> >> Any thougts about MC14490 (Contact Bounce Eliminator)? It's around >> 3.5 USD a piece (on their web site): > > If you were thinking of a chip solution, a cheaper option might > be a monostable made from NOR (eg 4001, 7402) gates. Using > a 4001 with 1M for R and 100nF for C you might expect a > period of around 50ms. The first L-H transition sets the o/p high > and any further triggers (ie noise) are ignored until the timing > period is over. Unfortunately, switches also make noise when > they release too, so an RC filter on the i/p would help avoid > re-triggering on release. You could filter the signal ad nauseum > with both s/w and h/w (even a couple of transistors arranged as > a Schmitt Trigger) but could still be caught out by a rubbish > switch > -- For hardware debounce, I like RC filters driving a schmitt trigger. Since the interrupt inputs are, as I recall, schmitt trigger inputs, you could have a pull-up resistor on the switch (or use a SPDT to switch the line between +5 and ground), then an R to the pin with a C to ground at the pin. The edge becomes slow moving so bounce has a smaller voltage change across the capacitor than the hysteresis of the input. Harold -- FCC Rules Updated Daily at http://www.hallikainen.com -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist