electonic guitar tuner
TRANSCRIPT
-
7/29/2019 electonic guitar tuner.
1/16
-
7/29/2019 electonic guitar tuner.
2/16
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
-
7/29/2019 electonic guitar tuner.
3/16
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
-
7/29/2019 electonic guitar tuner.
4/16
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
-
7/29/2019 electonic guitar tuner.
5/16
Guitar Frequency Spectrum
-
7/29/2019 electonic guitar tuner.
6/16
-
7/29/2019 electonic guitar tuner.
7/16
Design: Block Diagram
3 main components: input, DSP, output
-
7/29/2019 electonic guitar tuner.
8/16
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
-
7/29/2019 electonic guitar tuner.
9/16
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
-
7/29/2019 electonic guitar tuner.
10/16
Design: Digital Signal Processor
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.
-
7/29/2019 electonic guitar tuner.
11/16
Design: Digital Signal Processor
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.
-
7/29/2019 electonic guitar tuner.
12/16
Design: Digital Signal Processor
DSP Algorithmcont.6.) Write corresponding values to the Data
register for Port B.
7.) Port B outputs values to display.
-
7/29/2019 electonic guitar tuner.
13/16
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
-
7/29/2019 electonic guitar tuner.
14/16
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.
-
7/29/2019 electonic guitar tuner.
15/16
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
-
7/29/2019 electonic guitar tuner.
16/16
Summary
Designed and implemented tuner.
Accurate within approximately 10 cents.
Accuracy could be increased by taking
longer FFT.
Lower sampling rate
Easily Marketable