TA-Trak - APRS modulator powered by a single AA-battery ======================================================= Jarkko Vääräniemi, OH8HQL, jarkko.vaaraniemi @! oulu.fi Pekka Pussinen, OH8HBG, pekka.pussinen @! oulu.fi This design is an APRS-modulator with switching mode power supply. All the parts are quite easily available for hobbyists (in Finland at least). The designs is compatible with TinyTrak 1 design of Byonics ltd. The software used by TA-Trak design is made by Rolf Bleher, DK7IN, which can handle static intervall APRS beaconing AND smart beaconing (ie. the intervalls between position packets varies when the speed or course of the station varies). TA-Trak uses Microchip PIC16F84A-microcontroller which has internal SRAM- and flash-memory. With this and a couple of external componens the interfaces for radio and GPS receiver have been implemented to single sided PCB. The interfaces has been filtered with capacitors to prevent RFI. The power of the design has been realized with Maxims MAX857 swithcing mode power supply chip. This part is obsolote, but it is available in local elecronics shop (SP-Elektroniikka, http://www.spelektroniikka.fi/) in Oulu. This chip makes the use of the TA-Trak possible with only one battery. The power design could be removed and the design could be powered with regulated +5V power supply; if voltage more than 3,9 V is used, one must also replace zener-diodes in input with 5,1V versions. To build this TA-Trak, manufacture PCB from the picture and gather parts mentioned in BOM-file (BOM-file have a column for page reference in SP-Elektroniikkas catalog 2004). Build the whole thing up, and you can program the chip with in-circuit programming cable (known as LudiPipo or JDM). Programming could be done (for example) with NT Pic Programmer (Windows) or PonyProg (Windows or Linux) programming software. After programming, reset the device; LED should blink three times. The parameters to the TA-Trak could be programmed with original configuration software of the TinyTrak (by Byonics ltd.) or PERL-based configuration tool by DK7IN. More about the design and more accurate instructions about programming the chip is available in Finnish document. Try to understand... If you want to publish the article, contact the authors of the project.