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2.5 Reading Button Value

In this lesson, we’ll learn how to read input from a pushbutton using the Raspberry Pi Pico 2. So far, we’ve used the GPIO pins mainly for output, like lighting up LEDs. Now, we’ll use a GPIO pin as an input to detect when a button is pressed. This is a fundamental skill for creating interactive projects.

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	1(10KΩ)	BUY
6	Button	1	BUY

Circuit Diagram

As long as one side of the button pin is connected to 3.3v, and the other side pin is connected to GP14, then when the button is pressed, GP14 will be high. However, when the button is not pressed, GP14 is in a suspended state and may be high or low. In order to get a stable low level when the button is not pressed, GP14 needs to be reconnected to GND through a 10K pull-down resistor.

Button Not Pressed: The GP14 pin is connected to GND through the resistor, so it reads LOW (0).
Button Pressed: The GP14 pin is connected to 3.3V through the button, so it reads HIGH (1).

Wiring Diagram

A four-pin button is shaped like an H. Its left two pins or right two pins are connected, which means that when it crosses the central gap, it connects two half rows with the same row number. (For example, in my circuit, E23 and F23 are already connected, as are E25 and F25).

Until the button is pressed, the left and right pins are independent of each other and current cannot flow from one side to the other.

Writing the Code

We’ll write a simple program that prints a message when the button is pressed.

Note

Open the 2.5_read_button_value.py from newton-lab-kit/micropython or copy the code into Thonny, then click “Run” or press F5.
Ensure the correct interpreter is selected: MicroPython (Raspberry Pi Pico).COMxx.

import machine
import utime

# Initialize GP14 as an input pin
button = machine.Pin(14, machine.Pin.IN)

while True:
    if button.value() == 1:
        print("Button pressed!")
        utime.sleep(0.2)  # Debounce delay

When the code is running, you will observe the following phenomenon:

Not Pressed: No message should appear.
Pressed: “Button pressed!” should appear in the console each time you press the switch.

Understanding the Code

Import Modules:
- machine: Provides access to the hardware functions.
- utime: Allows us to use time-related functions like delays.
Set Up the Button Pin:
- button = machine.Pin(14, machine.Pin.IN): Initializes GPIO pin 14 as an input.
Main Loop:
- while True: Creates an infinite loop.
- if button.value() == 1: Checks if the button is pressed.
- button.value() returns 1 when the pin reads high (button pressed).
- print("Button pressed!"): Prints a message to the console.
- utime.sleep(0.2): Waits for 200 milliseconds to debounce the button.

Alternate Wiring: Pull-Up Resistor

You can also wire the button using a pull-up resistor configuration.

Connect a 10kΩ resistor between GP14 and the 3.3V rail. This pulls the pin high when the button is not pressed.
- Button Not Pressed: The GP14 pin is connected to 3.3V through the resistor, so it reads HIGH (1).
- Button Pressed: The GP14 pin is connected to GND through the button, so it reads LOW (0).

Modified Code for Pull-Up Configuration.

import machine
import utime

# Initialize GP14 as an input pin
button = machine.Pin(14, machine.Pin.IN)

while True:
    if button.value() == 0:
        print("Button pressed!")
        utime.sleep(0.2)

Using Internal Pull-Up/Pull-Down Resistors

The Raspberry Pi Pico 2 allows you to enable internal pull-up or pull-down resistors, eliminating the need for external resistors.

Using internal resistors simplifies wiring and saves space by eliminating the need for additional external resistors on the breadboard.

Enabling Internal Pull-Down Resistor:

import machine
import utime

# Initialize GP14 as an input with an internal pull-down resistor
button = machine.Pin(14, machine.Pin.IN, machine.Pin.PULL_DOWN)

while True:
    if button.value() == 1:
        print("Button pressed!")
        utime.sleep(0.2)

Enabling Internal Pull-Up Resistor:

import machine
import utime

# Initialize GP14 as an input with an internal pull-up resistor
button = machine.Pin(14, machine.Pin.IN, machine.Pin.PULL_UP)

while True:
    if button.value() == 0:
        print("Button pressed!")
        utime.sleep(0.2)

Experimenting Further

Multiple Buttons: Connect additional buttons to other GPIO pins and modify the code to handle multiple inputs.
LED Control: Combine button input with LED output to toggle the LED state when the button is pressed.

import machine
import utime

button = machine.Pin(14, machine.Pin.IN, machine.Pin.PULL_DOWN)
led = machine.Pin(15, machine.Pin.OUT)
led_state = False

while True:
    if button.value() == 1:
        led_state = not led_state  # Toggle LED state
        led.value(led_state)
        utime.sleep(0.2)

Conclusion

Reading input from a button is a fundamental skill in microcontroller programming. It allows you to make your projects interactive and responsive to user input. Understanding how to use pull-up and pull-down resistors ensures reliable and stable readings from your input devices.