Micro:bit Traffic Lights

A simple, but fun, application of the BBC Micro:bit is to build a set of pedestrian traffic lights. You push the button, the lights cycle to red, it goes pip-pip-pip then the lights cycle back to green.



Pin 0 goes to the active piezo buzzer, pins 13, 14, 15 are the G, Y, R LEDs and the "cross" switch is on pin 16. The LEDs have series 330R resistors (the current must be limited to less than 5mA for the micro:bit), and the switch has a pull up resistor of 10k to 3V.

Code

# Traffic lights
# pins 330R-LED-GND: 13 green, 14 yellow, 15 red, 16 switch(10k pull-up, active LOW)

# import the micropython library
from microbit import *

# set period of pin 0 pwm output
pin0.set_analog_period(400)
pin0.write_analog(0)

while True:
    # green on
    pin13.write_digital(1)
    display.show("G")
    
    # wait for switch
    if pin16.read_digital() != 1:
        
        # green off, yellow on
        pin13.write_digital(0)
        pin14.write_digital(1)
        display.show("Y")
        sleep(2000)
        
        # yellow off, red on, pip-pip-pip
        pin14.write_digital(0)
        pin15.write_digital(1)
        display.show("R")
        pin0.write_analog(200)
        sleep(8000)
        
        # yellow on, red remains on, pip off
        pin14.write_digital(1)
        display.show("Y")
        pin0.write_analog(0)
        sleep(2000)
        
        # red & yellow off
        pin14.write_digital(0)
        pin15.write_digital(0)

# loop

Press the button to cross the road