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2.2 - Display the Level

In this lesson, we’ll learn how to control an LED Bar Graph using the Raspberry Pi Pico 2 W. 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.

• LED Bar Graph

Required Components

In this project, we need the following components.

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

Name	ITEMS IN THIS KIT	PURCHASE LINK
Pico 2 W Starter Kit	450+	Pico 2 W Kit

You can also buy them separately from the links below.

SN	COMPONENT INTRODUCTION	QUANTITY	PURCHASE LINK
1	Getting to Know Pico 2 W	1
2	Micro USB Cable	1
3	Breadboard	1	BUY
4	Jumper Wires	Several	BUY
5	Resistor	10(220Ω)	BUY
6	LED Bar Graph	1

Schematic

The LED Bar Graph contains 10 LEDs, each of which is individually controllable. Here, the anode of each of the 10 LEDs is connected to GP6~GP15, and the cathode is connected to a 220ohm resistor, and then to GND.

Wiring

Writing the Code

Note

• You can open the file 2.2_display_the_level.ino under the path of pico-2w-kit-main/arduino/2.2_display_the_level.

• Or copy this code into Arduino IDE.

• Don’t forget to select the board(Raspberry Pi Pico) and the correct port before clicking the Upload button.

// 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

1. Defining the LED Pins:

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

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

2. Initializing the Pins:

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

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

3. 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.

   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.

  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.