I have done the requisite search and cannot find an answer so here is my problem.
What I need is for two devices to be able to tell that they are within a couple of feet of each other. Exact positioning is not important. Exact range is not important just within a couple of feet. It needs to be omnidirectional.
Both devices will be battery powered. One device serves only as a locator and will be stationary. The other device will move into and out of range. The idea being that the moveable device only functions when it is in range of the stationary device, so it doesn’t even need to transmit any data.
I first thought RFID but the range is too short from everything I could tell.
With GPS, it seems that it would be tough within such a small space.
RF wouldn’t work at all unless I could severly limit the power but I am afraid this would be unreliable.
This leaves Bluetooth which seems to be the most logical choice. But I know nothing about Bluetooth. Assuming this would function as expected, what is the typical range of a bluetooth device and how long does it take to wake up and recognize a signal? The stationary device only has to see the moveable device and there will only be one moveable device although I am not sure this matters. All of the bluetooth info I have found is about connecting Phones to devices or computers to devices. What about device to device?
I’m not sure this would really work for my purposes. More detail on my project might help.
The moveable device will be in a hardcase (pelican knockoff) carried by someone. They have to get within a few feet of the stationary device before they can activate the functions of the components in the case. Because it is in a hardcase the infrared beacon idea just doesn’t function for me because the case could be at literally any orientation.
This is for a game and will be one of many parts of a LARP (Live Action Role Playing) game. Think of it like a suitcase bomb (which it will likely be at least once). I don’t want them to be able to activate it until they are where they are supposed to be. This was the easiest way to set that up because I want the stationary location to be moveable so that it is reusable in other aspects of the game. There is a timer associated with the hardcase. If they were able to acitvate before they were in place, it would let them cheat the system since the opposition would have limited time to try to deactivate it. We are talking hours, not minutes but consider that the person with the case activates it at home and then drives to the location, they could reduce the reaction time of the opposition dramatically and since they won’t know about the case until after it has been placed…well you see the point.
Use a cheap radio transceiver that has an RSS pin. You use the RSS level to determine how “close” it is. Also, you can detune the antenna to weaken the signal. using a radio for distance is unreliable but for general proximity it could be made to work. http://www.sparkfun.com/products/9582 looks like a possibility. You can also send an ID if you want to have multiple pairs of devices. Or you could salvage the RF section from one of those old 27 mhz remote control toys. The distance on those things was about 30 ft max. With the antenna off, it was more like 10 ft.
Your game has some resemblance to the old Ham Radio “fox-n-hounds” game.