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[aprssig] APRS RFID reader?

Jason Rausch jason at ke4nyv.com
Mon Feb 1 21:32:08 UTC 2010


I played around with this for a while.  I have several of these units:

http://www.sparkfun.com/commerce/product_info.php?products_id=8419

They are cheap (~$30), easy to interface and work very well.  Simple 9600 baud RS232 interface.  I had a simple logging program I wrote in VB6 to catch the strings and log them, but I wanted to move forward with a PIC-based interface to feed the strings to a TNC.

The read range is short, but I think that is good for the same RF noise mentioned before.  Just have it at major doorways and have people swipe their card when they come in.

Jason KE4NYV
RPC Electronics, LLC
www.rpc-electronics.com


--- On Mon, 2/1/10, Patrick <winston at winston1.net> wrote:

> From: Patrick <winston at winston1.net>
> Subject: Re: [aprssig] APRS RFID reader?
> To: bruninga at usna.edu, "TAPR APRS Mailing List" <aprssig at tapr.org>
> Date: Monday, February 1, 2010, 4:14 PM
> The issue is you run into is with the
> magnetic field generated.  Passive rfid tags are being
> powered by the magnetic inductance of the field they are
> moved through, so you run out of power the further away from
> the reader you are.  This is sorta on purpose because
> they also typically do not contain collision handling
> ability so you can't have more then one tag in the read area
> at the same time.
> 
> There are commercial grade reader / chip systems which
> don't have the same constraints, but the costs go up
> accordingly.
> 
> That said you really don't need more range.. Instead of
> putting the chips on their hats, put them on their
> feet..  if people are walking through the door with
> both their feet 10" off the floor, then they are purposely
> making themselves unreadable.  This is the way most
> RFID based timing systems work for distance races.
> 
> p
> 
> Quoting Robert Bruninga <bruninga at usna.edu>:
> 
> > 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
> > 
> > 
> > _______________________________________________
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> > aprssig at tapr.org
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> > 
> 
> 
> 
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