Middle School
Automatic Parking Barrier
Combine a sensor and a servo to build a gate that opens automatically when a car arrives.
- Level
- Builder
- Time
- 1 hr
- Parts
- 6
- Hardware-checked
- Not yet
What this build assumes
- Measuring distance
- Calibrating a threshold
0 of 5 build milestones complete
What this build is
Real parking garages open their gate automatically once a sensor detects a car waiting.
This project combines the distance sensing from your last build with the servo motion from your first to create one automated machine.
How it works
System architecture
Input
The sensor detects a car has arrived.
Decision
Your code checks its state so it doesn't reopen an already-open barrier.
Output
The servo raises the barrier, then lowers it after a delay.
Parts
Microcontroller board × 1
Reads the sensor and decides when to move the barrier.
Micro servo motor × 1
Lifts and lowers the barrier arm.
Ultrasonic distance sensor × 1
Detects when a car (or hand) has arrived at the gate.
Barrier arm (craft stick or included arm piece) × 1
Acts as the physical gate attached to the servo.
Breadboard × 1
Holds the sensor and servo wiring in place.
Jumper wires × a handful
Wire the sensor and servo to the board.
Build
- 1
Attach the barrier arm to the servo
Fix the barrier arm to the servo horn so it swings up when the servo rotates.
Barrier arm attachment diagram
Not drawn yet. We only publish a diagram once someone has built this with real parts and checked it — so rather than guess at the connections, we are telling you they are missing. The written wiring notes are accurate.
- 2
Mount the distance sensor at the gate
Position the sensor so it faces where a car (or your hand) will approach.
Sensor placement diagram
Not drawn yet. We only publish a diagram once someone has built this with real parts and checked it — so rather than guess at the connections, we are telling you they are missing. The written wiring notes are accurate.
- 3
Wire the sensor and servo
Connect the sensor's and servo's power, ground, and signal pins to your board.
Sensor and servo wiring diagram
Not drawn yet. We only publish a diagram once someone has built this with real parts and checked it — so rather than guess at the connections, we are telling you they are missing. The written wiring notes are accurate.
- 4
Upload the automation code
Connect your board to your computer and upload the code below.
- 5
Test the open/close timing
Trigger the sensor and confirm the barrier opens, holds, then closes on its own.
Wiring
Automatic Parking Barrier wiring diagram
Not drawn yet. We only publish a diagram once someone has built this with real parts and checked it — so rather than guess at the connections, we are telling you they are missing. The written wiring notes are accurate.
The distance sensor's power/ground connect to 5V/GND, with trigger and echo on two digital pins. The servo's power/ground also connect to 5V/GND (or a separate supply if it draws more current than your board can provide), with its signal wire on a PWM-capable digital pin — match all pins in your code below.
Code
1#include <Servo.h>2 3Servo barrier;4const int servoPin = 9; // update to match your wiring5const int trigPin = 10; // update to match your wiring6const int echoPin = 11; // update to match your wiring7const int openThresholdCm = 10;8 9bool isOpen = false;10 11void setup() {12 barrier.attach(servoPin);13 pinMode(trigPin, OUTPUT);14 pinMode(echoPin, INPUT);15 barrier.write(0);16}17 18void loop() {19 digitalWrite(trigPin, LOW);20 delayMicroseconds(2);21 digitalWrite(trigPin, HIGH);22 delayMicroseconds(10);23 digitalWrite(trigPin, LOW);24 25 long duration = pulseIn(echoPin, HIGH);26 long distanceCm = duration * 0.034 / 2;27 28 if (distanceCm < openThresholdCm && !isOpen) {29 barrier.write(90);30 isOpen = true;31 delay(3000);32 barrier.write(0);33 isOpen = false;34 }35}36 - Line 9: isOpen tracks the barrier's current state, so the code only opens it once per car instead of repeatedly.
- Line 31: This delay is the hold-open time — how long the barrier stays open before automatically closing.
Expected behaviour
- 1Upload the code and bring your hand close to the sensor, like a car arriving.
- 2The barrier should swing open and hold for a few seconds, then close automatically.
- 3Confirm it doesn't try to reopen while already open.
Diagnosis
Symptoms and their usual causes. Work down the list — each check rules out a subsystem.
- The barrier doesn't open.
- Verify trigPin and echoPin match your sensor wiring, and that openThresholdCm fits your test distance.
- The barrier opens and closes rapidly.
- This usually means isOpen isn't being tracked correctly — make sure that logic wasn't accidentally removed.
- The servo strains or resets the board.
- The servo may need its own power source rather than pulling current from the same board as the sensor.
Open problems
Extensions
Small change
Add a hold-open delay
Keep the barrier open for a few seconds so a car has time to pass fully.
Add something
Add a warning blink
Blink an LED for a moment before the barrier closes.
Design it yourself
Count how many cars pass
Keep a running count each time the barrier opens and closes.
You decide how it works. No steps for this one.
Check your understanding
1. What two building blocks does this project combine?
2. Why does the barrier need to track whether it's currently open or closed?
3. What is automation, in the context of this project?
Where this leads
You now know:
- Reading a sensor's input
- Controlling a motor with code
- Using conditional (if/else) logic
- Tracking state across a program
- Combining sensor input with motor output
- Designing automated behavior
What this leads to
Line-Following Robot
Automatic Parking Barrier leads straight into this one.
What this leads to
Smart Home
Automatic Parking Barrier leads straight into this one.