On Thu, 25 May 2000, David Huisman wrote:

> The idea of using 2 square waves that are low pass filtered and then summed
> is used often. You just need to adjust the gain of each signal relative to
> each other to get the required 2dB pre-emphasis on the high group tones, and
> the absolute level at the line less than maximum allowable (-5dBm I think
> ???) You need to check the levels according to the local telecom approval
> authority.

Check out Eric Smith's DTMF dialer:

http://www.brouhaha.com/~eric/pic/dtmf.html

Scott