Headphone-controlled servo motors
Channel: Jim MacArthur
Date: 2012-08-12

Controlling continuous rotation servo motors using the headphone jack of a mobile phone. This is a really simple robot chassis I built with two continuous rotation servos. It may not work with all phones.
More details at http://srimech.blogspot.co.uk/2012/08/controlling-servos-from-headphone.html
Since I've published this I've found http://www.gluemotor.com which is also good and worth checking out.