Can anyone tell me what the 4 terminals are for the attached stepper motor please? I took it out of an old printer and the datasheet doesn't say. A book I have says it is a bi-polar stepper where the terminals are pulsed.

I am using an ARM mbed and the digi outputs are only 3.3V/45mA while I need 24V/500mA. Usually I would use bjt's as a switch but I,m not sure how or if that would work.

 

Test 2 wires at a time with an ohm meter. When you find 2 that have continuity / resistance, call them 1a and 1b. The other 2 are 2a and 2b. Search online for an "H bridge" circuit as the driver.

 

It's a standard 4-wire bipolar stepper.

Like DNA_Robotics said you need a h-bridge type stepper driver.

Ebay has some full-bridge full step/half step drivers very cheap.