Model Railway Forum

Hi, for some reason i can't quite get this right. I have a single bi red/green 3 leg led running off 12 volt DC with a 1k resistor on the center leg.
If i apply + power to the green leg all is bright, if i do the same to the red leg it is not so bright. Now i realize the red takes a little more power but am i better putting in 1 extra resistor on the green leg or would i be better putting 2 different resistors on the red & green legs & no resistor on the center leg. If so what size resistor on A B C. Hope it makes sense. Thanks

Hi
Use two resistors one in each leg marked A & B. No resistor on the common middle lead C.
What values these need to be is really a trial and error check! Suggest 1K0 in the red and 5K in the Green? but that is only guessing. If wrong try swapping them around and see what it looks like then.
The alternative is to temporarily use a 10K linear pot wired in series with a 1K0 resistor. Wire this combination into the red lead and adjust pot to get the correct illumination level. Disconnect pot and series resistor and read on a multimeter the Ohm value of the Pot and series resistor combined. Obtain the nearest fixed value resistor for the lead tested. Then do the same with the other lead and again read value of pot and resistor combination.
Note: The added series 1K0 resistor prevents accidental turning of the pot to zero OHMs during testing and blowing the LED!

Thanks, Brian,
i wasn't sure if resistors could go anywhere on the circuit. I have sent off for a more comprehensive lot of resistors & will make up a 12v board with a selection of built-in resistors & an adjustable pot for testing led's

Thanks

Chris