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Case 03 Function Selector

Our Goal

  • Use basic kit to create a function selector.

Material

Hardware Connection

  • Connect the crash sensor to P0 port on basic:bit and connect the potentiometer to P1. See picture below.

Software

  • Microsoft Makecode

  • The crash sensor analog read the return value of I/O port. Here's the values:

  • Button A <10

  • Button B: 10-80
  • Button C: 80-130
  • Button D: 130-160
  • Button E: 160-600

Programming

Step 1

  • Create a forever loop, read the value of P0 port in analog way, and then assign the return value to variable itmmm so as to judge which button is pressed.
  • If itmmm is under 10, it means button A is pressed. When button A is pressed, call function func_A and set variable flag(Variable for judging the internal loop in the function) to 0 after call.
  • If itmmm is under 80, it means button B is pressed. When button B is pressed, call function func_Band set variable flag to 0 after call.
  • If itmmm is under 130, it means button C is pressed. When button B is pressed, call functionfunc_C.

Step 2

  • Function func_A: When flag is beyond 600(i.e. no buttons pressed), read the value of P1 port and plot it on micro:bit screen. Read the button status of P0 port. When button E is pressed, the loop is terminated and the function call is finished.
  • Function func_B: When flag is beyond 600(i.e. no buttons pressed), display a flashing heart. Read the button status of P0 port after each flash. When button E is pressed, the loop is terminated and the function call is finished.
  • Function func_C: Clear the screen and finish the call of function.

Program

The link of the whole program: https://makecode.microbit.org/_cuufKuP6FARo

You can also check the program from the page below.

Result

  • When startup, micro:bit will display an image of house.
  • Press button A to call function func_A. We can use potentiometer to control the brightness of the LED screen . And we can press any button to finish the call of function.
  • Press button B to call function func_B, and micro:bit will display a flashing heart. And we can press any button to finish the call of function.
  • Press button C to call function func_C and clear the screen.
  • For other situations, micro:bit will display a house image.

Think

Q: why there is nothing happened when a button is pressed down?
A: The button status judgement is not always happen. When other section of code is running, the button program will stop judge.

Relative Readings

Interrupt: When something unexpected occured during the operation of a computer, it will stop the current program and transfer to a new program. Once the new program is processed, it will return to and continue its original suspended program.