Automatic gate with ultrasonic sensor

Parts in this circuit

Wiring, pin by pin

Red = 5 V, orange = 3.3 V, black = GND, other colours = signals. “Pin” is the position on the 40-pin header; the GPIO number is what the code uses. Power the Pi from a 5.1 V supply and wire with the power off.

Python code (gpiozero)

from gpiozero import AngularServo, DistanceSensor, LED
from time import sleep

gate = AngularServo(17, min_angle=-90, max_angle=90)    # 0 = closed, 90 = open
sensor = DistanceSensor(echo=24, trigger=23, max_distance=2)
red = LED(23)
green = LED(22)

def car_near():
    return sensor.distance * 100 < 40

def close_gate():
    gate.angle = 0
    red.on()
    green.off()
    print("Gate CLOSED")

def open_gate():
    gate.angle = 90
    red.off()
    green.on()
    print("Gate OPEN")

close_gate()
while True:
    if car_near():
        open_gate()
        while car_near():             # stay open while the car is in the way
            sleep(0.2)
        sleep(2)                      # extra time for the car to pass
        close_gate()
    sleep(0.2)

How the code works

• car_near() returns True when the object is closer than 40 cm.
• The inner while loop keeps the gate open for as long as the car is there.
• After the car has gone, a 2 second delay gives a safety margin before closing.

Parts to buy

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