[aprssig] APRS RFID reader? (Details...)

Robert Bruninga bruninga at usna.edu
Tue Feb 2 07:27:19 CST 2010

Wes, Excellent ideas...

> How do you know if someone is coming or going?  
> What if there were two RFID readers... and ...
> two sequential reads... you'd know I was outbound
> [or inbound].

Yes, Another way might be a "charging coil" prior to the reader.
My tiny understanding is that the majority of the delay in
reading is waiting for the tag to charge up from the 125 KHz
carrier.  If the charging coil was before the sense coil, then
we would only detect that one way.  Just a thought... Be cheaper
to build a 125 KHz oscillator than another $30 reader...

> As for the door mat, put the sensor coil 
> in the center and advise people to wear 
> the tag in their left shoe.  Most people 
> end up walking on the right anyway and 
> that keeps the tag in the center of the door...

Or, based on that, put the chip in the right shoe and the coils
on the right of the doorway going in and then have a higher
probability of detecting arrivals.

By-the-way, yesterday I put an old credit card in my right shoe
and after a few minutes and it conformed to my arch, I cannot
feel it.  It is still there.  I want to see if it complete
disappears from my senses.

> I really really wish there was a way to 
> map my callsign to the reader locally.

How about this.  If the local RFID reader node does not
recognize the tag, it sends out the RFID code raw on APRS where
the global APRS-IS RFID engine picks it up and then sends BACK
the matching callsign to the RFID reader node so it can then
originate the local packet.

> ... I'd like to see the reader programmed 
> such that it would know the boundaries of 
> a room (pre programmed) and randomly scatter 
> each person's location within that room...

The plan would be just like APRStt.  That is, the local RFID
Reader node would diddle the LATITUDE hundredths digit so that
all the callsigns present appear as a list on the map.  The RFID
node has been pre-set to where the best location of that list
is.  You can see how this works with APRStt at Dayton, where the
list is built over in the grove of trees in the SW corner of the
property where no-one ever is. See aprs.org/aprstt.html

> it would be nice to have a keypad which beeped 
> at unknown tags and asked the person to 
> enter their callsign.

Great idea.  I'm sure it can be built into the RFID reader


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