Re: Help for Uber Newbie - GPS trigger
- From: zsoltar@xxxxxxxxx
- Date: 26 Feb 2007 07:51:47 -0800
On Feb 25, 1:35 pm, ehsjr <e...@xxxxxxxxxxxxxxxx> wrote:
zsol...@xxxxxxxxx wrote:
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.
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?
Ed
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
sent.
.
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