Sometime ago I posted a question about getting my el cheapo car alarm to succesfully lock and unlock the car.
Thanks to Television, I discovered that by grounding any of the three wires that ran to the pump caused the car to unlock and 12v to the same wire caused it to lock.
The problem in my case was that the alarm unit only pulsed for 0.7 seconds. The W124 needs about 2.5 to three seconds to fully switch over. Most car alarms should let you do this, indeed mine was supposed to by changing a jumper setting, but it didn't work.
I needed a single shot delay relay for both the unlock and lock. I tried to find something, but most were expensive and too bulky. In the end I got two standard switching relays and put a 16v 10,000 microfarad capacitor between the incoming trigger and earth. 10,000 microfarads will keep a standard switching relay powered for about 2 seconds. This did the trick for me so I thought I would share.
Anyone with more electronic knowhow than me, could probably do something similar with a transistor and small capacitor, but this approach works if a little bulky.
Cost of the capacitors were 2 pound each from ebay.
Thanks to all on this forum for the initial help
Jon
Thanks to Television, I discovered that by grounding any of the three wires that ran to the pump caused the car to unlock and 12v to the same wire caused it to lock.
The problem in my case was that the alarm unit only pulsed for 0.7 seconds. The W124 needs about 2.5 to three seconds to fully switch over. Most car alarms should let you do this, indeed mine was supposed to by changing a jumper setting, but it didn't work.
I needed a single shot delay relay for both the unlock and lock. I tried to find something, but most were expensive and too bulky. In the end I got two standard switching relays and put a 16v 10,000 microfarad capacitor between the incoming trigger and earth. 10,000 microfarads will keep a standard switching relay powered for about 2 seconds. This did the trick for me so I thought I would share.
Anyone with more electronic knowhow than me, could probably do something similar with a transistor and small capacitor, but this approach works if a little bulky.
Cost of the capacitors were 2 pound each from ebay.
Thanks to all on this forum for the initial help
Jon
