Is this a human safety issue that forces the minimum range?

I don't know of any radio based solution that's going to give you range in
a repeatable manner, in a cluttered or unspecified environment.
Time of flight assumes a direct path, and sometimes the best path isn't the
direct one.
Optical triangulation of the remote might help..



On Thu, Jul 31, 2014 at 10:04 AM, Denny Esterline <desterline@gmail.com>
wrote:

> 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 t=
o
> 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 provide=
s
> > 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 o=
f
> 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 sca=
le
> > 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 strengt=
h
> -
> > 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
> time
> > > than the signal takes to travel, so this may be challenging :-) I hav=
e
> > some
> > > thoughts, but this would be vastly easier if there were some supporti=
ng
> > > functions in the radio module.
> > >
> > > -Denny
> > > --
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