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Topic: Car proximity smart key (Read 7125 times) previous topic - next topic


it has to be an active component, as the battery needs to be replaced in just a little over a year on a Lexus smart key.
I think it depends on the complexity of the key and what features it has. My car has basic keys with that proximity thing and 3 buttons (lock, unlock, trunk), so this could be battery assisted. Others offer realtime car information like battery, door closed, windows closed, etc. Those might be active.

After checking some specs, I realized that such feature (proximity sensing) can be achieved using bluetooth low energy. Bluetooth enabled in the "key" and bluetooth enabled in the "car". The "car" is in advertising mode; the "key" is scanning (it also works viceversa; the choice is made so the "key" consumes less current). When the "key" sees the "car" it connects to it (pairing previously set up) and they start talking.
BLE scanning uses very small current, <<1mA. BLE advertising also is very low power. The range is around 10 meters, maybe more in open areas, maybe less in crowded spaces.
I used quotes because I was talking about a similar system that I may implement (obviously the car keyless system doesn't use bluetooth).

Using bluetooth is more feasible as the documentation and components are easier to find and widely used.

Thanks for the help on this one!

If no one has anything to add, I think the topic can be closed with the following conclusions:
   The keyless car system with proximity feature uses a Battery Assisted Passive RFID or an Active RFID. This allows the key to operate from a year to a couple of years without replacing the battery. A similar diy project is hard to create because the hardware and documents describing hardware and schematics for BAP or Active RFID are scarce, or they come as end products (most of them as keyless systems for cars).

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