[aprssig] APRS RFID apps? (in/out-1 reader)

Bob Bruninga bruninga at usna.edu
Wed Feb 10 22:55:32 CST 2010

In/Out with same HotSpot!

And I just figured out how we can do IN and OUT with just one HotSpot reader!  User training!  Afterall, this is an active participant evolution.  Here's how...

The readers spit out continuous numbers as long as the RFID is in the read range.  TADA!

If you are going IN, you aim to SWING your right foot over the Hot spot.  If you are going OUT, you STEP on the Hot Spot.
Indoor and fixed spot hot-spots such as at the APRS booth would not be progrmmed to distinguish the diferenec, but those at the doors do.  The algorithm is simple.

If number of dupes of an RFID tag are less than X, then the guy is going in.  If the dupes are greater than Y then he "stepped out"...  Only one report is made for that tag on the local RFID frqeuency.

> why 144.800?  

Because some trackers are designed with fixed frequencies.  144.39 (USA) and 144.800 (Europe).  So we can use the 144.800 trackers for this application and they are cheaper than the freqnecy agile ones...  The Argent Data systems SMT transmitter is frequency agile.  

>why not 70cm or high end 2m band?

UHF would be preferred, but I dont know of any off-the-shelf low cost tracker with integrated UHF transmitters...


>On Feb 10, 2010, at 6:18 PM, "Bob Bruninga " <bruninga at usna.edu> wrote:
>> 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:
>> http://www.sparkfun.com/commerce/product_info.php?products_id=8709
>> 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
>> http://byonics.com/microtrak/mt300.php
>> 3) OR ArgentData.com:  Combine a OpenTracker+SMT
>> https://www.argentdata.com/catalog/product_info.php?cPath=22&products_id=64
>> with a SRBMX146 transmitter tuned to 144.800
>> https://www.argentdata.com/catalog/product_info.php?cPath=22&products_id=64
>> 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?
>> Bob, WB4APR
>> ------------------------
>> 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.
>> http://www.sparkfun.com/commerce/product_info.php?products_id=8709
>> 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:
>> SPOTID-I>RFdddd:dddddd
>> 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):
>> Header:  CALL-SS>APRFID,WIDE2-2:
>> 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
>> CLE is CR/LF/ETX.
>> 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:
>> http://www.sparkfun.com/commerce/product_info.php?products_id=8310
>> Anything I missed?
>> Bob, WB4APR
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