On Wed, 10 Mar 2010 10:58:15 -0800 (PST), alan smith wrote: > Never a daft question! > > The PLL is an indication that the carrier is present, used for a different > purpo > se, while of course the FSK has the data packets. But I am open to other > choice > s on data transmissions but I do need some indication that the carrier is > presen > t. Afternoon Alan, The Goertzel algorithm should tell you whether the carrier is present and give an indication of the presence of any other frequencies of interest; as long as there are relatively few frequencies you're checking for (and aren't worried about retrieving phase information) then it's a lot cheaper than a full FFT. If you use the dsPIC to do your processing, you can remove the 567 and associated circuitry and just use one of the dsPIC pins as a 'detected' indicator to whatever the 567's 'lock' pin currently goes to. I seem to remember Wikipedia's article had a pseudo-implementation of a DTMF decoder, obviously showing how the algorithm can be used with multiple frequencies, but alas I am either mistaken or it has been removed: You might also want to take a look at some of Scott Dattalo's pages for some other (rather nifty) alternative decoding techniques: Although to be honest, with a dsPIC at your disposal I'd just stick to using Goertzel. Hope this helps. Regards, Pete Restall -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist