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.. _ar_bar_graph:

2.4 LED Bar Graph
==================

Overview
--------

In this lesson, you will learn something about LED Bar Graph. Generally,
LED Bar Graph works as a battery level indicator, Audio equipment,
industrial control panel. If we want, we can also find its other
application.

Components Required
-------------------

.. image:: img/list_2.4.png

* :ref:`cpn_mega2560`
* :ref:`cpn_breadboard`
* :ref:`cpn_wires`
* :ref:`cpn_bar_graph`
* :ref:`cpn_resistor`

Fritzing Circuit
----------------

In this example, we use digital pins 2~11 to drive the LED Bar Graph.
LED Bar Graph has ten separate LEDs inside and each LED has two pins.
The left pins 1~10 of LED Bar Graph are connected with the digital pins
2~11 respectively; the right side pins 11~20 are separately extended to
same side of these 220ohm resistors whose other sides are identically
connected to GND.

.. image:: img/image82.png

Schematic Diagram
-----------------

.. image:: img/image427.png

Code
----

.. note::

    * You can open the file ``2.4_ledBarGraph.ino`` under the path of ``sunfounder_vincent_kit_for_arduino\code\2.4_ledBarGraph`` directly.
    * Or copy this code into Arduino IDE.



.. raw:: html

    <iframe src=https://create.arduino.cc/editor/sunfounder01/0614541f-58d0-4f5c-b7c9-c3b893178fda/preview?embed style="height:510px;width:100%;margin:10px 0" frameborder=0></iframe>

Uploaded the codes to the Mega2560 board, you can see that the LEDs on the LED Bar Graph flash in sequence.

Code Analysis
-------------
The codes in setup() use the for loop to initialize pins 2~11 to output mode in turn.  

.. code-block:: arduino

    for(int i=2;i<=11;i++)
    {
        pinMode(i,OUTPUT);
    }

The for loop is used in loop() to make the LED flash(turn on 0.5s, then turn off 0.5s) in sequence.

.. code-block:: arduino

    for(int i=2;i<=11;i++)
    {
        digitalWrite(i,HIGH);
        delay(500);
    digitalWrite(i,LOW);
        delay(500);
    }

Refer to **Part 1-1.2 Digital Write** for more details about controlling the LED by using digital pins. 

:ref:`ar_digital_write`

Phenomenon Picture
------------------

.. image:: img/image84.jpeg