Paul_M

I have a cobra 7900 series alarm fitted to my Audi and I want to change the lock/unlock pulse duration to 3 secs. Any ideas how this is done? The system doesn't have a touch-key but I do have a PIN code for it if required.

Nick@avs

Only early Audi's required this method of locking configuration. The problem is that the 7900 series hasn't got the option of 3 second pulse or 6 wire locking but Cobra do sell a vacuum locking interface which the installer would be able to order and install.

Paul_M

I wasn't going to go into the details cos I thought it was irrelevant, but here goes!

I don't actually need the extended pulse for the locks - they work fine with a 1 sec pulse. The way I've done it is set to negative output, two relays to provide the required neg/pos pulse to the system for lock and unlock.

The one issue I have is the courtesy light - amazingly there's no output for it on this alarm (to switch it on when unlocking). No probs I thought, connect the unlock negative pulse via a diode to the door trigger which makes the system think a door has been opened and switches the light on.

It works - but then goes off again after a second. The reason being that the car automatically cancels the light delay while the doors are locked, but this feature doesn't seem to be switched off quick enough so even though the doors are now unlocked it switches the light off once the pulse goes away!

It's not due to the alarm - the exact same effect can be observed locking then unlocking with the key and immediately opening then closing the door. If I could make it pulse for 3 or more secs that would be long enough for the delay cancel to be disabled and the light would stay on for 20 secs or whatever.

Now you'll see why I wasn't going to explain before! So if the pulse time can't be changed on this system, I guess I'll just have to resort to the old-fashioned resistor-cap delay method, what a PITA but there you go

Nick@avs

Paul, the Blue/pink wire puts a pulse on unlock by default but if somebody has put a diode in because they used the same wire for the boot circuit then it won't put a neg down that line. If, however you remove the diode and connect the boot via a diode to the blue or grey (won't give door open bleeps) that will do the job and keep it simple.

Paul_M

Hi Nick,

The blue/pink is connected directly to the door circuit. Doesn't seem to provide a neg pulse on this system, it was the same when it was installed in the Scooby. I know it's quite an old system so maybe it's not a feature on this model unfortunately.