PIC Current Limiter

The PIC/Generation 1 electronics do not have any form of current limitting. They rely on the stepper motors resistance to keep the current below 2 Amps at 12 Volts. Unfortunatly the more commonly available Steppers of the size used in RepRap have much lower resistances. e. g. The current BitsFromBytes supplied Steppers have a resistance of XXXX. Be
PIC Current Limiter - schematic

low is the schematic for a single coil, each stepper motor has two coils. As each coil requires one comparator an LM393 (dual comparator) could be used. It is almost certainly cheaper though to use an LM339 (quad comparator) and build the circuit to handle 4 coils / 2 motors.

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