Wireless sensoring/comm in a short range (10 to 15 meters)

Hi, there!

I need to have a device identifying itself to another device when the first (mobile) reaches a distance of 10 to 15 meters from the second (steady) which will take some action when it identifies the mobile one as it reaches that distance range.

I have considered using a bluetooth, a NRF24L01, IR, RFID and so on but did not come up with the appropriate solution.

The main purpose for this is to trigger the opening of a garage door when the car is about 10 to 15 meters far from the garage.

So, I appreciate any help on identifying the most appropriate technology for succeeding on my intent. Thank you all in advance for any possible help.


Perhaps a sensor in the driveway would solve your problem - instead of measuring 10-15 meters from somewhere (which can be tougher), just sense the vehicle (or RFID) with a sensor under the driveway (or beside it).

The typical "real world" car sensor is a wire loop buried under the road. The inductance changes when a car is over it.

I have a lot of experience with the little RFM22B transcievers, which sell for about $5 apiece. If I were going to do this, I would put a unit on the garage, which broadcasts a beacon signal whenever the door is closed. In the car, I would put another unit which listens for the beacon signal, and transmits a unique signal back when it hears the beacon. As to distance, you can turn the power down on these units to a low of about 1 mw., but that may be more range than you want. However, you could read the RSSI (received signal strength) (a simple routine in the RadioHead library for the RFM22B) of the incoming beacon, and not transpond until it reached a certain level. This would take experiment.

Of course, there are other transceivers out there as well that would do. Be sure to use a low frequency (e.g., 433 MHz.) because higher freqs are more attenuated by rain.