4. LEDs with resistors

4.1. Connections

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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4.2. 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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4.3. 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.

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4.4. Turn on and off pin0

Pressing A turns on the LED on pin0.

Pressing B turns off the LED on pin0.

from microbit import *


def turnon_0():
    pin0.write_digital(1)


def turnoff_0():
    pin0.write_digital(0)


while True:
    if button_a.is_pressed():
        turnon_0()
    elif button_b.is_pressed():
        turnoff_0()
    sleep(500)

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4.5. Blink All

Pressing A blinks all 3 LEDS in order.

Pressing B blinks all 3 LEDS together.

from microbit import *


def blink_all_in_sequence():
    pin0.write_digital(1)
    sleep(1000)
    pin0.write_digital(0)
    pin1.write_digital(1)
    sleep(300)
    pin1.write_digital(0)
    pin2.write_digital(1)
    sleep(1000)
    pin2.write_digital(0)


def blink_all():
    pin0.write_digital(1)
    pin1.write_digital(1)
    pin2.write_digital(1)
    sleep(1000)
    pin0.write_digital(0)
    pin1.write_digital(0)
    pin2.write_digital(0)


while True:
    if button_a.is_pressed():
        blink_all_in_sequence()
    elif button_b.is_pressed():
        blink_all()
    sleep(500)

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4.6. Blink using for i in range

Repeated blinking can be done with a for-loop.

The for-loop below runs 3 times, with i values of 0, 1, and 2.

from microbit import *


def blink0():
    for i in range(3):
        pin0.write_digital(1)
        sleep(1000)
        pin0.write_digital(0)
        sleep(1000)


blink0()

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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. A-button 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 *


def do_A():
    pin0.write_digital(0)
    pin1.write_digital(0)
    pin2.write_digital(1)


def do_B():
    pin0.write_digital(0)
    pin1.write_digital(1)
    pin2.write_digital(0)
    sleep(3000)
    pin0.write_digital(1)
    pin1.write_digital(0)


while True:
    if button_a.is_pressed():
        do_A()
    elif button_b.is_pressed():
        do_B()
    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 *


def blink_A():
    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)


def blink_B():
    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)


while True:
    if button_a.is_pressed():
        blink_A()
    elif button_b.is_pressed():
        blink_B()
    sleep(500)

Q3

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

from microbit import *


def red_on():
    pin0.write_digital(1)
    pin1.write_digital(0)
    pin2.write_digital(0)


def yellow_on():
    pin0.write_digital(0)
    pin1.write_digital(1)
    pin2.write_digital(0)


def green_on():
    pin0.write_digital(0)
    pin1.write_digital(0)
    pin2.write_digital(1)


while True:
    if button_a.is_pressed() and button_b.is_pressed():
        red_on()
    elif button_a.is_pressed():
        yellow_on()
    elif button_b.is_pressed():
        green_on()
    sleep(500)

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4.7. 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 making use of write_analog on pin0.

from microbit import *


def pulse_on():
    sleeptime = 40
    stepsize = 30
    for i in range(0, 1024, stepsize):
        pin0.write_analog(i)
        sleep(sleeptime)
    pin0.write_analog(0)


def pulse_off():
    sleeptime = 40
    stepsize = 30
    for i in range(1023, -1, -stepsize):
        pin0.write_analog(i)
        sleep(sleeptime)
    pin0.write_analog(0)


while True:
    if button_a.is_pressed():
        pulse_on()
    elif button_b.is_pressed():
        pulse_off()
    sleep(500)

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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).

Q1

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

from microbit import *


def pulse_all_on():
    sleeptime = 40
    stepsize = 30
    for i in range(0, 1024, stepsize):
        pin0.write_analog(i)
        pin1.write_analog(i)
        pin2.write_analog(i)
        sleep(sleeptime)


def pulse_all_off():
    sleeptime = 40
    stepsize = 30
    for i in range(1023, -1, -stepsize):
        pin0.write_analog(i)
        pin1.write_analog(i)
        pin2.write_analog(i)
        sleep(sleeptime)


while True:
    if button_a.is_pressed():
        pulse_all_on()
    elif button_b.is_pressed():
        pulse_all_off()
    sleep(500)

Q2

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 *


def pulse_all_diff_on():
    sleeptime = 50
    stepsize = 30
    for i in range(0, 1704, stepsize):
        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(sleeptime)



def pulse_all_diff_off():
    sleeptime = 50
    stepsize = 30
    for i in range(1704, -1, -stepsize):
        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(sleeptime)
    pin0.write_analog(0)


while True:
    if button_a.is_pressed():
        pulse_all_diff_on()
    elif button_b.is_pressed():
        pulse_all_diff_off()
    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 pinlist = [pin0, pin1, pin2] to make a list of pins to choose from. See: https://www.w3schools.com/python/ref_random_choice.asp.

3. V2 microbit: Use power module so that the B-button puts the microbit into a deep sleep for 10 minutes. Wake it on pressing the A-button. Turn on random LEDS at random brightness every 3 seconds, then off.

Q1

from microbit import *
import random


def random_colours():
    randval = random.randrange(0, 1024)
    randpin = random.randrange(0, 3)
    if randpin == 0:
        pin0.write_analog(randval)
    elif randpin == 1:
        pin1.write_analog(randval)
    elif randpin == 2:
        pin2.write_analog(randval)


while True:
    random_colours()
    sleep(100)

Q2

from microbit import *
import random

pinlist = [pin0, pin1, pin2]


def random_pin_brightness():
    randval = random.randrange(0, 1024)
    randpin = random.choice(pinlist)
    randpin.write_analog(randval)


while True:
    random_pin_brightness()
    sleep(100)

Q2

from microbit import *
import random
import power


pinlist = [pin0, pin1, pin2]


def random_pin_brightness():
    randval = random.randrange(0, 1024)
    randpin = random.choice(pinlist)
    randpin.write_analog(randval)


def turnoff():
    pin0.write_digital(0)
    pin1.write_digital(0)
    pin2.write_digital(0)

@run_every(s=3)
def wakeup_call():
    random_pin_brightness()
    sleep(2000)
    turnoff()


while True:
    if button_b.was_pressed():
        sleep(300)
        power.deep_sleep(wake_on=button_a,ms=600 * 1000,run_every=False)
    sleep(1000)