John, You need to know the voltage/current required & then choose the switching FETs to suit the motor/power required. Will chase up the article for further info.
L.
ps. Found the issue. It's May 2002 Silicon Chip.(
www.siliconchip.com.au)
pps. Found this update/modified circuit for a 4 wire stepper motor.
This thread may need to be moved. L.