How it Works

How It Works

  • Watch the animation as it repeats, and answer each of the questions below about the differences between pressed and not pressed.  Optionally, view higher res version with pause control: pb-top-button-digital-read.mp4.

 

  1. At the bottom, what value does pin6.read_digital() return that gets stored in the state variable?  
    • Pressed __________, not pressed __________.
  2. What is the voltage at the P6 pin?  
    • Pressed __________, not pressed __________.
  3. In the schematic, is the 3.3 V supply connected to (or insulated from) the rest of the circuit.
    • Pressed __________, not pressed __________.
  4. Which supply voltage do you think the right terminal strip’s (a-e, 25) row is connected to?    
    • Pressed __________, not pressed __________.
  5. In the micro:bit, what value does it switch to internally if its pin P6 is set to input?  (Hint: The answer is shown near the USB connection.)
    • Pressed __________, not pressed __________.

(Answers are in the Teacher's Guide.))


Inside the pushbutton_test Script

This script is short, but it contains some important instructions that are unique to the micro:bit module hardware.

To begin, the state = 0 statement just creates a variable named state that will be used inside the while True loop.  

state = 0

The micro:bit module’s P6 pin is part of the module's 5x5 LED display grid.  The display.off() call prevents the LED circuits built into the micro:bit from interfering with the pushbutton circuit you just built on the breadboard.

display.off()

The 10 kΩ resistor connected to the pushbutton is called a pull-down resistor.  More about that later!  P6 also has an internal pull-down resistor enabled by default, and this statement disables it since a 10 kΩ pulldown resistor has been added to the circuit on your breadboard. Many microcontrollers used in

pin6.set_pull(pin6.NO_PULL)

Inside the main loop, when the pushbutton is pressed, the circuit applies 3.3 V to the P6 pin.  The pin6.read_digital() call returns 1 when it detects 3.3 V.  If the button is released, the circuit applies 0 V to the pin, and pin6.read_digital() returns 0 instead.  In state = pin6.read_digital(), the state variable stores that 1 or 0 result.      

while True:
    state = pin6.read_digital()

Next, the print statement displays "state = " followed by the 1 or 0 that just was stored in the state variable.  

    print("state = ", state)

Last in the loop, the sleep(250) call just slows down the display to make it easier to observe the transitions from 0 to 1 and 1 to 0.

    sleep(250)

 

Try This

The binary (1 or 0) value returned by the pin6.read_digital() method can be used as the argument to turn the LED light on and off in pin13.write_digital(state).  When state is 1 because the button is pressed, pin13.write_digital(state) becomes pin13.write_digital(1).  This sets the P13 LED light to on.  When the state variable is 0 because the button is not pressed, pin13.write_digital(state) becomes pin13.write_digital(0).  This sets the LED light to off.

  • Enter the button_light_loopback script into the python.microbit.org editor.
  • Set the Script Name field to button_light_loopback.
  • Click Load/Save, and then click Download Project Hex to save your work.  
  • Close the Load/Save dialog box after downloading the .hex file.
  • In the python.microbit.org editor, click Connect, and then click Flash.   
  • Verify that the green light connected to P13 stays off when the button is not pressed.
  • Press and hold the button.  Verify that the P13 light stays on while the button is held down.