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Radio remote - especially emergency stop

Discussion in 'General Electronics Discussion' started by sergiu.mihu, May 28, 2010.

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  1. sergiu.mihu

    sergiu.mihu

    2
    0
    May 28, 2010
    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. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,501
    2,841
    Jan 21, 2010
    Yes, definitely encode your signal, and decode it to get the 8 channels or whatever. Also consider sending either a synchronisation signal first, or repeating the command code several (many) times to minimise the chance of noise or other factors affecting your signal. A checksum, or perhaps reading the same bit pattern more than once should be employed to ensure that the signal has not been corrupted.

    Emergency stop -- via wireless? Is this a class exercise? There is a particular way to do it, IF you really wanted to. Not that I'd recommend it.
     
  3. sergiu.mihu

    sergiu.mihu

    2
    0
    May 28, 2010
    I was thinking about sending each message with it's own incremented ID... from 0 to 32768... or at least to 256. This ID would be incremented by the remote, so if a message is lost, the receiver would know how many messages were lost.

    I am not an expert in communication standards, but this is the way I would do it.

    In case the machine does not receive anything a period of 50 ms let's say, it would directly generate an emergency stop.

    In this case I must have the E-Stop relay integrated in the E-Stop circuit... I don't know.

    Siemens and AllenBradley have E-Stop buttons integrated in remote controls. Crane remote controls have certified E-Stops in their remotes...
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,501
    2,841
    Jan 21, 2010
    Yes, that's correct. An emergency stop must be actuated by loss of signal, rather than by the presence of a signal.

    To do otherwise would disable the emergency stop if out of range, flat battery, RFI, or other failure of the device.

    There is probably not much need for an incrementing counter, but I can see what you're thinking -- it may be good insurance if more than one of these devices are working in the same area. A unique code for each remote may be more useful.
     
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