The Self Tuning Guitar Kit Group 5 ECE 445: Senior Design Tom DaMario & KyungJin Lee December 4, 2008

Introduction Kit provides fast, easy way to tune almost any guitar automatically Combines TI DSP, a simple microcontroller, and a stepper motor Gives easy user interface to make anyone could tune the guitar

Features Universal Design 3 different tuning configurations Standard, Drop-D, Open-G Simple operation Accurate to +/- 4.906Hz

Objectives Portability: 100% Battery Powered Device and should be able to fit in guitar case Universal: Device should fit on any guitar Functionality: Device should have multiple tuning modes

Tuning Configurations String Number Standard Tuning Drop-D Tuning Open-G Tuning Note Frequency [Hz] 6 E 82.4 *D 73.4 5 A 110 *G 98 4 D 146.8 3 G 196 2 B 246.9 1 e 329.6 293.6 * Strings that change from standard tuning. Source: http://entertainment.howstuffworks.com/guitar3.htm

Hardware Overview DSP: C6713 DSK PIC 16F877A Takes analog signal from guitar and runs ADC Runs FFT on digital signal Takes difference between desired signal and received signal PIC 16F877A Takes string number from DSK and outputs to Hex display Receives two signals from DSK to turn motor Motor: Parallax #900-00008 Turns guitar tuning peg until desired frequency is reached

Software Overview Code Composer Studio v3.3 Used to connect to DSK Program/Run DSK Flashburn PIC C compiler and MPLAB IDE Used to convert .c program to assembly to load program on PIC 16F877A

Project Flowchart

Output from Guitar Without Amplification: Noise Level: Ave noise level = 22.8mVp-p Ave signal level = 150.3mVp-p Noise % = 1- { (150.3 - 22.8) / 150.3 } = 15.16% Noise Level: String 3 without Amplification:

Signal After Amplification Amplifier Circuit: After Amplification:

Original plan: Use C5509A Has built-in A/D converter Design to draw low power (Easy to make Portable) Problems: Emulator could not detect target DSP chip Back current between CVdd and DVdd

C6713 DSK Board

C6713 Board DIP switches for user input Built-in LED for tuning config Analyze the audio input from guitar to find different frequency in real time Send the motor control output to PIC

Flowchart of DSP Software Holding DIP Switch 3 Analyzes the Signal in Real Time To ignore any input when guitar is not plucked, we add this part in the code. Simplify the output to PIC to control the motor Only two bits of GPIO are required

Only Run FFT When String is Plucked Without any audio input With guitar audio input String 6 Max ≈ 4 String 6 Max ≈ 90

Calculating the Frequency Lowest sampling frequency of A/D converter is 8kHz # of sample = 2048 Step size in frequency = 8000/2048 ≈ 3.906Hz Frequency = (step)(3.906Hz) 1st Peak: 84 2nd Peak: 168 3rd peak: 252 Mean difference ≈ 84 Freq = (84)(3.906) = 328.1Hz Frequency difference = 1.496Hz

Testing the DSP To test the user input from DIP switch, use LED on the board and check desired frequency from the memory To test the FFT, compare graphs from CCS to make sure the peak frequency of FFT is same as the frequency of input signal

DSK Challenges Find the common ground – to solve this problem we use TP32 as common ground from DSP board Find I/O from DSP – Use HPI to output as GPIO Cannot find the way to send any input to DSP – Use DIP switch as the user input Get the right speed for motor to turn, and prevent any delay

Increasing the Accuracy Increase the number of samples taken by the DSP Would make the running time longer Requires more memory space Formula that filters out unclear guitar inputs When the first peak of FFT is smaller than other peaks of FFT

Daughter Card

Wire Wrapping Technique Disadvantages: Wires not soldered in place Time requirement Messy

Voltage Regulator for Battery Power

Motor Specifications Parallax Continuous Rotation Servo #900-00008 Stepper Motor Powered with 5VDC Torque = 3.40 kg-cm (47 oz-in) Need about 37 oz-in to turn peg

Motor Power Consumption String Number Average Current [A] Max Current [A] Average Power [W] Max Power [W] Clockwise Counter Clockwise 6 0.35 0.17 0.45 0.18 1.75 0.85 2.25 0.9 5 0.33 0.36 1.65 1.8 4 0.31 0.19 0.34 0.2 1.55 0.95 1.7 1 3 2 0.29 1.45 0.3 1.5 Max Power Consumed: 2.25 Watts (String 6 Clockwise) Average Power Consumed: 1.25 Watts

Motor Resolution Find Hz/Degree for each peg using motorRes.c while (input(PB1)==1) //Push Button 1 is pressed, rotate clockwise { delay_ms(500); //wait for button to be depressed so that exact //number of pulses measured for (k=0; k<85; k++) //send 85 pulses to motor output_high(motor); delay_ms(1); output_low(motor); delay_ms(20); } Adjust k until motor turns exactly 360⁰

Data Taken from Pic.c String Number Clockwise 360⁰ Turn [Steps] Counter Clockwise 360⁰ Turn [Steps] Clockwise Resolution [⁰/Step] Counter Clockwise Resolution [⁰/Step] No Load 51 49 7.06 7.36 6 56 84 6.43 4.29 5 60 81 4.44 4 3 2 62 5.81 1 63 86 5.71 4.19

Motor Resolution (continued) String Number Frequency at θ = 0⁰ [Hz] Frequency at θ = 360⁰ [Hz] Frequency at θ = 720⁰ [Hz] Frequency at θ = 1080⁰ [Hz] 6 52.63 82.65 105.26 125 5 108.7 129.87 142.86 4 119.05 144.93 166.67 181.82 3 156.25 196.08 223.21 263.16 2 211.86 250 280.9 333.33 1 297.62 362.32 384.62 Θ = Standard Tuning – Frequency of 360⁰ Peg Turn

Motor Resolution (continued) String Number Equation 6 f = 0.067θ+79 5 f = 0.056θ+110 4 f = 0.058θ+140 3 f = 0.097θ+190 2 f = 0.110θ+250 1 f = 0.081θ+330 Observations: Strings 6-4 have different slopes than strings 3-1 due to manufacturing process

Motor Resolution Results String Number Frequency/Rotation [Hz/⁰] Rotation/Step [⁰/Pulse] Resolution [Hz/Pulse] Clockwise Counter Clockwise 6 0.067 6.430 4.290 0.431 0.287 5 0.056 6.000 4.440 0.336 0.249 4 0.058 0.348 0.258 3 0.097 0.582 0.416 2 0.110 5.810 0.639 0.488 1 0.081 5.710 4.190 0.463 0.339 Average Clockwise Resolution = .467 Hz/Pulse Average Counter Clockwise Resolution = .340 Hz/Pulse

Motor Challenges Motor designed to run on up to 6VDC Running on 5VDC reduced torque Running daughter card and motor on same power supply reduced current to motor Gave motor separate battery More power supplies tied to common ground Needed to slow motor & still provide adequate torque

Motor Bracket

Future Improvement Increase Frequency Accuracy Flashburn Create PCB with DSP chip embedded No need to have unused board components Power consumption at a minimum Convert entire project to battery power Reduces size Increase Number of Tuning Configurations

Ethical Considerations Complies with IEEE Code of Ethics Tried to make kit as universal as possible One guitar maker will not benefit over others

Capacitors/Resistors/Diodes Cost Analysis Parts: Item Manufacturer Cost Per Item Quantity Total Cost C6713 DSK Board Spectrum Digital $415.00 1 PIC 16F877A Microchip $3.71 Voltage Regulator Estek $0.90 2 $1.80 Crystal Oscillator Fox $0.40 Capacitors/Resistors/Diodes N/A $0.10 15 $1.50 Hex Display HP $10.56 Battery 9V Duracell $4.00 $8.00 Protoboard Silicon Labs $15.00 DaughterCard $99.99 Code Composer Studio v3.3 Texas Instruments $995.05 Guitar Tuner TU-80 Boss $24.95 Audio Cable 20' Peavy $19.95 Stepper Motor #900-00008 Parallax $12.99 Mounting Bracket Machine Shop $50.00 TOTAL   $1,658.90 Labor: $40.00/Hr x 2.5 x 200Hr x 2 People = $40,000 Total = $40,000 + $1,658.90 = $41,658.90

Special Thanks Professor Gary Swenson Ben Graf Texas Instruments University Division ECE Machine Shop ECE Parts Shop

Questions ???