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You may only need 3 readers. Some off the shelf detectors can read RFIDs from 200 meters away (though they are physically quite large)



Can you somehow triangulate an exact position by using the 3 readers? It's not enough to know a student is merely in range.


It would critically depend on the frequencies used by RFID (and multipath) but perhaps it could be done by measuring the time of transit?


Can you point me to any?

I've searched before and never found something that would work for me.

Thanks!


http://www.iautomate.com/products/Wavetrend-L%252dRX201-Long...

Not quite the 200 meters that 'someone_here' posted, but the quoted max range of 450 feet is more than usual (I also don't have any idea how well it works).


Thanks for the link!

That seems like it could work! It also has different antenna options for different uses which would also work for what I had in mind! ( I have 2 projects in mind, 1 is for short range 2-10ft, the other is long range 50ft or so )

EDIT: Yikes! Just saw the prices for the tags, at $25-50/tag its too expensive :( I dont mind if the reader is expensive but the tags must be cheap less than $1 would be ideal


For that range it's probably using active tags, which is why they cost so much. On the other hand passive readers often cost a few thousand dollars and have tiny ranges so I think that active systems end up being cheaper in many deployments.

I'm working on an active tag system for my phd actually, and our readers only cost as much as our tags and have the same range but they still cost somewhere in the $30-$50 range depending upon how many we make at a time. In a few years we'll probably have the cost down to a dollar or so in mass production but your projects will need to wait a while.




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