ignition controlled door lock/unlock

ok, i'm trying to hook up ignition controlled door locks and unlocking... the locking is easy.. i'll use the constant to momentary from the ignition wire and that'll lock my door.. but i'm baffeld how to unlock my doors when my ignition is turned off?

maybe i hook up the capacitor's + end to another relay to trigger it to unlock doors.. like the capcitor will start to drain the energy to the resistor, but it can also drain to to another relay and trigger door unlock?  help, i need this quick! thanks

One thing you could try is to wire a relay as a normally-closed switch that opens (relay turns on) when ignition is on, and closes (provides pulse) when the key is turned off. Basically, tap into your ignition wire and tie it to one of the trigger terminals of the relay (85 or 86). Tie the other trigger wire of the relay to ground. Naturally, this will cause the relay to be energized while the ignition is on. Now, take the common post of the relay (30), and tie it to one end of a capacitor. Tie the other end of the cap to either 12V constant or ground, depending on what kind of signal your system requres for unlock. Note that the cap polarity will obviously depend on what kind of signal you need. Now, tie the normally-closed pin (87a) to your door unlock trigger wire. Finally, tie a 1k ohm resistor from pin 87 to the capacitor on the side facing AWAY from the relay.

What this SHOULD do is this:  When you turn the ignition off, the relay will shut off, connecting pins 30 and 87a. Providing there is a proper circuit to energize on the outside of pin 87a (like your door locks), this will cause current to flow through the capacitor on pin 30 and out pin 87a to your unlock wire until the cap becomes fully charged. You'll have to experiment with different value capacitors to get the desired pulse duration, which will be direcly affected by the resistance of your door unlock trigger mechanism. 4700 microfarad might be a good place to start. The cap will remain charged and no current will flow through it until the ignition is once again turned on. When this happens, the relay will again energize, causing the resister tied into pin 87 to be inserted in parallel with the capacitor, thus draining it so it can again provide the quick pulse when the ignition shuts off. If you notice that you have to leave the ignition on for a considerable amount of time before the unlock pulse works when you turn the key off, you can use a smaller value resister to drain the cap.

Side note: you may need to use a second relay to provide the actual signal to your unlock wire. If the pulse coming out of the first relay makes the unlock work erratically, and/or if the unlock mechanism draws too much current and the pulse is too short, use that pulse to trigger a second relay, which itself can send the necessary current to the unlock wire. You might even need to use a smaller, lower current relay like the ones found at Radio Shack. That, or keep trying bigger caps.

hope this helps!

the teknishn