This is a project for the guitar electronics geek. Traditionally guitar effects pedals used analogue circuits made up of clever combinations resistors, capacitors etc. Digital signal processing chips now allow analogue effects circuit to be simulated in software. This project shows the a prospective pedal maker how to build a guitar pedal with an Arduino for lo-fi digital signal processing..
If you like tinkering with electronics this page on home-wrecker.com describes some modifications to the vox v87 wah wah pedal. By changing some of the components, you can tweak the range and limits of the wah effect.