Project 3

Project Description

This project uses a Raspberry Pi Pico W, an LED, a buzzer, a button, an S8050 transistor, and a 220Ω resistor to create a simple interactive circuit. When the button is pressed, the LED will turn on and the buzzer will make a sound. The LED will also blink continuously when the button is not pressed.

Wiring Diagram

Demo Code

#include "pico/stdlib.h"

// Define GPIO pins
const int BUTTON_PIN = 14;
const int LED_PIN = 15;
const int BUZZER_PIN = 16;
const int TRANSISTOR_PIN = 17;

// Function to initialize GPIO pins
void init_pins() {
    gpio_init(BUTTON_PIN);
    gpio_set_dir(BUTTON_PIN, GPIO_IN);
    gpio_pull_up(BUTTON_PIN); // Enable internal pull-up resistor

    gpio_init(LED_PIN);
    gpio_set_dir(LED_PIN, GPIO_OUT);

    gpio_init(BUZZER_PIN);
    gpio_set_dir(BUZZER_PIN, GPIO_OUT);

    gpio_init(TRANSISTOR_PIN);
    gpio_set_dir(TRANSISTOR_PIN, GPIO_OUT);
}

// Function to check if the button is pressed
bool is_button_pressed() {
    return gpio_get(BUTTON_PIN) == 0; // Button is pressed if pin is LOW
}

int main() {
    stdio_init_all(); // Initialize serial communication
    init_pins();      // Initialize GPIO pins

    while (true) {
        if (is_button_pressed()) { // Check if the button is pressed
            gpio_put(LED_PIN, 1); // Turn on LED
            gpio_put(TRANSISTOR_PIN, 1); // Turn on transistor to activate buzzer
            gpio_put(BUZZER_PIN, 1); // Turn on buzzer
            sleep_ms(500); // Wait for 500ms
            gpio_put(LED_PIN, 0); // Turn off LED
            gpio_put(TRANSISTOR_PIN, 0); // Turn off transistor
            gpio_put(BUZZER_PIN, 0); // Turn off buzzer
            sleep_ms(500); // Wait for 500ms
        } else { // If the button is not pressed, blink the LED
            gpio_put(LED_PIN, 1); // Turn on LED
            sleep_ms(500); // Wait for 500ms
            gpio_put(LED_PIN, 0); // Turn off LED
            sleep_ms(500); // Wait for 500ms
        }
    }

    return 0;
}

• CMakeLists.txt file content:

  cmake_minimum_required(VERSION 3.25)
  
  include($ENV{PICO_SDK_PATH}/external/pico_sdk_import.cmake)
  
  pico_sdk_init()
  
  set(PICO_BOARD pico2_w)
  
  project(project3 C CXX)
  
  set(CMAKE_C_STANDARD 11)
  set(CMAKE_CXX_STANDARD 17)
  
  add_executable(project3 main.c)
  
  target_link_libraries(project3 pico_stdlib)
  
  pico_add_extra_outputs(project3)
  
  # enable USB and UART
  pico_enable_stdio_usb(project3 1)
  pico_enable_stdio_uart(project3 1)
  

Code Explanation

1. GPIO Initialization:
2. The init_pins() function initializes the GPIO pins for the button, LED, buzzer, and transistor.
3. The button pin is set as an input with an internal pull-up resistor to ensure a stable signal.

4. The LED, buzzer, and transistor pins are set as outputs.

5. Button Press Detection:

6. The is_button_pressed() function checks if the button is pressed by reading the state of the button pin. If the pin is LOW, the button is considered pressed.

7. Main Loop:

8. When the button is pressed, the LED is turned on, the transistor is activated to turn on the buzzer, and both are turned off after 500ms. This sequence repeats.

9. When the button is not pressed, the LED blinks continuously with a 500ms interval.

10. Transistor Control:

11. The S8050 transistor is used to control the buzzer. When the transistor is activated (HIGH signal on the base), it allows current to flow through the buzzer, making it sound.

This project demonstrates how to use a transistor to control a buzzer and how to manage GPIO pins for button presses and LED control on the Raspberry Pi Pico W.

Compile and upload

mkdir build 
cd build
cmake -DPICO_BOARD=pico2_w ../ 
make -j4 

• upload *.uf2 to pico 2w as project1.

cp project3.uf2 /media/pi/RP2350/ 

Demostration

Experiment in C/C++

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