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Proximity Alarm device

Discussion in 'General Electronics Discussion' started by slim182, Jun 10, 2013.

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  1. slim182

    slim182

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    Jun 10, 2013
    Hi guys, I'm trying to build a mini RX/TX alarm but quite the opposite (The alarm is triggered when the two devices move away from each other) , basically what I want to do is to have a receiver and a transmitter, the idea is that when they are both near (less than 3 metters aprox) they are ok and then they are further than that then they start beeping (a slight alarm) so basically it will work like one of those IR door Alarms that when it stops receiving the signal the alarm pops up.

    But in this case I need it a bit different as the 2 devices may not be aligned all the time. Imagine one of the devices on my pocket and the other on my dog collar and that when he walks away i get the alarm.

    Any ideas? also it is important to make it as small as possible.

    Thanks for the help!.

    George
     
  2. davenn

    davenn Moderator

    13,561
    1,856
    Sep 5, 2009
    hi there
    welcome to the forums

    This a commonly themed question for which there is no easy answer
    IR will not work if the TX and RX are not facing each other and thats apart from the problems of operating IR outside in sunshine. And to get it to alarm at a specific distance, even within a few metres of accuracy isnt going to work

    Radio has the same problem.. the signal doesnt just stop at a fixed distance say 2, 10, 20 metres etc so to get the gear to trigger an alarm if signal lost after say 10 metres is pretty much impossible

    Bluetooth radio links do have a limited and probably the most predictable dropout at ~ 10 - 15 metres

    else there isnt a lot of choices

    Dave
     
  3. slim182

    slim182

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    Jun 10, 2013
    Thanks Dave!

    Thanks Dave!, so i guess it will have to be a bit more complex, is there any way to measure distance by radio or bluetooth maybe? I know it can be meassured with a laser wave and a sensor, (the way a cop can know you were speeding lol)

    It is not that important to get a 100% perfect number for the distance either, just to be able to make it more or less accurate, what I'm thinking is maybe simply limit it to a really weak signal, and when the signal get losts between the 2 gears it triggers.

    Do you think it is possible that way to get a theory going? :)
     
  4. sirch

    sirch

    109
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    Dec 6, 2012
    How small does it need to be and how directional?

    With a lot of help from this forum I have been putting together an ultrasonic measurement device that could be adapted to what you want. Basically it consists of a radio transmitter with ultrasonic receiver and a radio receiver with ultrasonic transmitter. The module with the radio transmitter sends a signal to the receiver and starts a timer. The module with the radio receiver sends out an ultrasonic pulse, when this is received by the ultrasonic receiver the timer is stopped. The time taken is proportional to distance.

    I have this project basically working although it needs boxing up and testing in the field and I really need to get it written up. The issue I see with this approach for your application is that the ultrasonic transducers are fairly directional (i.e. they need to be pointing at each other) and making sure your dog is pointing the right way could be a problem. Having lots pointing in all directions would be bulky.
     
  5. slim182

    slim182

    3
    0
    Jun 10, 2013
    Sounds interesting sirch!, but the idea would be to make it omnidirectional, a radius area, also is possible that some things might be in the middle of both gears, like some plants or a tree etc.

    Was also thinking at the begining to do it like a radio controlled garage door, but might have to be sending the signal all the time.
     
  6. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,268
    Nov 28, 2011
    That sounds like a very interesting project.

    I don't recall seeing the thread that relates to it. Is it https://www.electronicspoint.com/remote-distance-sensing-t254967.html about mapping cave profiles?

    Do you have any documentation on the project so far, that you could share with us?
     
  7. sirch

    sirch

    109
    1
    Dec 6, 2012
    That's the initial one, plus quite a few of my other questions about op-amps radio modules, etc. What I have is not well organised at the moment but I will get round to tidying up the documention and post it back in that thread eventually.
     
  8. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,268
    Nov 28, 2011
    I hope so. I'm interested in this project.
     
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