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Help for Uber Newbie - GPS trigger

Discussion in 'Electronic Design' started by [email protected], Feb 23, 2007.

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  1. Guest

    Hello all,

    I have a car alarm that I want to use the output (say the horn) to
    trigger a GPS locator so that if the alarm is triggered, it will
    notify by e-mail that there is an alarm situation. The problem is,
    arming and disarming produces an output. I need some sort of circuit
    that will look for a pulse longer than the chirp (or double chirp)
    that indiciates arming / disarming. Did I mention I'm an Uber newbie?
    Someone mentioned this may be possible with an RC circuit. The output
    it would require would be negative, though if someone has a circuit
    that creates a positive output, I can get around this with a relay.
    Your help is greatly appreciated.
  2. Lefty

    Lefty Guest

    Pretty simple task to work out the pulse delay thingee. A one shot
    multivibrator and some logic gates can seperate the short pules from a
    long one. Of course these days an 8 pin PIC would probably be the best
    solution. Now getting a pulse to send an E-mail is software magic that
    I don't have a clue about, but of course I know it can be done.
  3. linnix

    linnix Guest

    Send the email is simple, once you have the hardware figure out.
    You can have a socket connection to your mail server's smtp port.
    To do so, you must have hardware like GSM/GPRS radio.
    Anything can be done, with the right price of course.
  4. ehsjr

    ehsjr Guest

    As I understand it in general terms, you have a horn "output"
    that you want to use to control something, if, and only if,
    that output is active for longer than a "chirp". You mentioned
    RC and a relay, so this circuit is designed with that in mind.

    + ----+------------+-----+
    | | |
    | 1N4001 [D1] [Rly] Omron G5LE-14-DC12
    | |a |
    | +-----+
    | |
    P ---
    500K O<---+---[2.2K]---/_\ TL431
    T +| |
    | [CAP] 10uF |
    | | |
    Gnd ---+----+-------------+

    The + and Gnd come from the horn relay. That way, it
    doesn't matter if the horn is switched + or switched -.
    All you need is an R/C combination that keeps the
    voltage on the gate of the TL431 below about 2.5 for
    the double chirp period, then rises above 2.5 volts
    after that. Using a pot allows you to adjust it to fit
    your needs. A bigger cap could be used for a longer delay,
    but it is doubtful that you need it. The relay specified
    (available at Mouser for 96 cents) draws about 35 mA, well
    within the 100 mA the TL431 can handle.

    Another consideration: most car alarms activate the horn
    intermittently. The relay in the circuit above will drop
    out when the horn stops, and energize again when the
    horn beeps again. So that begs the question: how long must
    the relay stay energized, and does it matter if it drops
    out between beeps of the alarm?

  5. Guest

    Thank you for all your answers to everyone who responded. I had
    already written a response, but Firefox crashed and I did not get a
    chance to send it off, so this will be brief. The GPS unit looks for a
    negative input, which causes a notification to be sent by e-mail. The
    relay should stay energized for about 5-10 minutes even after the drop
    in the horn pulse to prevent an overload of e-mail notifications to be
  6. ehsjr

    ehsjr Guest

    Ok, that requires something different. You can
    still use the TL431 circuit, but have it trigger
    a timer. Replace the relay with a 1K resistor and
    eliminate D1, like this:

    + from battery---+-------------------+
    | |
    + ----+---->|----+ | |
    | D1 | | ----- |
    P [1K] [10K] +---1| |8-+------+
    500K O<---+ | | | | 555 | |
    T | +------+---------2| |7-+-[1M]-+
    | [2.2K] | D1 | | | | |
    | | --- +- | --3| |6-+----- | -+
    | +----/_\ TL431 | | | | | |
    | +| | | | +-4| |5-+ | |
    | [10uF | | | | ----- | | |
    | | | | | | [.01uF] | |
    Gnd ---+----+-----+ +-[1K]-+ | | | | |
    | | +---+------ | -----+ |
    2N3904 --- | | | |
    e / \c | [1K] | [470uF]
    | | | | | |
    | +------ | ----+---+ | |
    | | | | |
    Gnd from battery --+-----------+-------------+---------+
    +---> to GPS

    Build a 555 monostable that is powered from
    the battery (not the horn - the TL431 circuit
    still gets power from the horn relay).
    Tie pin 2 of the 555 to + from the battery
    through a 10K resistor, and to the TL431 circuit
    as above. You can find the 555 circuit here:
    A 470 uf cap and a 1Meg resistor for the 555 circuit
    will give you a long (+) output roughly 8-9 minutes.
    I drew the circuit above with a 2N3904 transistor
    to give you a (-) output for the GPS, but you could
    use a relay if you want.

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