[aprssig] APRS RFID apps? (hardware)

Bob Bruninga bruninga at usna.edu
Wed Feb 10 17:18:29 CST 2010

RFID HotSpot Hardware:

Here are some possible off-the-shelf TRACKERs I see that might be able to do this APRS HotSpot RFID reader for under $130 with just a software upgrade.  I'd welcome other possibilities:

1) Buy the RFID Reader:

And combine it with a TRACKER (with transmiter) assuming the authors are willing to write new code for the tracker to recognize the RFID serial string instead of a GPS. 

2) Either BYONICS.COM:  Get a Microtracker set on 144.800

3) OR ArgentData.com:  Combine a OpenTracker+SMT

with a SRBMX146 transmitter tuned to 144.800

I can envision a standard sized rubber floor mat with the APRS Hot Spot in the center, and the embedded card reader, tracker, flat Polaroid battery, and embedded 2 meter dipole making it an all-in-one laydown device.

Though I'm not sure how to make the tracker and reader chips survive being stepped on without making them bulky enough that then becomes a TRIP hazard.  BIG issue...  One way is to make them BIG along one edge and then insist that they can only be set down right-justified against the RIGHT door jamb.  Makes sense in common door sizes but is a stretch for walkers when set in the wide door of the Hara Arena.  

The alternative of running a wire pair to the mat coil can equally be a trip hazard, OR the bigger problem is that the tuning of the HotSpot coil antenna will be too dependent on exact placement of the mat and the wire and the tracker module a few feet away that performance will suffer.  Or it becomes a set-up headache.

This mechanical design is going to be the hard part.  Just looking at the pictures, it appears that maybe the SMT tracker and the SMT tiny transmitter from ARGENT might be able to be low profile enough to  be integrated into the mat itself.

I checked on flat-pack Polaroid batteries and apparently they are not made anymore.  Surely there is another flat-battery somewhere?



The following is a possible design of an innexpensive ham radio APRS RFID system for application in large venues such as the Dayton Hamvention to keep track of walking operators.  Ten Inch round RFID yellow/red hot spots are placed in each doorway or special location.  APRS participants wear a $2 RFID card in their shoe.  When they cross an APRS hot spot, the hot-spot reader sends the RFID to a centralized on-site PC that associates that RFID to a callsign and then generates an APRS packet on the APRS network showing that person at that location. 

APRS RFID READER:  A $25 RFID reader is the only new hardware required. 

The 9600 baud serial output from this device is connected to a PC for one-door applications or, for large multi-door locations, to a typical APRS "tracker" which has special parsing code to convert the RFID number into a special AX.25 short-range packet (preferably on a separate frequency from he national APRS channel).  The RFID packet format is: 


Where the SSID of the hotspot reader (I) contains 4 bits of additional info such as direction, speed, etc. The initial "RF" will make this an ALTNET (non-APRS) packet, and the dddd:dddddd is the 10 byte HEX ASCII RFID code.  In addition, a SPOTID position packet is sent out once every 10 minutes direct so that the SPOTID itself shows up on the map.

The central processor receives the above RIFID from a given SPOTID and then matches the RFID to a callsign and generates the following standard APRS position packet for the local network (and/or APRS-IS): 

 Packet:  !DDMM.mmNRDDDMM.mmWAdddddddddd free text 

Where CALL-SS is the callsign associated with that card. The APRS SYMBOL is "R and A". The RFID number is included in the first 10 bytes of the packet (which happens to show up well on most mobile and handheld APRS displays.  The Free text is associated with that hotspot.  Such as "Entering HARA", Leaving HARA, or ARRL Booth, or KENWOOD Booth etc. 

The position of someone passing over the RFID HotSpot is built by incrementing .01 Latitude from an origin on the map associated with that RFID HotSpot.  This way, everyone that crosses that hot spot will appear in a neat vertical table on the map. 

The users CALLSIGN and SSID is associated with each of his RFID tags.  There are two schools of thought depending on your own use of your tags.  Either make them all have your CALL-7 SSID to show you were walking, or make them the same as your car CALL-9 so that when you arrive or leave a place, your CALL-9 goes with you and is not left at the HotSpot.

CALLSIGN ASSOCIATION:  The initial RFID number to callsign association is made at the central processor or point-of-sale of the RFID card -OR- anywhere else that a keyboard or keypad is attached.  Or even send it in an APRS packet from any other radio.  It doesnt matter, since EVERY such association will generate the above APRS packet and from that , ALL systems locally or globally can collect these associations from the APRS-IS.  Also clubs with large numbers of card holders can submit RFID files to pre-load the APRS-IS system.  Or anyone with any APRS system can manually prepare the above packet and send it once from their HT or Mobile.  From then on, the association is made. 

RFID READER SERIAL DATA:  The RAW output from the RFID reader is at 9600 baud and can be read on any serial port.  The format is as follows: 

 Where S is STX (02h) 
 DDDDDDDDDD are 5 bytes in 10 ASCII HEX characters 
 KK is a HEX checksum 

Special code in a "tracker" type pic processor can read this and generate the local RFID Reader packet which is sent on a separate frequency to the central processor.  Or for one-door applications, direct into a local PC connected to the APRS system (RF or Internet). 

RFID Tag (125 KHz): The Credit card sized RFID's are under $2 depending on quantity.  They are available from: 


Anything I missed? 
Bob, WB4APR 

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