Monitoring a pulley.

Discussion in 'General Electronics Chat' started by slayerforce, Dec 16, 2009.

  1. slayerforce

    Thread Starter New Member

    Dec 16, 2009
    I would like to build a device so that each time a pulley turns a small solenoid will actuate (only need it to move about 1/4 of an inch) and if the pulley turns the other way a different solenoid will actuate. The pulley already has a magnet installed inside it so I was thinking of using a reed switch but then realized if the pulley stopped right on the reed switch the solenoid would stay deployed. Then I thought about using two reed switches, one that charged a capacitor and the second would discharge the capacitor to deploy the reed switch. I like this idea because I could use this to detect backwards pulley movement but I do not know if reed switches and capacitors would work at a 60 rpm. Could you please tell how this should be done. Also, I am a computer science person and have little knowledge about hardware.

    Thank you in advance
  2. mik3

    Senior Member

    Feb 4, 2008
    What is the solenoid going to control?

    Once it is activated, does it needs to stay activated or deactivate it after some time?
  3. SgtWookie


    Jul 17, 2007
    Reed switches are best used with very low currents.

    You could use a reed switch to trigger a 555 timer wired in a monostable multivibrator configuration.

    Some reed switches can operate at a very high rate of speed.

    There are also Hall-effect devices, like a UGN3130. Some Hall-effect devices have a linear response, some are latching, and some are basically "on-off" type. The UGN3130 is in this last category.

    Reed switches are mechanical devices; their switch contacts will "bounce".
    Hall-effect switch devices are purely electronic devices, and have hysteresis; they have an "on" threshold that is higher than their "off" threshold. Once they turn on, the magnetic field has to drop below the off threshold to turn off. This makes the output quite stable.
    The UGN-3130 is obsolete.
    An ATS137 would work.
    Mouser stocks them:
    Last edited: Dec 16, 2009
  4. BillB3857

    AAC Fanatic!

    Feb 28, 2009
    With the need to sense direction, you need two sensors (hall devices would be great) that will act with a small positional difference between them. Their outputs would need to have a small overlap in order to generate a quasi quadrature signal. One would indicate direction by either being open or closed before the other which would indicate a revolution. A simple logic circuit would then give output 1 for forward or output 2 for reverse direction. Firing a one-shot for either and ANDing the output of the oneshot with either output 1 or output 2 should do it. What do you think, Sgt? Would that do it?
  5. Duane P Wetick

    Senior Member

    Apr 23, 2009
    If this is a magnetic pulley, the hall effect sensors will not work as the polarity is all the same on one side and opposite on the other side. I would suggest a directional zero speed switch coupled to the driven pulley. This will give you a positive indication of fpm and the internal switch can be used to energize your solenoid(s). I'm just throwing out this suggestion as I do not know anything about your system, but I have worked with magnetic pulleys.

    Regards, DPW [ Spent years making heaters out of op-amps.]
  6. SgtWookie


    Jul 17, 2007
    Let's wait until our OP comes back before replying again.
  7. zgozvrm

    Active Member

    Oct 24, 2009
    That's exactly how I'd do it. Or, without magnets, you could attach a couple of "nubs" that protrude from the side of the pulley and are sensed by inductive proximity switches (rather than reed switches). Being solid state devices, the proximity switches will last longer and be able to switch at a higher rate, allowing for faster pulley speeds.