Brainstorm: Wireless network of beacons that glow when near eachother

Projects General Guidance
1

Hi all,

I am in the early stages of this project and would love some feedback, ideas, or useful links. I really appreciate it!

I am trying to create a collection of small wireless devices that activate (light up) when they are near one another. So far I'm thinking this will be easiest/cheapest/lowest power if I use RF to communicate. There are cheap transceivers available such as the HopeRF RFM12BSP that operate in the 315/434/915 MHz ISM bands.
Some things that I am considering:

  • The devices are transmitting almost no data. They're basically saying "hey, is one of my friends out there?" and then listening for the same thing, and lighting up when they get a match. Is RF overkill? Should I use something other wireless tech?
  • It would be awesome if they got brighter as a "friend" got closer. This would require some way of detecting proximity, and the only thing I can think of is checking signal strength. That may not really work.
  • I was planning on prototyping this using Arduino, but I want to make the devices as simply as possible. Ideas for some elegant design that doesn't even need a microcontroller?

Anyway, thanks a ton. This is totally for Burning Man. I want to be able to hand these out to people in my camp (think like a necklace charm or something) and then they can tell when someone is near. I'm sure it's been done before, I'm just having a hard time finding any resources online.

)'(
ratchet

2

I went to SparkFun to check your transceiver out. The price is right, and the data on it says that it has signal strength (RSSI) readout. Looks ideal for your purpose. Build each one with a DIP switch, or jumpers, to set unique ID's. The only difficulty is if too many are in close proximity, a given receiver may have trouble getting a clear signal, and determining proximity with multiple signals would be difficult. Also, signal strength is generally a very poor indicator of proximity, since walls, fences, people, and everything else in the vicinity is a reflector or absorber of radio waves.

So I wouldn't count much on proximity or location capability unless you've got a big budget. And if you don't have too many of them distributed, you may not experience too much signal collision. Of course, you could put a real-time clock chip in each one (some are dirt cheap), and then actually have transmissions scheduled to not overlap. Clock drift will occur, so this requires an analysis as to how many users will be involved, and how much clock drift might occur during the course of the event.

Just some thoughts from an old RF comm guy.

Good luck

John Doner