Control a fan motor (with PWM IC burned out)
You need two H-bridges to do what you want to do. Wire the opposite coils together, and program an Arduino to switch the polarities at an adjustable speed, then give the fan a spin and try to adjust the switching speed to the point when it starts working. Look at the following schematic, voltage sources represent ends of H-bridges.

However, the Arduino controlled fan won't work nearly as well as the original one, as it needs to have some sort of speed feedback, which it doesn't, so spinning up is dumb luck. That's why you need to start it by hand and then the coils will pick up.







simulate this circuit &ndash; Schematic created using CircuitLab