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operate relay by phone...

Discussion in 'Electronic Basics' started by Andy C, Feb 18, 2007.

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  1. Andy C

    Andy C Guest

    hi there - does anyone know of any device or can think of any simple way to
    momentarily operative a relay remotely by phone ?
    our cctv cameras run on a PC which we need to be able to reset remotely if
    there are any problems (e.g. the software crashes)- the relay would just
    'press' the reset button on the pc
    all i can think of is to buy a cheap mobile phone which somehow operates the
    relay if it rings... but this has the problem that it might ring when it's
    not wanted (wrong number etc.)
    anyone got any good ideas? maybe there is some suitable device already on
    the market? there is a second pc on site if that is any help
    many thanks !
  2. You might want to look for "watchdog" cards for the PC. They will detect a
    hung machine and perform a reboot automatically. There are also variations
    that have a dial-in ability. If you have full-time internet, then that
    would provide a path in as well. For example:
  3. Rich Webb

    Rich Webb Guest

    Do a 'net search for "DTMF kit" or "DTMF remote" or similar. There are
    scores of kits (and full-up modules) that use the "bleepty-bleep" DTMF
    tones to remotely control relays.

    One example of a kit
    and a commercial unit <>

    There are also plans/prints/sourcecode if you're into roll-yer-own.
  4. John Fields

    John Fields Guest

    Do a ring detect to take the phone line off-hook and connect it to a
    DTMF decoder, then when you press the desired digit (or series of
    digits) on the remote keypad, decode the output of the DTMF decoder
    and use that to start a one-shot which operates the relay and then
    puts the line back on-hook when it times out.
  5. Bob Masta

    Bob Masta Guest

    Hmm, phone answering machines often have a
    provision for you to retreive your messages from
    another phone. Typically you wait for the machine to
    pick up, then enter a 2-digit code. I wonder if there is
    some way to hot-wire one of these to be the "front end"
    that drives your relay?

    Just a thought...

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    Scope, Spectrum, Spectrogram, Signal Generator
    Science with your sound card!
  6. Si Ballenger

    Si Ballenger Guest

    The below x10 telephone gizmo has been used by sys admins for
    many years to reboot remote servers that have hung. Just put the
    control module on the power supply to the computer to toggle the
    power and cause a cold reboot. Looks like they are now being
    phased out.

  7. Here is a commercial product used in CATV and remote video switching
    by TV stations.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  8. jasen

    jasen Guest

    I think there's an X10 module for that.
    many phones can be programmed to ignore calls from unknown numbers.

    another option would be to make a silent ringtone for calls from most
    numbers and a noisy one for your designated numbers
  9. Clint Sharp

    Clint Sharp Guest

    Lots of decent DVR cards have a built in watchdog circuit that will
    reset the PC if it crashes.
    Sure, send it an SMS, buy the latest PDF issue of EPE Mag from

    It's got a project that uses an old Nokia mobile phone to control remote
    appliances via SMS messages, you send the 'phone the correct message, it
    resets your PC.
  10. Rich Grise

    Rich Grise Guest

    Get an ordinary answering machine, tap into the speaker, and use a 2-tone
    (DTMF) decoder on the audio output to give you one or a sequence of
    keypresses, that will then trigger your relay. You'd need either a micro
    of some kind or a handful of ordinary logic.

    Call the remote number, when the machine picks up, punch in your code
    and hang up. The code is important so that if somebody mistakenly dials
    your remote, it won't automatically reset your system.

    Good Luck!
  11. Andy C

    Andy C Guest

    the card actually does have this feature - i didn't realise what it was
    though !
    i'll try it :)
    lots of really good ideas - thanks everyone ! that nokia project looks like
    it would be absolutely perfect !
    anyone (in the UK) fancy building one for me for a fee ? !!
    email if interested remove the word 'bogus'
    from the email address
    this is another similar project i found...
    thanks again,
  12. quietguy

    quietguy Guest

    You can buy units that will operate a relay etc upon receiving an SMS call - a
    cheap and easy way that should do the trick

  13. quietguy

    quietguy Guest

    Whoops, forgot to add that Jaycar sells those SMS controllers - have a look at
    their online catalog

  14. Andy C

    Andy C Guest

    perfect! i ordered it !
    many thanks :)
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