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Emitter and Multiple Receivers

  1. Aug 15, 2011 #1
    Hi everyone, havent been posting here for a while now...And as always, I come with a doubt xD

    I want to activate a simple circuit (one that swtiches a transistor ON and OFF) via RF (any other wireless communication method is very well welcomed, except optical of course).

    The thing is, I want to activate multiple of this simple circuits with one Emitter instead of having one for each receiver.

    Is there any way to do this? I'll be taking this class in a month, so Im pretty green in the subject.

    Thanks.
     
  2. jcsd
  3. Aug 15, 2011 #2

    berkeman

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    Staff: Mentor

    When working with RF, you need to understand your government's regulations for how much power can be transmitted in which RF band, and which bands require licenses.

    Having said that, there are some bands that you can generally do things in as long as you are careful, and try to use pre-approved modules if possible. One such band is the "microwave oven band" or ISM band around 2.4GHz.

    You can also generally transmit in the public AM or FM bands, as long as you limit how much power you transmit. The power limitation typically limits your range to only 20-30m though.

    You will also need to take antenna size into account. 2.4GHz antennas can be reasonably small while still being efficient. FM radio antennas for the 100MHz type broadcast FM radio frequencies that are typical in the US are moderatly big for small devices, at about 1.5m across for a dipole.

    You might also look into the Bluetooth line of RF control modules, and look at the Cypress Wireless USB (WUSB) modules. Those are along the lines of what you are trying to do, I think.
     
  4. Aug 17, 2011 #3
    I was thinking of buying a RF kit with a Transmitter and a Receiver, and do the signal encoding and decoding with the IC pairs HT12D and HT12E.
    Links for images showing the transmitter and receiver are shown below, also a ciruit schematic.
    http://4.bp.blogspot.com/_WUOs26kM_...AAAL0/YegxC5w9Ylo/s1600-h/TWS315+-+RWS315.jpg
    http://2.bp.blogspot.com/_WUOs26kM_Ko/S0AjDiiNysI/AAAAAAAAAME/adoGDqIHI2o/s1600-h/Diagrama_TX.jpg
    http://2.bp.blogspot.com/_WUOs26kM_Ko/S0AjHw8wAVI/AAAAAAAAAMM/ndUzT-rCI9k/s1600-h/Diagrama_RX.jpg

    I have a question, it seems this technology is no longer used, can someone gave me a good reason for that? It just seems so low cost and functioal, but the components are difficult to get even in the interenet (well, not if you live in India, where they make those).
     
  5. Aug 18, 2011 #4

    berkeman

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    Staff: Mentor

    Looks like a good find. What frequencies are used? They may have fallen out of favor if the band they use got re-allocated for some other use...
     
  6. Aug 18, 2011 #5
    The frequency depends on the Transmitters+Receivers.
    There are a few available: 433MHz, 315MHZ, and a few more....
     
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