> ----/\/\/\/\------|----- > 3.3K | > = .47uF > | > GND > > If I read the stuff I found on passive LPF design right, that should give > me a 102Hz cutoff, correct? Yup, 102.6 Hz, +-20% for the component . > The PIC (I'm using a 12CE674 for development, but will switch to 12C671 > for real) looks for a low pulse on its input, which *should* be the peak > of the cycle of the string's fundamental frequency. We start Timer 0 > running and wait for the next pulse, indicating the next cycle. If Timer > 0 overflows, we increment a high-byte counter, ending up with a 16 bit > counter for the cycle time. We accumulate 32 of these samples, then > divide by 32 for an average (crude, yes, I know - I may work on that). I'm not sure I follow exactly what you are saying, but you can certainly use timer 0 with pulse interrupts to measure the period. Using a CCP module in capture mode will make your life a lot simpler and will improve accuracy because you don't have to worry about being in a timer 0 overflow interrupt when a pulse comes in. I've done a bunch of frequency/period measuring projects, and CCP modules are real handy for that. ***************************************************************** Embed Inc, embedded system specialists in Littleton Massachusetts (978) 742-9014, http://www.embedinc.com -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body