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Topic: Car Keypad (Read 38447 times) previous topic - next topic



If a typical car battery is about 45 amp hours, and I'm pulling 20mA or so, does that mean it would have to run for 1125 hours (almost 47 days) to half-discharge the battery?  

Yup.  Unless something shorts out, you won't drain the car battery with the Arduino.

I guess the math is correct but I'm surprised.  20ma seems like no load at all but 47 days is not an outlandish period for a car to sit idle and having half my battery drained by my door lock key pad seems a bit alarming.  Maybe it's a Canadian winter thing but I'd be worried!


I wish that I had ever gotten around to actually testing what the rest of the car pulls when it's off.  Has anyone else done this?  My car has never sat idle for more than three days it's whole life, so a month and a half wouldn't be a problem for me.  The winters are rather mild here in Florida. :)


Nice work on the finished product.

How did you interface the keypad with your existing electronic locks. I read you used a relay, but where did you splice into the system?

The reason I ask is because I want to add keyless entry into my car, and i found the existing switch in the car door to just be two simple contact switches, one for lock, and one for unlock. Did you just add the relay in parallel with something like that?


My door lock buttons are also just simple contact switches.  They way that they signal the car to lock or unlock all the doors is by connecting two wires in the door together with either a 100 or 330 ohm resistor.  One is for lock, the other for unlock.  One of the wires was pulled high to 5v and the other was a ground, so any ground should work.

Instead of trying to send wires from my box to my door control's box and soldering on that board, I just used my own 100 and 330 ohm resistors and used the solid state relay to close the same two wires together with them.

Since this forum is more about the electronics and less about the car, I didn't bother with which wires in the door I used, etc.  It would be different with each car.
This is the relevant post from my thread over at CaliberForumz:

For the switching I used this solid state relay:
It was handy because I can drive it directly from my arduino's pins (I put a resistor on it to be safe).


I just realized that I haven't posted a parts list yet.  Still waiting on that last board, I suppose.  When I get it installed I'll release the board info (at BatchPCB) and the parts list along with it.



Ok, after many hours yesterday, the keypad is wired in.  It works fully, and I finished ALL the software for it.

But it wasn't easy.

Congrats - can't wait to see the video!


Jun 24, 2009, 03:49 pm Last Edit: Jun 24, 2009, 03:52 pm by neonpolaris Reason: 1
I needed to find something that would hold my wire loom to the door skin, not flopping around and out of the way so the window doesn't rub it when it goes down.  I went to Lowes and this was the only thing I found that didn't involve screws:

Unfortunately, they detached from the door when it got hot (summer in Florida).  So I replaced the crappy foam tape with some decal tape that I've used alot and has never failed me.

It may be hard to see, but here's my wireloom coming from the keypad, down to the bottom of the door and up the other side.  That's the connector on the bottom right.

Here's my box with the hole cut and some tape covering some pins to protect my wires.  I used my first board since my new one didn't work out, but I was too impatient to try and troubleshoot it.  I'll worry about it if I have any problems with this one (I haven't yet).

The back of the box, ready for mounting:

Here is an example of my splices into the door.  Soldered together and double walled heat shrink with adhesive.  This is the door lock sense wire, I believe.

Here's the box mounted.  I can assure you that it's quite secure.  I used just a tiny piece of the decal tape to hold it up temporarily while I was waiting for the other board, and it was harder than I expected to come off.  Fully taped will definately hold it.

So it's been in my car for a while now, and I've had no problems from it at all.  I'm very pleased with it.  I don't used it all the time, most of the time my keys are more convenient, but there has been more than once that I was already outside and wanted something from my car and didn't have my keys on me.  So it has already fulfilled its purpose.  I'll sure be happy I did it if I ever lock my keys in my car.


I needed to find something that would hold my wire loom to the door skin

What you found is pretty nice.

Another option is known as a "cable tie mount".  It's a plastic tab with slots to accept a cable tie on one side and adhesive on the other, so you tie the cables to the mount.



I was looking for a cable tie mount, even checked NAPA, but had no luck.  Where does one find these?  I know I'll want them again in the future.

Also, I've published the board at BatchPCB, so anyone can have one made whenever they want.


I was looking for a cable tie mount, even checked NAPA, but had no luck.  Where does one find these?

I got them through an electrical distributor for work.

For personal use, I'm pretty sure I have picked them up at the local borg (home depot, lowe's, etc) in the electrical department.




I posted a simple video by request of bill2009.  It shows locking, unlocking, and the anti-scan.  Don't worry, that combo was just a user-code that I added and have since erased. :)


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