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RF switch? — Parallax Forums

RF switch?

InteractivesInteractives Posts: 83
edited 2005-06-14 18:33 in BASIC Stamp
Hello, I need a switch that can sense when one circuit or component gets close to another circuit or component. It needs to be able to sense within a 5 inch diameter, more or less. For instance, if I had a necklace around my neck, and got within 5 inches of the sensor, then a high input signal gets sent to stamp. If there was such thing as a very sensitive hall effect sensor, that would work- but I dont think it would be within my price range. Any ideas?

Comments

  • cyberbiotacyberbiota Posts: 79
    edited 2005-06-14 15:59
    Interactives-

    How about a low-output modulated IR beacon on one circuit and a detector/demodulator on the other. It should be relatively inexpensive and well within the capabilities of the Stamp. The only difficulty would by the geometry of the emitter/detector and the possibility that it would be too sensitive. What, precisely, are you trying to accomplish?

    peter

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    Peter C. Charles

    Director, Research and Technology
    CyberBiota, Incorporated
    Peter.charles@cyberbiota.com
    http://www.cyberbiota.com
  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-06-14 16:33
    How about RFID? Parallax sells these here and provides sample code. They have a range upto 4".
  • InteractivesInteractives Posts: 83
    edited 2005-06-14 17:16
    Think of a wristwatch that would signal an alarm every time you got close to a certain object. So it would really be a simple interaction between the beacon and the detector. You dont think the RF id thing is overkill?
  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-06-14 17:52
    Interactives said...
    You dont think the RF id thing is overkill?
    Yes it is, but I was trying to think of a solution which was painless to implement as possible. There are other RF modules which should work, but Im not aware existing stamp code for them and modification may be nessesary because most are designed to communicate over 50' between the pair (and calculating time of flight isn't possible with a stamp without additional circuitry).
  • JonathanJonathan Posts: 1,023
    edited 2005-06-14 18:33
    Int,

    5 inches can easily be done with a Hall effect sensor and a NIB magnet, and cheaply. Look for one with a linear output and use an op amp and comparator to adjust range and sensitivity. Allegro makes a lot of good Hall effect sensors. If you don't need security ID, this would be very easy to implement and the coding a breeze.

    Jonathan

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