My roommate has an old 1991 Suzuki Swift which he likes to “pimp” a bit !
For example he adds a 3D printed cup holder, and homemade aluminum profiles roof ski rack.
As there is no central locking system, it is really annoying to open and close his car.

As it’s a two doors car we decided that if we put a finger print door lock on the driver side it’s worth to put a second motor on the other door.
We choose the fingerprint sensor available here or ebay.com for many reasons. It has an embed memory, serial communication, a kind of datasheet, it’s in Chinese, but it become almost understandable with Google translate.

We used 2 “car door lock actuator” available on the bay for less than 4$ each.

To detect if the car is open or locked, we used a IR barrier, but as we didn’t have one, we built it with a tcrt5000, that we split.

We put a small 3D printed part on the rod, to cut the IR barrier when closed. We had to put some electrical tape on it, because surprisingly the 3D printed part wasn’t IR proof.

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Here is the complete wiring diagram, there is (normally) nothing missing!

EDIT: The 3 10Kohm resistors used for driving the relays should be replaced by 2K7 or so resistors. I made a mistake, with the 10k, the transistor isn’t saturated, and die pretty early!

Let’s see how it works.

– First of all, the 12V from the battery is filtered through 4 capacitors, 1nF,100nF,10uF and 1mF, to have a clean 12V to power the whole thing.

– Then the 12V goes into the MAX5024, wich give 5V for the Arduino. The MAX5024, and the Arduino are the only two things always powered up. This is why we choose a low quiescent current regulator for that, we also removed the pwr led of the arduino. Now when the arduino is in sleep mode, the regulator and the arduino only consume about 10uA.

– The arduino is in sleep mode and all relays are in the NC position.

– Somebody push the switch.

– Arduino is woken up, it close first relay, now there is 12V available after relay 1, and 5V after the 7805.

– As the IR sensor is now powered, it check if the door is open or locked. If open, it just locks the doors, by controlling motors diving relays, and goes sleep again.

– Else, if doors are closed, it waits a valid finger during 10 sec. If one is shown it open the doors by controlling motors diving relays, and go sleep again.

– If no valid finger has been shown, during 10 sec, it goes in sleep mode again, and doors are still closed.

Then code will  repeat, at the next switch push.