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Unipolar Stepper — Parallax Forums

Unipolar Stepper

michertemicherte Posts: 2
edited 2010-01-07 18:29 in Accessories
My Propscope works well with the Stamp applications but not for measuring a unipolar stepper motor (6V, 200mA) which is controlled by an unknown controller (no Stamp involved); see attachment.

When I want to measure the voltage pattern of a stepper motor the Propscope shows some results but the motor stops turning or turns extremely slowly.·Therefore, I do not know whether the measured signals are right (I·connect the ground probe to the ground of the motor and positive probe to one of non-ground wires). When I disconnect the probes the motor start turning again.

Any help for the right measurement set-up is welcome.
Slide2.GIF
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Comments

  • James LongJames Long Posts: 1,181
    edited 2010-01-05 02:12
    micherte said...
    My Propscope works well with the Stamp applications but not for measuring a unipolar stepper motor (6V, 200mA) which is controlled by an unknown controller (no Stamp involved); see attachment.


    When I want to measure the voltage pattern of a stepper motor the Propscope shows some results but the motor stops turning or turns extremely slowly. Therefore, I do not know whether the measured signals are right (I connect the ground probe to the ground of the motor and positive probe to one of non-ground wires). When I disconnect the probes the motor start turning again.



    Any help for the right measurement set-up is welcome.

    Can you read without the ground?

    I have the same problem with a PCF8575. I can read the SCL line, but not the SDA line. This is probably due to the signal attenuation which probably happens when the probe is connected.

    James L

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    James L
    Partner/Designer
    Lil Brother SMT Assembly Services

    Are you addicted to technology or Micro-controllers..... then checkout the forums at Savage Circuits. Learn to build your own Gizmos!
  • michertemicherte Posts: 2
    edited 2010-01-05 02:44
    Yes, I can read without the ground; both channels. Thank you.

    For better results, should the ground of my oscilloscope be connected to the ground of the motor's power supply? Or, are the data equally good?
  • James LongJames Long Posts: 1,181
    edited 2010-01-05 03:11
    micherte said...
    Yes, I can read without the ground; both channels. Thank you.

    For better results, should the ground of my oscilloscope be connected to the ground of the motor's power supply? Or, are the data equally good?

    Well....if the motors are slowing down, with the ground, you may not have a choice.

    The probes always work better with a ground, but sometimes grounding them will cause problems like with your motors.

    If the ground doesn't cause a major problem (shouldn't) I try to ground when ever I can.

    James L

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    James L
    Partner/Designer
    Lil Brother SMT Assembly Services

    Are you addicted to technology or Micro-controllers..... then checkout the forums at Savage Circuits. Learn to build your own Gizmos!
  • kwinnkwinn Posts: 8,697
    edited 2010-01-07 18:29
    Unless the scope is isolated from AC ground connecting the scope ground to one of the windings may short it to ground as well. The other alternative is to use both channels in differential mode if the scope has that capability.
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