Since I can't post a new thread until I've replied 25 times, I guess I'll have to piggyback on this thread.
First off, I don't have a real grounding in electronics design. I can put a circuit together from a schematic but when things go wrong it doesn't take much for me to get stuck.
So, having said that...
I *thought* I could use the 5v output of an Arduino to switch a 1W luxeon on by using a 2803A. The Arduino can only handle 40ma on output so driving a 350ma LED from that isn't a good idea.
To test the idea I connected a 2803 pin 9 to ground, pin 10 to +5v and pin 1 to +5v to test the trigger. What I get on pin 18 isn't 5v. I get 0.5v. Disconnect pin 1 and the output drops to 0.
What basic element am I missing?