ECE 445 Automatic Guitar Tuner

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ECE 445Automatic Guitar Tuner

• Group 14
• Ryan Freeberg
• Darren Pocci
• Tiffany Kasettratut

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Introduction

• Our project will detect the fundamental frequency
  of a plucked string and compare that to a
  predefined tuning set that the user specifies
• Automatically pluck string and turn tuning pegs
  to adjust string tension

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Similar Devices

• Tronical PowerTune System
• Gibson Robot Guitar
• Requires modification to guitar

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Similar Devices

• String Master
• Handheld device
• One tuning style
• No modification necessary

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Objective

• Create a guitar stand such that user can
• Put guitar in tuner
• Attach tuning motors
• Select desired tuning style
• Start tuning process
• Remove tuned guitar when tuning complete

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Original Design

• Modified standard guitar stand
• Tuning Motors
• Auto-Plucker
• Works with multiple makes and models
• Adjustable tuning motor placement
• Tunes guitar within 2 minutes

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The Automatic Guitar Tuner
Data Acquisition Board
Signal Processor
Tuning Motors
User Interface
Auto-Plucker
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Features

• Different tuning configurations to choose from
• Standard, Drop D, Open G
• Auto-Plucker component
• User does not need to pluck string
• Works with most electrical guitars with six
  tuning pegs on same side

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Block Diagram
Tuning Motors
LabVIEW Signal Processor
BasicX-24 Microcontroller
Guitar
Auto-Plucker
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Block Diagram
Tuning Motors
LabVIEW Signal Processor
BasicX-24 Microcontroller
Guitar
Auto-Plucker
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User Interface

• Displays tuning style and progress of tuner to
  user
• Communicates to Signal Processor and Motors when
  to begin and which tuning style is chosen

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User Interface Schematic
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User Interface Parts

• PIC16F877A
• Communicates buttons with LCD, Signal Processor,
  and Motors
• Samsung UC-20102-GNARS 20x1 LCD screen
• Displays current state of tuner
• Five Push Button Switches
• Standard, Drop-D, Open-G, Start, Reset

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Block Diagram
Tuning Motors
LabVIEW Signal Processor
BasicX-24 Microcontroller
Guitar
Auto-Plucker
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Signal Processor

• Done in LabVIEW 8.2
• Uses PCI-6036E DAQ Card
• Allows easy input and output of analog and
  digital signals
• Only 7 working Digital I/O lines

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Signal Acquisition

• Used PCI-6036E Card with TBX-68 Adapter
• Low amplitude
• Upper limit 2V
• DAQ limit 10V
• Multiple harmonics and overtones
• Good and bad

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Sampling

• Want at least 10 harmonics
• Need to satisfy Nyquist
• Know highest frequency we will look for is 330 Hz
• Minimum sampling frequency is 6600 Hz
• Used 10,000 Hz for added harmonics

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Frequency Detection

• Used Harmonic Distortion Analyzer VI for final
  version
• Looks for highest peak in FFT
• Utilized advanced search function

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Block Diagram
Tuning Motors
LabVIEW Signal Processor
BasicX-24 Microcontroller
Guitar
Auto-Plucker
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BasicX-24 Processor

• BASIC programmable microcontroller
• Outputs PWM signals to control motors
• Reads signal processor inputs
• Calculates when tuning is complete

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Block Diagram
Tuning Motors
LabVIEW Signal Processor
BasicX-24 Microcontroller
Guitar
Auto-Plucker
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Parallax Servo Motor

• Adjustable potentiometer to center the servo
• Continuous rotation
• Required for turning guitar pegs
• Average Speed 60 rpm (with no torque)
• Torque 3.40 kg-cm/47oz-in
• Sufficient to turn guitar pegs

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Functionality of Servo Motor
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Tuning Motors

• Needed bracket attached to motor to turn guitar
  pegs
• Modified guitar winders
• Aligned in linear array to match six pegs

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Control of Guitar Tuning

• Sharp and Flat signals read from signal processor
• Signals read when Auto-Plucker is stationary
• Sharp rotates motors CCW
• Flat rotates motors CW

Signal is Sharp
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Block Diagram
Tuning Motors
LabVIEW Signal Processor
BasicX-24 Microcontroller
Guitar
Auto-Plucker
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Auto-Plucker

• Specialized threaded dowel
• Mounted motor
• Guitar pick holder
• Motor rotation direction determines linear
  direction of pick movement
• Velcro attachment

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Control of Auto-Plucking

• Individual String Plucking
• BasicX outputs pulses controlling pick movement
• Guitar pick moves until tunable signal acquired
• Re-Plucking String
• Signal decays below tunable level for duration
• Auto-Plucker plucks string twice moving back to
  original position

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BasicX Tuning Motors Auto-Plucker Schematic
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Block Diagram
Tuning Motors
LabVIEW Signal Processor
BasicX-24 Microcontroller
Guitar
Auto-Plucker
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Unforeseen Challenges

• Frequency detection robustness
• Assume string within certain frequency range
• If not, tuner detects wrong fundamental frequency
• Auto-Plucker and signal processor miscue
• Signal processor would advance to next string
  while Auto-Plucker would not

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Unforeseen Challenges

• Guitar pick hits more than current string
• Results in noise, though little effect in
  frequency detection
• Changing tension of current strings changes
  tension of tuned strings
• Changed tuner to tune strings twice
• Lengthened tuning process (5 minutes)

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Unforeseen Challenges

• Minimize lateral guitar movement due to
  Auto-Plucker
• Two guitar wall mounts
• Floating Ground
• Wrong input would be acquired

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Recommendations for Unforeseen Challenges

• Plucking and reading states of signal processor
• Would be fixed if 8th digital output was
  available
• Introduce better frequency detection algorithm
• Build device to hold other strings while current
  string is being plucked

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How well did it work?
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Tuning Results

• Standard tuner shows difference in cents
• 1,200 cents 1 octave
• Each tick is 5 cents
• Frequency of note N
• Number of cents away from N C
• Frequency F

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Tuning Results Standard
Tuned string to 2 Hz of correct frequency
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Improvements

• Adjust tuner to adapt to multiple makes and
  models of guitars
• Adjustable tuning motor placement
• Flexibility of tuning styles
• Increase portability
• Use DSP chip opposed to LabVIEW
• Increased Speed

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Credits

• ECE Machine Shop
• Professor L. Haken
• Tony Mangognia
• Professor S. Carney
• Gary Pocci
• CV Lloyde

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Thank You
Questions?
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Ethical Issues

• Minimize damage when setting and removing guitar
  from tuner
• Warn about possible broken strings
• Due to assumed frequency range of guitar
• Standalone guitar tuner
• Wall mount ? User Injury

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Alternate Frequency Detection Techniques

• Extract Single Tone Information VI
• SINAD Analyzer VI
• Cepstrum Analysis

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Tuning Results Drop D
Tuned string to 2 Hz of correct frequency
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Tuning Results Open G
Tuned string to 2 Hz of correct frequency