IR tx rx synchronisation

Discussion in 'Electronics Resources' started by ragul07, Aug 1, 2013.

  1. ragul07

    Thread Starter New Member

    Aug 1, 2013
    1
    0
    how to synchronize the infrared tx and rx in an array so that interference between each pair of the Tx and Rx are avoided??
    Or Is there any method to use IR tx and rx without interference..?
    this project is similiar to IR curtain :)
    need ur help fellas :)
    thanx in advnce :)
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,087
    3,027
    I think the best way would be a digital solution. I mean, code the signal at each transmitter and then accept only that code at the matching receiver. Like when you point your remote to turn on the TV, it doesn't turn on other devices even though they "see" it.

    It may still be a challenge if each receiver "sees" multiple transmitters all transmitting at the same time.
     
  3. crutschow

    Expert

    Mar 14, 2008
    12,977
    3,221
    If you have more than one transmitter on at the same time then you may need to go to different color LEDs with appropriate color filters over the receivers.
     
  4. joeyd999

    AAC Fanatic!

    Jun 6, 2011
    2,673
    2,712
    Or, alternatively, you could modulate each transmitter at a different frequency (would need to be at least 10x the data rate), and filter and envelop detect the signal on the receiving end. This is a nice solution since it will also eliminate interference from ambient lighting (especially with respect to fluorescent lighting). Also, you could add an automatic gain control that can compensate for varying distances between the transmitters and receivers.
     
  5. WBahn

    Moderator

    Mar 31, 2012
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    4,788
    Depending on the system capabilities and requirements, this is exactly the kind of situation that concurrent code spread spectrum was developed for. Each emitter forms a packet that is addressed to one of the receivers. The receivers receive all messages that they see, even if they stomp on each other, and only responds to the ones addressed to it.

    This affords a MAC-less communications protocol and as long as the total amount of time that at least one emitter is on doesn't rise above about 33%, things are fine. This can significantly simplify many aspects of system design because each transmitter and receiver can pretend -- within limits -- they are the only players on the air.

    But the approach isn't without its costs. The receivers have to have enough processing power to decode the packets, but if your data rate isn't too high that isn't hard to achieve. The transmitters also need some processing capability, but it is tame by comparison. You are also intrinsically packet-based and you can't start decoding a packet until the entire packet has been seen. So this builds in a latency. But it also means that both the transmitter and the receiver need to have sufficient memory to store at least one packet's worth of bits in a buffer. Then, like any spread spectrum system, you trade data rate for interference immunity.

    If you can give an idea of how many transmitters you will have and what your data rate goal is, then I can give you some numbers on the kind of constraints you will need to work with.
     
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