If you just want to play around with some LEDs and resistors to get a feel for them, get a 0 - 5K ohm 1/4 watt potentiometer from the electronics store and put that in series with your resistor. Start off with higher values of resistance, then vary the potentiometer to see what the LED does as for brightness goes. If you can measure the current too, then all the better. Be aware that they do make low current draw LEDs that can handle only 2mA instead of the normal 20mA. These need alot higher resistnace in series than the normal ones.

Andy - Adding and substracting...hadn't thought of that yet. Now I think I'm more needing some additional resistance. Using my logic which may or may not apply in semiconductoria, the resistance should double if I were to put two resistors in series.. Two 500 ohm transistors making 1000 ohm, basically. Any chance that this might work then?

Yes, a good chance that will work. What value was the resistors they sold you? Or the color code? Do you have a meter, VOM, DMM, multimeter, whichever your term may be? You can use it to measure the resistor value and the voltage across it, your source voltage, and the curent thru it. You can also check your source voltage with it, so you won't be guessing. You will find the meter to be invaluable if you are going to do much more of this kind of thing. It's well worth the investment! I'm not too sure I would go back to that same store for it, though.

If my understanding of Ohm's law is correct, if you took 4 1000 ohm resistors, and connected them in parralel pairs you get 2 resistors at 500 ohms but double the wattage. Now if you hook two sets in series, you get 1000 ohms with double the wattage. It would be better to use one large resistor than 4 small ones, but if you already have the smaller ones, this will save you from having to just throw what you have away.

I agree with Russ. If you have four 1000 ohm, 1/8 watt resistors, you could make two parallel groups. These would be the equivalent of 500 ohm 1/4 watt resistors. If you put the two parallel groups in series, this group of four resistors would be the equivalent of a 500 ohm, 1/2 watt resistor.

Yeah seriously, i've managed to figure out that i have everythign i need to add led's to just about everything i have rolling around my tracks .. welll... except of course the acutal leds... but i'm working on that . I have a ton of old computer parts, boards cdrom drives etc that i can scavenge for leds. :0