stepper motor as input device HELP

Discussion in 'General Electronics Chat' started by jr102893, Jan 18, 2011.

  1. jr102893

    Thread Starter New Member

    Jan 18, 2011
    I do not know if it is possible but i was wondering if anyone has successfully determined the direction a stepper motor is being turned or knows of a theoretical way? My goal is to make a "stepper motor combination lock" but i currently don't have the ability to analyze the output of a turned stepper motor to determine what information can be gathered. Can anyone help?
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    A stepper can be used to generate modest amounts of electricity, as can any PM motor. The polarity of voltage out the coil leads will give the direction the shaft is turning.

    The output from a small movement of the shaft is going to be quite small, though. The output relates to the speed the magnetic lines of force cut across the copper windings, so small, slow movements may only result in a tiny voltage and current, perhaps on the same order of magnitude as the output of a tape head.

    Whatever output there might be would require amplification to be useful, which probably makes the device not worth the trouble.
  3. jr102893

    Thread Starter New Member

    Jan 18, 2011
    i know the output would be small but amplification is not a problem determining speed and amount of rotation is also not exceedingly hard. What i haven't managed to do is determent the direction it is being turned.

    the reason i want it to be a stepper motor is that it can also work as a motor to do another function saving me space in my project design
    Last edited: Jan 18, 2011
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    You could use a dead stepper motor to add weight to the "feel" of the dial, while actually reading a quadrature encoder mounted to the shaft to get the actual combination.

    Even wiring a working stepper up so the poles are in series could be rectified and produce enough voltage to wake up the processor for reading the encoders. I wouldn't try using the pulses themselves as measurements, as there would be way to many at too low of a level to count accurately. In addition, the amplitude would vary with the speed of the dial.

    So to unlock, give it a clockwise spin to wake up the processor, then dial the combination (which would be read by the processor through a quadrature encoder).