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[aprssig] APRS RFID reader?

Robert Bruninga bruninga at usna.edu
Mon Feb 1 23:41:43 UTC 2010


> The system I have uses dual frequency 
> tags made by IPICO, has two read 
> antennas each of which is 1 x 2m, and 
> reads a bubble around 20cm beyond 
> and above the mat. 

Wow, that's big.  The reader I was looking at suggests a 6"
coil.  SO that is why I was thinking a door mat would need
several of these 6" coils widely spaced so that they did not
interfere with each other, but placed so that a foot passes
through at least one of their fields.  Data sheet for the $30
reader:
http://www.sparkfun.com/datasheets/Sensors/ID-12-Datasheet.pdf

> Diode-oring the readers is unlikely to be 
> reliable because you will run into situations 
> when the tag will be in between to readers 
> and they will both be reading...

I'm assuming the independent sensors will have to be widely
spaced to both improve the capture volume and to minimize
interference.  SO by definition, no two can read at the same
time..

Bob, WB4APR
> 
> Robert Bruninga wrote:
> >> The setup I have for race results is self contained 
> >> with ethernet and usb to computer.. I find around 
> >> 90% read  success of runners passing through the 
> >> read area.
> >>     
> >
> > What is that read area?  With say a reliable 6 inch read
range,
> > I would think that for a 3 foot wide door mat, one would
need
> > about 6 separate readers probably spaced a foot apart in two
> > rows.  Each of these I assume has its own "reader"
electronics
> > which really drives up the cost from one $30 reader, to 6.
I
> > wonder if we can just diode-OR the 9600 baud outputs.  Seems
> > only ONE would make a detection at the same instant.
Especially
> > if we spread them out in the direciton of the walker...
> >
> > I have updated my web page www.aprs.org/aprs-rfid.html to
show
> > the new APRS boots idea...
> >
> > Bob, WB4APR
> >   
> >>> Robert Bruninga wrote:
> >>>       
> >>>> I still think APRS-RFID... Is a next thing for APRS
> >>>> experimenting
> >>>>
> >>>> Every ham hat could have a $2 chip in it.
> >>>>
> >>>> Then we can tell who enters the clubhouse or EOC... (it
> >>>>         
> > gets
> >   
> >>>> converted to APRS...)
> >>>> See http://www.aprs.org/aprs-rfid.html
> >>>>
> >>>> Problem is, the maximum range reader I can find is only
> >>>>         
> > good for
> >   
> >>>> 10 inches max and it costs about $24:
> >>>>
> >>>>         
> >
http://www.sparkfun.com/datasheets/Sensors/ID-12-Datasheet.pdf
> >   
> >>>> It has provisions for a  wind your own antenna but still
> >>>>         
> > can
> >   
> >>>> only get to about 10 " (25cm).  But since hams are RF
> >>>> experimenters, it would seem that we could improve on
this.
> >>>>         
> > One
> >   
> >>>> sentence in the limited docs says that there has to be
> >>>>         
> > enough
> >   
> >>>> energy to activate the chip.  This implies to me that the
> >>>>         
> > limit
> >   
> >>>> is on the energy transmitted to the chip, not necessarily
> >>>>         
> > the
> >   
> >>>> read range.  Frequency is 125 KHz.
> >>>>
> >>>> To get reliable coverage for people walking through a
door,
> >>>>         
> > I
> >   
> >>>> think we need about 48" range...
> >>>>
> >>>> Does anyone want to fill us in on the details?  I assume
a
> >>>>         
> > 125
> >   
> >>>> KHz carrier in the antenna coil provides the energy for
the
> >>>>         
> > RFID
> >   
> >>>> chip (this can be scaled up... Just needs more power)...
> >>>>         
> > But
> >   
> >>>> then I guess it has some off cycles so the chip can send
> >>>>         
> > back
> >   
> >>>> the 32 bit code?
> >>>>
> >>>> Bob, WB4APR
> >>>>
> >>>>
> >>>> _______________________________________________
> >>>> aprssig mailing list
> >>>> aprssig at tapr.org
> >>>> https://www.tapr.org/cgi-bin/mailman/listinfo/aprssig
> >>>>
> >>>>
> >>>>         
> >>> _______________________________________________
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> >>>
> >>>       
> >>
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> >>
> >>     
> >
> >
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> >   
> 




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