How do I incorporate a button for pedestrian crossing when making traffic lights?

Question

Here's a link to what I have been trying a accomplish: https://projects.raspberrypi.org/en/projects/physical-computing/9

Near the bottom of the page it says, "Try adding the button for a pedestrian crossing. The button should move the lights to red (not immediately), and give the pedestrians time to cross before moving back to green until the button is pressed again."

This is what I currently have for code:

from gpiozero import Button, TrafficLights
from time import sleep
from signal import pause

button = Button(21)
lights = TrafficLights(4, 5, 6)

print("Normal operation")
def sleep1():
        for i in range(100):
                sleep(0.1)
                if button.is_pressed:
                        sleep(4)
                        lights.off()
                        lights.amber.on()
                        sleep(3)
                        lights.amber.off()
                        lights.red.on()
                        print("Pedestian crossing")
                        sleep(10)
                        lights.off()
                        lights.green.on()
                        sleep(6)

while True:
        lights.green.on()
        sleep1()
        lights.green.off()
        lights.amber.on()
        sleep(3)
        lights.amber.off()
        lights.red.on()
        sleep(10)
        lights.off()

It sort of does what I want it to do. I would like for the "while True" sequence to restart once the "Pedestrian" sequence is completed. Does anyone have any suggestions?

Answer 1

Try the when_pressed method of the Button class from earlier project in the same tutorial.

It would be great if you could make the LED switch on only when the button is being held down. With GPIO Zero, that’s easy. There are two methods of the Button class called when_pressed and when_released. These don’t block the flow of the program, so if they are placed in a loop, the program will continue to cycle indefinitely.

Answer 2

I was trying to solve this same issue and found the need for a global variable to keep track of the status of if the button had been clicked or not. It seems that button.when_pressed starts a new thread and the code in the loop continues to execute along with the function assigned to the button call. The accepted answer does not explain how to solve this problem, but just suggests a method to use without giving an explanation of how to implement it.

Notice the for loop and if statement in the run_lights() function. You have to make sure that you sleep for the accumulated amount of time that your function runs that was triggered by the button press.

Also, by turning the green light back on at the end of the pressed() function fixed an issue where there could be >1 second with no lights on due to a mid-second button push.

from gpiozero import LED, Button, TrafficLights
from time import sleep

traffic_light = TrafficLights(16, 20, 21)
button = Button(26)
white_light = LED(19)

is_pressed = False


def pressed():
    if traffic_light.green.is_lit:
        global is_pressed
        is_pressed = True

        white_light.on()
        sleep(1)
        traffic_light.green.off()
        traffic_light.yellow.on()
        sleep(3)
        traffic_light.yellow.off()

        white_light.off()
        traffic_light.red.on()
        sleep(10)
        traffic_light.red.off()
        traffic_light.green.on()


def run_lights():
    global is_pressed
    while True:
        button.when_pressed = pressed

        traffic_light.green.on()

        for i in range(10):
            sleep(1)
            if is_pressed:
                button.when_pressed = None
                sleep(14)
                break
        if is_pressed:
            is_pressed = False
            continue

        traffic_light.green.off()

        traffic_light.yellow.on()
        sleep(3)
        traffic_light.yellow.off()

        traffic_light.red.on()
        sleep(10)
        traffic_light.red.off()


def main():
    run_lights()


if __name__ == '__main__':
    main()