Good day folks. I was wondering if it's possible to use my car's key fob (Renault) as a remote for controlling other stuff. I have quite a few generic 433Mhz remotes and modules I picked up on Ali for various projects, but instead of having another remote dangling off the key chain, I thought I could use the car's own fob for more than unlocking my car. Say I come home and wish to switch on a light at my front door. I know for a fact my fob uses a PCF7946, but there's little info on it and how it operates. For reference, I attached a picture of the board inside the fob, except mine doesn't have the third button. The PCF chip is there and there's nothing on the bottom - that's where the batteries go.
The only thing I want to achieve is to pick up the signal from the fob and turn on a pair of relays: one for the "unlock" button, one for the "lock" button as long as the button's held down, with some very basic security to ensure it doesn't respond to EVERY key fob that's similar to mine. I don't want to try to emulate the fob to unlock the car - we can forget about the car entirely for this discussion.
I already tried putting one of my generic receivers in pairing mode and hitting one of the 2 buttons on the car fob and of course it didn't work. As I later learned, there's the matter of fixed vs. rolling codes, so that's not going to work out of the box, at least not with devices you find all over Aliexpress
A project that comes close to achieving this is this one, so I tried it myself, but this didn't work either. I'm guessing because it's for a HCS chip and not a PCF one and the way they operate is different....either that, or I'm doing something wrong, because I have an Arduino Mega, as opposed to the Uno shown in the project and I'm not entirely sure I'm doing the interrupt thing right. I had it connected to pin 2 (physical pin 2). I couldn't find any projects specifically for PCF-based fobs, unfortunately. Any ideas on how I can achieve this, if at all possible ? Please bear in mind I'm no programmer or radio-control expert, but have decent knowledge of electronics and can at least follow along. Thank you.
Correct. Otherwise, I would've gone straight with the off the shelf remotes and relay boards, since I have a couple of those on hand and they work perfectly out of the box. Trouble is, I'd be adding another thing to my keychain
The good news is that the fob is not a rolling code device. That would have been problematic for what you want.
The bad news is that the device appears to be essentially dumb. It even gets power from the radio signal emitted by the base station. That means "generic receiver" is never going to work. You have to have a base station designed to work with your fob. In addition, you will very likely need one or more secrets stored inside the fob so the two things can be paired. It's a little difficult to tell from the datasheet but it's possible those secrets cannot be accessed; that they're essentially write-only. If that's true then you would have to create new secrets, program your new base station, reprogram the fob, and reprogram your car.
It even gets power from the radio signal emitted by the base station
Are you referring to the immobilizer part, which detects if the correct key is in the ignition barrel before it allows the engine to start ? Yes, I assume that's "passive" and works like an RFID tag when the key is inserted in the barrel.
I was hoping I could just "pluck" whatever the fob sends out over the air and do stuff with it later on in my code
It means there are variations of the PCF7946 that do not need a battery. You walk close to your car. Your car is emitting a 125 KHz radio signal. There is a simple external circuit in your fob that is able to collect enough energy from that radio signal to power the PCF7946. If you are not within a reasonable distance of your car then the fob has no power.
For your application that would mean the fob is only usable when it's within a reasonable distance of your car. You would only be able to control other devices when you're close to your car.
Obviously, yours may have a battery.
That may be possible. As far as I can tell the device is too simple to encrypt the over-the-air data. There does appear to be a good description of the protocol. You would have to run some experiments using a 125 KHz receiver that can frame packets exchanged between the base station and the fob.
It has a battery - I mentioned this in my first post
This is where stuff starts to go a bit over my head. Unless someone already did some project that I may adapt to my needs, I wouldn't know where to start
