Radio remote - especially emergency stop

Discussion in 'The Projects Forum' started by sergiu.mihu, May 28, 2010.

  1. sergiu.mihu

    Thread Starter New Member

    May 28, 2010
    3
    0
    Hi guys,

    I am trying to design a remote control probably on 400 MHz range, as I think will be enough for the data I want to send.

    8 channels, solid state transistor outputs.

    The thing is that I never used radio modules before. I was looking at the Microchip RF modules, but I don't know exactly what to do if I have more devices transmitting on the same channel or so. What advice would you have in this way for me? Would using a PIC and coding and decoding the message be enough?

    What do I need to have in mind if the surrounding area will be full of electromagnetic waves? (industrial noise)

    About an emergency stop button - what algorithm or what way of designing the remote would one use for that?

    Thank you.
     
  2. BMorse

    Senior Member

    Sep 26, 2009
    2,675
    234
    go here and check out their line of RF modules and encoder/decoder IC pairs... basically you would use addressable encoder/decoders to distinguish one transmitter from another, these can have up to 10 address lines you can set. and if used with one of the Linx Transceivers it could be a very robust and reliable medium to use. Best part, no microcontroller needed!!

    www.rentron.com

    B. Morse
     
    Last edited: May 28, 2010
  3. whale

    Active Member

    Dec 21, 2008
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    0
    it will be better if you make use of non-licence band in your country.
    so that external interface and disturbance can be avoided.
     
  4. sergiu.mihu

    Thread Starter New Member

    May 28, 2010
    3
    0
    BMorse - I have seen that. The microcontroller does not scare me, anyway I cannot think of another way to implement a controlled E-Stop besides using a microcontroller as a simple method.

    Whale: that's what I'm trying to do, use a band that does not need to buy a license, a free band. I was actually thinking of using a 2.4 GHz transciever, but I don't know so much about them either. With the 2.4 I would actually be capable to use an IP or something, but as I said, I am not an expert on that side.
     
  5. BMorse

    Senior Member

    Sep 26, 2009
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  6. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    Use short burst transmissions, with heavy error-checking both within each data packet (like CRC16), and tell-me-three-times style checking at the receiver, so no data is acted on until identical copies have been received several times.

    Transmit each changed data (when a switch is operated) several times with short gaps, and send 'heartbeat' data a couple of times a second, repeating the last frame, when there is no other data to send.

    We use a system like this.

    The safety interlock we use has an extra 'virtual switch' bit in the data that is toggled at a couple of Hz (which in turn triggers the heartbeat transmission as the switch data is changed).

    If the receiver does not see a change in that bit for one second, the emergency stop is triggered. A direct switch channel for the emergency stop button can also trip that without the delay.
     
  7. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
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    your E stop circuit must be hard wired 'and'. Loosing your RF signal may not be a reason to cause an E stop, so a simple latched relay in series with your hard stops would be sufficient.

    Note that this is not an 'E' stop , but a simple stop. 'E' stops MUST be hardwired.
     
  8. sergiu.mihu

    Thread Starter New Member

    May 28, 2010
    3
    0
    I will probably go with the MiWi. I have seen that before and it seems a really good and safe solution to what I need.

    The only issue I see right now with this system is that the outputs go directly into a PCI board in a computer and there is no way at this point I could integrate a E-Stop relay from the remote receiver into the E-Stop hard wired circuit.

    For the regular commands I don't see any issues - I mean I will use CRCs and message IDs, but for the E-Stop, I will have to test it thoroughly before being confident about it.

    Thanks a lot for the replies.
     
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