At 11:27 PM 3/27/2010, MCH wrote: >567s are notoriously unstable. Actually, my experience is quite the opposite. I have several designs that use 25HZ, 35Hz, 400Hz, 1KHz, 8KHz, 20KHz and 24KHz signaling and they have apparently all been reliable for more than 20 years. Some units for more than 30 years. I occasionally will get one of the units in for repair or just checking out and one of the things we check is the center frequency on the 567 tone decoders. They are always bang on the money. I think the choice of capacitor and resistor & trimmer have far more to do with the stability than the chip itself. dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist