-----Original Message----- From: Mark G. Forbes >Something I've done which works really well is this: > >If I need to sink a medium-current sort of load to ground, >I use a ZTX849 NPN transistor (Zetex, great part!) and >put a series LED in the connection between the PIC pin >and the base of the transistor. This seems to work >adequately for most kinds of loads, though you'd probably >want a 10K base/emitter resistor to handle leakage currents >for very light loads. That should work well, as long as the output is a voltage source, plus you get the added on/off indicator. Remember that a transistor, unlike a logic gate is a current device, input voltage dosen't mean a hoot except that it causes current to flow. Although prototyping isn't particularly cost-sensitive, it's a very good idea to proto what you will produce. Otherwise come production time, you can get the "boobytrap suprise". Still, I've seen times when 10 protos worked flawlessly, and production had 50% dead. That one was a clear violation of the spec, and the justification was that "all the protos work".. Hobbyists can get away with a lot that wouldn't fly in production, but I think that's where a lot of them get in trouble, when they accurately build someone's "cool device" and include the other fellow's mistakes, which don't work with the batch of parts they got. Hobbyist magazines are full of things that Horowitz and Hill wouold have put in the "bad ideas" section! It's always a good idea to walk back through the specs and make sure you're doing it right. Zetex parts are wonderful, I've used that 849 in a couple of devices, no problems ever. Their ZVN4206 is a nice little FET too. TO-92, low RDSon, but beware of inductive loads. It goes into avalance so fast that a 350 mhz DSO can't see it!