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.
../_images/47ohm.png
Bend the resistor by holding it at the bend position so it is U-shaped.
../_images/resistor_shape.png
Place the resistor in the breadboard so that the legs go in about 5mm.
../_images/resistor_on_breadboard_low.png

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.

../_images/3LEDS_1_bb.png ../_images/3LEDS_2_bb.png ../_images/3LEDS_3_bb.png ../_images/LEDS.jpg

3.2. Write digital

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.

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)

3.6. Write analog

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 cycles through a brightness list using write_analog on pin0.
from microbit import *

brightness = [0, 205, 511, 716, 1023]
sleep_time = 250
while True:
    if button_a.is_pressed():
        # pulse_on
        for i in brightness:
            pin0.write_analog(i)
            sleep(sleep_time)
        pin0.write_analog(0)
    elif button_b.is_pressed():
        # pulse_off
        for i in brightness
            pin0.write_analog(1023-i)
            sleep(sleep_time)
        pin0.write_analog(0)
    sleep(500)
Here is some sample code which pulses the LED on and off.
from microbit import *


while True:
    if button_a.is_pressed():
        # pulse_on
        sleep_time = 40
        step_size = 30
        for i in range(0, 1024, step_size):
            pin0.write_analog(i)
            sleep(sleep_time)
        pin0.write_analog(0)
    elif button_b.is_pressed():
        # pulse_off
        sleep_time = 40
        step_size = 30
        for i in range(1023, -1, -step_size):
            pin0.write_analog(i)
            sleep(sleep_time)
        pin0.write_analog(0)
    sleep(500)

Tasks

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

  2. Write code to pulse all 3 LEDs but with an analog difference of about 340, so that when the red LED is at 1023 the yellow is at (1023 - 340) and the green LED is at (1023 - 340 -340).

Modify the code to pulse on and off all 3 LEDs together.

from microbit import *


while True:
    if button_a.is_pressed():
        # pulse_all_on
        sleep_time = 40
        step_size = 30
        for i in range(0, 1024, step_size):
            pin0.write_analog(i)
            pin1.write_analog(i)
            pin2.write_analog(i)
            sleep(sleep_time)
    elif button_b.is_pressed():
        # pulse_all_off
        sleep_time = 40
        step_size = 30
        for i in range(1023, -1, -step_size):
            pin0.write_analog(i)
            pin1.write_analog(i)
            pin2.write_analog(i)
            sleep(sleep_time)
    sleep(500)

Write code to pulse all 3 LEDs but with an analog difference of about 340, so that when the red LED is at 1023 the yellow is at (1023 - 340) and the green LED is at (1023 - 340 -340).

from microbit import *


while True:
    if button_a.is_pressed():
        # pulse_all_diff_on
        sleep_time = 50
        step_size = 30
        for i in range(0, 1704, step_size):
            pin0.write_analog(min(1023, i))
            pin1.write_analog(max(0, min(1023, i - 340)))
            pin2.write_analog(max(0, min(1023, i - 680)))
            sleep(sleep_time)
    elif button_b.is_pressed():
        # pulse_all_diff_off
        sleep_time = 50
        step_size = 30
        for i in range(1704, -1, -step_size):
            pin0.write_analog(min(1023, i))
            pin1.write_analog(max(0, min(1023, i - 340)))
            pin2.write_analog(max(0, min(1023, i - 680)))
            sleep(sleep_time)
        pin0.write_analog(0)
    sleep(500)

Exercises

  1. Investigate the use of the randrange function for creating random light displays. See: https://www.w3schools.com/python/ref_random_randrange.asp

  2. Investigate the use of the choice function for creating random light displays. Use pin_list = [pin0, pin1, pin2] to make a list of pins to choose from. See: https://www.w3schools.com/python/ref_random_choice.asp.

from microbit import *
import random


while True:
    # random_colors
    rand_val = random.randrange(0, 1024)
    rand_pin = random.randrange(0, 3)
    if rand_pin = 0:
        pin0.write_analog(rand_val)
    elif rand_pin = 1:
        pin1.write_analog(rand_val)
    elif rand_pin = 2:
        pin2.write_analog(rand_val)
    sleep(100)

from microbit import *
import random

pin_list = [pin0, pin1, pin2]

while True:
    # random_pin_brightness
    rand_val = random.randrange(0, 1024)
    rand_pin = random.choice(pin_list)
    rand_pin.write_analog(rand_val)
    sleep(100)