Efficient AVR DTMF Decoding
Copyright (c) 2015, Paul Stoffregen
I originally developed this 8 bit AVR-based DTMF decoding code in 2009 for a special one-off project. More recently, I created a superior implementation for 32 bit ARM Cortex-M4 in the Teensy Audio Library.
http://www.pjrc.com/teensy/td_libs_Audio.html
I highly recommend using the 32 bit version for new projects. However, this old 8 bit code may still be useful for some projects. If you use this code, I only ask that you preserve this info and links to the newer library.
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice, development history, 32 bit audio library links, and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.