This stepper motor driver can control two independent steppers via RS232 interface. Control commands can be sent by using simple terminal program like HyperTerminal. Circuit is capable to drive two unipolar stepper motors operating in full step mode. Motors can be powered from 24V and consume up to 0.5A of current.
ATtiny2313 microcontroller sends control pulses via ULN2803A chip, which can drive up to 500mA. Firmware is developed by using BASCOM AVR software. Or you can just download hex file which is ready to flash to microcontroller. This might be useful device for testing stepper motors.