Project 02: Traffic Lights

1. Overview

In this project, we adopt three LEDs( red, yellow and green), a speaker on micro:bit board and 5x5 LED matrix to make a model of traffic lights.

2. Components

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micro:bit board *1

micro:bit T-type expansion board *1

micro USB cable *1

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red LED *1

yellow LED *1

green LED *1

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220Ω resistor *3

jump wires

breadboard *1

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battery holder *1
(self-provided AA batteries *2)

traffic lights card *1

3. Components Knowledge

Speaker

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Micro: bit comes with a speaker, which makes it easy to make sound in your project.

4. Wiring Diagram

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Note: the micro:bit board needs to be inserted into the T-type expansion board as shown below. The micro:bit board LED matrix should be on the same side with the logo of the expansion board.

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5. Code Flow

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6. Test Code

The code file is provided in folder Project 02：Traffic Lights, file Project-02-Traffic-Lights.py.

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Complete code:

'''
Function: traffic lights with countdowns and buzzes
Compiling IDE: MU 1.2.0
Author: https://docs.keyestudio.com
'''
# import microbit related libraries
from microbit import *

pin1.write_digital(0) # set P1 pin to low
pin2.write_digital(0) # set P2 pin to low
pin8.write_digital(0) # set P8 pin to low

import music # import music libraries

while True:
   pin1.write_digital(1)  # P1 pin to high
   display.show('6')  # LED matrixs shows 6
   sleep(1000)        # delay 1s
   display.show('5')
   sleep(1000)
   display.show('4')
   sleep(1000)
   display.show('3')
   sleep(1000)
   display.show('2')
   sleep(1000)
   display.show('1')
   sleep(1000)
   display.show('0')
   sleep(1000)
   pin1.write_digital(0)
   pin2.write_digital(1)
   music.play("C4:4")    # speaker plays C4 tone
   display.show('2')
   sleep(500)
   pin2.write_digital(0)
   music.reset()         # no tone
   sleep(500)
   pin2.write_digital(1)
   music.play("C4:4")
   display.show('1')
   sleep(500)
   pin2.write_digital(0)
   music.reset()
   sleep(500)
   pin2.write_digital(1)
   music.play("C4:4")
   display.show('0')
   sleep(500)
   pin2.write_digital(0)
   music.reset()
   sleep(500)
   pin8.write_digital(1)
   display.show('6')
   sleep(1000)
   display.show('5')
   sleep(1000)
   display.show('4')
   sleep(1000)
   display.show('3')
   sleep(1000)
   display.show('2')
   sleep(1000)
   display.show('1')
   sleep(1000)
   display.show('0')
   sleep(1000)
   pin8.write_digital(0)

7. Test Result

Click “Flash” to load the code to the micro:bit board.

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After downloading the code to the board, power on via micro USB cable or external power supply(turn the DIP switch to ON), and press the reset button on the board.

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The green LED turns on and the 5×5 LED matrix counts down 6 seconds. After the green LED is off, the yellow LED flashes and the matrix counts down 3s with speaker sounding. At last, the red LED is on with a countdown of 6s. These actions repeat.

ATTENTION: If the wiring is correct but you cannot see the results, press the reset button on the back of the board.

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When powering on via external power supply, turn the DIP switch to ON.

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