# The Red/Green LED Guide

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## Introduction: The Red/Green LED Guide

The Bi-color LED is a handy little component that allows two colors (red and green) in a single LED while only having two pins (cathode and anode). The color of the LED depends on the polarity of the connection only allowing one color at a time. Similar LED's that provide two or even three colors usually have three or four pins allowing for a wide range of mixed colors. One would think having two pins is a disadvantage; not so. This LED can easily be applied to a circuit to visually indicate polarity direction. Or in my case it can save me an extra i/o pin on a forthcoming arduino project.

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## Step 1: Straight Out of the Package

The first thing you'll notice is that this looks like any other common LED, but with a white diffused lens. It has a short negative lead (cathode), and a long positive lead (anode). On the inside there are two LED's in parallel to each other, one forward and one reverse. The package included with the LED from radio shack provides a similar looking schematic to the one I provided above.

## Step 2:

Using circuitlab.com I made this simple schematic. I actually used 3 86R resistors in the demo video so don't worry too much about getting the resistor values exact (Resistor's Here). Just try not to go any lower than that.

In this design you will see exactly how the bi-color LED operates. When the button is open the LED shine one color, either red or green. When the button is closed the other color will light up. So if the LED was green when the button was open, it will change to red when the button is closed. Simple enough.

## Step 3: Using BI-Color LED's in Your Projects

The whole reason I purchased a bi-color LED was to be used in a forthcoming Arduino project. The output pin on the arduino (when used in conjunction with a Relay) will act as our push button in the previous step. The idea is to have the led glowing red until certain perimeters are met. Upon meeting a certain criteria the output pin will go HIGH causing the LED to glow green.

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## 8 Discussions

Thanks for your guide (especially circuit picture :) ). I was using 12V as source so I had to increase value of resistors (to 2k2), but everything works great.

I'd call this a fast question but when you are looking to use it on a Float charger it becomes more specific, Like many other here or there, :) That use float chargers on many projects I always need a 12 volt back up in case of power failure from my 12 Volt devices, Duh.. but, a few times I had float chargers go bad and didn't catch them because the little Red light stays on when the power adapter fails.. IN Short they stay red no mater which way the power flows, so I wanted to crack the case open "easy" and remove the 2 pin red that shows power plug in to wall or not as long as the 12 v battery has juice with a Bi-color led that will show a green when charging and a red when the adapter fails with a red, Off hand anyone here try that yet? Just wondering.. I think it would be a good Idea to use since nobody checks the AC adapter for power if the red led is lit and who wants to replace a battery because they didn't check it? Anyways here's a pic of the Float charger I use or should I say 1 of 8 that are in use today.. Thanks for any advice. BCB....

Great!! it's a pin saver solution. Is this method usable for two separate LEDs paralleled by reverse polarity?

yes you can implement the same concept with two seperate LED's.

Hi, I'm glad you wrote on this little LED. I've not been too sure how to use it. I'm pretty new to Arduino. How would I alternate colors without having a physical switch? How can I wire it to just do it via software (arduino sketch)?