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.. _1.1.3_js:

1.1.3 LED Bar Graph
======================

Introduction
-------------

In this project, we sequentially illuminate the lights on the LED Bar
Graph.

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

In this project, we need the following components. 

.. image:: img/list_led_bar.png

It's definitely convenient to buy a whole kit, here's the link: 

.. list-table::
    :widths: 20 20 20
    :header-rows: 1

    *   - Name	
        - ITEMS IN THIS KIT
        - LINK
    *   - Raphael Kit
        - 337
        - |link_Raphael_kit|

You can also buy them separately from the links below.

.. list-table::
    :widths: 30 20
    :header-rows: 1

    *   - COMPONENT INTRODUCTION
        - PURCHASE LINK

    *   - :ref:`cpn_gpio_board`
        - |link_gpio_board_buy|
    *   - :ref:`cpn_breadboard`
        - |link_breadboard_buy|
    *   - :ref:`cpn_wires`
        - |link_wires_buy|
    *   - :ref:`cpn_resistor`
        - |link_resistor_buy|
    *   - :ref:`cpn_bar_graph`
        - \-

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

.. image:: img/schematic_led_bar.png

Experimental Procedures
------------------------------

**Step 1**: Build the circuit.

.. note::
    Pay attention to the direction when connecting. If you connect it backwards, it will not light up.

.. image:: img/image66.png

**Step 2**: Go to the folder of the code.

.. raw:: html

    <run></run>

.. code-block:: 

    cd ~/raphael-kit/nodejs/ 

**Step 3**: Compile the code.

.. raw:: html

    <run></run>

.. code-block:: 

    sudo node led_bar_graph.js

After the code runs, you will see the LEDs on the LED bar turn on and off regularly.

**Code**

.. code-block:: js

    const Gpio = require('pigpio').Gpio;

    var pins = [17, 18, 27, 22, 23, 24, 25, 2, 3, 8];
    var leds = [];
    for (let i = 0; i < pins.length; i++) {
        leds[i] = new Gpio(pins[i], { mode: Gpio.OUTPUT });
    }

    function oddLedBarGraph() {
        for (let i = 0; i < leds.length; i++) {
            if (i % 2 == 1) {
                leds[i].digitalWrite(1);
            } else {
                leds[i].digitalWrite(0);
            }
        }
    }

    function evenLedBarGraph() {
        for (let i = 0; i < leds.length; i++) {
            if (i % 2 == 0) {
                leds[i].digitalWrite(1);
            } else {
                leds[i].digitalWrite(0);
            }
        };
    }

    var odd_even = 0;

    setInterval(() => {
        odd_even = (odd_even + 1) % 2;
        if (odd_even == 1) {
            oddLedBarGraph();
        } else {
            evenLedBarGraph();
        }
    }, 500);
  

**Code Explanation**

.. code-block:: js

    var pins = [17,18,27,22,23,24,25,2,3,8];

Because the led bar graph will use multiple pins, we create a constant array ``pins`` to store them in batches.

.. code-block:: js

    var leds = [];
    for (let i = 0; i < pins.length; i++) {
        leds[i] = new Gpio(pins[i], { mode: Gpio.OUTPUT });
    }

Instantiate these pins as leds objects with a for loop.


.. code-block:: js

    function oddLedBarGraph() {
        for (let i = 0; i < leds.length; i++) {
            if (i % 2 == 1) {
                leds[i].digitalWrite(1);
            } else {
                leds[i].digitalWrite(0);
            }
        }
    }

Implement an ``oddLedBarGraph()`` function to make the LEDs on the 
odd digits of the LED bar graph light up.    

.. code-block:: js

    function evenLedBarGraph() {
        for (let i = 0; i < leds.length; i++) {
            if (i % 2 == 0) {
                leds[i].digitalWrite(1);
            } else {
                leds[i].digitalWrite(0);
            }
        };
    }

Implement an ``evenLedBarGraph()`` function to make the LEDs on the 
even digits of the LED bar graph light up. 

.. code-block:: js

    var odd_even = 0;

    setInterval(() => {
        odd_even = (odd_even + 1) % 2;
        if (odd_even == 1) {
            oddLedBarGraph();
        } else {
            evenLedBarGraph();
        }
    }, 500);

The working state of the LED is switched every 500ms.

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

.. image:: img/image67.jpeg