Negative pulses.

Hi, I am facing a problem with my car remote locking/unlocking system. My car has central locking but not remote, so the plan was to tap into the wires that send the signal to lock/unlock using a relay and a 433mhz remote to actuate it.

Now, upon actually starting the project, I'm faced with unknowns. I have meddled with arduino now and then, but I am by all accounts a complete noob, also at electronics in general.

I found a thread on a specific forum regarding the installation of an aftermarket lock/unlock kit, it shows which wires to tap into and to connect to the kit. However this does not help me, using the arduino.

It says the unlock brain (in this case the arduino) is supposed to tap into two lines (shown here) and send negative impulses to one for locking, the other for unlocking. The problem is I have no idea what negative pulses even are, as far as I knew this was just going to be a close a circuit by tapping into it with a relay and done.

Can anyone enlighten me on how I would produce and deliver negative pulses into those wires? Thanks

Measure the voltage on those two wires - my guess is they are high and the "negative pulse" refers to pulling it down to ground briefly.

Similar to what gpsmikey said, it sounds like "negative pulses" are meaning it normally has power going to it (+ to -) and a negative pulse may be a (- to -) so just grounded negative. I am sure there is a better explanation and anybody please correct me if I am wrong. Good luck!

In the diagram, it’s pretty clear that each line only has to be pulled to ground and doesn’t actually need a ‘negative’ pulse as such:-
(Right-click and “View Image” or similar for full size.)
Central Locking Hack.jpg
You just need to work out how much current you’re switching, then use an appropriate device, controlled by your Arduino. A relay or MOSFET should do the job. A logic-level MOSFET would probably be best/simplest. It looks very straightforward.

Hah ! As I suspected. Now if I could just find any kind of wiring diagram for my new GMC truck - it seems all wiring etc. is only available to the dealer (for which they pay $$$). Make sure if you use a MOSFET that you pick one with a good voltage rating (I would go at least 60v) and put a protection diode across it (ideally, the diode would be across the coil in the lock/unlock solenoid, but getting to that may be more effort than it is worth).

gpsmikey: Hah ! As I suspected. Now if I could just find any kind of wiring diagram for my new GMC truck - it seems all wiring etc. is only available to the dealer (for which they pay $$$). Make sure if you use a MOSFET that you pick one with a good voltage rating (I would go at least 60v) and put a protection diode across it (ideally, the diode would be across the coil in the lock/unlock solenoid, but getting to that may be more effort than it is worth).

Protection diode across the MOSFET? No, a protection TVS or zener is required. MOSFETs already are a diode (its an integral part of the design), which won't do any good at all when the voltage transient on the drain is +ve anyway! Any zener or TVS has to soak up the full current of the solenoid briefly so rate it suitably power rating. A 22V zener might be about right on a 12V system, you need to be sure the thing will only conduct on spikes, even when the alternator regulator fails.

Yeah, what Mark said. That is the correct answer. :)