Turn on/off power to a item using 2 trigs
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Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=40392
Printed Date: May 14, 2025 at 7:50 PM
Topic: Turn on/off power to a item using 2 trigs
Posted By: jamac010
Subject: Turn on/off power to a item using 2 trigs
Date Posted: October 06, 2004 at 1:08 PM
I have a 1997 BMW 328i with factory alarm. I am adding a 2 zone prox sensor. I tapped in to the alarm harness for power, ground and hood trigger for the internal part of the proximity sensor (with diodes). Since the factory alarm doesnt have a prewarn feature, I attempted to add the exterior sensor with ground, power and trigger from the proximity alarm to a
Replies:
Posted By: hotwaterwizard
Date Posted: October 06, 2004 at 5:23 PM
First does the Proximity Sensor Open or Close when it is activated? You can use a Relay to do the job. ------------- John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !
Posted By: jamac010
Date Posted: October 06, 2004 at 9:03 PM
I think it opens when its activated. I want it to shut off the power to the sensor when car is unlocked and on when doors are locked. Or it can act like a momentary switch if i hook the two triggers together (turning off power then back on each signal passed)??
Also I think the lock and unlock triggers are Positive triggers. +12DC
Posted By: hotwaterwizard
Date Posted: October 06, 2004 at 10:46 PM
The problem I see is a constant current draw from a relay doing it this way. the easiest way is to disable it when key switch is on accessories and on. A relay could easily do the job. 
------------- John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !
Posted By: jamac010
Date Posted: October 06, 2004 at 11:01 PM
Yes disabling it with the ignition would work but since its a external proximity sensor (dual zone). The
Posted By: hotwaterwizard
Date Posted: October 06, 2004 at 11:39 PM
 ------------- John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !
Posted By: the1alchemist
Date Posted: October 12, 2004 at 8:51 AM
just put a diode (stripe facing away from the sensor) in the GROUND for the sensor,and hook it up to an ignition wire..the bmw doesnt really have acc,some,if not all may stay on until the key is removed,you might as well use that wire..that way when the ign is on,the sensor won't have power,because there is little if any voltage potential on the power wires for the sensor,then when you turn off the ign,the 12v sw wire will provide a ground to the sensor..
switches,relays,etc..alot of stuff you dont need for a sensor that draws milliamps..i do the same thing with 'scanners',instead of their way of wiring them,that way they are always on when the ign is off..the orange wires don't usually do exactly what you expect..this way the alarm is out of the loop,as we all should know,an alarm is a deterrent,that is just reinforced with the 'scanner'
i have used it for many things,jus figure you dont have a ground when on,but will provide it when off..
now for some newer gm's(for example) the wires @ the ign draw milliamps,so you must test them for function,the more whatever draws,the less likely it is to work.. but a sensor draws almost mothing,so it shouldnt matter,and in such a situation,a diode could be very important..a relay instead of a sensor may actually leave something running..just a thought..
-------------
'Stereo' Mike
The Audio CARtist,LLC
9600 Balt. Ave.
College Park,MD 20740
301-474-6260
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