Use a set of BiQuads tuned to the appropriate frequencies. It would be nice to have an envelope follower unit generator (I'll write this shortly) which you could monitor the average energy of the output of each BiQuad. Finding the row and column would tell you the appropriate key (number or symbol). PRC On Mon, 2 Jan 2006, Lewis Liu wrote:

Dear all, I hope to analysis the frequency of DTMF tone from input (adc). Could you have any idea or suggestion or reference for this in chuck programming?? Thanks a lot!! Best Regards Lewis

Best Regards Lewis