A 'Mint Idea' APRS Tracker

In a perfect world, I would have a Kenwood TM-D700A dual-band mobile transceiver with integrated packet data TNC and a Garmin V Street Pilot GPS unit custom mounted in the console of a Ferrari 575M.  In the real world, and in the true spirit of Amateur Radio do-it-yourself experimenting, I settled for a less elaborate APRS tracker mounted in a Ford Explorer. If you are content with simply beaconing your position to the Automated Position Reporting System network, a portable or mobile APRS tracker does not have to be an expensive proposition. The project described here was built on a rainy weekend for a total cost of under $100.

TinyTrak-II,  www.byonics.com, is a GPS position encoder which, when connected to a GPS and a radio, will transmit its location at an adjustable rate. TinyTrak-II is a construction project providing an inexpensive way to build a mobile tracker without the need for a full TNC.  TinyTrak-II is personalized for your call sign by connecting to a computer's serial port and running a simple configuration tool which allows setting of all user options. Construction consists of a hand-full of supplied components that must be populated on the PC card and soldered. It can be completed in under an hour. Mounting in a suitable enclosure, connection to a radio transceiver, configuration and testing require additional planning and time. There is an on-board mounted +5V regulator which allows powering from a variety of external sources. I mounted the unit in a tin Altoids Mints box to provide some measure of RF shielding and added a DB-9 connector wired as a Kantronics KPC-3 compatible radio port. This allows easy interfacing to a transceiver using common Kantronics data cables. This is consistent with the interfacing scheme I've used for other digital data radio projects such as a PSK-31/packet sound card interface and commercial TNCs. 

The 12-channel OEM GPS board is manufactured by Talon Technology. The one I used was 'hacked' from a Rand McNally Streetfinder GPS for Palm III.  I removed the GPS board and passive antenna disk from the molded plastic case designed to attach to the Palm III PDA. Then, I separated the Talon OEM GPS board from the Palm III data port interface and battery charging PC board to which it was mated. Two minor modifications are required to make the GPS self-start and run from an external power supply. Complete instructions on how to 'hack' this unit can be found at  www.radiohound.com.  With a little experimenting I've found that the board will operate satisfactorily from a supply voltage of +4.5V to +15V DC. This, like the TinyTrak-II, allows for a wide range of power options for fixed, mobile and portable operation. 

I mounted the GPS board and DB-9 connector in a tin Altoid Mints box. This provides good RF shielding and antenna isolation. The GPS antenna is mounted to the Altoid box top lid. The DB-9 connector is used to connect the GPS to a computer serial port. For the time being, until I come up with a permanent placement, the stacked boxes sit on the dash of the SUV with the status LEDs positioned so I can monitor operation and channel activity. The receiver is surprisingly sensitive and the disk-shaped ‘patch’ antenna has a wide angle of view. When the RS-232 level GPS receiver output is monitored from a notebook computer, it is not uncommon for it to lock on eight or nine satellites. Four satellites are required for true 3-D positioning. 

I used a PS-2 mouse/keyboard extension cable to connect the GPS to the TinyTrak-II. I cut each connector end off leaving about 4” to 6” of cable attached, using the male connector on the GPS side and female connector on the TinyTrak-II side. When connected, ground and +12V power is supplied to the GPS from the TinyTrak-II box and GPS data output is supplied to the TinyTrak-II from the GPS box. The two boxes are attached to each other using Velcro strips.

When the boxes are separated, I can insert the DB-9 connector on the GPS box directly into the serial port of my notebook computer and plug the male PS-2 connector into the PS-2/mouse connector on the notebook to draw +5V power for the GPS board. This allows use of the GPS with UI-View, Rand McNally Streetfinder, DeLorme Street Atlas USA or other APRS/GPS/mapping software running on the notebook computer. Alternately, I can leave the GPS box attached to the TinyTrak-II box and connect a short serial cable from the GPS to the notebook computer. This allows GPS position data to be routed to both the notebook computer for real-time navigation and to the TinyTrak-II which beacons my exact position to the APRS network. My son likes to play navigator in the shotgun seat of the SUV while I'm driving, calling out intersections and points of interest from the mapping software on the notebook computer. 

These links will give you more info on the GPS board.

Talon Technology: http://www.talon.co.nz/

NAVMAN review: http://www.gpsnuts.com/myGPS/GPS/Hardware reviews/RandMcNally/rand_mcnally_gps.htm

The Streetfinder GPS for Palm III units are now discontinued by Rand McNally, but are regularly featured on numerous e-Bay auctions.  Average winning bid prices range from $20 - $40 US.

     TinyTrak-II Design

TinyTrak-II Configuration Program

Recommended TinyTrak-II Settings

Click Here to see my DigiTraker APRS project. 

ã2002, N2IXD rev.050615

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