Looking for some advice on where to start.

What I want: I want two circuits that control the brightness of their respective LEDs depending on their proximity to each other. Should start lighting at about the 1 meter mark and continue to get brighter the closer the circuits are together. Also, no line of sight as the circuits will be hidden inside an enclosure, so IR sensors are out. Also, battery powered and relatively compact. Oh and preferably inexpensive.

Looked around a bit and found this abandoned post which sounds like what I want but no answers were given.
Found another post that talked about RF tx/rx circuits and found these modules but I'm thinking it might be overkill for this simple(?) of a circuit and too long of a range. Each circuit should be both a tx and rx so mag reed switches are out.

Any ideas? Will I just have to bite the bullet and go the microcontroller/rf route or is there a simpler way to accomplish this?

 

For what you are describing I am not sure the RF will work simply. How did you actually plan on measuring the distance/proimity of the 2 devices? If you are thinking about measuring RF signal level that may work so long as orientation doesn't change. Even omni directional antennas aren't. Depending on the relative positioning (vert and horiz angles) the signal level will change even if the distance hasn't.

It appears you want something cheap but this may be a bit hard. If you can afford a little extra have a look at industrial proximity detectors. You can get some that work upto a few metres and use magnetics. Unfortunately I think this would aonly be able to be used in one direction.

 

That was my thought, yes, but you're right, depending on their orientation the signal level could change drastically. And yes, the magnetic sensors I've seen would only work in one direction.

Ok, I don't think I'll be able to go analog so tell me what you think of this. I could use one of the industrial proximity detectors you mention below to find the distance between the two circuits and then send that distance back to the other circuit over RF so they can adjust their brightness accordingly and in synchronization. Sound feasible?

I did a quick search for "industrial proximity sensors" and found some that will work up to a tenth of a meter but I'm hoping for something to start working around 1 meter. WK, do you have a link to something that might work here?

Any other thoughts on how to make this happen? Now that I've decided to go digital it should open up some more options.

 

Can you explain why you can't have IR devices exposed on the outside of the boxes?

Also you could consider ultrasonic transducers. They can be used for metres but would also require to be exposed.

 

Yeah, the idea is to have all the circuitry hidden. They won't be in boxes but a sort of natural enclosure that isn't completely opaque, they will let enough light through to allow you to see the LEDs glowing inside but not clear enough to see any detail of what's inside. Specifically one of these, http://www.google.com/products?q=ro...esult_group&ct=title&resnum=3&ved=0CEYQrQQwAg

An update on my progress, it looks like there is a lot of work currently being done with RTLS with RFID and with other tech like Bluetooth. Looks like a calculation using TDOA is in order but the time spans are so small that getting something to measure that will be difficult.

Anyway, I came on here hoping to find an easy way to do this. I don't think there is. I figured "They make those radio fences for dogs, what I'm wanting should be simple" Well those operate on signal attentuation and require the receiver/collar to be in a certain orientation. While I could probably live with that limitation I'm going to explore some other options first. Anyway, thanks for your help. If I do come across a simple solution I'll post it here.