👥 Occupancy Sensing Tutorial
Bi-Directional People Counter
Using Arduino UNO
A smart room occupancy monitor using two PIR sensors. Tracks entries and exits in real-time, displaying the live count on a 16×2 LCD — hands-free, automatic, and scalable.
🎯 Intermediate Level
✅ Full Code Included
🔬 Tinkercad Simulation
How It Works — Direction Detection
Two PIR sensors are placed at the doorway. The Arduino reads the order in which they trigger to determine if someone is entering or exiting.
🚪 Person Entering
Sensor 1
→
Sensor 2
Count + 1 ↑
🚶 Person Leaving
Sensor 2
→
Sensor 1
Count − 1 ↓
Decision Flowchart
START / Loop
→
Read PIR 1 & PIR 2
↓
Sensor 1 first?
Yes →
Count++ (Entry)
→
Update LCD
Sensor 2 first?
Yes →
Count-- (Exit)
→
Update LCD
Count cannot go below 0 — safeguarded in code.
Components Required
🎛️
Arduino UNO
× 1 — Controller
👁️
PIR Sensor
× 2 — HC-SR501
🖥️
16×2 LCD
× 1 — Non-I2C
🔘
Potentiometer
× 1 — 10kΩ
🧩
Breadboard
Half or full size
🔌
Jumper Wires
M-M, M-F
🔋
Power Supply
5V USB or adapter
Circuit Diagram
Place both PIR sensors ~5 cm apart at the doorway, one behind the other in the direction of travel.
LCD Display Output
The 16×2 LCD (connected in 4-bit mode) continuously shows the current room occupancy:
People In Room:
Count: 3
The count updates instantly whenever a person enters or exits. Count is protected from going below 0.
Pin Connections
PIR Sensors → Arduino UNO
Component Pin Arduino Wire PIR Sensor 1 VCC 5V Red PIR Sensor 1 GND GND Black PIR Sensor 1 OUT (Signal) D2 Teal PIR Sensor 2 VCC 5V Red PIR Sensor 2 GND GND Black PIR Sensor 2 OUT (Signal) D3 Rose
16×2 LCD → Arduino UNO (4-bit mode)
LCD Pin Label Connects To 1 VSS (GND) GND 2 VDD 5V 3 V0 (Contrast) Potentiometer wiper 4 RS D7 5 RW GND 6 EN (Enable) D8 11 D4 D9 12 D5 D10 13 D6 D11 14 D7 D12 15 A (Backlight +) 5V via 220Ω 16 K (Backlight −) GND
Step-by-Step Build Guide
1
Plan Your Doorway Placement
Decide which side of the door is "inside" vs "outside". PIR Sensor 1 (entry detection) should be on the outer side, Sensor 2 on the inner side. Space them ~5 cm apart along the direction of travel.
2
Connect PIR Sensor 1 to Arduino
VCC → 5V, GND → GND, OUT → D2. Use a red wire for power, black for ground, and teal for signal for easy identification.
3
Connect PIR Sensor 2 to Arduino
VCC → 5V, GND → GND, OUT → D3. You can share the 5V and GND rails on the breadboard for both sensors.
4
Set Up the 16×2 LCD in 4-bit Mode
Connect VSS→GND, VDD→5V, RW→GND. Connect RS→D7, EN→D8, D4→D9, D5→D10, D6→D11, D7→D12. Add 220Ω resistor on backlight anode.
5
Wire the Potentiometer for LCD Contrast
Connect the two outer legs of the 10kΩ pot to 5V and GND. Connect the wiper (middle leg) to LCD pin 3 (V0). You'll adjust this after powering on.
6
Install the LiquidCrystal Library
In Arduino IDE, go to Sketch → Include Library → Manage Libraries. Search for "LiquidCrystal" by Arduino and install it. (It may be pre-installed.)
7
Upload the Arduino Code
Paste the code below into Arduino IDE. Select "Arduino UNO" as board, choose your COM port, and click Upload.
8
Adjust LCD Contrast & Test
Turn the potentiometer until the LCD text becomes clearly visible. Then test by walking through the doorway in both directions. The count should increment and decrement correctly.
9
Calibrate PIR Sensitivity
Most HC-SR501 PIR sensors have two orange potentiometers on the back — one adjusts sensitivity, the other adjusts delay time. Set delay to minimum (~0.3s) for fast person detection.
Arduino Code
Uses the built-in LiquidCrystal library — no extra installs needed.
Arduino C++
// ============================================
// Bi-Directional People Counter | MakeMindz
// 2× PIR Sensors + 16×2 LCD + Arduino UNO
// Tinkercad: tinkercad.com (see simulation)
// ============================================
#include <LiquidCrystal.h>
// LCD pin mapping: RS, EN, D4, D5, D6, D7
LiquidCrystal lcd(7, 8, 9, 10, 11, 12);
// PIR sensor pins
const int PIR1 = 2; // Entry sensor (outer)
const int PIR2 = 3; // Exit sensor (inner)
int count = 0;
bool pir1State = false;
bool pir2State = false;
bool entrySeq = false;
bool exitSeq = false;
void setup() {
pinMode(PIR1, INPUT);
pinMode(PIR2, INPUT);
lcd.begin(16, 2);
lcd.print("People Counter");
lcd.setCursor(0, 1);
lcd.print("makemindz.com");
delay(2000);
updateDisplay();
Serial.begin(9600);
}
void loop() {
bool s1 = digitalRead(PIR1);
bool s2 = digitalRead(PIR2);
// Entry: PIR1 triggers first
if (s1 && !pir1State) {
pir1State = true;
entrySeq = true;
exitSeq = false;
}
if (s2 && entrySeq && !pir2State) {
count++;
pir2State = true;
entrySeq = false;
updateDisplay();
Serial.print("Entry! Count: ");
Serial.println(count);
}
// Exit: PIR2 triggers first
if (s2 && !pir2State) {
pir2State = true;
exitSeq = true;
entrySeq = false;
}
if (s1 && exitSeq && !pir1State) {
if (count > 0) count--; // Never below 0
pir1State = true;
exitSeq = false;
updateDisplay();
Serial.print("Exit! Count: ");
Serial.println(count);
}
// Reset states when sensors go LOW
if (!s1) pir1State = false;
if (!s2) pir2State = false;
delay(50);
}
void updateDisplay() {
lcd.clear();
lcd.setCursor(0, 0);
lcd.print("People In Room:");
lcd.setCursor(0, 1);
lcd.print("Count: ");
lcd.print(count);
}
🔬
Try the Tinkercad Simulation
This exact project has a ready-made Tinkercad simulation — open it and run the code without any hardware.
The Tinkercad link above is the exact simulation for this project — no setup needed.
Key Features & Applications
✅Detects entry and exit direction
✅Real-time occupancy display
✅Automatic counting — no manual input
✅Low cost, easy installation
✅Suitable for small–medium rooms
✅Hands-free, contactless operation
📍 Where to Use It
🏫 Smart Classrooms
🏢 Office Monitoring
📚 Library Control
🛒 Shopping Stores
🔬 Lab Safety
🚀 Possible Upgrades
Buzzer Alert at Max Capacity
Add a passive buzzer to pin D13 — trigger it when count reaches a defined limit (e.g., 30 people).
Automatic Light Control
Connect a relay to automatically turn room lights on when count > 0 and off when the room is empty.
IoT Cloud Monitoring
Add an ESP8266 Wi-Fi module to push occupancy data to platforms like ThingSpeak or Blynk for remote monitoring.
More Arduino Projects
🟢 Beginner Projects
Ultrasonic Distance Measurement
Traffic Light Simulation
16×2 LCD Display
Temperature Measurement
LDR Street Light
Kids Piano Circuit
🔵 Intermediate Projects
Servo + Potentiometer
Temperature Controlled Fan
LPG Gas Leakage Detection
Auto Door Lock
Digital Clock
RGB Lamp Control
🔵 Advanced Projects
Circuit Diagram
Place both PIR sensors ~5 cm apart at the doorway, one behind the other in the direction of travel.
LCD Display Output
The 16×2 LCD (connected in 4-bit mode) continuously shows the current room occupancy:
People In Room:
Count: 3
The count updates instantly whenever a person enters or exits. Count is protected from going below 0.
Pin Connections
PIR Sensors → Arduino UNO
| Component | Pin | Arduino | Wire |
|---|---|---|---|
| PIR Sensor 1 | VCC | 5V | Red |
| PIR Sensor 1 | GND | GND | Black |
| PIR Sensor 1 | OUT (Signal) | D2 | Teal |
| PIR Sensor 2 | VCC | 5V | Red |
| PIR Sensor 2 | GND | GND | Black |
| PIR Sensor 2 | OUT (Signal) | D3 | Rose |
16×2 LCD → Arduino UNO (4-bit mode)
| LCD Pin | Label | Connects To |
|---|---|---|
| 1 | VSS (GND) | GND |
| 2 | VDD | 5V |
| 3 | V0 (Contrast) | Potentiometer wiper |
| 4 | RS | D7 |
| 5 | RW | GND |
| 6 | EN (Enable) | D8 |
| 11 | D4 | D9 |
| 12 | D5 | D10 |
| 13 | D6 | D11 |
| 14 | D7 | D12 |
| 15 | A (Backlight +) | 5V via 220Ω |
| 16 | K (Backlight −) | GND |
Step-by-Step Build Guide
1
Plan Your Doorway Placement
Decide which side of the door is "inside" vs "outside". PIR Sensor 1 (entry detection) should be on the outer side, Sensor 2 on the inner side. Space them ~5 cm apart along the direction of travel.
2
Connect PIR Sensor 1 to Arduino
VCC → 5V, GND → GND, OUT → D2. Use a red wire for power, black for ground, and teal for signal for easy identification.
3
Connect PIR Sensor 2 to Arduino
VCC → 5V, GND → GND, OUT → D3. You can share the 5V and GND rails on the breadboard for both sensors.
4
Set Up the 16×2 LCD in 4-bit Mode
Connect VSS→GND, VDD→5V, RW→GND. Connect RS→D7, EN→D8, D4→D9, D5→D10, D6→D11, D7→D12. Add 220Ω resistor on backlight anode.
5
Wire the Potentiometer for LCD Contrast
Connect the two outer legs of the 10kΩ pot to 5V and GND. Connect the wiper (middle leg) to LCD pin 3 (V0). You'll adjust this after powering on.
6
Install the LiquidCrystal Library
In Arduino IDE, go to Sketch → Include Library → Manage Libraries. Search for "LiquidCrystal" by Arduino and install it. (It may be pre-installed.)
7
Upload the Arduino Code
Paste the code below into Arduino IDE. Select "Arduino UNO" as board, choose your COM port, and click Upload.
8
Adjust LCD Contrast & Test
Turn the potentiometer until the LCD text becomes clearly visible. Then test by walking through the doorway in both directions. The count should increment and decrement correctly.
9
Calibrate PIR Sensitivity
Most HC-SR501 PIR sensors have two orange potentiometers on the back — one adjusts sensitivity, the other adjusts delay time. Set delay to minimum (~0.3s) for fast person detection.
Arduino Code
Uses the built-in LiquidCrystal library — no extra installs needed.
Arduino C++
// ============================================ // Bi-Directional People Counter | MakeMindz // 2× PIR Sensors + 16×2 LCD + Arduino UNO // Tinkercad: tinkercad.com (see simulation) // ============================================ #include <LiquidCrystal.h> // LCD pin mapping: RS, EN, D4, D5, D6, D7 LiquidCrystal lcd(7, 8, 9, 10, 11, 12); // PIR sensor pins const int PIR1 = 2; // Entry sensor (outer) const int PIR2 = 3; // Exit sensor (inner) int count = 0; bool pir1State = false; bool pir2State = false; bool entrySeq = false; bool exitSeq = false; void setup() { pinMode(PIR1, INPUT); pinMode(PIR2, INPUT); lcd.begin(16, 2); lcd.print("People Counter"); lcd.setCursor(0, 1); lcd.print("makemindz.com"); delay(2000); updateDisplay(); Serial.begin(9600); } void loop() { bool s1 = digitalRead(PIR1); bool s2 = digitalRead(PIR2); // Entry: PIR1 triggers first if (s1 && !pir1State) { pir1State = true; entrySeq = true; exitSeq = false; } if (s2 && entrySeq && !pir2State) { count++; pir2State = true; entrySeq = false; updateDisplay(); Serial.print("Entry! Count: "); Serial.println(count); } // Exit: PIR2 triggers first if (s2 && !pir2State) { pir2State = true; exitSeq = true; entrySeq = false; } if (s1 && exitSeq && !pir1State) { if (count > 0) count--; // Never below 0 pir1State = true; exitSeq = false; updateDisplay(); Serial.print("Exit! Count: "); Serial.println(count); } // Reset states when sensors go LOW if (!s1) pir1State = false; if (!s2) pir2State = false; delay(50); } void updateDisplay() { lcd.clear(); lcd.setCursor(0, 0); lcd.print("People In Room:"); lcd.setCursor(0, 1); lcd.print("Count: "); lcd.print(count); }
🔬
Try the Tinkercad Simulation
This exact project has a ready-made Tinkercad simulation — open it and run the code without any hardware.
The Tinkercad link above is the exact simulation for this project — no setup needed.
Key Features & Applications
✅Detects entry and exit direction
✅Real-time occupancy display
✅Automatic counting — no manual input
✅Low cost, easy installation
✅Suitable for small–medium rooms
✅Hands-free, contactless operation
📍 Where to Use It
🏫 Smart Classrooms
🏢 Office Monitoring
📚 Library Control
🛒 Shopping Stores
🔬 Lab Safety
🚀 Possible Upgrades
Buzzer Alert at Max Capacity
Add a passive buzzer to pin D13 — trigger it when count reaches a defined limit (e.g., 30 people).
Automatic Light Control
Connect a relay to automatically turn room lights on when count > 0 and off when the room is empty.
IoT Cloud Monitoring
Add an ESP8266 Wi-Fi module to push occupancy data to platforms like ThingSpeak or Blynk for remote monitoring.
More Arduino Projects
🟢 Beginner Projects
Ultrasonic Distance Measurement
Traffic Light Simulation
16×2 LCD Display
Temperature Measurement
LDR Street Light
Kids Piano Circuit
🔵 Intermediate Projects
Servo + Potentiometer
Temperature Controlled Fan
LPG Gas Leakage Detection
Auto Door Lock
Digital Clock
RGB Lamp Control
🔵 Advanced Projects
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