SparkFun Forums 

Where electronics enthusiasts find answers.

All things pertaining to wireless and RF links
By guitarmansam87
#163170
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.
By fll-freak
#163216
Creating a wireless comm system that was limited to just a few feet might be a trick. With such low power, a device within range may start to have comm problems if an object came between the base and the satellite.

An audio system where the base emitted a high frequency tone (outised of human hearing) that the satellites could listen to might be much simpler to implement. You could then symply lower the amplitude of the tone to set the range. You will still have the problems with reflections and interference, but it would be a good first step in the right direction.
By jremington
#163236
Measuring distances accurately with radio is a very difficult task; less so with sound. So, a lot depends on the value of "x" and how accurately you want the satellite-hub distance to be estimated.
By stevech
#163243
guitarmansam87 wrote: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.
If the "satellite" devices are always consistent in having line of sight to the hub, and there are never objects in the path, and the devices don't change orientation, etc., etc...

RF signal strength is a poor indication of range. You could arrange transmitter power, antenna gains, etc., to usually have loss of signal at distance X plus or minus 200%.

There are other better ways.
By Mee_n_Mac
#163327
stevech wrote:There are other better ways.
I agree. We need more requirements before a good recommendation could be made.

I could make a case for each satellite to visually observe the center beacon and measure it's angular extent and thereby derive the distance btw the two.