A pulse generator for the lavet-type stepper motor typically found in (cheap) clock movements, like this.
This library is based on the circuit and code presented here: http://www.cibomahto.com/2008/03/controlling-a-clock-with-an-arduino/ Which is a good reference for the kind of circuit you'll need to use this, and the code available there does basically the same thing; but in the Arduino IDE, using delays.