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Jakes21

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Hi, I have a 12v pulse (on/off) for about 15seconds, there after it stabilezes and stays on 12v.i want it to activate a relay only when the current stays on...and not when it goes on off.how could i accomplise that?any ideas?
 
A simple integrator will work, but what is the on/off cycle of the 12V pulse, and why 15 seconds? That's a LONG time for something to stabilize.
 
Hi, I have a 12v pulse (on/off) for about 15seconds, there after it stabilezes and stays on 12v.i want it to activate a relay only when the current stays on...and not when it goes on off.how could i accomplise that?any ideas?

Use a switch debouncer set to 15+ seconds.
 
Willbe, a capacitor and resistor large enough to give you a 15 second time constant is going to be very temperature sensitive and very inaccurate as far as timing goes.
 
Willbe, a capacitor and resistor large enough to give you a 15 second time constant is going to be very temperature sensitive and very inaccurate as far as timing goes.

Good point. Mr. 21, what kind of specs are you looking for on accuracy, repeatibility, etc.?
 
Okay, the thing is i hooked up a 12v car relay to my car alarm...when the alarm is activated the relay goes on/off for like 8seconds...too be mre accuratly....and then it stays on....all i want is to design sumthing so that when i activate the alarm the relay would stay on......so would a integrator still work?
 
You said it turns on and off for 8 seconds, how fast does it turn on and off?
 
Okay, the thing is i hooked up a 12v car relay to my car alarm...when the alarm is activated the relay goes on/off for like 8seconds...too be mre accuratly....and then it stays on....all i want is to design sumthing so that when i activate the alarm the relay would stay on......so would a integrator still work?

Use a FF that triggers on the rising edge of the first "on" pulse and drive the relay from the FF Q output with a transistor/suppressor diode. You may need some kind of reset circuit for the FF, since it has memory.
 
I take it that the output is just a relay meant to flash a light when you arm it. I would assume it flashes at a 1Hz rate or so. A diode, a capacitor and a sensitive relay may be all you need. This would make the relay stay on steady as soon as you armed it. To make the relay come on AFTER the pulsing is stopped is a little more difficult.
 
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The time interval between the flashes is like 250 ms...i thought of using 3 caps for this..was thinking sumthing in the line of when the caps were fully charge, then the relay would be activated and stay on....i dont want the relay to flash.. Im stil struggling..
 
I'll help you, but you must answer this question first:
Is it OK that the new relay turns on steady and remains on when the output of the car alarm starts "flashing"?
 
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Something like this should work:
relay-png.22043
 

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There must be some more direct access to the alarm signal then tapping into the lights.
 
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