GPS _may_ be possible, though I'm not convinced the necessary accuracy &
resolution would be easier.

Customer requirement is "wireless control link with proximity sensing to
prevent operation when operator is less than X feet from unit" Expect X to
be about 25-30 feet. That leaves a lot of really big questions about
sensing and "what happens if..."

-Denny



On Wed, Jul 30, 2014 at 10:59 AM, Mike Hord <mike.hord@gmail.com> wrote:

> 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 bett=
er
> 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 ha=
ve
> > 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 th=
e
> > 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
> up
> > 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
> theoretically
> > possible to query remote module and measure the time from query to
> > response. Any digital signal processing is going to take vastly more ti=
me
> > than the signal takes to travel, so this may be challenging :-) I have
> some
> > thoughts, but this would be vastly easier if there were some supporting
> > functions in the radio module.
> >
> > -Denny
> > --
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> >
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