Skip to content

Buttons

On this page we will learn

  • how to check whether button A or B is being pressed
  • how to check whether a button was pressed earlier
  • how to count how many times a button was pressed

Terminology

  • push button – a button that detects when it is pressed and held down, such as buttons A and B on the micro:bit.

The micro:bit has two push buttons, A and B, that detect when they are pressed.

Possible uses:

  • controlling games
  • starting and stopping timers
  • answering questions
  • moving through menus

Connect it

The buttons are built into the micro:bit, so we don't need to connect anything.

  • Each example is a main.py file. See Your First Program for how to create, upload and run it.
  • In code, the buttons are called button_a and button_b. Every method below works with either button.

Set it up

The buttons are part of the microbit library. We import it at the top of every program:

1
from microbit import *

Methods

Method Parameters Returns Description
button_a.get_presses() none int Number of presses since the last call, then resets the count to 0
button_a.is_pressed() none Boolean True if the button is being held down right now
button_a.was_pressed() none Boolean True if the button has been pressed since the last call

get_presses()

Counts how many times the button has been pressed. Each call resets the count to 0.

1
2
3
4
5
6
7
from microbit import *

# Main loop
while True:
    presses = button_a.get_presses()
    display.show(presses)
    sleep(1000)

PRIMM

  1. Predict what you think will happen. Be specific.
  2. Run the program.
  3. Time to investigate the code. What does each line do?
Code explanation
  • line 1 → imports all the commands from the microbit library.
  • line 4 → starts an endless loop.
  • line 5 → gets the number of times button A was pressed since the last check and stores it in presses.
  • line 6 → shows the number of presses.
  • line 7 → waits 1 second, giving you time to press the button again.

is_pressed()

Checks whether the button is being held down right now.

1
2
3
4
5
6
7
8
from microbit import *

# Main loop
while True:
    if button_a.is_pressed():
        display.show(Image.HAPPY)
    else:
        display.show(Image.SAD)

PRIMM

  1. Predict what you think will happen. Be specific.
  2. Run the program.
  3. Time to investigate the code. What does each line do?
Code explanation
  • line 1 → imports all the commands from the microbit library.
  • line 4 → starts an endless loop.
  • line 5 → checks if button A is being held down.
  • line 6 → if it is, shows a happy face.
  • line 7 → if it isn't…
  • line 8 → …shows a sad face.

was_pressed()

Checks whether the button has been pressed since the last check, even if it has been let go. Each call clears the press, so the button must be pressed again before it returns True again.

1
2
3
4
5
6
7
8
9
from microbit import *

# Main loop
while True:
    if button_a.was_pressed():
        display.show(Image.HAPPY)
    else:
        display.show(Image.SAD)
    sleep(2000)

PRIMM

  1. Predict what you think will happen. Be specific.
  2. Run the program.
  3. Time to investigate the code. What does each line do?
Code explanation
  • line 1 → imports all the commands from the microbit library.
  • line 4 → starts an endless loop.
  • line 5 → checks if button A was pressed since the last check.
  • line 6 → if it was, shows a happy face.
  • line 7 → if it wasn't…
  • line 8 → …shows a sad face.
  • line 9 → waits 2 seconds. A press during this wait is still detected on the next loop.

is_pressed() or was_pressed()?

is_pressed() only sees the button while it is held down. was_pressed() remembers a press, so a quick press during the 2-second wait in the was_pressed() example is still detected.

Documentation

Documentation is the official guide written by the people who made the code library, and we can use it to look up every method and its parameters, including ones that aren't covered on this page.

Exercises

PRIMM

Time to modify the code and see what happens.

Starter files are in the buttons folder of your tutorial files. Solutions are on the Exercise Solutions page.

Exercise 1

Starter: buttons/ex1_press_challenge

Can you create a program that challenges the player to press button A a certain number of times before time runs out?

Exercise 2

Starter: buttons/ex2_counter

Can you create a program that counts how many times button A is pressed? The count starts at 0 and goes up by 1 with each press. Pressing button B resets the count to 0.

Exercise 3

Starter: buttons/ex3_reaction_timer

Can you create a program that tests the player's reaction time? It should:

  • randomly choose which button to press: A or B
  • count down 3-2-1, then show the button to press
  • time how long it takes to press the correct button. running_time() may help.
  • show the reaction time on the display

Exercise 4

Starter: buttons/ex4_memory_game

Can you create a memory game that:

  • randomly generates a 6-letter pattern using A and B
  • shows the pattern to the player
  • asks the player to repeat the pattern using the buttons
  • shows a happy face if the pattern matches, or a sad face if it doesn't?