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Building a dog detector?

  1. Oct 30, 2009 #1
    This is not homework, although I am an EE student. If the solution is cool/complex enough, this might become a design project, although it'll most likely end up as something to do over the summer.

    some time ago, I purchased a motorized doggie door. The dog wore a high frequency sound generator on it's collar, which triggered a sensor in the door when the dog was within a few feet.

    The chassis of the system is good, but the electronics sucked, and the company support was terrible, so I'm looking to gut and rebuild the innards.

    The system shouldn't be complicated, a microcontroller monitors a sensor, when the sensor kicks the MCU turns on the motor, when the sensor stops kicking the MCU turns off the motor and the weight of the door closes it (I think reverse-current protection was missing from the original design, which might help explain the short MTBF).

    I'm looking for ideas for a dog-detector that can:
    1: detect the dog from about 3 feet away
    2: work on both sides of the door (multiple antennas is acceptable)
    3: not be too ugly that people will ask why there's a big coil of copper on the floor
    4: should have a decent off-angle response, since my dog's not that bright, and won't
    always come straight at the door
    5: detect my dog, but not my cats, or the local wildlife
    6: no batteries on my dog, if possible

    RFID seems to be the best solution, but most sensors seem to be either very short range (10cm) or very long range (300ft) and very expensive.

    One of my classmates suggested a strong magnet on her collar, with an inductive coil on the floor, but this would violate rule 3, and the dog may end up with all kinds of stuff hanging from her collar.

    I'm not afraid of soldering, programming, or research, but I could use some bright ideas.

    Any suggestions?
  2. jcsd
  3. Oct 30, 2009 #2


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    I was thinking RFID as soon as I started reading your post...

  4. Oct 30, 2009 #3
    I still think it's the best idea, but the dog can't be counted on to swipe her tag within 10cm of a reader. Is it feasible to extend the range to 3'?
  5. Oct 30, 2009 #4
    How fast does the doggie-door unlock, and how long does it take for the doggie-door to lock after the dog opens it? We have a small scottie, and we have seen two coyoties in our garden recently.........
    Bob S
  6. Oct 30, 2009 #5
    the door slides vertically, pulled by a steel wire connected to a motor. The cable is attached (on teh door side) to the locking mechanism, so whenever it's down, it's locked.

    unlocking and opening are pretty quick, although I never timed it.

    With the old mechanism, it would be closed within 15 or 20 seconds of the dog leaving the area, but that may change as I'm replacing the motor as well.
  7. Oct 30, 2009 #6


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    There is an effect where if you have an oscillator and bring a tuned circuit resonant at the same frequency as the oscillator near it, the tuned circuit will absorb some power from the oscillator and the level of signal in the oscillator will dip sharply.

    The is the principle of the "grid dip oscillator" used to detect the resonant frequency of tuned circuits.

    Used with big coils, it might have enough range to operate at a distance of a foot or so. Maybe more. The tuned circuit could be a capacitor and a coil wound on the dog's collar.

    If it did, maybe you could have a board that the dog has to walk on and this turns on a switch which turns on the oscillator. Maybe with a strain gauge it could weigh the dog?

    How about this?..........................:smile:

    dog bar code.jpg
    Last edited: Oct 31, 2009
  8. Oct 30, 2009 #7


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    Staff: Mentor

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