> I would like to write some code to make DTMF tones.  However I can't
figure
> out even how to produce noise.  I have to hook up a capaciter or
> something...  I can't find any sample circuits and then even if I did.
What
> do I send?  A pulse of some sort?


This is one that might be better done in an external chip.

You need to produce two tones, that have no harmonic relationship, with
fairly low harmonic content or distortion.   If all you want is simething
that works  most of the time, then you can get there with a resistive ladder
D/A and following lowpass filter. If you want to get part 68 (or foreign
telco) approval, then the external chip, or micro with onboard dedicated
hardware is the easy way to go. Cost, about $1.  My favorite is the
EFG71891, an 8 pin DIP that needs power, three proc pins (can share one) and
a crystal and resistor.

Doing it externally also means more CPU left for doing other things.

The specs for the tones are widely available, and are in the EFG datasheet.
Email me if you want it, and I'll send it off the list.