3. LEDs_with_resistors

The examples below use sequence only. No definition blocks are used.

For better organising code into def blocks see: https://pc-microbit-micropython.readthedocs.io/en/latest/breadboards/LEDs_with_resistors_2.html

The LEDs must be placed in line with a 47 ohm resistor.

The 47 ohm resistor has Yellow, Violet, Black, Gold coloured bands.

LEDS are normally connected to pin0, pin1, or pin2.

All LEDS are also connected to the 0V pins.

Bend the resistor by holding it at the bend position so it is U-shaped.

Place the resistor in the breadboard so that the legs go in about 5mm.

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3.1. Model

1. Place the resistors first.

2. Place the LEDs with the long lead (leg) so that it is closest to the pin side of the circuit. In this model, the long lead is on the left side of the breadboard.

3. Check that the red LED is connected to pin0, yellow to pin1, and green to pin2.

4. Connect with the jumper wires.

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3.2. Write digital

pinx.write_digital(value)

pinx is the pin. e.g pin0, pin1, pin2.

value is 1 for on and 0 for off.

To turn the LED on fully use pin0.write_digital(1) for the LED on pin0.

To turn the LED off use pin0.write_digital(0) for the LED on pin0.

For the other pins, just replace pin0 with pin1 or pin2.

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3.3. Turn on and off pin0

Pressing A turns on the LED on pin0.

Pressing B turns off the LED on pin0.

from microbit import *


while True:
    if button_a.is_pressed():
        pin0.write_digital(1)
    elif button_b.is_pressed():
        pin0.write_digital(0)
    sleep(500)

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3.4. Turn all on and off

Pressing A turns on the LED on pin0, pin1 and pin2.

Pressing B turns off the LED on pin0, pin1 and pin2.

from microbit import *


while True:
    if button_a.is_pressed():
        pin0.write_digital(1)
        pin1.write_digital(1)
        pin2.write_digital(1)
    elif button_b.is_pressed():
        pin0.write_digital(0)
        pin1.write_digital(0)
        pin2.write_digital(0)
    sleep(500)

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Tasks

Remember that the red LED is on pin0, yellow on pin1, and green on pin2.

1. Write code so that pressing A turns on the red LED only and pressing B turns on the yellow and green LEDs only.

2. Write code so that pressing A turns on the green LED only and pressing B turns on the yellow and red LEDs only.

Q1

Write code so that pressing A turns on the red LED only and pressing B turns on the yellow and green LEDs only.

from microbit import *


while True:
    if button_a.is_pressed():
        pin0.write_digital(1)
        pin1.write_digital(0)
        pin2.write_digital(0)
    elif button_b.is_pressed():
        pin0.write_digital(0)
        pin1.write_digital(0)
        pin2.write_digital(1)
    sleep(500)

Q2

Write code so that pressing A turns on the green LED only and pressing B turns on the yellow and red LEDs only.

from microbit import *


while True:
    if button_a.is_pressed():
        pin0.write_digital(0)
        pin1.write_digital(0)
        pin2.write_digital(1)
    elif button_b.is_pressed():
        pin0.write_digital(1)
        pin1.write_digital(1)
        pin2.write_digital(0)
    sleep(500)

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3.5. Blink All

Pressing A blinks all 3 LEDS in order, one after the other every one and a half seconds.

Pressing B blinks all 3 LEDS together every one and a half seconds.

from microbit import *


while True:
    if button_a.is_pressed():
        pin0.write_digital(1)
        sleep(500)
        pin0.write_digital(0)
        pin1.write_digital(1)
        sleep(500)
        pin1.write_digital(0)
        pin2.write_digital(1)
        sleep(500)
        pin2.write_digital(0)
    elif button_b.is_pressed():
        pin0.write_digital(1)
        pin1.write_digital(1)
        pin2.write_digital(1)
        sleep(750)
        pin0.write_digital(0)
        pin1.write_digital(0)
        pin2.write_digital(0)
        sleep(750)

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3.6. Blink using for i in range

Repeated blinking can be done with a for-loop.

The for-loop below runs 3 times in 6 seconds then sleeps for 3 seconds before repeating.

from microbit import *


while True:
    for i in range(3):
        pin0.write_digital(1)
        sleep(1000)
        pin0.write_digital(0)
        sleep(1000)
    sleep(3000)

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Tasks

Remember that the red LED is on pin0, yellow on pin1, and green on pin2.

1. Write code so that pressing A turns on the green LED only and pressing B turns on the yellow LED for 3 seconds then turns on the red LED only.

2. Write code so that pressing A blinks red and yellow 3 times, while pressing B blinks yellow and green 3 times.

3. Write code to turn on each of the LED’s separately with button presses. e.g. button-A turns on red and turns the others off.

Q1

Write code so that pressing A turns on the green LED only and pressing B turns on the yellow LED for 3 seconds then turns on the red LED only.

from microbit import *


while True:
    if button_a.is_pressed():
        pin0.write_digital(0)
        pin1.write_digital(0)
        pin2.write_digital(1)
    elif button_b.is_pressed():
        pin0.write_digital(0)
        pin1.write_digital(1)
        pin2.write_digital(0)
        sleep(3000)
        pin0.write_digital(1)
        pin1.write_digital(0)
    sleep(500)

Q2

Write code so that pressing A blinks red and yellow 3 times, while pressing B blinks yellow and green 3 times.

from microbit import *


while True:
    if button_a.is_pressed():
        for i in range(3):
            pin0.write_digital(1)
            pin1.write_digital(1)
            sleep(1000)
            pin0.write_digital(0)
            pin1.write_digital(0)
            sleep(1000)
    elif button_b.is_pressed():
        for i in range(3):
            pin1.write_digital(1)
            pin2.write_digital(1)
            sleep(1000)
            pin1.write_digital(0)
            pin2.write_digital(0)
            sleep(1000)
    sleep(500)

Q3

Write code to turn on each of the LED’s separately with button presses. e.g. button-A turns on red and turns the others off.

from microbit import *


while True:
    if button_a.is_pressed() and button_b.is_pressed():
        pin0.write_digital(1)
        pin1.write_digital(0)
        pin2.write_digital(0)
    elif button_a.is_pressed():
        pin0.write_digital(0)
        pin1.write_digital(1)
        pin2.write_digital(0)
    elif button_b.is_pressed():
        pin0.write_digital(0)
        pin1.write_digital(0)
        pin2.write_digital(1)
    sleep(500)

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3.7. Write analog

pinx.write_analog(value)

pinx is the pin. e.g pin0, pin1, pin2.

value is an integer from 0 to 1023.

To turn the LED on fully use pin0.write_analog(1023) for the LED on pin0.

To turn the LED off use pin0.write_analog(0) for the LED on pin0.

write_analog can have values from 0 to 1023.

write_analog can be used to dim the LED.

Here is some sample code that set various brightnesses using write_analog on pin0.

from microbit import *

while True:
    if button_a.is_pressed():
        pin0.write_analog(256)
        sleep(500)
        pin0.write_analog(512)
        sleep(500)
        pin0.write_analog(768)
        sleep(500)
        pin0.write_analog(1023)
        sleep(500)
        pin0.write_analog(0)
        sleep(500)
    sleep(500)

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Tasks

1. Write code to use the A button to turn on all 3 LEDs at half brightness and the B button to turn them all off.

2. Write code to use the A button to turn on the red LED at half brightness, yellow at three quarter brightness and green at full brightness and the B button to turn them all off.

Q1

Write code to use the A button to turn on all 3 LEDs at half brightness and the B button to turn them all off.

from microbit import *

while True:
    if button_a.is_pressed():
        pin0.write_analog(512)
        pin1.write_analog(512)
        pin2.write_analog(512)
    elif button_b.is_pressed():
        pin0.write_analog(0)
        pin1.write_analog(0)
        pin2.write_analog(0)
    sleep(500)

Q2

Write code to use the A button to turn on the red LED at half brightness, yellow at three quarter brightness and green at full brightness and the B button to turn them all off.

from microbit import *

while True:
    if button_a.is_pressed():
        pin0.write_analog(512)
        pin1.write_analog(768)
        pin2.write_analog(1023)
    elif button_b.is_pressed():
        pin0.write_analog(0)
        pin1.write_analog(0)
        pin2.write_analog(0)
    sleep(500)

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Here is some sample code that cycles through a brightness list using write_analog on pin0.

from microbit import *

brightness_list = [0, 256, 512, 768, 1023]
sleep_time = 250
while True:
    if button_a.is_pressed():
        # pulse_on
        for i in brightness_list:
            pin0.write_analog(i)
            sleep(sleep_time)
    sleep(500)

Here is some sample code that cycles through a brightness list using write_analog on pin0.

The brightness value in the list is subtracted from 1023, so as the list value increases, the LED brightness decreases.

from microbit import *

brightness_list = [0, 256, 512, 768, 1023]
sleep_time = 250
while True:
    if button_b.is_pressed():
        # pulse_off
        for i in brightness_list:
            pin0.write_analog(1023-i)
            sleep(sleep_time)
    sleep(500)

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Tasks

1. Modify the code to pulse on all 3 LEDs together.

2. Modify the code to pulse off all 3 LEDs together.

Q1

Modify the code to pulse on all 3 LEDs together.

from microbit import *

brightness_list = [0, 256, 512, 768, 1023]
sleep_time = 250
while True:
    if button_a.is_pressed():
        # pulse_all_on
        for i in brightness_list:
            pin0.write_analog(i)
            pin1.write_analog(i)
            pin2.write_analog(i)
            sleep(sleep_time)
    sleep(500)

Q2

Modify the code to pulse off all 3 LEDs together.

from microbit import *

brightness_list = [0, 256, 512, 768, 1023]
sleep_time = 250
while True:
    if button_b.is_pressed():
        # pulse_all_off
        for i in brightness_list:
            pin0.write_analog(1023-i)
            pin1.write_analog(1023-i)
            pin2.write_analog(1023-i)
            sleep(sleep_time)
    sleep(500)

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EXT Exercise

1. Write code to pulse on all 3 LEDs but with delay of 1 step in the list for yellow using brightness_list[i - 1] and 2 steps for green using brightness_list[i - 2].

2. Write code to pulse off all 3 LEDs but with delay of 1 step in the list for yellow using brightness_list[i - 1] and 2 steps for green using brightness_list[i - 2].

Q1

Write code to pulse on all 3 LEDs but with delay of 1 step in the list for yellow using brightness_list[i - 1] and 2 steps for green using brightness_list[i - 2].

from microbit import *

brightness_list = [0, 256, 512, 768, 1023, 1023, 1023]
sleep_time = 250

while True:
    if button_a.is_pressed():
        # Pulse LEDs with staggered delays
        for i in range(len(brightness_list)):
            pin0.write_analog(brightness_list[i])  # Red LED
            if i >= 1:
                pin1.write_analog(brightness_list[i - 1])  # Yellow LED (1 step delay)
            if i >= 2:
                pin2.write_analog(brightness_list[i - 2])  # Green LED (2 step delay)
            sleep(sleep_time)

    sleep(500)

Q2

Write code to pulse off all 3 LEDs but with delay of 1 step in the list for yellow using brightness_list[i - 1] and 2 steps for green using brightness_list[i - 2].

from microbit import *

brightness_list = [0, 256, 512, 768, 1023, 1023, 1023]  # Adjusted valid range with max brightness at end
sleep_time = 250

while True:
    if button_b.is_pressed():
        # Pulse LEDs using inverted brightness values
        for i in range(len(brightness_list)):
            pin0.write_analog(1023 - brightness_list[i])  # Red LED (inverted brightness)
            if i >= 1:
                pin1.write_analog(1023 - brightness_list[i - 1])  # Yellow LED (1 step delay, inverted)
            if i >= 2:
                pin2.write_analog(1023 - brightness_list[i - 2])  # Green LED (2 step delay, inverted)
            sleep(sleep_time)
    sleep(500)