I want to create a system so that when a RFID fob is over 12 feet away a circuit will open. The system will be 12 volt DC, and I hope to use a passive tag that can be worn, and is waterproof. I've seen two boards but I don't know which one will do what I want. Looking forward to your questions and advice. Thanks in advance.
Bj
I think you have a very simple project. just leave the circuit open.
since you cannot detect an RFID chip that is more than a few inches away, your circuit will always be open. saves on the labor and expense of actually doing any work.
and, since I am more than 12 feet away, you cannot smack me for being a smart-alec.
sailbj:
I want to create a system so that when a RFID fob is over 12 feet away a circuit will open. The system will be 12 volt DC, and I hope to use a passive tag that can be worn, and is waterproof. I've seen two boards but I don't know which one will do what I want. Looking forward to your questions and advice. Thanks in advance.
Bj
Hi,
Welcome to the forum.
Please read the first post in any forum entitled how to use this forum.
http://forum.arduino.cc/index.php/topic,148850.0.html
Can you post links to the two you have looked at?
As @Delta_G has pointed out, 12feet is a long way.
You need to research how RFID works.
What is the application?
Thanks..Tom.. 
I single hand my 25' sailboat. At the start and finish, I run my diesel engine with my tiller tied off. (heading up wind.) I go forward to work sails, pull my anchor, or what ever. What happens if I go overboard?
I am looking for a "wireless tether" to kill the engine. The engine is not electrically controlled, so I have to install a solenoid and activate it ... somehow.
I am thinking when a rfid fob gets out of range it would activate the solenoid. Is there a better way? (electric fuel pumps are out of the question)
Battery operated fobs are OK, if they are waterproof!
Forgot to mention, I have an Uno-3 with RFID 522
there are commercial systems out there, but they interrupt electrical signal to the engine, and cost a bundle. This is also a challenge for me!
Just use Bluetooth or any other RF dongle that can handily reach your required distance. Get below deck and the extra material in the way reduces the range, you don't want it to be so sensitive that it shuts off because of that.
RF doesn't work under water (the water blocks the radio waves with in a few mm), so the moment you go overboard even right next to your engine the contact is lost.
wvmarle:
Just use Bluetooth or any other RF dongle that can handily reach your required distance. Get below deck and the extra material in the way reduces the range, you don't want it to be so sensitive that it shuts off because of that.
RF doesn't work under water (the water blocks the radio waves with in a few mm), so the moment you go overboard even right next to your engine the contact is lost.
Brilliant solution to a very xy problem.