Hey guys, this is my first post here. I hope it's in the right section.

I'm working on a project involving a central "hub" and several satellite devices. The sole purpose of this project is that each device will go into a sort of "panic mode" if it is >x distance away from the hub (we're talking a matter of a few feet). Simply put, each satellite device would need to say "Hey, I'm too far from the base. Let's flash lights"

Either I could use a system that measures distance and just uses a an if > operation to do this, but accurate distance measurement on this scale probably wouldn't be feasible. The other thing I was thinking is that I'd just exploit the range of whatever protocol and have logic on the satellites that panics with loss of communication (which would presumably involve pinging on short intervals and flipping the logic after a few no-replies)

Any suggestions on where to start? I'm not an wireless guy, so I'm reaching a bit far by taking this project on.

Cheers and thank you in advance.

 

The second one is easier. It's called a dead man switch. Instead of trying to measure the distance, which requires 2 way communication, you just reduce the transmitting level or the receivers sensitivity until it won't work at 4 feet or 10 feet.

Beyond this, I am lost. I don't do RF.

 

Your hub could send out an RF (or IR) pulse and an ultrasound pulse simultaneously and your satellites could time the difference between the arrival of the RF and the ultrasound, which would be proportional to distance.

 

...each device will go into a sort of "panic mode" ...

hmmmmmm....