While it is fairly easy to write DTMF dialer code that uses a D/A converter, for minimum parts count I wanted to use pulse width modulation instead. At the time the code was written, Microchip was only rating the PIC16C54 for operation at a maximum of 8 MHz. I needed at least a 20 KHz sample rate, so this was very challenging.

The code for this project is available under the terms of the Free Software Foundation's General Public License, Version 2. If you agree to the terms of the license, you may download a copy in either tar or zip format:

David Thomas has also written a DTMF encoder program for the PIC. His is much simpler as it doesn't use PWM and it only generates square waves.

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Last updated October 12, 1995

Copyright 1995 Eric Smith