worked, or had some
  portion working
• Analog and Digital Tuning worked
• Display worked correctly
• Pieces of software worked, but not all in one
  program

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State of Received Tuner

• Tuner did not work as expected when connected to
  power supply
• Programmer was faulty, PALs were broken
• Unit did not work until mid-March
• Analog meter ceased to work (not sure if problem
  with hardware or software)
• No software located for manual tune

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Proposed Modifications

• Manual Tune completion
• Automatic Gain Control
• Expand Digital Tuning
• Auto-Tune Mode completion

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Manual Tune

• Software for Manual Tune could not be located
• Scope was too large, given that no code was
  available to work from
• Due to time constraints, was not able to complete
  Manual Tune mode

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Automatic Gain Control

• Attempted several different configurations in the
  Spring
• Gain circuit with Varistor
• Circuit with an FET

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Varistor
Vin
Vout
LPF
Gain circuit with Varitstor in parallel
Low amplitude signal
Vin
Vout
gnd
Gain circuit with FET in feedback loop
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Automatic Gain Control

• Found article with an AGC circuit which involves
  a digital potentiometer
• Parts did not come in, so AGC could not be
  implemented

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x(t)
y(t)
E(t)
CONTROL

_
Eref
AGC Circuit which utilizes a Digital Potentiometer
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Digital Tuning

• Wanted to expand digital tuning from 5 LEDs to 9
  LEDs
• Intended to take place of analog meter
• Expanded the truth/logic tables
• Not enough memory or bits available to implement
  the expansion
• Required major re-design of hardware and doing
  the wire wrapping over again

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Excerpts of Expansion of the Truth Tables
(formerly only A15-A11 needed)
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Auto-Chromatic Tuner
LED/LCD Display
E b 6
Octave
Pitch
G
B
B
Y
Y
O
O
R
R
Auto
Manual
Tuning
Tuning
Off
Audible Pitch
Pitches G Green LED 3 cents B Blue
LED 4-10 cents Y Yellow LED 11-20
cents O Orange LED 21-30 cents R Red
LED 31-50 cents
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Auto-Tune Mode

• Worked with pre-selected octave only
• Learned how Timer 0 Overflow worked in
  relationship to counting the period
• When overflow occurred, decremented the octave
  and reset the divide by 2n
• Once a pitch is successfully detected, reset the
  divide by 2n to the 9th octave
• Device is then ready to search again

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Milestones CriticalProblems

• Critical Problems
• Unit did not work initially
• Not enough memory to expand LEDs
• Lack of software for manual tune
• Parts for AGC did not come in

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Milestones CriticalProblems

• Milestones
• Getting unit up and running
• Expanding tables for LEDs
• Determined a good duty cycle and waveform for the
  Audible Reference Pitch with a function generator
• Determined design for AGC circuit
• Successfully implementing Auto Tune Mode

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Future Work

• Manual Tune
• Audible Reference Pitch
• Expanded LED Display
• Packaging
• Automatic Gain Control
• New Hardwaremicrophone, speaker, CPU, and memory

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Any Questions?