There are many different stepper drivers around. Here I describe 3 different types. Main target are the unipolar stepper drivers.
Simple drivers circuits:
The most simple drivers will have 4 inputs somekind of converter to higher voltage and 4 outputs towards the coils of the (unipolar) stepper. If connected to the LPT some kind of isolation to the low power side is needed. There are 3 isolation possibilities:
- No isolation, direct transistor driven, potentially damaging to computer
- Optical isloation, safe up to 1500~3000V
- Buffer/driver isolation, like the 7407 or ULN2803
The circuit could look like one of the following:
