How to tell when two objects are near each other?

Forum 2005-2010 (read only) Hardware Interfacing
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I'm a newbie at Arduino and I'm trying to figure out if my project idea will work. I would like to have a system where I have several objects and they can tell when one is in proximity of another. So if I have Object A, B, and C, and I put A and C next to each other, it will send this information back to the board that A and C are close. I don't need to know how close, just a true or a false.

I have been looking through some of the available products and it seems like a couple things I could use are RFIDs or color sensors (if I make each one a distinct color). I can't really see how either of those things work though, so I'm not sure if they are plausible solutions.

I'm sure someone else must have done a project where they want to achieve this, so is there some known solution for this? A tutorial would be wonderful. Thanks!

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It depends on what your sensing distance is and how aligned the units need to be.
The simplest is by using IR and flashing messages between the two systems.
However, I would probably do with an AC magnetic field and sensor coil a bit like the way an RFID reader works.
problem is you have to be careful with any system that your transmissions don't deafen the receiver.
I haven seen any writeups on this sort of thing though.

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Thank you very much for your reply. I guess this project is over my head. I'm going to just try and do the same thing by plugging the objects onto a breadboard instead. Then maybe I can upgrade it one day in the future once I've learned more.

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