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Rf transmitter with 2 receivers

Discussion in 'Radio and Wireless' started by crazybry79, Jan 3, 2016.

  1. crazybry79

    crazybry79

    34
    2
    Mar 10, 2014
    I have another thread on here about AFADs (automatic flagge assistance devices). Basically, they are trailers that get parked on the side of the road and replace a human flagger. (Stop / slow guys)

    In order to make these work, they need to be remote controlled. I have very limited Rf experience, and minimal electronics experience.

    Here's what I need to do....
    I have 2 trailers 1000' apart. The operator will sit in the middle and operate both AFAD trailers via remote. Each trailer needs to receive 3 channels - one for "stop" one for "slow" one for "horn".

    I require the Rf distance be 1000' minimum range. Even though the operator is 500' away, I want a safety margin.

    I've searched online, and I've found various remote controls, 3 - 4 channels and more. But I am having problems finding a setup with one controller, and 2 receivers.

    In a perfect world, I'm looking for a remote that has...(abs I realize they won't be labled, stop, slow, etc)
    (1) stop button
    (2) slow buttons
    (1) horn button
    The stop button would send a signal to BOTH AFADs every time it's pressed.
    Each slow button would have its own trailer.
    The horn button would send a signal to both AFADs.

    Possible? Am I barking up an expensive tree?
     
  2. Osmium

    Osmium

    67
    17
    Jan 28, 2013
    Totally possible because, you know, complete systems are available "off the shelf" http://www.autoflagger.com/products/autoflagger-76/

    I have to ask, why are you re-inventing this particular wheel? I understand if this is a fun project, but if you're looking to save time/money/hassle then this path is unlikely to achieve any of those.
     
  3. crazybry79

    crazybry79

    34
    2
    Mar 10, 2014
    The link that you have there, is very similar to what I'm building. The modem 76 you have shown I'd the bare bones basic stop/slow (S/S) model. They offer a red/yellow as well.

    I am building a hybrid of both - no other manufacture builds that hybrid. Plus, the bare bone 76S/S is $19,900 plus delivery - that's for one. I will have less than $2k into my entire setup, minus Rf equipment. That's for a pair or AFADs.

    That's why I'm reinventing the wheel.
     
  4. Osmium

    Osmium

    67
    17
    Jan 28, 2013
    OK. In that case...

    You need a microprocessor controlled transmitter and two microprocessor controlled receivers.

    The idea is that the transmitter sends messages out to both receivers. The receivers are designated 1 and 2. Each message sent consists of an ID and a command. The ID can be 0 meaning "This is for both of you" so both receivers respond to that message. Otherwise, receiver 1 responds to messages with an ID of 1, and 2 with an id of 2. The commands are Stop, Slow or Horn represented by a command code of, say, 1, 2 and 3.

    Typical messages:

    01 = Stop to both
    11 = stop 1
    23 = horn on 2
    12 = slow on 1

    And so on. The transmitter/receiver modules can be something like https://www.linxtechnologies.com/en/products/modules/lr-rf-transmitter-receiver

    The microprocessors can be anything that is easily interfaced to the tx/rx modules.

    The transmitter is enclosed in a small case with the buttons as you've described.

    You'll need some help in the form of an electronics hobbyist/engineer who is used to dealing with microprocessors and can program the (very simple) messaging system outlined above.

    You may need to add a small amount of complexity to improve reliability eg: Sending the message several times for each button press, including some extra parity information in the messages to reduce the possibility of false triggering.
     
  5. crazybry79

    crazybry79

    34
    2
    Mar 10, 2014
    Ok. After first read of your post - totally lost.

    Now I've re-read it, and makes sence.

    I'll look around for more info on micro controllers and the like.

    Every adventure is a new page! That's why I love it!
     
  6. Osmium

    Osmium

    67
    17
    Jan 28, 2013
  7. Osmium

    Osmium

    67
    17
    Jan 28, 2013
    Thinking about it some more. I'm not sure how much those evaluation kits cost; you'll need to ring and check it out. However, if they could supply an extra receiver eval board and antenna you would have potentially a complete solution. There are 8 buttons. If you set up both receivers so that they respond identically to the one transmitter, then you could use 4 of the buttons as follows:

    B1 Stop - Both receivers go into stop mode
    B2 Slow Rcvr1 - Receiver 1 goes into Slow mode, Receiver 2 ignores (just don't connect this output on receiver 2)
    B3 Slow Rxvr2 - Receiver 2 goes into Slow mode, Receiver 1 ignores
    B4 Horn - Both receivers go into Horn mode

    Job done... mostly...
     
  8. Osmium

    Osmium

    67
    17
    Jan 28, 2013
    Hope that was clear. If not...

    Each receiver has 8 outputs. Those outputs go high whenever a corresponding button is pressed at the transmitter. Both receivers behave identically. Output 1 goes high on both when the transmitter button 1 is pressed. Same for all the other buttons. Both receivers are connected such that output 1 always makes the AFAD go into STOP mode. Both receivers are connected so that output 4 makes the AFAD go into Horn mode. Outputs 2 and 3 are treated differently. Receiver 1 only uses output 2 to go into SLOW mode and output 3 is not connected. Receiver 2 uses output 3 to go into SLOW mode and output 2 is not connected.

    Make sense?
     
  9. Osmium

    Osmium

    67
    17
    Jan 28, 2013
    and furthermore...

    Because you don't want both AFADs to go into slow mode, 'cos that would be bad... If at, for example, receiver 1 you made the STOP mode trigger if Output 1 OR Output 3 went high (so that'd be an OR gate). For receiver 2 it would be Output 1 OR Output 2. You might need some logic at the transmitter so that if both SLOW buttons are pressed together it either sends nothing or sends STOP.
     
  10. Osmium

    Osmium

    67
    17
    Jan 28, 2013
    actually... just put all the logic at the receivers. leave the transmitters as is.
     
  11. Osmium

    Osmium

    67
    17
    Jan 28, 2013
    I think this is the logic...

    Code:
    B1    B2    B3    B4    AFAD1    AFAD2
    1    X    X    X    STOP    STOP
    X    X    X    1    HORN    HORN
    0    1    0    0    SLOW    STOP
    0    0    1    0    STOP    SLOW
    0    1    1    0    NOP    NOP
    
    X = Don't care
    NOP = No operation = do nothing (or could be STOP)
     
  12. Osmium

    Osmium

    67
    17
    Jan 28, 2013
    Hi Crazy,

    I don't know where you're at with this but I've found these eval kits on digi-key: http://www.digikey.com/product-detail/en/EVAL-418-LR/EVAL-418-LR-ND/670150

    At that price, you could order two kits and then add the enclosures, extra logic and so on for under $400 (my estimate) for the finished RF solution - which, in my book, is not bad at all. You might be able to do better.

    Anyhow, have fun and let us know how you go.
     
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