[aprssig] APRS RFID apps? (Hot Spots design!)

Bob Bruninga bruninga at usna.edu
Wed Feb 10 13:11:33 CST 2010

OK, here is a draft concept for APRS RFID:


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 applicaitons or, for large multi-door locations to a typical APRS "tracker" which has special parsing code to convert the RFID number into a speical 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) can contains 4 bits of additional info such as direction, speed, etc. The initial "RF" will make this an ALTNET (non-APRS) packet, and the DDDDD-D:DDDD is the 10 byte HEX ASCII RFID code.

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):


Where the SSID is always -7 from any card operated under that callsign. Where a special unique RFID SYMBOL is used, and the RFID number is included in the first 10 bytes of the packet.  The Free text is associated with that hotspot.  Such as "Entering HARA", Leaving HARA, or ARRL Booth, or KENWOOD Booth etc.

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

This CALL-7 is used for ALL RFID tags that might be owned by that ham CALL so that no mater what shoes he is wearing or how he is reporting his position, they will all overwrite each other so that only the most recent one ever exists in APRS.

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.  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 o 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 
C is CR and L is LF and E is ETX. 

Special code in a "tracker" type pic processor reads this and generates 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 from $2 down to $1.50 depending on quantity.  They are available from:


Anything I missed?

More information about the aprssig mailing list