Drive a simple set of (UK) traffic lights using a Raspberry Pi and PiFace.

traffic_lights.py

import piface.pfio
import time
import sys

class trafficlight:
        """ A (UK) Traffic light """

        def __init__(self, red_pin, amber_pin, green_pin, start_on_red = False):
                self.red_pin = red_pin
                self.amber_pin = amber_pin
                self.green_pin = green_pin
                if start_on_red == True:
                        self.status = 'red'
                        piface.pfio.digital_write(self.red_pin, 1)
                else:
                        self.status = 'green'
                        piface.pfio.digital_write(self.green_pin, 1)

        def toggle(self):
                # Toggle lights according to the UK sequence
                if self.status == 'red':
                        piface.pfio.digital_write(self.red_pin, 1)
                        piface.pfio.digital_write(self.amber_pin, 1)
                        time.sleep(2)

                        piface.pfio.digital_write(self.red_pin, 0)
                        piface.pfio.digital_write(self.amber_pin, 0)
                        piface.pfio.digital_write(self.green_pin, 1)

                        self.status = 'green'
                else:
                        piface.pfio.digital_write(self.green_pin, 0)
                        piface.pfio.digital_write(self.amber_pin, 1)
                        time.sleep(2)

                        piface.pfio.digital_write(self.amber_pin, 0)
                        piface.pfio.digital_write(self.red_pin, 1)

                        self.status = 'red'


def main(argv):
        piface.pfio.init()

        # initialise our lights
        light1 = trafficlight(0,1,2, True)
        light2 = trafficlight(3,4,5)

        loop = 0
        while loop < 10:
                # Quick lights
                time.sleep(5)

                # we want to turn the green one red before turning the red one green - safety first!
                if light1.status == 'green':
                        light1.toggle()
                        light2.toggle()
                else:
                        light2.toggle()
                        light1.toggle()

                loop = loop + 1


if __name__ == "__main__":
    sys.exit(main(sys.argv))