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stepper driver help!

Discussion in 'Electronic Basics' started by [email protected], Feb 24, 2006.

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  1. Guest

    So I've designed a translater using basic 74 series ttl gates. I've
    designed both a half and full step translater. I finished soldering
    together the parts and i tested out the four outputs and the full step
    sequence was correct. However I hooked up the outputs to a ul2003
    darlington array chip to the stepper motor and it would not move at
    all.... I probed the inputs and it looks like the translator output is
    greatly attenuated. is there a way to keep the origial signal without
    attenuating? could i just use a 7407 buffer between the driver and
  2. Chris

    Chris Guest

    The ULN2003 darlington array is made to sink current. It needs a power
    source. If you've got a unipolar stepper with 6 or 8 wires, your
    wiring could look like this (view in fixed font or M$ Notepad):

    | VCC VCC
    | + +
    | | |
    | ___ | ___ ___ | ___
    | .-UUU-o-UUU-. .-UUU-o-UUU-.
    | | | | |
    | |2/7 ULN2003| |2/7 ULN2003|
    | O O O O
    | / \ / \ / \ / \
    | (___) (___) (___) (___)
    | | | | |
    (created by AACircuit v1.28.5 beta 02/06/05

    It might help if you describe your stepper motor. Voltage, current
    requirement, how many wires (4, 6, 8).

    Good luck
  3. Can you put a number on "greatly attenuated"? A 74xx series TTL gate
    should be able to drive a ULN2003 with no problems (to a couple
    hundred mA output current anyhow). The input voltage will drop a bit,
    but probably still more than 2.5V. Are you pulling the supply down?
    Best figure out what you are doing wrong first.

    Best regards,
    Spehro Pefhany
  4. Robert Baer

    Robert Baer Guest

    I have not looked at the scnematic of that driver, but...
    *If* it is nothing more than a number of darling transistors (as
    mentioned) and if the emitters go to ground, the bases will not go above
    (roughly) 1.3V - which is significantly less that an OC TTL output,
    hence the term "attenuated".
    Maybe that severe load over-stressed the TTL and so now cannot drive
    the bases enough to "saturate" the darlingtons?
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