Guitar Tuner

ECE 5330

Embedded Systems Design

Final Project Proposal

Mike Heiny

November 17, 2008

Background

• I used to play guitar, 20 to 25 years ago.

• But I stunk.

• And I always had trouble tuning.

• I still have my guitar and amp, though.

• I’ve seen electronic tuning gadgets used by roadies at concerts, seems like an interesting thing to design.

Basic Proposal

• Implement hardware to allow connecting an electric guitar to the board.

• User selects which string is to be tuned.

• User plays the string.

• AVR “listens” to the note and communicates to the user, via LEDs, how close to perfect the note is and whether it is high or low.

Hardware

Software

TBD 1

• What is the output of an electric guitar?– I think I read +/- 5 mV was typical– That’s too small to be much use and will have

to be amplified.– Does it put that out with no input, or will I need

to power it somehow?

TBD 2

• How accurate does it need to be?– Strings are 82, 110, 147, 196, 247 & 330 Hz.

(I was really surprised at how low they are.)– When you tune you can hear the wah-wah-

wah of interference. – That’s noticeable to about once every 3 or 4

seconds, which would be ~0.3 Hz. – If I shoot for within 0.1 Hz of target, that’s

0.03%, which is pretty tight.

TBD 3

• Determining Frequency– I plan to have the AVR determine the period

of the input signal and from that determine the frequency.

– But the difference in periods between 330 Hz and 330.1 Hz is less than 1 μs!

– I think this is the biggest challenge.

Other TBDs

• How should the board communicate to the user?

• What will it do when no note is played, and how will it know?

• How will it start and end?

Possible Additional Features

• Add a microphone to allow acoustic guitar tuning.

• Have the program automatically detect which string is being tuned.

• Allow user-specified target frequencies for tuning basically anything.