POCSAG paging project moves forward

There has been a long-going project to do POCSAG paging on amateur bands. Some time ago at Kauniainen Radio Club we talked about that again and decided to give it a try, as we coul determine a handful of services for such system. DX spots could be delivered to either group message or individual customized spots, APRS messages could be delivered to pagers (this is also being processed and projected by Bob Bruniga), tropo condition alerts, club notifications locally etc.

I have purchased a small batch of programmable pagers some years ago and it was time to dig them out, we had started to play with a AVR POCSAG encoder by N2RVQ, but had some trouble compiling the code to a compatible ATTINY-processor. Last night we eventually got things running after finding out that some pull-up resistors were missing from the proto board and the main loop of the code did not run because of that...

The picture shows the test TX (Motorola GM340) and the AVR proto board which houses the AVR processor to send out the POCSAG page controlled from a RS232-line.

I hope to update you with a working page video or other proof of functionality next week!


Anonymous said…
Dear friend please tell me what compiler to use the AVR source.
Thank you!
Anonymous said…
I just got my own encoder up and running using a AVR-P20 prototype board.

Hardware-wise, I only had to add 3 wires at first to get it going, TX to pin 2 on the ATTINY, RX to pin 3 and CTS to pin 8. (NB: TX,RX marked on the AVR-P20 are the reverse of how they are referenced on the N2RVQ schematic)

Codewise, I installed AVR Studio 4, started with AVR POCSAG rev1.1 by N2RVQ and applied the ATTINY2313 patch by OH3HZB. I commented out the TX_INHIBIT, INP_1 and INP_2 related code as I'm not using it and hadn't soldered in pull-up resistors and I moved the LED function to PORTB-7 as that is where an LED is on the AVR-P20.

Finally, when programming the chip, you must set the fuses correctly. Select external crystal 3-8MHz for the clock option and turn off the clock divide by 8 fuse.

Subsequently, I added a comparator to the POSAG_OUT line. The comparator V+ and V- are connected to pins 2 and 6 of the MAX232 to get +/-9V giving a balanced output that I use to drive a kit built VHF transmitter (Vectronics VEC-1202K bought from Maplin)

Great to see it all finally working -DP