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.
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.
#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);
}
}
