The point made here is that the top contact can only pull the PIC pin between 0.5 Vdd (when open - ie: the 'resting' state due to the R-R voltage divider) and 1.0Vdd (when closed). Similar logic results in the same thinking for the lower contact - 0 to 0.5 Vdd If the thresholds of the Schmitt are guaranteed to be > 0.8Vdd and < 0.2Vdd then this will debounce quite nicely, with 0.3Vdd margin. Still, I don't like the complexity -- I'd certainly just use a single R to Vdd and have the switch pull the pin low - then use software debouncing. But ... if I had to be absolutely, positively sure that the switch couldn't bounce (like if it controlled power in a nuclear reactor or some such) then I might be more comfortable with this hardware solution. Bob Ammerman RAm Systems ----- Original Message ----- From: "Bob Barr" To: Sent: Tuesday, May 21, 2002 9:29 AM Subject: Re: [OT]: There are more things in heaven and earth, Horatio, On Tue, 21 May 2002 21:49:47 +1200, Jinx wrote: >> Bouncing at bottom contact will produce 0 - 0.5 Vdd noise. >> Bouncing at top contact will produce 0.5 - 1 Vdd noise. > >Exsqueeze me ? > >Noise coming from the switch will be 0-5V regardless. It >must be as a consequence of the contacts touching or >otherwise the switch wouldn't be a switch, unless it came >from the Pisspoor Switch Co catalogue Isn't that a division of DirtCheap Enterprises? :=) A real favorite of purchasing managers worldwide. Regards, Bob -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu