Project 2 Buttons

Button-Controlled LED Modes with Raspberry Pi Pico 2W

Here's an interesting experiment using the Raspberry Pi Pico 2W, a button, and an LED. The goal is to control different LED flashing modes using a button. Users can switch between three modes: Constant On, Blinking, and Fading.

Objectives

  • Use a button to switch between different LED flashing modes.
  • The LED will have three modes:
  • Mode 1: Constant On
  • Mode 2: Blinking (Fast On/Off)
  • Mode 3: Fading (Gradually Brightening and Dimming)
  • Each button press will switch to the next mode.

Hardware Requirements

  • 1 x Raspberry Pi Pico 2W
  • 1 x button with button cap
  • 1 x LED indicator
  • 1 x 220 ohm Resistor
  • 1 x Jumper wires
  • 1 x Breadboard
  • 1 x MicroUSB programming cable

Wiring Diagram

LED:

  • Connect the LED's positive (anode) pin to a GPIO pin on the Pico (e.g., GPIO 15).
  • Connect the LED's negative (cathode) pin to GND.

Button:

  • Connect one end of the button to a GPIO pin (e.g., GPIO 14).
  • Connect the other end of the button to GND.

wiring

以下是Markdown格式的代码和代码说明部分：

Demo Code

# Import necessary modules
import machine
import utime

# Initialize the LED and button
led_pin = machine.Pin(15, machine.Pin.OUT)  # LED connected to GPIO 15
button_pin = machine.Pin(14, machine.Pin.IN, machine.Pin.PULL_UP)  # Button connected to GPIO 14, with internal pull-up resistor

# Define three modes for the LED
def mode_constant():
    print("Mode 1: LED Constant On")
    led_pin.value(1)  # Turn the LED on constantly
    utime.sleep(0.1)  # Brief delay to avoid overloading the CPU

def mode_blink():
    print("Mode 2: LED Blinking")
    led_pin.toggle()  # Toggle the LED state (on/off)
    utime.sleep(0.5)  # Blink interval

def mode_fade():
    print("Mode 3: LED Fading")
    pwm = machine.PWM(led_pin)  # Use PWM to control LED brightness
    pwm.freq(1000)  # Set PWM frequency
    for duty in range(0, 65535, 1000):  # Brighten from dim to bright
        pwm.duty_u16(duty)
        utime.sleep(0.01)
    for duty in range(65535, 0, -1000):  # Dim from bright to dim
        pwm.duty_u16(duty)
        utime.sleep(0.01)
    pwm.deinit()  # Stop PWM
    utime.sleep(0.1)
    led_pin.value(0)  # Ensure LED is off after PWM

# Main program
current_mode = 0  # Current mode
modes = [mode_constant, mode_blink, mode_fade]  # List of modes
last_button_state = button_pin.value()  # Previous button state

print("Press the button to switch LED modes!")
print(last_button_state)
while True:
    button_state = button_pin.value()  # Get the current button state
    print(button_state)
    if button_state == 0 and last_button_state == 1:  # Detect button press (high to low)
        current_mode = (current_mode + 1) % len(modes)  # Switch to the next mode
        utime.sleep(0.2)  # Debounce delay
        print(f"Switched to Mode {current_mode + 1}")
    last_button_state = button_state  # Update button state

    # Call the function for the current mode
    modes[current_mode]()

Code Explanations

Hardware Initialization

  • The LED and button are initialized using machine.Pin.
  • The button is connected to GPIO 14 with an internal pull-up resistor, making it high by default.

LED Modes

  • mode_constant: The LED stays on constantly.
  • mode_blink: The LED blinks rapidly.
  • mode_fade: The LED fades in and out using PWM to adjust brightness.

Button Detection and Mode Switching

  • The button state is checked using button_pin.value().
  • When a button press is detected (high to low), the mode switches to the next one in the list.
  • A delay (utime.sleep(0.2)) is used to debounce the button.

Main Loop

  • The loop continuously checks the button state and calls the function corresponding to the current mode.

Experiment Outcome

  • Mode 1: The LED stays on constantly.
  • Mode 2: The LED blinks at a rate of about twice per second.
  • Mode 3: The LED gradually brightens and dims in a loop.
  • Each button press switches to the next mode, cycling back to the first mode after the last one.