Outdoors? Could you use GPS?

XBee modules can give you signal strength, but that really only provides
reliablity
information. In general, in fact, I don't think you'll be able to do better
than
order-of-magnitude approximation, and not even that, indoors. Outdoors,
especially in a relatively isolated location, you may do better.

Mike


On Wed, Jul 30, 2014 at 11:38 AM, Denny Esterline <desterline@gmail.com>
wrote:

> Needed - wireless transceiver module for north american operation. I have
> control over both ends, so most any protocol is reasonably possible
> (Bluetooth, zigbee, wifi, etc) Likely a 16bit micro on both ends.
> Functionally I need bi-directional control and status information on the
> order of 100 bytes a second, desired latency under 50mS.
> Minimum range of 100 feet line of sight. (practical operating range 30-50
> feet)
> Unit cost not too-too critical $50 ea ok, $20 ea better.
> Relatively small, has to fit into a hand held device about the size of a
> DMM.
> Integrated antenna desirable.
> Power requirements not constraining - other parts of the system use 10's =
of
> watts, shaving milliwats here somewhat pointless.
> Immediate demand perhaps 100 units, if all goes well, may need to scale u=
p
> to 1000 units a year.
>
> (This next bit is the difficult part)
>
> I need a way to measure the distance between two operating modules.
> I'm thinking I can get a reasonable approximation from signal strength - =
so
> I would need to be able to read signal strength information at least.
> Other option I'm chewing on is time of flight. It's at least theoreticall=
y
> possible to query remote module and measure the time from query to
> response. Any digital signal processing is going to take vastly more time
> than the signal takes to travel, so this may be challenging :-) I have so=
me
> thoughts, but this would be vastly easier if there were some supporting
> functions in the radio module.
>
> -Denny
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