Spehro Pefhany wrote: > Quoting Dr Skip : > > >> I've got a Sunbeam heating pad that seems to be pic controlled with >> a triac for >> controlling the load and no opto or anything there. It's all just silicon >> anyway. Build it to keep fingers out of everything (case covers all >> - plastic). >> If the barrier fails and it destroys part of the circuit, which would be >> replaced anyway in a failure, then do it. If you're driving it with >> an external >> device, or an expensive device, where you wouldn't want to destroy it, then >> opto it and lay it out appropriately. >> > > It goes without saying that using an emulator or a programmer on a "live" > circuit of that kind without proper isolation will probably spell the end of > the board, the programmer/emulator, and the computer it is connected to. > > Even when there is isolation built in you need to be double careful and > vigilant as you're only a bridge or a stray wire away from disaster. It's > best to use both optos and an isolation transformer for development. When > everything is working you can reduce it down. And even so, be VERY careful, > keep everything super neat, all wires fastened down, all cables dealt with > neatly, no 'haywired' mods, and keep metal objects (such as bench tops) > well away from the circuit. Don't poke around with a test probe at all-- > shut the power off and FIRMLY attach test leads. > > Also, if you're testing fuses, etc, keep in mind that the triac gate does not > always behave as a passive input- it can source and sink a fair bit of current > at a low voltage even if the triac itself is not damaged. > > > > >>> Well-spoken, Spehro. Be careful with line-operated designs. When I design one I use an ISOLATION TRANSFORMER. Note carefully: this provides 120VAC for the circuitry but there is NO physical connection between the raw AC input and the secondary. Nothing that I am aware of replaces this setup. --Bob A -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist