I'm trying to make my Si1000 (and my 433 Mhz 3dradio) development board transmit direct tones with the hope of being able to generate APRS data packets.
has anyone tried this? I'm trying to modify the TxTone example fro SiLaba and toggle one of the output ports at 1200 hz and route it to one of the GPIO pins that's setup for direct modulation. I do see the I/O pin toggling, however all I get is a constant carrier, no tone.
Has anyone else done this?
Greg K7RKT
Replies
Hi Greg,
The TxTone example sets the modulation type (MODULATION_MODE_CONTROL_2) to zero. That means it will do no modulation at all, and just produce a carrier. If you set it to OOK, FSK or GFSK you should get a tone as long as you are feeding it data correctly.
You may also find it easier to generate a sequence of 0xAA data inside the 8051 to create the tone, rather than bothering with an external source and the GPIO pins. You could use the FIFO, but with the packet handler disabled so you don't get all the packet encapsulation stuff.
I think that with a bit of work you could modify the SiK firmware that ships with the 3DR radios to completely support APRS over the serial port, including the tones and encoding/decoding the data.
I'm just in the process of getting my amateur foundation license now, and it might be fun to work on this together if you are interested. The 3DR radio, wired directly to a MTK or UBlox GPS, would make a small, cheap and quite nice APRS system. You wouldn't need an external microcontroller at all - I think it could all be done by the 8051.
btw, is 70cm APRS commonly used? I thought it was mostly on the 2m band?
Cheers, Tridge