I've been wanting to set up a lamp to be tap on/off and so have been messing around in darlington pairs. Following http://www.instructables.com/id/Breadboarding-The-Darlington-Pair/?ALLSTEPS I made a curcuit running off a 9v battery connected through a darlington pair made of two 3904 transistors and an LED (with a resistor of course).
When I touch the wire connected to the first base the LED does light up but only just barely and . I believe it should look just as bright (or nearly so) as when connected with just the resistor. Is there a problem with using the 3904 for doing this? Or am I missing something else?
My setup is exactly that with is described in the tutorial I linked to. Unless I have it hooked up wrong, in which case a schematic won't be very helpful. I have work this morning but I'll try and put up my own schematic this afternoon.
Not a very robust design. Very sensitive to selection of transistors. No current limiting resistors in his circuit if used on 5V, risky. Doesn't define what he means by "LED capable of handling 5V".
I am using the 9V setup which does have a limiting resistor. Why is this type of design so sensitive to transistor selection, and what setup would be less so?
