[McHUG] Arduino Packet Transmission Working!

[n3sb at qis.net]

I finally found and fixed the last bug in my packet code. I can now send UI
packets from an Arduino!

This is a fairly huge step. It means that I've got the interrupt based frequency
generation right, the bit timing right, the data formatting right, the checksum
generation right, and the bit stuffing right, among other things.

The packet data frames I can now generate are Unnumbered Information (UI)
frames, which are fine for APRS purposes. It would be easy to add some
additional code to send telemetry info, like what the PICetSAT module does
today. The program only takes 4.2 kbytes right now, so there's 10 kbytes left
on a base Arduino for adding custom functionality.

There's another layer of protocol that still has to be worked out to connect to
another station (or allow another station to connect) and exchange data. 

I'll get that layer worked out after I get all the Packet Receive stuff working.
Receiving will be a bit easier to figure out now that I have a better
understanding of all the low-level formatting. 

I'll post the source code after getting it cleaned up and properly commented. 

On the hardware side, six resistors and a capacitor are needed to make a simple
D/A converter to generate reasonably clean sinewaves. An additional resistor
and an NPN transistor will have to be added (I haven't done this yet) to key a
transmitter. 

More to come. I'll have some time to continue this project over the holiday
break.

73; Steve, N3SB