Consider also doing hydraulic. The plates won't have to move as much vs pneumatic to sense a valid input (in fact the user may not notice the rock moving at all), and hydraulic will be less susceptible to crushed lines and water infiltration (as pressures should be similar). It should also be fairly cheap overall, the components are ubiquitous. Hydraulic oil in not generally conductive, so lightning strikes would pose less of an issue. You could sell them on changing one to a hydraulic unit with a local pressure sensor, and if it works ok over time, swap the others out and extend the lines for lightning protection, as well as central maintenance. If well put together, the hydraulic rams and tubes should never need maintenance. Consider using cheap brake cylinders for this end, since the seals are included. If a pressure sensor needs to be replaced, it's done in one box. You could even double up and have two sensors per line for added redundancy. -Adam On 5/24/07, Bob Blick wrote: > Just wait for the new immigration bill to pass, then > hire guest workers to observe the foot traffic and > push buttons to activate the fountains. > > Seriously though, the reliability of most methods is > more dependent on the underground electrical > connections than on the method itself. Direct your > focus to that area and find out what is causing the > failures. > > Cheerful regards, > > Bob > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Moving in southeast Michigan? Buy my house: http://ubasics.com/house/ Interested in electronics? Check out the projects at http://ubasics.com Building your own house? Check out http://ubasics.com/home/ -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist