Hello. I have gone around in circles trying to find a low cost, simple solution for activating processes on an Arduino by having something come within a couple feet proximity of it. I require more than the couple inch range provided by passive RFIDs. and higher end RFIDs are cost prohibitive. It does not need to be a secure or unique ID connection, it does not need to send any data. I just need to be able to sense when something is in range of the Arduino. But it has to be able to know the difference between something I want to detect (something with the "beacon") and something I don't want to active it (everyone else walking by). so IR prox sensors and simple visual type systems are not the answer. any suggestions?
think high tech doggy door, though this is not my application. the dog could wear something that unlocks the door (if you ignore the security of the system).
any suggestions would help! especially if you've had luck doing something similar. thanks!