Alternate between lock and unlock with xem access controller v2

hey everyone,

I’m getting everything together that I need to use the xem access controller v2 to unlock my car and was wondering if anyone came up with a solution to alternate between lock and unlock when scanning. As it stands I can wire it up for unlock only but having both lock and unlock would be an added bonus. Also will I need a voltage regulator to keep the voltage at or below 12V or will 13.5V not be a problem?

I could probably figure something out with an arduino but iirc that will have a significantly higher power draw while idling which wouldn’t be ideal for something connected to a car battery.

IIRC, the xAC draws about 60mA. A microcontroller will draw orders of magnitude less. In fact, the power supply for it may draw more than the MCU itself; a 7805 takes like 5mA all to itself.


If you’re planning to sacrifice a key fob to lock and unlock your car, this wiring diagram should work.

Warning: SPST Relays need Flyback Diodes.
Amazon Link for SPST Relays
Amazon Link for Bistable Self-Locking Relays

If you have different plans, this other topic may have what you’re looking for:


That’s pretty much exactly what I was looking for. I have a spare key fob I’m going to use for the project, I’ll put it together and test to see if it’ll pull too much power and kill the battery if the car is stopped for a few days.

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Just a couple of thoughts for you

Do you know how to test current draw?
Do you have a low volt cutout?
You could put a switch or sensor to power on only when needed…


I am fairly new to hobby electronics. I have some extensive knowledge about troubleshooting automotive electronics and circuits but I don’t really know what off the shelf components are available to build circuits. What type of sensor could I integrate into the circuit to power on only when needed, the only two I know of would be something like a photoresistor or a reed switch and I don’t think either of those would be useful for this application. I wanted to make a working prototype and then find a way to mitigate excess idle power consumption. I had also thought of getting something like a 5w solar panel with a charge controller to power this and any other future projects as well as keep the battery topped off but I’m not sure how that would affect battery longevity.

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My plan if I ever get around to it,
Is to simply use a momentary button, possibly with a 1-3 minute timing circuit,
And rig the button on the exterior of my side mirror

There was suggestion of using a pir sensor, but there was question it would function thru glass, because infrared

I also don’t like it because your back to actively using power, and I’d like to use no power when idle

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