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.. _ar_7_segment:

2.5 7-Segment Display
======================

Overview
--------

In this lesson, you will learn something about 7-Segment Display. 7-Segment Display has so many advantages that it is widely used in electrical equipments, especially in household appliances that display numerical information, such as display, air conditioner, water heater, refrigerator and so on. LEDs on the 7-Segment Display emit light by the input of different electrical signals to the different pins of it. The numerical information it can display includes time, date, temperature and so on.

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

.. image:: img/list_2.5.png

* :ref:`cpn_mega2560`
* :ref:`cpn_breadboard`
* :ref:`cpn_wires`
* :ref:`cpn_7_segment`
* :ref:`cpn_resistor`

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

.. image:: img/image429.png

Connect each of pin a-g of the 7-Segment Display to one
220ohm current limiting resistor respectively and then to pin 4–11. GND
connects to GND.

The wiring between the 7-segment display and the Mega2560 board as shown
below :

.. image:: img/image430.png

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

.. image:: img/image431.png

Code
----

.. note::

    * You can open the file ``2.5_7segment.ino`` under the path of ``sunfounder_vincent_kit_for_arduino\code\2.5_7segment`` directly.
    * Or copy this code into Arduino IDE.



.. raw:: html

    <iframe src=https://create.arduino.cc/editor/sunfounder01/c8b782c0-162e-447a-8406-c32a1378cc59/preview?embed style="height:510px;width:100%;margin:10px 0" frameborder=0></iframe>

Once upload the codes, you can see the 7-segment display displaying 1, 2, 3, 4, 5, 6, 7, 8, 9, A, b, C, d, E, F in sequence. 

Code Analysis
-------------

Take the pin numbers on 7-segment as names, and declare the pins on the Mega2560 board.  

.. code-block:: arduino

    const int a=7; //a of 7-segment attach to digital pin 7
    const int b=6; //b of 7-segment attach to digital pin 6
    const int c=5; //c of 7-segment attach to digital pin 5
    const int d=11;//d of 7-segment attach to digital pin 11
    const int e=10;//e of 7-segment attach to digital pin 10
    const int f=8;//f of 7-segment attach to digital pin 8
    const int g=9;//g of 7-segment attach to digital pin 9
    const int dp=4;//dp of 7-segment attach to digital pin 4

Install a series of subfunctions to package the level state at each
block during the number display of the 7-segment. For example, when the
character 「2」 is displayed, the block F and the block c are turn off;
the other blocks are lit up.

.. image:: img/image89.jpeg

First, we need to understand how the numeral **2** appears on the 7-Segment display. It is achieved by powering on segments a, b, d, e, and g. In programming, pins connected to these segments are set to a High level while c and f are set to Low level. We start by using the function ``turnOffAllSegments()`` to turn off all segments and then light up the required ones.

After running this part, the 7-segment will display **2**. Similarly, the display of other characters are the same. Since the letters b and d in upper case, namely **B** and **D**, would look the same with **8** and **0** on the display, they are displayed in lower case instead.

.. code-block:: arduino

   ...
   void digital_2()  //diaplay 2 to the 7-segment
   {
     turnOffAllSegments();
     digitalWrite(a, HIGH);
     digitalWrite(b, HIGH);
     digitalWrite(g, HIGH);
     digitalWrite(e, HIGH);
     digitalWrite(d, HIGH);
   }
   ... 

In loop(), call the function that displays the number.

.. code-block:: arduino

    void loop()
    {
    digital_1();//diaplay 1 to the 7-segment
    delay(1000);//wait for a second
    digital_2();//diaplay 2 to the 7-segment
    delay(1000); //wait for a second
    digital_3();//diaplay 3 to the 7-segment
    //... 
    }

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

.. image:: img/image90.jpeg