[First post here, please make allowances..] I want to use a triac as a solid-state SPST switch for a normal 120VAC receptacle. The on/off state will be controlled by a low-voltage DC circuit through an opto-isolation MOC3020. http://ken.coar.org/images/opto-triac.png [Broken] So far so good. However, I want to be able to detect faults in either the diac or the triac -- faults being defined as: the diac conducting when TP1 is low, or failing to conduct when TP1 is high; and/or the triac conducting when the diac isn't (VTP2 = 0), or failing to conduct when the diac is. I'm basically a low-voltage DC kinda guy, so I'm unclear on how to detect the lack of signal at TP2 and TP3 in general, or at TP3 when nothing's plugged into J1 in particular. Any/all pointers appreciated.. Thanks!