How to use Christmas light LEDs in your model railroad.
You can save quite a bit of money by using LEDs removed from strings of Christmas lights. You can buy them cheap at after Christmas sales as well as flea markets and yard sales.
Removing the LEDs from the protective plastic tubing is quite easy. Simply split the plastic by running a hot soldering iron quickly over it. The video below shows how I do it.
The anode and cathode will be much shorter and thicker than those on LEDs that you buy off the shelf. And you will have to test to identify which is the anode and which is the cathode.
Check the amperage it passes when powered by 5 volts. Add a resistor of high enough value to bring that amperage down to about .25ma. With some of these you can probably run at a higher amperage but you want to keep it as low so that you do not overpower your Arduino. (See powering an Arduino).
They are rather nice to use on a breadboard because they present a low profile around which it is easy to run your jumper wires.