Fun with LEDs III

This is a continuation of two previous posts:

Fun with LEDs

Fun with LEDs II

We now have enough knowledge to start connecting LEDs to other things like DCC decoders and signal systems. This can be done in one of two ways, you can use the LED with just a resistor or you can use the 'universal' LED with a resistor and rectifier. There is no drawback to using the simpler LED+resistor for situations, like a DCC decoder, where the polarity of the lighting output is known and constant (users of DCS and TMCC/Legacy will have to determine for themselves whether the light outputs are of constant polarity).

On the other hand, using the universal LED reduces the possibility of error or of accidental damage should the decoder fail the LED can withstand full DCC voltage.

Here's the set up with the 'universal' LED. The decoder is an NCE D13SRJ, which is a basic decoder. Following the DCC color code, the DCC signal is being brought in on the red and black alligator clips; the DCC system driving this is a Lenz Compact, which is my bench DCC system.



The LED is connected to the headlight function output on the blue and white wires coming out of the decoder. Since I do not have a blue alligator clip, I've connected the blue lead via the yellow alligator clip. The blue lead coming out of all decoders is common to all function outputs and it is the POSITIVE lead. By using the universal, rectifier-equipped LED you can ignore the polarity and hook up either wire to either terminal on the rectifier.

Here's the proof in the pudding, the LED lights up:



Here's the set-up with the plain LED+resistor:



And a close-up of the LED hook-up:



In left of the picture above you see the yellow alligator clip connected to the blue lead. The yellow clip is connected, in turn, to the anode of the LED which has the resistor in the lead. If you hook-up this type of LED backwards, you'll likely burn it out; possibly damaging the decoder in the process. I did this once, for this reason I use the rectifier-equipped LEDs, either made by me or those from Evans Designs. The choice is yours, you can do it either way.