Tim, Assuming you have some form of PCB to mount the triac on, make the output trace nice and wide and straight. Tthen cut two slots each side parallel with this output trace. Then wrap some very small thin, insulated wire perpendicular to the trace and using the two slots keep wrapping so you circle the output trace. This wound wire will pick mains hum and create a current from it, etc etc Then feed this into an op amp, convert the ac to dc (possibly before the op amp) and you'll have a pcb mounted current sensor. If the light is on current flows, if not none flows... Nice and simple and isolated from the mains. I've never tried this but I did think the idea up a while ago when I was stuck in traffic and wondered how my car's ECU knows when a bulb has blown. I'm also no expert on mains and current and such stuff, so it might not work at all but I thought it was an idea that might be worth sharing... Good luck... Cheers Kev/. ----- Original Message ----- From: "Tim ODriscoll" To: "Microcontroller discussion list - Public." Sent: Wednesday, December 14, 2005 11:32 PM Subject: Re: Re: [EE:] Detecting a blown lamp > On Wed, 2005-12-14 at 17:10 -0500, mchipguru@charter.net wrote: >> Any reason not to simply look for the light when the lamp is on? You know >> using an opto detector of some type. > > Unfortunately the light is outside on the wall illuminating the > driveway. My control box is inside the roof space, so putting in an ldr > would mean burying my hand up to the shoulder in rock wool insulation to > poke a couple of wires out, then I'd have to get up a ladder on the > outside of the house to mount it all.. So wiring in a new control box is > the nicer option in this instance :-) > > Cheers, > > Tim. > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist