Smart Parking System Using Arduino UNO – HC-SR04 + Servo + LCD | MakeMindz

🚗 Smart City Automation Project

Smart Parking System
Using Arduino UNO

Manage 3 parking slots automatically using ultrasonic sensors, control the entry gate with a servo motor, and display live availability on a 16×2 LCD — all simulated in Tinkercad.

🔲 Arduino UNO 📡 4× HC-SR04 ⚙️ SG90 Servo 🖥️ 16×2 LCD 🅿️ 3 Parking Slots 🏙️ Smart City

This project simulates a fully functional Automatic Smart Parking System using the Arduino UNO in Tinkercad. It manages three parking slots using HC-SR04 ultrasonic sensors, controls an entry gate with a servo motor, and displays live parking availability on a 16×2 LCD display.

The system detects vehicles entering each slot in real-time and automatically opens or closes the gate based on availability. When all slots are full, the LCD displays "Parking Full" and the gate stays closed.

🧩 Components Required

🔲Arduino UNOMain controller for all logic

📡HC-SR04 ×43 for slots + 1 for entry detection

⚙️SG90 ServoEntry gate open/close mechanism

🖥️16×2 LCDDisplays slot status and messages

🔧Potentiometer10kΩ for LCD contrast control

🧪BreadboardFor prototyping all connections

🔗Jumper WiresMale-to-male connection wires

🔌USB CablePower and programming via USB

🅿️ Parking Slot Layout

3 Parking Slots + Entry Detection — Live Status Example

🚗

Slot 1 — Occupied

TRIG: D4 · ECHO: D5

Distance < threshold

⬜

Slot 2 — Free

TRIG: D6 · ECHO: D7

Distance ≥ threshold

⬜

Slot 3 — Free

TRIG: D8 · ECHO: D9

Distance ≥ threshold

🚘

Entry Sensor — HC-SR04 (TRIG: D2 · ECHO: D3)

Detects incoming vehicles at the gate. If free slots exist → servo opens gate. If full → LCD shows "Parking Full".

⚡ System Logic Flow

📡 Check All 3 Slot Sensors

↓

🔢 Count Free Slots

↓

🖥️ Update LCD: "Slots Available: X"

↓

🚘 Vehicle Detected at Entry?

↓ Yes

🅿️ Any Free Slots?

↓

✅ YES

⚙️ Open Gate (90°)

↓

⏳ Wait → Close Gate (0°)

❌ NO

🛑 Gate Stays Closed

↓

🖥️ LCD: "Parking Full"

↓

🔁 Loop — Check Again

🖥️ LCD Display States

✅ Slots Available

Slots Available: 2 S1:Occ S2:Free S3:F

🚘 Vehicle Entering

Vehicle Detected! Opening Gate...

🛑 Parking Full

Parking Full! Please Wait...

🔄 All Free

Slots Available: 3 S1:F S2:F S3:F

🔌 Circuit Diagram

📋 Pin Connection Table

Sensor / Device	Pin	Arduino Pin	Wire	Notes
Entry HC-SR04	TRIG	D2	Grey	Trigger pulse out
Entry HC-SR04	ECHO	D3	Grey	Echo return in
Slot 1 HC-SR04	TRIG	D4	Purple	Slot 1 trigger
Slot 1 HC-SR04	ECHO	D5	Purple	Slot 1 echo
Slot 2 HC-SR04	TRIG	D6	Orange	Slot 2 trigger
Slot 2 HC-SR04	ECHO	D7	Orange	Slot 2 echo
Slot 3 HC-SR04	TRIG	D8	Green	Slot 3 trigger
Slot 3 HC-SR04	ECHO	D9	Green	Slot 3 echo
All HC-SR04	VCC	5V	Red	All 4 sensors powered at 5V
All HC-SR04	GND	GND	Black	Common ground
SG90 Servo	Signal	D10	Orange	PWM gate control
SG90 Servo	VCC	5V	Red	Servo power
SG90 Servo	GND	GND	Black	Common ground
16×2 LCD	RS	D11	Blue	Register select
16×2 LCD	EN	D12	Blue	Enable pin
16×2 LCD	D4–D7	A0–A3	Blue	4-bit data bus
16×2 LCD	VSS	GND	Black	LCD ground
16×2 LCD	VDD	5V	Red	LCD power
16×2 LCD	VO	Pot middle	Yellow	Contrast via 10kΩ potentiometer
Potentiometer	Pin 1	5V	Red	One end to 5V
Potentiometer	Pin 3	GND	Black	Other end to GND

📝 Step-by-Step Instructions

Install the LiquidCrystal Library

Go to Sketch → Include Library → Manage Libraries. The LiquidCrystal library (by Arduino) and Servo library are both built-in — no installation needed. Confirm they appear under Installed.

Wire All 4 HC-SR04 Ultrasonic Sensors

Entry sensor: TRIG → D2, ECHO → D3
Slot 1 sensor: TRIG → D4, ECHO → D5
Slot 2 sensor: TRIG → D6, ECHO → D7
Slot 3 sensor: TRIG → D8, ECHO → D9
All sensors: VCC → 5V, GND → GND (use breadboard power rails)

Wire the SG90 Servo (Gate)

Servo Signal (orange) → D10
Servo VCC (red) → 5V
Servo GND (brown) → GND
0° = gate closed, 90° = gate open

Wire the 16×2 LCD Display

LCD RS → D11, EN → D12, D4 → A0, D5 → A1, D6 → A2, D7 → A3
LCD VSS → GND, VDD → 5V
LCD VO → middle wiper pin of the 10kΩ potentiometer
Potentiometer: one outer pin to 5V, other to GND

Set the Distance Threshold

In the code, int threshold = 10; means a slot is "Occupied" when the measured distance is less than 10 cm. Adjust this value based on your physical slot depth — typical values are 10–30 cm depending on parking space dimensions.

Upload and Test

Select Tools → Board → Arduino UNO, choose your COM port
Click Upload — LCD should show Slots Available: 3
Place an object within 10 cm of a slot sensor — it should show as Occupied
Simulate a vehicle at the entry sensor — gate servo should open then re-close
Fill all 3 slots — LCD should show Parking Full!

Adjust LCD Contrast

Turn the potentiometer knob slowly until text on the LCD is clearly visible. Too far one way = blank screen; too far the other = black blocks. Find the sweet spot for crisp readable characters.

💡

Tinkercad Simulation Tip

In Tinkercad, use the distance slider on each HC-SR04 component to simulate a vehicle being present or absent. Set the entry sensor below threshold to trigger the gate. Use the "Start Simulation" button to watch the LCD and servo respond in real time.

💻 Arduino Code

ARDUINO C++ · SmartParking.ino

/*
 * Smart Parking System Using Arduino UNO
 * 4x HC-SR04 Ultrasonic Sensors + SG90 Servo + 16x2 LCD
 *
 * Sensors:
 *   Entry: TRIG=D2, ECHO=D3
 *   Slot1: TRIG=D4, ECHO=D5
 *   Slot2: TRIG=D6, ECHO=D7
 *   Slot3: TRIG=D8, ECHO=D9
 * Servo Gate: D10
 * LCD: RS=D11, EN=D12, D4=A0, D5=A1, D6=A2, D7=A3
 *
 * Tutorial: https://www.makemindz.com
 */

#include <LiquidCrystal.h>
#include <Servo.h>

// LCD pins: RS, EN, D4, D5, D6, D7
LiquidCrystal lcd(11, 12, A0, A1, A2, A3);

Servo gateServo;

// Ultrasonic sensor pin pairs [TRIG, ECHO]
const int entryTrig = 2,  entryEcho = 3;
const int slot1Trig = 4,  slot1Echo = 5;
const int slot2Trig = 6,  slot2Echo = 7;
const int slot3Trig = 8,  slot3Echo = 9;
const int servoPin  = 10;

// Slot occupied if distance (cm) is less than this
const int threshold = 10;

bool slot1Occ, slot2Occ, slot3Occ;
int  freeSlots;

void setup() {
  lcd.begin(16, 2);
  lcd.print(" Smart Parking ");
  lcd.setCursor(0, 1);
  lcd.print("  System v1.0  ");
  delay(2000);

  gateServo.attach(servoPin);
  gateServo.write(0);  // Gate starts closed

  // Setup all sensor pins
  int trigPins[] = {entryTrig, slot1Trig, slot2Trig, slot3Trig};
  int echoPins[] = {entryEcho, slot1Echo, slot2Echo, slot3Echo};
  for (int i = 0; i < 4; i++) {
    pinMode(trigPins[i], OUTPUT);
    pinMode(echoPins[i], INPUT);
  }
}

// Measure distance using HC-SR04
long getDistance(int trigPin, int echoPin) {
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  return pulseIn(echoPin, HIGH) / 58;  // Returns cm
}

void checkSlots() {
  slot1Occ = (getDistance(slot1Trig, slot1Echo) < threshold);
  slot2Occ = (getDistance(slot2Trig, slot2Echo) < threshold);
  slot3Occ = (getDistance(slot3Trig, slot3Echo) < threshold);
  freeSlots = (int)!slot1Occ + (int)!slot2Occ + (int)!slot3Occ;
}

void updateLCD() {
  lcd.clear();
  lcd.setCursor(0, 0);
  if (freeSlots == 0) {
    lcd.print("Parking Full!   ");
  } else {
    lcd.print("Slots Avail: ");
    lcd.print(freeSlots);
  }
  lcd.setCursor(0, 1);
  lcd.print("S1:"); lcd.print(slot1Occ ? "Occ" : "F  ");
  lcd.print(" S2:"); lcd.print(slot2Occ ? "Occ" : "F");
}

void handleEntry() {
  long entryDist = getDistance(entryTrig, entryEcho);
  if (entryDist < threshold) {
    // Vehicle detected at entry
    if (freeSlots > 0) {
      // Open gate
      lcd.clear();
      lcd.setCursor(0, 0);
      lcd.print("Vehicle Detected");
      lcd.setCursor(0, 1);
      lcd.print("Opening Gate...");
      gateServo.write(90);   // Open gate
      delay(3000);          // Wait for vehicle to pass
      gateServo.write(0);    // Close gate
      lcd.clear();
      lcd.print("Gate Closed.    ");
      delay(1000);
    } else {
      // Parking is full — gate stays closed
      lcd.clear();
      lcd.print("Parking Full!   ");
      lcd.setCursor(0, 1);
      lcd.print("Please Wait...  ");
      delay(2000);
    }
  }
}

void loop() {
  checkSlots();    // Read all 3 slot sensors
  updateLCD();    // Show slot status on LCD
  handleEntry(); // Check entry sensor and control gate
  delay(500);     // Poll every 500ms
}

📐 diagram.json (Wokwi Simulation)

ℹ️

Using diagram.json in Wokwi

Go to wokwi.com → New Project → Arduino UNO. Replace the default diagram.json with the content below, paste the sketch above, and click ▶ Run to simulate. Use the HC-SR04 distance slider to simulate vehicles.

diagram.json · Wokwi Smart Parking Circuit

{
  "version": 1,
  "author": "MakeMindz",
  "editor": "wokwi",
  "parts": [
    { "type": "wokwi-arduino-uno",   "id": "uno",    "top": 80,   "left": 180,  "attrs": {} },
    { "type": "wokwi-hc-sr04",      "id": "entry", "top": -80,  "left": -200, "attrs": { "label": "Entry" } },
    { "type": "wokwi-hc-sr04",      "id": "slot1", "top": 20,   "left": -200, "attrs": { "label": "Slot 1" } },
    { "type": "wokwi-hc-sr04",      "id": "slot2", "top": 120,  "left": -200, "attrs": { "label": "Slot 2" } },
    { "type": "wokwi-hc-sr04",      "id": "slot3", "top": 220,  "left": -200, "attrs": { "label": "Slot 3" } },
    { "type": "wokwi-servo",        "id": "gate",  "top": -80,  "left": 480,  "attrs": {} },
    { "type": "wokwi-lcd1602",      "id": "lcd",   "top": 80,   "left": 480,  "attrs": {} },
    { "type": "wokwi-potentiometer", "id": "pot",   "top": 260,  "left": 480,  "attrs": { "value": "10000" } }
  ],
  "connections": [
    [ "entry:TRIG", "uno:2",    "gray",   ["h0"] ],
    [ "entry:ECHO", "uno:3",    "gray",   ["h0"] ],
    [ "entry:VCC",  "uno:5V",   "red",    ["h0"] ],
    [ "entry:GND",  "uno:GND.1","black",  ["h0"] ],
    [ "slot1:TRIG", "uno:4",    "purple", ["h0"] ],
    [ "slot1:ECHO", "uno:5",    "purple", ["h0"] ],
    [ "slot1:VCC",  "uno:5V",   "red",    ["h0"] ],
    [ "slot1:GND",  "uno:GND.2","black",  ["h0"] ],
    [ "slot2:TRIG", "uno:6",    "orange", ["h0"] ],
    [ "slot2:ECHO", "uno:7",    "orange", ["h0"] ],
    [ "slot2:VCC",  "uno:5V",   "red",    ["h0"] ],
    [ "slot2:GND",  "uno:GND.3","black",  ["h0"] ],
    [ "slot3:TRIG", "uno:8",    "green",  ["h0"] ],
    [ "slot3:ECHO", "uno:9",    "green",  ["h0"] ],
    [ "slot3:VCC",  "uno:5V",   "red",    ["h0"] ],
    [ "slot3:GND",  "uno:GND.4","black",  ["h0"] ],
    [ "gate:PWM",   "uno:10",   "yellow", ["h0"] ],
    [ "gate:V+",    "uno:5V",   "red",    ["h0"] ],
    [ "gate:GND",   "uno:GND.5","black",  ["h0"] ],
    [ "lcd:RS",     "uno:11",   "blue",   ["h0"] ],
    [ "lcd:EN",     "uno:12",   "blue",   ["h0"] ],
    [ "lcd:D4",     "uno:A0",   "blue",   ["h0"] ],
    [ "lcd:D5",     "uno:A1",   "blue",   ["h0"] ],
    [ "lcd:D6",     "uno:A2",   "blue",   ["h0"] ],
    [ "lcd:D7",     "uno:A3",   "blue",   ["h0"] ],
    [ "lcd:VSS",    "uno:GND.6","black",  ["h0"] ],
    [ "lcd:VDD",    "uno:5V",   "red",    ["h0"] ],
    [ "lcd:VO",     "pot:SIG",  "yellow", ["h0"] ],
    [ "pot:VCC",    "uno:5V",   "red",    ["h0"] ],
    [ "pot:GND",    "uno:GND.7","black",  ["h0"] ]
  ],
  "dependencies": {}
}

🚀 Try the Live Simulations

Test the full parking system in your browser — adjust sensor distances and watch the servo gate and LCD respond in real time!

▶ Open Tinkercad Simulation 🔧 Build in Wokwi ⬇ Download Project Files

🎓 What Students Learn

📡

Multi-Sensor Integration

Managing 4 ultrasonic sensors simultaneously on a single Arduino

⚙️

Servo Motor Control

PWM-based gate open/close automation with position control

🖥️

LCD Interfacing

Real-time display of dynamic sensor data in 4-bit mode

🧠

Automation Logic

Conditional gate control based on sensor readings and slot count

📊

Real-Time Monitoring

Polling multiple sensors every 500ms for live status updates

💻

Embedded Programming

Functions, arrays, conditionals, and hardware abstraction in C++

🏙️ Applications

🛒 Shopping Mall Parking 🏙️ Smart City Infrastructure 🏢 Apartment Parking 🏗️ Office Parking Management 🌐 IoT Smart Parking Systems ✈️ Airport Parking 🎓 STEM Demonstrations 🔬 Science Exhibition

🚀 Possible Upgrades

🌐 IoT Remote Monitoring

📱 Mobile App Parking Status

📷 Camera Vehicle Detection

🔖 RFID Entry System

💳 Automated Billing System

☁️ Cloud Data Logging

🔔 Buzzer for Full Alert

🔢 More Parking Slots