need help with right size resistor for the led's I bought ?

Ahhh.... that explains everything - problem solved!

Hope it all works when you get back.

David.

On Sun, 22 Oct 2006 18:54:43 +0100, I said, "Pick a card, any card" and "David French" instead replied:

You could turn it on to high power, run your train around the layout once and slice all of your scenery at headlamp level for easy access. Save a lot of time that way.

-- Ray

As long as only one of the LEDs will be turned on, yes!

Chuck D.

Ahh... I now see the light! Those aren't standard-run-of-the-mill LEDs used to illuminate locomotive headlights or EOT devices.

Blue LEDs are quite sensitive to reverse voltage, so I can see why there would be a protection diode built-in. It is uncommon but not totally out of the question.

Thanks for the clarification.

For some wild LEDs check out

Yes, you are right - I tried a few of the other LEDs in my collection and they do not pass current in reverse.

David.

You may. However there are some restrictions. First is that the resistor can't supply more current than what one LED can take so as a result, the resistor value doesn't change from the one resistor, one LED situation. This may be good for you as you already have that value of resistor. Second is that the brightness of the LEDs turned on will be less than just having one on. There is no destructive part of this but just rather that the LEDs will both (considering that there are two LEDs on) use some of the current coming through the resistor. Third, you may just make a mess by miswiring by trying this. The KISS principle works best here, especially since your knowledge of electronics and so forth isn't the best.

-- Yeppie, Bush is such an idiot that He usually outwits everybody else. How dumb!

I always use a separate resistor for each LED. If you run two LED's off one resistor one LED will hog most of the current, leaving the other LED dim. Sometimes when the LEDS just happen to match well, they will share the current evenly, but this is not a common occurance. If you give each LED its own current limiting resistor they will always work. When you put two (or more) LEDS on a single resistor sometimes it works and sometimes it doesn't.

David Starr