Pulse – Flashing LED using micro:bit

by richard | Nov 30, 2017 | 0 comments

In this project we connect the micro:bit to an LED and make it pulse at various intervals.

You’ll need:

A micro:bit
A USB cable to link your micro:bit to the computer
A battery pack
Two crocodile clip connectors
An LED

Connect your micro:bit

Using your crocodile clips, carefully connect:

the Ground (GND) pin to the smaller of the two legs of the LED
Data pin 0 (0) to the other, larger leg of the LED

It should look like this:

Make sure that the two legs and connectors are not touching each other.

We’ve created an electronic circuit that uses power from the micro:bit to turn on the LED, but we can turn this on and off by changing the state of pin 0.

Load the Mu editor and type in the code to the right:

As before, we first we need to load the micro:bit libraries so that we can access all the micro:bit functions.

Now we can light the LED by setting the state pin 0 to high (1). By doing this we are turning pin 0 on and completing the electric circuit.

Try it: download to the micro:bit and check the LED is lit. If not, check your connections.

# Load the micro:bit libraries
from microbit import *

# Set pin 0 high (turn it on)
pin0.write_digital(1)

To create a pulse, we need to turn the LED off, which we do by adding a line to set pin 0 to low (0), breaking the circuit.

We need a pause in between otherwise it would be too fast to see. We are using the sleep command with 500 milliseconds so the LED should stay lit for half a second

Finally, we put this in a forever loop. Remember to be careful to tab out the code inside the loop.

Try it: the LED should now be flashing

# Load the micro:bit libraries
from microbit import *

# Loop forever
while True:
    # Set pin 0 high (turn it on)
    pin0.write_digital(1)
    sleep(500)
    # Set pin 0 low (turn it off)
    pin0.write_digital(0)
    sleep(500)

To control the speed of the pulse, we need to store the sleep time in a variable, which we can then change using the buttons.

Try changing the value of pulse, download it and see the effect.

# Load the micro:bit libraries
from microbit import *

# Set starting pulse at 0.5s
pulse = 500

# Loop forever
while True:
    # Set pin 0 high (turn it on)
    pin0.write_digital(1)
    sleep(pulse)
    # Set pin 0 low (turn it off)
    pin0.write_digital(0)
    sleep(pulse)

To change the pulse using the buttons we look for button press events, which looks this this:

Add this to your code, and try it. Pressing A increase the pulse by 0.1 seconds making the delay longer. Pressing B does the opposite.

Finally, add some images so that we get some extra feedback when we press a button:

# Load the micro:bit libraries
from microbit import *

# Set starting pulse at 0.5s
pulse = 500

while True:
    # Set pin 0 high (turn it on)
    pin0.write_digital(1)
    sleep(pulse)
    # Set pin 0 low (turn it off)
    pin0.write_digital(0)
    sleep(pulse)
    
    # Check for increase/decrease
    if button_a.was_pressed():
        display.show(Image.ARROW_N)
        pulse = pulse + 100
    elif button_b.was_pressed():
        display.show(Image.ARROW_S)
        pulse = pulse - 100

Pulse – Flashing LED using micro:bit

Connect your micro:bit

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