Add working traffic lights

main.py

@@ -0,0 +1,55 @@
+#!/usr/bin/env python3
+
+from gpiozero import Button, LED
+import time
+
+# define both traffic lights in order: red, amber, green
+# set main light to green and side light to red
+MAIN_LIGHTS = [LED(p, initial_value = i == 2) for i, p in enumerate((0, 5, 6))]
+SIDE_LIGHTS = [LED(p, initial_value = i == 0) for i, p in enumerate((13, 19, 26))]
+BTN = Button(20)
+
+# constants
+GREEN_BLINK_RATE = 0.5
+AMBER_STOP_DURATION = 2.5
+AMBER_GO_DURATION = 1
+SWITCH_SIDE_DELAY = 3
+SIDE_GREEN_DURATION = 5
+
+def green_to_red(lights):
+    # blink green
+    lights[2].blink(GREEN_BLINK_RATE, GREEN_BLINK_RATE, 2, False)
+    lights[2].off()
+    # show amber
+    lights[1].blink(AMBER_STOP_DURATION, 0, 1, False)
+    # show red
+    lights[0].on()
+
+def red_to_green(lights):
+    # show amber and red
+    lights[1].blink(AMBER_GO_DURATION, 0, 1, False)
+    lights[0].off()
+    # show green
+    lights[2].on()
+
+ongoing = False
+def sequence():
+    global ongoing
+    if ongoing:
+        return # block input if there's an ongoing sequence
+    ongoing = True
+
+    green_to_red(MAIN_LIGHTS)
+    time.sleep(SWITCH_SIDE_DELAY)
+    red_to_green(SIDE_LIGHTS)
+    time.sleep(SIDE_GREEN_DURATION)
+    green_to_red(SIDE_LIGHTS)
+    time.sleep(SWITCH_SIDE_DELAY)
+    red_to_green(MAIN_LIGHTS)
+
+    ongoing = False
+
+BTN.when_pressed = sequence
+
+input()
+