How can I invert a negative voltage into a positive one ?

Here is the basic layout of the situation that I'm into.

I have a remote starter on my car. It's remote can lock and unlock the doors. The way it does it, is through the same wire that outputs a positive or a negative voltage to either lock or unlock the doors.

I want to splice in that wire and send the signal to a latch relay to trigger a device on both lock and unlock signal (kill switch in that case).

That would open the kill switch's circuit when the lock signal is sent and close it back (to a functionnal state) when the unlock button is pushed on the remote.

In order to drive the latch relay, it needs to get a positive inpulse to trigger the coil (or maybe a negative can still work, you let me know).

How can I invert the negative inpulse into a positive one ?

This is either a 5v or 12v voltage, yet to be determined.

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Perhaps a pair of optocouplers? If you wire the LED sides in parallel but swap one, then they'll protect each other from reverse voltage, and you can wire up the transistor sides any way you like.

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DJ Delorie

You sure the latching relay is polarity sensitive? Mechanical ones that I've seen don't care...

If it is polarity sensitive, then just a standard relay in the circuit would work just fine to switch the 12v as needed.

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Check it with a meter - they don't normally use a different polarity in autos but try to make everything work off of 12 VDC.

There are two options the most likely is they are using a motor drive lead screw type of "solenoid" (actuator) produces a lot more force than a solenoid can, and is becoming ubiquitous in autos for door and trunk locks.

They can easily reverse the voltage going to the locks using an H-bridge type of driver (search on it, it is easy to understand and use).

They can also use a mechanical interlock in the actuator itself. Extreme travel to one extreme or the other flips a built in switch to reverse polarity and remove power to the stalled motor - the switch is part of the motor and works so that one time it closes the next time it opens - this is not common though, since they also have to incorporate some other mechanical magic to have it recover if power is interrupted .

Check out the actual device and voltages it may not work the way you think it does.

You can invert the voltage by converting the 12 V to pulsating 12 V and then using a cap and diode (two diodes) to invert the output - search for "voltage inverter"

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simple low power one

That one only outputs 100 ma or a little more - but the basic idea can work up to a few amps.

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How abouts you read the data sheet? Many do care. How are we supposed to know what you are planning on using?

Well, a bridge rectifier would output unipolar DC for whatever polarity of DC you feed into it. You could connect the coil, if it is polarity sensitive, to the +/- "output" of the bridge, and the DC of either polarity would go into the "AC" terminals. Eg. W06:

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It drops a bit of voltage, but still probably okay on a 12V relay. Best regards, Spehro Pefhany

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Spehro Pefhany

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