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Re: induction-loop sensor

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  • xxxtoytech
    Induction loop sensors are fairly easy to design, just take an RL oscillator such as a Colpitts and use the coil as your pickup. When chunk of metal comes near
    Message 1 of 2 , Jan 7, 2004
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      Induction loop sensors are fairly easy to design, just take an RL
      oscillator such as a Colpitts and use the coil as your pickup. When
      chunk of metal comes near it the frequency of the oscillator changes.
      You can use a phase-locked loop to get your control signal. Just use
      standard circuits (available from a variety of sources) and cobble
      together something. A single transistor is all you need for the
      oscillator and a single PLL IC can be used.

      I've built a few induction sensors before but have always found them
      a problem to adjust, they're always sort of cranky.

      Why not use an IRLED/phototransistor combination to sense the train?
      You can mount it between the tracks (reflective) or use a beam break.
      Connect the phototransistor to the trigger of a 7555 (CMOS Timer) to
      help debounce it. Proper masking of the source and sensor will
      improve reliability greatly. One thing you could do also is to mount
      bar codes on the bottom of the train and the phototransistor could
      read these as the train moves past. All kinds of possibilities.

      Regards
      xxxtoytech

      --- In home_electronics@yahoogroups.com, "Jon" <brockj@h...> wrote:
      > Does anyone have a circuit design for an induction-loop sensor for
      > detection of trains in a model railroad?
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