Dual Color LED
===============

    .. image:: Images/dualled.jpg
		:align: center

A dual color LED is composed of two LEDs each emitting a different color of light. Two types of dual color LEDs can be found: common anode and common cathode.

As a reminder on LEDs, to turn a normal LED on, the anode (longer leg) is linked to the VCC and the cathode (shorter leg) is linked to the ground.

In the case of a dual color LED, the internal LEDs share their anode or cathode through one pin: the middle pin. So the wiring depends on whether it’s a common anode or common cathode.

Below are the internal connections of a common anode and of a common cathode dual color LED to understand better the placement of the colored LEDs:

**Common Cathode**:

    .. image:: Images/common-cathode.jpg
		:align: center

**Common Anode**:
		
    .. image:: Images/common-anode.jpg
		:align: center

*In this example, we will be using a common anode composed of a green and a red LED.*
	
Circuit Connection
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As we mentioned previously, this is a common anode dual color LED. So to light both the green and the red internal LEDs, connect:

	1. The middle pin to 3.3V
	2. The right and left pin to a ground


    .. image:: Circuits/dualled-on.jpg
		:align: center

However in this example, we want to control the intensity and the color of our LED, so connect:

	1. The middle pin to 3.3V (pin 1)
	2. The right pin to a GPIO (pin 11)
	3. The left pin to a GPIO (pin 12)

    .. image:: Circuits/dualled-pwm.jpg
		:align: center


Python program to change the color of the LED
---------------------------------------------

    .. literalinclude:: Code/dualled.py
       :linenos:
       :language: python

After saving the code, you can run it by clicking on Run (or CTRL+F5).

You will then see the LED transition between multiple stages.

Here are three stages of the LED:

i=0 - Internal red LED on

    .. image:: Images/dualled-0.jpg
		:align: center
		:width: 60%

i=50 - Internal red and green LEDs equally on

    .. image:: Images/dualled-50.jpg
		:align: center
		:width: 60%


i=100 - Internal green LED on

    .. image:: Images/dualled-100.jpg
		:align: center
		:width: 60%