This page shows two examples on how to drive a unipolar stepper motor. These motors can be found in old floppy drives and are easy to control.
The prototyping board has been populated with a 10K potentiomenter that we connect to an analog input, and a ULN2003A driver. This chip has a bunch of transistors embedded in a single housing. It allows the connection of devices and components that need much higher current than the ones that the ATMEGA8 from our Arduino board can offer.