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[aprssig] APRS RFID reader?

Robert Bruninga bruninga at usna.edu
Tue Feb 2 17:25:35 UTC 2010

> If you get a reading from one reader, you 
> make darned sure the other one can't talk. 
> While I'm standing in the magic spot, the 
> outside door mat reads my ID.  It starts 
> sending serial data...

At 9600 baud, the 32 bits are sent in 3 milliseconds or so.

And by definition, no two readers can detect it at the same
time.  The two readers would be by definition spaced wide enough
apart to pickup additional capture volume and NOT overlap other

One step at a brisk 3 MPH pace swings my foot though the 6"
detection range of a 6" coil in about 100 ms. Plenty of time for
a detection and far from any other reader.

Oh, the one thing we need more info on is the reader coil.  The
example on the spark-fun web page is a 6 inch coil... But then,
that is for reading a card probably hand swipped through an
area.  I'd like to see more info on what would happen if you
made the coil larger.  Maybe the detection distance will go
down, but the effective area will go up?
And a walking foot does not rise more than an inch or 2 off the
floor.  Else why do we trip on the cracks in sidewalks...


> (presumably dumb tnc).  At the same time, it inhibits either 
> the power on the inside mat or the serial data out.  As I 
> cross the indoor mat, it reports nothing.  When I leave the 
> building I hit the indoor mat first, it reports and inhibits 
> the outside door mat for a few seconds.
> I just looked on the sparkfun website, and they have glass 
> modules that would easily be slipped inside the rubber inners 
> of my shoes for $5.  I'd like to keep my RFID device right 
> next to my shoe phone.  Unfortunately, the read distance is 
> only 10mm.  Even the button ID tag has a 32mm range...  The 
> credit card format seems to have the greatest range. :-(
> Wes
> On Tue, Feb 2, 2010 at 08:58, Lynn W. Deffenbaugh (Mr) 
> <ldeffenb at homeside.to> wrote:
> 	Richard Amirault wrote:
> 		Easy ... if you are not there .. and you 
> trigger the sensor .. then you *are* there.
> 		If after you are there .. you once again 
> trigger the sensor .. then you are *not* there.
> 	Not so easy.  Miss one update and the state is then 
> reversed.  S/He's there when gone and gone when there.   And 
> then you say, but put a timeout on it.  A person will never 
> be there longer than 12 hours....Oh wait, there's 24 hour 
> contests, ok, so force them to be gone after 24 hours....Oh 
> wait, they might move in to the station to staff a hurricane 
> for 2-3 days, so we'll time it out in that time....Oh wait, 
> this person is a hard-core station user that comes and goes 
> every other day, so s/he'll be perpetually in the wrong state.
> 	I do RFID systems professionally.  If your reader's 
> can't give you direction of motion, there's no 100% reliable 
> way to infer such information.  Any such inference amounts to 
> an assumption of some kind and we all know what happens when 
> we AssUMe.
> 	Lynn (D) - KJ4ERJ - Recloaking for this discussion 
> 	_______________________________________________
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> -- 
> Wes
> ---
> God help those who do not help themselves.

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