Simple Magnetic Sensor

Discussion in 'General Electronics Chat' started by crobertsbmw, Jan 22, 2012.

  1. crobertsbmw

    Thread Starter New Member

    Sep 7, 2011
    I am looking to make a sensor to tell when this box is going to be open or closed. We are going to have the magnets to lock it in place.

    Basically I want this circuit. Does it exist?


    I have heard a lot about hall effect sensors but I don't really know what I am doing to get them to work and I feel like there might be a more simple circuit.
  2. paulktreg

    AAC Fanatic!

    Jun 2, 2008
  3. praondevou

    AAC Fanatic!

    Jul 9, 2011
    What you have drawn is an electromagnet.

    The part connected to the circuit is supposed to be sensor, right?

    That would be a normally closed sensor, no magnetic field present --> it's closed, magnetic field present --> it's open.

    Look for a magnetic switch on main distributors.


    And yes, a reed switch is another possibility, it needs to be a NC.
  4. crutschow


    Mar 14, 2008
    If you can isolate the magnets just connect a wire to each and detect when the magnets make contact and close the circuit.

    In the circuit shown connect the resistor to the top magnet and take the output from the bottom magnet.
  5. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    That is the typical setup for magnetic window/door alarms which feature a magnet and a reed relay as stated above. Simply googling "window alarm magnet" gets you thousands of sources to buy that.
  6. colinb

    Active Member

    Jun 15, 2011
    People are confusing reed relay with reed switch (aka reed sensor).

    A reed relay consists of a coil and a reed switch.
  7. EB255GTX

    Active Member

    Apr 30, 2011
    Correct of course, but intereting point - not a lot of people seem to know that relays can be operated by an external magnetic field :)

    So if you only have a reed relay handy and need a reed switch - just use it!
  8. colinb

    Active Member

    Jun 15, 2011
    Maybe useful if you're stuck on a deserted island with only a reed relay and a magnet. :)

    However, it would be difficult to get good results since the reed switch is highly sensitive to the orientation of the magnet, and your working distance will be necessarily increased if the relay body keeps you from getting close to the reed switch inside.