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Motion sensor

  1. Dec 4, 2009 #1
    Im not sure if this should go here, but. . .
    Im building a motion detector.

    I have the breadboard hooked up the following way
    using an op amp, a potentiometer, photocells, resistor and led.

    So it seems to work fine, but I wanted to replace the LED with a relay switch, I was reading that you need a transistor to go with it to make a working switch. and I dont really know where to put the transistor, im guessing its between the op amp and the relay switch?

    The question is:
    How much voltage can go troug the relay?

    Im making a discharge from 5 capacitors (330V around 100uF) as soon as the photocell senses movement, what I want to know is how to wire it.

    heres my tought in a little drawing:
    http://img207.imageshack.us/img207/8531/relayswitch.jpg [Broken]


    or if anyone can tell me how to make one?
    also if someone can recomend a sensitive motion detector (i want it to sense a small projectile thats supposed to be moving fast, but it should pass right by the photocells

    ==thnkz in advance==

    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Dec 4, 2009 #2


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    Science Advisor

    If the projectile is moving quickly, you would need to use a phototransistor as your sensor, as CdS cells are very slow.

    You would also need to trigger a monostable to generate a long delay from the brief one caused by the moving projectile if you wanted to operate a relay. Relays are comparatively slow too, and yours would need a sustained pulse to pull it in.

    Setting up phototransistors and monostables is not difficult, but it does require some experience to get it all working properly.
  4. Dec 4, 2009 #3

    i have some soldering experience and little breadboard knowledge.
    Ive done a failing railgun and a successful single stage coil gun before
    if its not too hard would you mind giving me some tips/list/directions?

    anyways can the relay hold 330V as shown in the picture or will it fry?
  5. Dec 5, 2009 #4
    Can you post the sensor circuit diagram here?
  6. Dec 6, 2009 #5
    I dont really know how to symbolize an op amp. so i did what i could

    http://img260.imageshack.us/img260/7609/circuit.jpg [Broken]

    http://img260.imageshack.us/img260/7609/circuit.jpg [Broken]

    As I mentioned, it works fine (when it comes to making the LED blink)
    but I want to know how to change that LED for a 330V switch
    Last edited by a moderator: May 4, 2017
  7. Dec 6, 2009 #6
    Here the LED is connected between op-ampoutput and +Ve terminal. I expected it to be connected with -Ve terminal.

    So the LED blinks when opamp output is low. You may use any of following the two circuits.

    http://www.rentron.com/images/NPN-DRIVER1.GIF [Broken]
    http://www.rentron.com/images/PNP-DRIVER1.GIF [Broken]

    Also please go through the following document to understand relays.
    http://www.jaycar.com.au/images_uploaded/relaydrv.pdf [Broken]
    Last edited by a moderator: May 4, 2017
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