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Homemade Radio Unit Question

  1. Sep 20, 2012 #1
    First, I know nothing at all about this topic, which is why I'm looking for help. I'm interested in building a radio transmitter/receiver like a child locator at home. The difference would be I'd like the receiver to beep rather than the transmitter, if that's even the correct language to use. For example, if your kid (or cell phone, briefcase, etc.) strays too far, your transmitter automatically beeps and/or vibrates at a certain distance. I'm trying to find out the following questions: 2. How to have the receiver both vibrate and beep. 3. Would it be possible to have the transmitter be adjustable to various distances. 4. How small could the receiver be? 5. How much it would cost to build this at home, using the smallest units for each .Essentially I'd like the receiver to be able to fit on the back of a phone, key ring, etc., and the transmitter to be similar in size. I understand this is a lot of information, so any help is greatly appreciated, I'm at square one right now. Thanks in advance.
  2. jcsd
  3. Sep 20, 2012 #2


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    hi lightwait
    welcome to PF

    Thats not a problem

    no as there are too many variables that determine a distance a signal travels

    event where there are no objects to reflect and absorb the radio signal even a very low level signal say 10mW ( milliWatts) can travel 100's of metres or more

    you could have the unit small enough to be on a key ring ... those already exist for use as key finders

    The major design problems are the small size required, its not likely to be able to be done as a home project. Most radio technicians would not be able to produce the required circuitry small enough to do that. ie woould probably need to be commercially made

    The biggest overall problem wouold be powering the TX and RX units, even those lost key finders chew through batteries very very quickly. That really is what makes it impractable

    There are small transmitter and receiver units out there like these units They are easy to use but still require other electronics around them to produce a functions system to meet requirements

  4. Sep 20, 2012 #3


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    Would the child be wearing the receiver? Or the transmitter?
  5. Sep 21, 2012 #4
    The child, or in the instance I'd like to try- cell phone, wallet, etc. would have the receiver. So whenever the receiver reaches a certain distance you would be alerted. Thanks for the reply davenn, that's very helpful for pointing me in the right direction.
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