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 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.