ECE 445 Automatic Guitar Tuner

ECE 445Automatic Guitar Tuner Group 14 Ryan Freeberg Darren Pocci Tiffany Kasettratut

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

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

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

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

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

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

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

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

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

User Interface: Schematic

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

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

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

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

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

BasicX-24 Processor • BASIC programmable microcontroller • Outputs PWM signals to control motors • Reads signal processor inputs • Calculates when tuning is complete

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 Parallax Servo Motor

Functionality of Servo Motor

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

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

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

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

BasicX – Tuning Motors – Auto-Plucker Schematic

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

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)

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

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

How well did it work?

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

Tuning Results – Standard *Tuned string to ±2 Hz of correct frequency

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

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

Thank You Questions?

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

Alternate Frequency Detection Techniques • Extract Single Tone Information VI • SINAD Analyzer VI • Cepstrum Analysis

Tuning Results – Drop D *Tuned string to ±2 Hz of correct frequency

Tuning Results – Open G *Tuned string to ±2 Hz of correct frequency

ECE 445 Automatic Guitar Tuner