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Motor limit switch circuit?

Discussion in 'Sensors and Actuators' started by pityocamptes, Dec 19, 2013.

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  1. pityocamptes


    Jul 26, 2012
    I have a motor that will move an arm 90 degrees. The voltage on the motor will flip so that the motor can move counter clock wise and clockwise. However I need a limiter circuit that will stop the motor once the arm is at 0 degrees and then again when it rotates clockwise to 90 degrees. I thought about using the N/C push pins at 0 and 90 degrees so that when the arm contacts the pins the motor stops, however, when the voltage flips it won't be able to move back the other direction since the N/C pins won't allow voltage as they broke the circuit conductivity. Not sure how to do this. It will need to be automated as the circuit controlling the motor movement will be automated. Any help appreciated. Thanks.
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Assuming your motor is DC, this is rather simple.
    Yu need a DPDT switch for changing he motors direction.
    You need two end-switches that are open in the end-position (it is possibly easier to get SPDT switches for that purpose and use the open position).
    You connect the switches such that the DPDT switch changes the polarity of the voltage to the motor, thus changing dirction, while the end-switches stop the motor in the end position.
    The circuit looks like this:
    The trick is that the DPDT switch always uses the current path that is not interrupted to set the motor in motion.

    Attached Files:

  3. Arouse1973

    Arouse1973 Adam

    Dec 18, 2013
    Neat solution Harald.
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Thanks for the laurels. Not entirely my own ida. I borrowed from the most useless machine with a slight modifcation for a stop at both ends.
  5. BobK


    Jan 5, 2010
    I need to build one of those!

  6. shrtrnd


    Jan 15, 2010
    The U.S. industrial electronics industry calls Harald's 'end-switches' , 'limit switches', if you go looking them up in U.S. catalogs. I assume Harald is using the European
    name for them.
  7. pityocamptes


    Jul 26, 2012
    Hey, thanks! On a side note, how would one do this "electronically" with a solid state switch - if possible and as simple as possible... instead of using mechanical switches... Just wondering... thanks again...
  8. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    You can use a photoelectric sensor, e.g. a forked light sensor to detect the end position of the armature. You will then need to amplifiy the signal from the sensor to drive a Transistor which will act as a switch, replacing the mechanical switch.

    The list of possible solutions is long, goinf from a rather simple analog design, as above to digital logic up to using microcontrollers.
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