i need idea about rf based car control system ( 125khz)

hello

we have a project about car in/out tracking system ( which car is in park
which is out, which car is in which time and out etc.. )

i think to use 433.92 mhz premade modules from telecontrolli or
radiometrix. everything is ok to here. but i need a trigger system to the
know car is in door area and car must send code to the receiver.
if i use rf again there may be collisions some of cars can get the signal
same time and they want to try reply same time again. ( i dont want to use
receiver in the car because it is cost)

so i think to use 125khz waves for triggering. like RFID systems. i dont want to transfer energy and i need limited area illumination.
one side 125 khz transmitter coil and other side in the car 125 khz simple
receiver antenna looking forward to the transmitter antenna ( one coil and capacitor , a dioede and a simple opamp compare circuit )
the distance is about 1 meter. this is just triggering the car control computer.

i have a fex experinces in rf designs. what do you think is this idea works ?
pls share your suggestions and idea


regards.

I could not understand fully but it seems to be a nice idea. I saw someting like this thing which was optics based.

yes it is like optics based. i dont want to use RF signal because of
reflections and parasites can be problem. i dont want to use optics
because the dust and sun can be problem.

Hi,

I work on RFID and I think all tags reader available now can't work for a 1 meter distance. You have to pre-amplify signals and perhaps design a crazy antenna...

(The development kits provided by manufacturers reach 20cm distance with big antennas.)

But I think for a 125kHz system the amplification shouldn't be so hard (careful it is a bidirectionnal amplification !)

I suggest you Atmel RFID systems for the good documentation and easy to anderstand protocol. The offer in transponder is also large enough to reply to your need. You can find all with app. notes for long distance reading on the web atmel.com.

beuch