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Discussion in 'Electronic Design' started by [email protected], Feb 4, 2005.

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  1. Guest

    Hi, I am looking into a low cost RF solution to the following

    I am designing a product that must maintain a constant communication
    between device A and device B, with a range of just a few meters. I am
    looking at Linx Technologies LR series. Any thoughts?

  2. Active8

    Active8 Guest

    Aerocom and someone else does that too, but IIRC Linx isn't FHSS, is

    What's your data rate? If you only need up to say, 2400 baud, maybe
    4800, there's a cheaper (Tx/Rx < $10) 433.92 MHz solution.
  3. Mark Jones

    Mark Jones Guest

    Check this out:

    -- "Everything is interrelated - because it has to be. Experience is just
    energy, and energy cannot be created nor destroyed." MCJ 20050119
  4. Guest

    Well here is the dilemma... I need to know if object A is too far from
    object B, and if so will send a "1" to the chip in A. I was told that
    RFID is the only technology avaible to do this easily, but RFID is way
    too expensive to implement at this point. I was hoping to find another
    low cost RF solution.
  5. Mark Jones

    Mark Jones Guest

    Well, there are several things you could try. The easiest would probably be a
    simple low-power RF signal generator, which only puts out enough power to be
    measureable from your "good" distance. This has the disadvantage that simple
    obstructions may give a false "too far" result of your receiver.

    An other idea, much more involved, would be to send an RF pulse from B to A and
    back to B, measuring the delay in nanoseconds. You perhaps could do this with a
    fast microcontroller chip - enable interrupts, send RF pulse, start timer -->
    interrupt happens, stop timer, timer value = delay. Since the speed of RF in air
    is known, the time taken to ping-pong an RF pulse back and forth between these
    two points can be turned into a physical distance.
  6. Guest

    Thanks for your ideas!
  7. EE Matt

    EE Matt Guest

    Sorry I have been out of this whole thing. Working 60 hours a week
    does not leave much time for well, anything. About the RF and RFID.

    The reason that the system uses RF as well as RFID is as follows:

    If the system were to use simply just RF TX/RX to test for the presence
    of the rider, the transmitter as well as the receiver would need to
    constantly be using power. Unfortunately we do not have a lot of power
    to work with on the jacket.

    The benefit of using the RFID, although expensive, I believe is worth
    it. With RFID you can sense for the presence of the rider without
    using any power on the jacket. We can accomplish this by placing the
    RFID tag in the jacket and the reader on the bike. The tag uses
    absolutely zero power. The only power that would be being used would
    be by the RF TX/RX sitting in idle or standby. The RF in standby uses
    drastically less power than when it is actually transmitting or

    Another downside to just using RF is that with such significant power
    consumption you are limited as to how long you can wear the jacket and
    have the system functional until the battery needs to be
    recharged/replaced. This can cause the system to fail for riders going
    on rides of more than a couple of hours. This is a huge safety issue.

    I hope this helps and I will try to keep up with the questions and will
    add anything I can. Thanks guys.
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