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[aprssig] APRS RFID reader?

Wes Johnston, AI4PX wes at ai4px.com
Tue Feb 2 12:38:39 UTC 2010

Ohh, one question....

How do you know if someone is coming or going?

If I cross the threshold of the ham club and trigger and RFID, how do you
know I didn't get in my car and drive away?    Or am in the EOC at the

What if there were two RFID readers... and if they read the same card in the
order of READER 1, READER 2, you'd know I was inbound.  two sequential reads
on the same card from READER 2, READER 1, you'd know I was outbound.
Dunno.  That might work for a single doorway.  Or two readers near an
outbound and inbound door.  Note I'm suggesting that a single processor
listen to two RFID readers.  The processor could be programmed to look for
"one or the other" or "two in sequence" to determine in or outbound.

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 corridor.  The other part
of this... is if the door is usually closed and someone has to open it, I'll
bet you a box of doughnuts that 99% of people stand within the same 10" spot
to pull the door open.  That point is 2 feet straight back from the door
knob, just outside the arc that the door swings.
I really really wish there was a way to map my callsign to the reader
locally.  I hate to have to rely upon the "global aprs network" for
something that should be done locally.  Ideally, 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  (to prevent
everone piling up on top of each other on the map.  Not sure how much memory
the current crop of teeny tiny processors have but in the absence of being
able to change the serial number of the RFID tag, it would be nice to have a
keypad which beeped at unknown tags and asked the person to enter their
callsign.  Surely we would never have a need for more than 100 RFID to
callsign mappings???

As for diode ORing two of them together.... do these spark fun modules
support flow control?  If one started to "talk" first, could it inhibit the
power on the other neighbor module?  What if you had 6 under a mat like Bob
suggested and if any one got a hit and started to send data, it would glitch
the power on the other 5 for say, two seconds.  That way only one would talk
at a time, right?  It also solves the in/out bound problem.... if the
inbound doormat triggers first, the outbound doormat sensor will be sleeping
by the time I step over it.
God help those who do not help themselves.
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