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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. 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.

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:

Name	ITEMS IN THIS KIT	LINK
Newton Lab Kit	450+	Newton Lab Kit

You can also buy them separately from the links below.

SN	COMPONENT	QUANTITY	LINK
1	Raspberry Pi Pico 2	1	BUY
2	Micro USB Cable	1
3	Breadboard	1	BUY
4	Jumper Wires	Several	BUY
5	Resistor	10(220Ω)	BUY
6	LED Bar Graph	1

Circuit Diagram

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

Writing the Code

Note

• Open the 2.2_display_the_level.py file under the path newton-lab-kit/micropython or copy the code below into Thonny. Then click “Run Current Script” or press F5 to execute it.

• Make sure the “MicroPython (Raspberry Pi Pico).COMxx” interpreter is selected in the bottom right corner of Thonny.

import machine
import utime

# Define the GPIO pins connected to the LEDs
pins = [6, 7, 8, 9, 10, 11, 12, 13, 14, 15]
leds = []

# Initialize each pin as an output and store it in the leds list
for pin_number in pins:
    led = machine.Pin(pin_number, machine.Pin.OUT)
    leds.append(led)

while True:
    # Turn on LEDs one by one to simulate increasing level
    for led in leds:
        led.value(1)  # Turn the LED on
        utime.sleep(0.2)
    # Turn off LEDs one by one to simulate decreasing level
    for led in leds:
        led.value(0)  # Turn the LED off
        utime.sleep(0.2)

When you run the program, the LEDs on the LED Bar Graph will light up sequentially from the first to the last, creating an increasing level effect. Then, they will turn off one by one, simulating a decreasing level.

Understanding the Code

In this project, we control multiple LEDs using lists and loops in MicroPython, which makes the code efficient and easy to read.

Let’s break down the key parts of the code:

1. Importing Modules:

   • import machine: Provides access to the Raspberry Pi Pico 2’s hardware functionalities.

   • import utime: Allows us to use time-related functions like delays.

2. Defining Pins and Initializing LEDs:

   • We create a list pins containing the GPIO pin numbers connected to the LEDs and initialize an empty list leds to store the LED objects.

     # Define the GPIO pins connected to the LEDs
     pins = [6, 7, 8, 9, 10, 11, 12, 13, 14, 15]
     leds = []
     

   • Using a for loop, we iterate over each pin number, set it as an output pin, and append the corresponding Pin object to the leds list.

     for pin_number in pins:
         led = machine.Pin(pin_number, machine.Pin.OUT)
         leds.append(led)
     

3. Creating the Level Display Effect:

   • The while True: loop runs indefinitely.

   • Increasing Level:

     • Use a for loop to iterate over each led in the leds list.

     • led.value(1) turns the LED on.

     • utime.sleep(0.2) adds a 200ms delay before the next LED turns on.

     for led in leds:
         led.value(1)
         utime.sleep(0.2)
     

   • Decreasing Level:

     • Turn off each LED one by one using another for loop.

     • led.value(0) turns the LED off.

     for led in leds:
         led.value(0)
         utime.sleep(0.2)
     

Experimenting Further

Feel free to experiment with the code:

• Change the Speed:

  • Adjust the delay in utime.sleep(0.2) to make the LEDs light up faster or slower.

• Reverse the Order:

  • Use reversed(leds) to reverse the sequence of the LEDs.

    for led in reversed(leds):
        led.value(1)
        utime.sleep(0.2)
    

• Create a Ping-Pong Effect:

  • Make the LEDs light up from left to right and then back from right to left.

    while True:
        for led in leds:
            led.value(1)
            utime.sleep(0.1)
        for led in reversed(leds):
            led.value(0)
            utime.sleep(0.1)
    

Conclusion

By controlling each LED individually, we’ve created a simple yet effective level display using the Raspberry Pi Pico 2. This project demonstrates the power of lists and loops in Python, allowing us to manage multiple outputs efficiently.

Understanding how to work with multiple GPIO pins and using programming structures like lists and loops is essential for more complex projects, such as creating animations, controlling multiple sensors, or building interactive devices.

References

• The for statement

• Lists