Adding a LED

[Tom Hogan]

I am adding an LED to my DCC board. I have the resistor attached to the LED.....but do not know which leg of the LED goes to the common or output pads?
Thanks

[Dan Love]

Connect it backwords and it won't work.

Make sure the resistor ohms and wattage is corect forr the voltage source and led.

The resistor connects to the anode of the LED.

The other side of the same resistor connects to Common (+).
The cathode of the LED goes to the switched "output"

Dan

[taz-of-boyds]

Please note, do not leave LED's wired backwards for very long.  They generally have a low reverse voltage tolerance and should be protected by a standard diode if they will commonly be exposed to reverse voltage.

Charles

[Jim Banner]

Some LEDs have one long and one short lead.  The long lead is positive and goes to the decoder blue wire.  Other diodes have a flat spot on the ring around their bases.  This is beside the negative lead which goes to the function output (white, yellow etc.)  One of the leads must connect through a resistor on its way to its decoder wire.  Which lead does not matter.

Some LEDs are quite low in the maximum reverse voltage department.  Even a short exposure to reverse voltage can affect them.  They may still work after a reverse voltage incident, but perhaps only for 100 hours instead of 100,000 hours.  A year from now you could be scratching your head over a mysterious LED failure.  Same thing happens with excessive current.