Project - 20 Foot Out of Range Detector

Discussion in 'The Projects Forum' started by Versus54, Jul 5, 2012.

  1. Versus54

    Thread Starter New Member

    Jul 5, 2012
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    Hey guys,

    Wanted to hear your opinions. I am kind of a newbie, but I would like to build/have built a sort of out of range system for my kid. What I would really like to achieve is when my kid goes 20 or 30 feet away from me, I will have a device that will beep loudly to alert me. I am thinking something will need to be in my kids pocket or strapped to him (like a bracelet or something) and I can hold the other piece. I would also like my piece to have an on and off switch. Any ideas or resources? Does this sound simple, or complex?

    Thanks so much and pardon my newbieness.
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,126
    3,048
    There are very similar systems used as portable, wireless pet fences. I think they mostly zap the pet when it strays out of range, which may or may not be suitable for a kid! ;)

    But anyway I'd reverse engineer from that starting point. And maybe the commercial devices are usable as-is if they allow you to not employ the zapping collar.
     
  3. #12

    Expert

    Nov 30, 2010
    16,298
    6,810
    The basic premise would be to make an oscillator and a receiver such that distance causes the receiver to lose the signal. Start with the antenna. Its size will demand a certain frequency. Then build an oscillator that can function with a low voltage and the small antenna you decided on. Next, build a receiver and adjust its sensitivity until you get the right range. Some part of the receiver will change voltage when it loses signal, and you use that change to activate the alarm.

    This is not simple. It requires radio frequency capability on both ends. Far better to find something retail if you aren't a radio frequency designer, and I can tell you aren't.
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    what about a Bluetooth device, how far do they transmit.
     
  5. strantor

    AAC Fanatic!

    Oct 3, 2010
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    do you want this to work while you're browsing through the mall or in the yard?
     
  6. MrChips

    Moderator

    Oct 2, 2009
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    Find a low cost RF transmitter/receiver pair such as the electronics in an abandoned garage door opener, wireless door bell or RC car.

    Add circuitry to trigger the transmitter once every 1-5 seconds.

    On the receiver end, use a >5 sec monostable that is triggered every time it receives a signal from the transmitter. If the receiver fails to receive a signal the monostable will time out and trigger an alarm.
     
  7. Sensacell

    Well-Known Member

    Jun 19, 2012
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    Note that any of the above solutions will be very sensitive to physical orientation, position of the body relative to antenna, etc... etc... This is why this product doesn't already exist- the concept is too unreliable to be useful.
     
  8. strantor

    AAC Fanatic!

    Oct 3, 2010
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  9. Versus54

    Thread Starter New Member

    Jul 5, 2012
    2
    0
    Hey guys,

    just an update. I actually found several products that fit my description EXACTLY. Sooo...it seems that there are products out there already that do this and a bit more. Even some that only do what I wanted. Thanks for all the help and I'll let you know how it works!
     
  10. Sensacell

    Well-Known Member

    Jun 19, 2012
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    Wow it exists! I still bet it's not of much practical use, just another *product* to spend your money on.
    If it really worked, every paranoid parent in America would have one, no?

    If it uses GPS, I could see it working as advertised, but not if it works via RF signal level alone.

    Can you get a GPS signal in a shopping mall?
     
    Last edited: Jul 6, 2012
  11. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
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    Tie a string around his neck, and tie the other end to your belt. Bingo! :)

    If you use a kevlar cord it takes a lot longer for them to chew through. (Just thinking out loud there).
     
    strantor and #12 like this.
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