>> I doubt this is Bob's patent, but here is a link to a short circuit >> diagnostic tool 2006. >> >> http://www.patentgenius.com/image/7031132-2.html >> >> Colin Can't believe he got a patent for that. I am no hardware guru but a quick=20 glance tells me he might easily exceed the reverse breakdown voltage of the= =20 LED (given that the AC supply is probably 24V for HVAC use). -- Bob Ammerman RAm Systems --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .