[wareagle900]

your post makes no sense..... Yeah, the car starts with a fob shaped something in the car.


The valet key only works when the key is in the fob holder thingy...

I would just like you to explain hoW a rfid chip can transmit a signal without power.....

It just seems illogical to me.

[wareagle900]

ok, been reading up on it and i suppose it makes sense to use a passive rfid

but if it indeed is a passive, then why have a battery at all?

[GenePoole]

For the lock remote.

[stealth.pilot]

I'm resurrecting this thread. I wonder if the OP managed to pull this off.

I also want to switch my F10 key into a credit card key. If it is a simple matter of powering an RFID chip, I can use the old credit card key from my Lexus as a shell for the BMW RFID chip.

[Yngvejos]

Originally Posted by wareagle900

your post makes no sense..... Yeah, the car starts with a fob shaped something in the car.


The valet key only works when the key is in the fob holder thingy...

I would just like you to explain hoW a rfid chip can transmit a signal without power.....

It just seems illogical to me.

The rfid chip receives power to transmit from an electromagnetic field made by the car.
Think wireless charging in small scale with low currents.

Originally Posted by wareagle900

ok, been reading up on it and i suppose it makes sense to use a passive rfid

but if it indeed is a passive, then why have a battery at all?

The RFID chip have to be really close to the antenna to transmit (like an access card on a card reader).
It needs it's own power supply (a battery) to be able to communicate with the car when you have the key in your pocket.

I believe CA uses 868MHz for normal communication while the passive RFID chip is a redundant system in case the fob runs out of battery.