On Sun, 29 Jul 2001, Joe Denehan wrote: > > If probe A is connected across a door sensor to check for continuity then > just connecting the non-grounded probe of B will > > cause if to think there is continuity. > It's crazy to use n batteries for n or n/2 measuring points. What you need is an AND logic to see if both door switches are closed. You don't need only one power supply for this and not two ( one +5 to +12V for 100 doors or more...) If you've using radio transmision to a central unit and independent modules at every door than maybe only 3 V... Vasile -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu