Build your own electric guitar tuner using the Arduino! I decided to make this because I wanted to experiment with audio input and frequency detection. I used Amanda Ghassaei's method for Arduino Frequency Detection in order to get frequency readings using the Arduino. I used LEDs that light up according to the frequency of the audio input, indicating whether the string being played is sharp, flat, or in tune. This works like any other guitar tuner, but you can make it yourself!
Step 1: What you need
(x1) TL082 Dual JFET Input Op Amp (RadioShack #276-1715)
(x1) 6x4x2" project enclosure (RadioShack #270-1806)
(x6) 5mm Yellow LED (RadioShack #276-021)
(x6) 5mm Red LED (RadioShack #276-041)
(x1) 5mm Green LED (RadioShack #276-022)
(x13) 150 Ohm Resistor (RadioShack #271-1109)
(x2) 9V Battery (RadioShack #23-1134)
(x2) 9V Snap Connector (RadioShack #270-324)
(x1) M-type power plug (RadioShack #274-1569)
(x1) SPST Rocker Switch (RadioShack #275-693)
(x1) 1/4" Mono Audio Jack (RadioShack #274-255)
(x1) Matching Printed Circuit Board (RadioShack #276-170)
(x1) Grid-Style Printed Circuit Board (RadioShack #276-149)
(x3) 100kOhm Resistor (RadioShack #271-1347)
(x1) 22kOhm Resistor (RadioShack #271-1339)
(x1) 10uF Capacitor (RadioShack #272-1025)
(x1) 100nF Capacitor
(x1) 6x4x.125" Acrylic Sheet
Step 2: Drill
Drill a hole beneath the on/off switch hole using a 23/64" bit. This hole is for your audio jack.
Step 3: On/Off Switch
Feed the snap and wire through the 13/16" hole in your enclosure and fasten it in place with its mounting nut.