Wednesday, September 09, 2009
PIC packet decoder
No big story here, at the same time I was looking for an APRS tracker found some schematic for an pic APRS decoder so why not build one also, I have no use for it at the moment since I make APRS on the TM-D700 but will probably incorporate it inside one of my vhf receivers or to take along on vacations.
I didn't compared side by side with the TM-D700 decoder but without optimization and using the ruber duck antenna inside house with the TH-F7 handie I think I got arround 20% of the packet's transmission. Probably with a good radio and some optimizasion the circuit will get 80% of it.
For testing I used Linux "minicom" software at 9600 8N1 without software or hardware flow (there's no flow, just receiving). The radio was with audio at mid volume seting.
Got the software from: http://www.ringolake.com/pic_proj/zcd/zcdmodem.html
Select "Simpler one chip ZCD decoder Both PC and GPS versions" (Simple decoder" button). Download de zip file, all the necessary files and schematic are there and also improvments for the circuit (I didn't do that).
For the pic programing I used the following command on a linux shell:
picprog --input-hexfile simpler_rx8.HEX --pic /dev/ttyS0 --burn
The pic programer hardware is at: http://speakyssb.blogspot.com/2009/08/pic-programing-for-aprs-tracker.html in this blog.
The PIC is an PIC16F628-04, I tried to use an 4Mhz ceramic filter as the oscillator but only the quartz crystal worked.