Stepper Driver Revisited - Questions

Discussion in 'The Projects Forum' started by tracecom, Feb 26, 2011.

  1. tracecom

    Thread Starter AAC Fanatic!

    Apr 16, 2010
    Attached is a revised schematic of my stepper driver circuit. I have previously prototyped a very similar circuit and it is working. However, I plan to go straight to PCB without another prototype and would appreciate it being checked again by someone other than me. The changes I have made are as follows.

    I changed the voltage regulator from a LM317 to an LM78L05. I am confidant of the .33uF and .1uF ceramics, but what about the 10uf electrolytic on the output? Is that large enough?

    Are diodes D1 and D2 needed? My objectives are to protect the regulator from reverse polarity on the input and from any counter EMF from the step motor. (I don't know if step motors have this potential.)

    I added a connector to bring Input 3 from the PICAXE, +5V, and GND out of the board. I don't know what I am going to do with it, but it seemed prudent. (I might need an external interrupt for the PICAXE.)

    Any other comments are welcome. Because this is a PICAXE circuit, I am also going to post the schematic there.

  2. SgtWookie


    Jul 17, 2007
    That's fine for the microcontroller circuit.

    The ULN2x03 has integrated diodes that will protect against reverse EMF, and you show them as connected. If there is no way possible to connect the input power in reverse polarity (which would destroy the Vreg) then you won't need D1 nor D2.

    One never knows. It's easier and better to add stuff beforehand and not need it, than to not add it and find out you need it afterwards - within reason of course.

    Good idea.
    Since I'm not very familiar with the Picaxe, I don't know if the values for R1/R2 are correct/appropriate - however, I'm sure you'll hear about it from those in the Picaxe forum if they aren't correct.
    tracecom likes this.