I am trying to design a system for my car that incorporates a push-button ignition combined with a passive locking mechanism. I do a lot of programming in C, Java, etc. and looking through the language documentation I don't foresee too many issues in that regard. I have also dabbled in electronics engineering and I have loads of experience messing with cars. That being said I have two things that have yet to really fall in place in the project.
Goal
As I'm walking to the car, the arduino detects a tag in my pocket and unlocks my doors...probably while I'm one/two feet away. At the same time, it begins monitoring a button in the dash. When this button is pressed once, it turns the ignition to ACC, press again and it's ON. Hold it and it energizes the starter relay.
Implementation
Tag: I'm not exactly certain what I could use here. Realistically I would need 1-3 feet of range. I could mount the receiver in the door and the receiver should be able to read it when I'm close and when I'm sitting in the driver's seat. From what I have read the passive RFID shields available for the Arduino only have 1-3cm of range. Are there any active rfid systems that might get me the 1-3 feet of range I need? I'm not so sure I want to use RF, because from what I've read they're power hungry and need to send a pulse every few second. I also don't feel like implementing some sort of rolling code system.
Car Interface: I know Arduino runs on 5v and outputs 5v. To power it I think I'm just going to use a cellphone adaptor but I'm a little fuzzy on outputing 12v to bring the ignition up/etc. From what I have gathered, this is the way the circuit would work for, say, a power window:
I'm sure this is wrong and I'm missing something. I'm not sure what sort of relay/transistor/zener diode I'd need. I'm also unsure if the relay coil to ground part is correct.
KE7GKP:
Now you know why the wireless locks used on modern vehicles have batteries in the key-fob transmitter. You can't get that kind of range from passive RFID tags without spending WAY more money than it is worth.
As for the button functionality, that is pretty easy stuff to do with Arduino, no fundamental problem there.
As for the power situation, dunno what role the "cellphone adapter" has here? At some point you will need to reveal exactly which of several dozen different Arduino boards you are asking about. Most have a "Vin" pin that will take vehicle 12V quite nicely.
In all likelihood I'm going to be using an arduino uno. If you think another arduino would be better suited to the task feel free to give me input...I'd like programming the device to be easy and I don't want to spend much in the way of programmers etc.
From what I know, when a car is running the alternator causes all sorts of nasty voltage spikes, backflow, and just generally unclean power which is no good for an arduino. If the uno can handle this environment that'd be awesome, otherwise what I meant was I am going to use a cigarette lighter style phone charger that I'll rip apart to feed the arduino 5v.
So is RFID completely out? No active RFID possibility? Too expensive?
I'm not even sure how I'd use an RF fob. I'd have to find a fob that sends a code every few seconds. Realistically I'd probably need to design another arduino based system to go in a key fob. bleh.
I don't know how my bike does it, but it won't start if I don't have the key fob on me. I don't need to press any buttons on it. I just have to have it nearby. It's a Harley, if you want to research how their system works.
Checking nearby for a passive RFID tag in a fob before starting the engine would not be too hard.
But doing a proximity check for a passive RFID tag near the door would be harder. The only way I can think of is to have an RFID receiver on all the time. Like one of those detectors in a music store or a library. And that might take too much power. Probably not too cheap, either.
