micro:bit Lesson 2. Controlling LEDs on Breadboard

by Simon Monk

published March 09, 2018, last edited March 08, 2024

Beginner

Skill guide

LED Brightness Control

As well as turning an LED on and off, you can also use it to control the brightness of the LED.

In this example, the A button will make the LED dimmer and the B button make it brighter. At the same time, the micro:bits built-in LED display will show a number between 0 and 9 indicating the brightness level.

JavaScript Block Code

To open the JavaScript Block code in a separate tab, click here.

As you can see, there is actually quite a lot going on here. Lets start with the on start block. This block is run just once when the micro:bit starts and it defines four variables:

min_power - the minimum output level for the LED when 0 is off and 1023 is maximum brightness
max_power - the maximum output level for the LED. These two variable allow you to set the possible range of brightnesses.
power_step - the brighness will be changed in 10 steps and so this value is calculated from the minumum and maximum.
brightness - the brightness level as a number between 0 and 10.

The forever loop which runs repeatedly sets the value of a variable called power according to the brightness level.

To increase and decrease the brightness, two handlers are used. These respond to either a press of button A or button B and then display the brightness level and set the output level on pin0 using the analog write block.

MicroPython

Here is the MicroPython code for the LED dimmer.

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from microbit import *

min_power = 50
max_power = 1023
power_step = (max_power - min_power) / 9
brightness = 0

def set_power(brightness):
    display.show(str(brightness))
    if brightness == 0:
        pin0.write_analog(0)
    else:
        pin0.write_analog(brightness * power_step + min_power)
   
set_power(brightness)
   
while True:
    if button_a.was_pressed():
        brightness -= 1
        if brightness < 0:
            brightness = 0
        set_power(brightness)
    elif button_b.was_pressed():
        brightness += 1
        if brightness > 9:
            brightness = 9
        set_power(brightness)
    sleep(100)

from microbit import *

min_power = 50
max_power = 1023
power_step = (max_power - min_power) / 9
brightness = 0

def set_power(brightness):
    display.show(str(brightness))
    if brightness == 0:
        pin0.write_analog(0)
    else:
        pin0.write_analog(brightness * power_step + min_power)
   
set_power(brightness)
   
while True:
    if button_a.was_pressed():
        brightness -= 1
        if brightness < 0:
            brightness = 0
        set_power(brightness)
    elif button_b.was_pressed():
        brightness += 1
        if brightness > 9:
            brightness = 9
        set_power(brightness)
    sleep(100)

Arduino Code

The Arduino code for using the micro:bit's display is a little different because it uses the Adafruit GFX Library.

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#include <Adafruit_Microbit.h>

const int ledPin = 0;

const int minPower = 50;
const int maxPower = 255;
const int powerStep = (maxPower - minPower) / 9;

int brightness = 0;
Adafruit_Microbit_Matrix microbit;

void setup() {
  pinMode(ledPin, OUTPUT);
  microbit.begin();
  pinMode(PIN_BUTTON_A, INPUT);
  pinMode(PIN_BUTTON_B, INPUT);
  setPower(brightness);
}

void loop() {
  if (digitalRead(PIN_BUTTON_A) == LOW) {
    brightness --;
    if (brightness < 0) {
      brightness = 0;
    }
    setPower(brightness);
    delay(200);
  }
  else if (digitalRead(PIN_BUTTON_B) == LOW) {
    brightness ++;
    if (brightness > 9) {
      brightness = 9;
    }
    setPower(brightness);
    delay(200);
  }
}

void setPower(int brightness) {
  microbit.print(brightness);
  if (brightness == 0) {
    analogWrite(ledPin, 0);
  }
  else {
    analogWrite(ledPin, brightness * powerStep + minPower);
  }
}

#include <Adafruit_Microbit.h>

const int ledPin = 0;

const int minPower = 50;
const int maxPower = 255;
const int powerStep = (maxPower - minPower) / 9;

int brightness = 0;
Adafruit_Microbit_Matrix microbit;

void setup() {
  pinMode(ledPin, OUTPUT);
  microbit.begin();
  pinMode(PIN_BUTTON_A, INPUT);
  pinMode(PIN_BUTTON_B, INPUT);
  setPower(brightness);
}

void loop() {
  if (digitalRead(PIN_BUTTON_A) == LOW) {
    brightness --;
    if (brightness < 0) {
      brightness = 0;
    }
    setPower(brightness);
    delay(200);
  }
  else if (digitalRead(PIN_BUTTON_B) == LOW) {
    brightness ++;
    if (brightness > 9) {
      brightness = 9;
    }
    setPower(brightness);
    delay(200);
  }
}

void setPower(int brightness) {
  microbit.print(brightness);
  if (brightness == 0) {
    analogWrite(ledPin, 0);
  }
  else {
    analogWrite(ledPin, brightness * powerStep + minPower);
  }
}

Page last edited March 08, 2024