.. note::

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.. _ar_led_bar:

2.2 Display the Level
=============================

In this lesson, we'll learn how to control an LED Bar Graph using the Raspberry Pi Pico 2. An LED Bar Graph consists of 10 LEDs arranged in a line, typically used to display levels such as volume, signal strength, or other measurements. We'll light up the LEDs sequentially to create a level display effect.

|img_led_bar_pin|


**What You'll Need**

In this project, we need the following components. 

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
    *   - Newton Lab Kit	
        - 450+
        - |link_newton_lab_kit|

You can also buy them separately from the links below.


.. list-table::
    :widths: 5 20 5 20
    :header-rows: 1

    *   - SN
        - COMPONENT	
        - QUANTITY
        - LINK

    *   - 1
        - :ref:`cpn_pico_2`
        - 1
        - |link_pico2_buy|
    *   - 2
        - Micro USB Cable
        - 1
        - 
    *   - 3
        - :ref:`cpn_breadboard`
        - 1
        - |link_breadboard_buy|
    *   - 4
        - :ref:`cpn_wire`
        - Several
        - |link_wires_buy|
    *   - 5
        - :ref:`cpn_resistor`
        - 10(220Ω)
        - |link_resistor_buy|
    *   - 6
        - :ref:`cpn_led_bar`
        - 1
        - 

**Circuit Diagram**

|sch_ledbar|

In this project, each of the 10 LEDs in the LED Bar Graph is connected to the Raspberry Pi Pico 2. The anodes (positive terminals) of the LEDs are connected to GPIO pins GP6 through GP15. The cathodes (negative terminals) are connected through 220Ω resistors to the GND (ground) pin.

**Wiring Diagram**

|wiring_ledbar|

**Writing the Code**

.. note::

   * You can open the file ``2.2_display_the_level.ino`` from ``newton-lab-kit/arduino/2.2_display_the_level``. 
   * Or copy this code into **Arduino IDE**.
   * Select the **Raspberry Pi Pico 2** board and the correct port, then click "Upload".

.. code-block:: Arduino

    // Define the GPIO pins connected to the LED Bar Graph
    const int ledPins[] = {6, 7, 8, 9, 10, 11, 12, 13, 14, 15};

    void setup() {
      // Initialize each pin as an output
      for (int i = 0; i < 10; i++) {
        pinMode(ledPins[i], OUTPUT);
      }
    }

    void loop() {
      // Turn on LEDs sequentially
      for (int i = 0; i < 10; i++) {
        digitalWrite(ledPins[i], HIGH); // Turn on LED
        delay(500);                     // Wait 500 milliseconds
        digitalWrite(ledPins[i], LOW);  // Turn off LED
        delay(500);                     // Wait 500 milliseconds
      }
    }    

After uploading the code, the LEDs on the bar graph should light up one after another, creating a level display effect. Each LED turns on for half a second and then turns off before the next one lights up.

**Understanding the Code**

#. Defining the LED Pins:

   Create an array ``ledPins`` that holds the GPIO pin numbers connected to each LED on the bar graph.

   .. code-block:: Arduino

      const int ledPins[] = {6, 7, 8, 9, 10, 11, 12, 13, 14, 15};

#. Initializing the Pins:

   In the ``setup()`` function, we set each pin in the ``ledPins`` array as an output.

   .. code-block:: Arduino

      void setup() {
        for (int i = 0; i < 10; i++) {
          pinMode(ledPins[i], OUTPUT);
        }
      }

#. Controlling the LEDs:

   In the ``loop()`` function, we use a ``for`` loop to iterate through each LED. We turn it on, wait for 500 milliseconds, turn it off, and then wait another 500 milliseconds before moving to the next LED.

   .. code-block:: Arduino

      void loop() {
        for (int i = 0; i < 10; i++) {
          digitalWrite(ledPins[i], HIGH);
          delay(500);
          digitalWrite(ledPins[i], LOW);
          delay(500);
        }
      }

**Experimenting Further**

* **Reverse the Order**: Modify the code to light up the LEDs in reverse order.

* **Create a Bounce Effect**: After reaching the last LED, make the sequence reverse back to the first LED.

  .. code-block:: Arduino
    
      void loop() {
        // Ascending sequence
        for (int i = 0; i < 10; i++) {
          digitalWrite(ledPins[i], HIGH);
          delay(200);
          digitalWrite(ledPins[i], LOW);
        }
        // Descending sequence
        for (int i = 8; i >= 0; i--) {
          digitalWrite(ledPins[i], HIGH);
          delay(200);
          digitalWrite(ledPins[i], LOW);
        }
      }

* **Adjust the Speed**: Change the delay times to make the LEDs light up faster or slower.

**Conclusion**

In this lesson, you've learned how to control multiple LEDs using the Raspberry Pi Pico and how to create visual effects using simple programming constructs like loops and delays. This foundational knowledge is essential for more advanced projects involving LED displays and indicators.