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

[Wolfgang]

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.

 

[DJ Delorie]

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.

 

[PeterD]

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.

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.

 

[default]

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.

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"

http://www.reconnsworld.com/power_voltinvert.html 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.
--

 

[Spehro Pefhany]

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

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

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

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:

http://www.diodes.com/datasheets/ds21202.pdf

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