electonic guitar tuner.

7/29/2019 electonic guitar tuner.

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Target Specifications

For use with acoustic guitar.

Accurate to 10 cents (musical term) for

entire range of guitar pitches

Easy to read output LED display


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Background - Musical terms

1 octave = 12 pitches

octaves are numbered (lowest to highest)

according to range of piano.

12 pitches: A, A#, B, C, C#, D, D#, E, F,

F#, G, G#

100 cents defined between each pitch


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Background - Guitar

Acoustic guitar ranges from E2 (pitch E in pianos

second octave) to C#6.

Plucked string: Fundamental frequency andharmonics

Guitar Spectrum: fundamental frequency has

lower power than some higher harmonics.

Lower frequencies have more power in harmonics than

higher frequencies.

Demonstrates acoustic non-linearity of string


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Guitar Frequency Spectrum


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Design: Block Diagram

3 main components: input, DSP, output


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Design: Input

Microphone to receive signal

Possibilities: dynamic, condenser, pressure

gradient microphone stylesDecision: dynamic

Why? Frequency response and range, availability

Amplifier: To increase microphoneamplitude (output Vpp ~ 5-10mV)

op-amp with gain of 100


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Design: Digital Signal Processor

Motorola 56302 DSP Evaluation Board

DSP board provides:

analog-to-digital conversion

Fast Fourier Transform (FFT) of signal

lookup tables for frequency conversion to pitch

and centsdigital output to LED display


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DSP Algorithm1.) Ready State for continuous, real-time

system

check input amplitude below threshold, stay in ready state

above threshold, proceed to FFT

2.) Take 1024 sample FFT. Store squaredmagnitudes in memory.

FOR MORE INFO...

See Handout for flowchart, DSP Algorithm.


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DSP Algorithmcont.3.) Start with ninth index, compare

magnitudes to a new threshold, which is set

above the level of the noise.4.) Find first peak in FFT data. This

corresponds to the fundamental frequency.

5.) Store this index value, use it for pitch andcents lookup tables.


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DSP Algorithmcont.6.) Write corresponding values to the Data

register for Port B.

7.) Port B outputs values to display.


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Design: Output

Digital high/low values from Port B of DSP

board

Output display:

hexidecimal display for note letters

1 LED indicating a sharp

10 LEDs: 5 corresponding to sharpness in unitsof 10 cents, 5 corresponding to flatness


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Verification

Test signals (pure sine and square waves)

from function generator.

Tested final circuit with guitar andcompared output to commercial guitar

tuner.

Verified correct identification of peak frommemory contents.


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Design Cost

Parts cost:

Item: Cost:

Motorola DSP + Eval. $165.00

Amplifier $2.00

11 LED's $5.00

Hexadecimal Display $2.00

Microphone $120.00

Misc. Comp. $2.00

Total Parts: $296.00

Labor: $3600.00

Complete Cost: $3,896.00


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Summary

Designed and implemented tuner.

Accurate within approximately 10 cents.

Accuracy could be increased by taking

longer FFT.

Lower sampling rate

Easily Marketable

electonic guitar tuner.

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