Modifying driver for CNC

Discussion in 'The Projects Forum' started by thebrent, Sep 16, 2012.

  1. thebrent

    Thread Starter New Member

    Sep 16, 2012
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    0
    Hello all,

    I am attempting to modify the following circuit for use with my existing power supplies / motors:

    http://cratel.wichita.edu/blogs/tommcguire/files/2007/08/cheapstep_r1.jpg

    I have two separate DC power supplies: one rated at 12 V / 2 A, and a second rated at 3.2 V / 6 A. The motor I am using requires 2.8 V / 2 A. I am modifying the circuit above by using the two different power supplies instead of one, so that I do not have to drop the voltage to power the motors. I am doing this by grounding the source of the MOSFETs to the 3.2 V supply, removing R2 (light bulb), and connecting the outputs of D1-4 to the V+ of the 3.2 V supply. This is then isolated from the 12 V supply powering the ICs by removing the trace between R1 and D1.

    When I do this, my power supply begins turning on and off and the motor randomly jitters. Does this outcome make sense to anyone?

    Thank you!
     
  2. #12

    Expert

    Nov 30, 2010
    16,346
    6,833
    "grounding the source of the MOSFETs to the 3.2 V supply"

    grounding to the 3.2 volts positive or grounding to the 0 volt connection of the 3.2 volt supply?

    Is the 3.2 volt supply sharing the 0 volt (ground) connection with the 12 volt supply?

    These questions would not be necessary if you also posted a schematic of "after" the modifications. Can you do that, please? Trying to translate words into a schematic offers a lot of opportunities for errors.
     
  3. thebrent

    Thread Starter New Member

    Sep 16, 2012
    4
    0
    Hi #12,

    No problem. Please see attached.

    Thanks!

    EDIT: Sorry, mislabeled the Voltage of the second supply. 3.8 V should be 3.2 V.
     
  4. #12

    Expert

    Nov 30, 2010
    16,346
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    Is that a CD4516 and a CD4020 chip?
    Not seeing anything obviously wrong, I will have to look up the datasheets and understand the circuit.
     
  5. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    5,003
    745
    Looks ok to me, common the 0v together, does it work ok if you increase the motor supply to 6v or 12v ?
    4516 is a binary up/down counter , 4520 is a 14 stage ripple counter.
     
    Last edited: Sep 16, 2012
  6. thebrent

    Thread Starter New Member

    Sep 16, 2012
    4
    0
    Close. They are CD4516 and CD4028. Here is a link for where I got the original circuit from:

    http://cratel.wichita.edu/blogs/tommcguire/the-stepper-motor-driver/

    I know many people have used it for the intended purpose. The only differences that I have are that:

    1. I am using a different motor with different voltage and power requirements
    2. I am using two different power supplies, because of #1.

    Do you know what would make a power supply cyclically turn on and off? It sounds like a short to me, but I can not tell where it is.

    I should also note that the circuit seems to power up fine when the motor is not connected. As soon as I connect the motor, the issues start.
     
  7. #12

    Expert

    Nov 30, 2010
    16,346
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    Thank you. That kind of information is very important. If you have any more like that, keep typing!
     
  8. #12

    Expert

    Nov 30, 2010
    16,346
    6,833
    I can't see anything wrong with the circuit, as verified by many other people that "have used it for the intended purpose".

    I have to go with something like, "you have the wrong motor" or, "you've wired it wrong".
    Nothing you didn't know before you got here. Sorry I couldn't point out a simple mistake and get it fixed.
     
  9. thebrent

    Thread Starter New Member

    Sep 16, 2012
    4
    0
    Hmm... Well, thanks for trying :>.

    I suppose it is possible I wired the motor incorrectly or it is broken. The only problem is that simply switching the wires would not result in a short.

    The only other issue I can think of is that the motor is rated for 2.8 V and I am supplying 3.2 V. But I did not think this would be an issue.
     
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