Second Project: Adding a Button!

May 16, 2024

Building on what we already have, I told ChatGPT this:

Now build on this project by adding something. Include code, code explanation, electronic components, and how to connect it all.

This is the answer ChatGPT gave me:

Let's enhance the project by adding a push button that controls the blinking of the LED. When the button is pressed, the LED will toggle its state, and when the button is released, it will stop toggling. For this enhancement, you'll need the following additional electronic component:

Push button switch

Here's how to connect the push button switch to the existing setup:

Push Button Switch:
- Place the push button switch on the breadboard.
- Connect one leg of the push button to a GPIO pin on the Raspberry Pi Pico. Let's use GPIO pin 1 (GP1).
- Connect the other leg of the push button to a GND (ground) pin on the Raspberry Pi Pico. You can choose any ground pin.
- Optionally, you can add a pull-up resistor between the GPIO pin and the button's leg connected to it to ensure stable readings. A resistor of 10k ohms is commonly used.

Here's the modified MicroPython code to incorporate the push button functionality:

# MicroPython code to toggle an LED connected to GPIO pin 0 (GP0) on Raspberry Pi Pico
# using a push button connected to GPIO pin 1 (GP1)

import machine
import utime

led_pin = machine.Pin(0, machine.Pin.OUT)  # Define GP0 as an output pin
button_pin = machine.Pin(1, machine.Pin.IN, machine.Pin.PULL_UP)  # Define GP1 as an input pin with pull-up resistor

button_state = 0  # Variable to track button state
prev_button_state = 0  # Variable to track previous button state

while True:
    button_state = button_pin.value()  # Read the state of the button
    
    if button_state != prev_button_state:  # If button state changes
        if button_state == 0:  # If button is pressed
            led_pin.toggle()  # Toggle the state of the LED
            
    prev_button_state = button_state  # Update previous button state
    utime.sleep_ms(20)  # Add a small delay to debounce the button

Explanation of the code:

We add a new pin definition button_pin for the push button connected to GPIO pin 1 (GP1). We specify it as an input pin with a pull-up resistor.
We introduce two variables button_state and prev_button_state to track the current and previous states of the button.
In the while loop, we continuously read the state of the button using button_pin.value().
If the button state changes (indicating a press or release), we toggle the LED state only when the button is pressed (button_state == 0).
We add a small delay of 20 milliseconds to debounce the button.

Connect the push button switch as described above, upload the modified code to your Raspberry Pi Pico, and you should now be able to control the blinking of the LED using the push button!

Ok, so it mentions a pull-up resistor, realizing some of folks reading this might not understand what a pull-up resistor is or does, or how to connect it to the project. I asked ChatGPT a follow up question of:

What is a pull up resistor and how do I connect it to the project?

ChatGPTs Answer:

A pull-up resistor is a resistor connected between a signal line and a positive voltage (typically Vcc or the supply voltage). It ensures that the signal line is pulled to a logical high state (usually the same voltage as the positive supply) when no other active device is driving the line to a low state. This configuration helps prevent floating or undefined states, providing a stable reference voltage when the line is not being actively driven.

In the context of a push button switch, a pull-up resistor is used to ensure that the input pin reads a logical high state when the button is not pressed. When the button is pressed, it connects the input pin to ground, overriding the pull-up resistor and causing the input pin to read a logical low state.

Here's how to connect a pull-up resistor to your project:

   1. Choose the resistor value: A commonly used value for pull-up resistors is around 10k ohms (10,000 ohms). However, depending on your specific requirements and components, you can adjust this value if needed.

   2. Connect the resistor: Connect one end of the resistor to the GPIO pin to which the push button is connected.Connect the other end of the resistor to the positive voltage supply (Vcc), which is typically the 3.3V pin on the Raspberry Pi Pico.

I also wanted to mention that there is such thing as a pull-down resistor as well. Both have there place, but for this project we are going to use a pull-up resistor.

Image of a circuit the pull-up on the left and pull-down on the right: