PIR Sensor for Robotics and Human-Robot Interaction

Introduction

Robots often need to detect people for safety, interaction, or following. PIR sensors provide a low-cost, low-power solution for human detection in robotics applications.

Applications in Robotics

Human Detection for Safety

When a robot detects a person nearby, it can slow down, stop, or change path to avoid collision.

Follow-Me Robots

A robot equipped with PIR sensors can follow a person by detecting their movement and direction.

Social Robots

Detect when a person approaches to initiate interaction.

Search and Rescue

Detect trapped people by their body heat in low-visibility environments.

Advantages for Robotics

• Low power: Can run continuously on battery
• Privacy-preserving: No camera images
• Works in darkness: Unlike cameras, no light needed
• Simple interface: Easy to integrate

Limitations

• Only detects moving warm objects (not stationary people)
• Limited range (5-10m typical)
• Cannot distinguish between different people
• No distance information (just detection)

Sensor Placement on Robot

• Front-facing: Detect people in front of robot
• Omnidirectional: Multiple sensors around robot for 360° coverage
• Tilted upward: Detect standing people at close range
• Curtain lens: Create a safety zone around robot

Multi-Sensor Direction Detection

With two sensors (left and right), a robot can determine the approximate direction of a person:

• Left sensor triggered first → person moving right relative to robot
• Right sensor triggered first → person moving left

Combining with Other Sensors

PIR works well with:

• Ultrasonic: For distance measurement (confirm PIR detection)
• LiDAR: For obstacle avoidance (PIR triggers attention)
• Camera: For identification (PIR wakes camera)

Code Example: Robot Following

int leftPIR = 2;
int rightPIR = 3;
int motorLeft = 5;
int motorRight = 6;

void loop() {
    if (digitalRead(leftPIR) == HIGH && digitalRead(rightPIR) == HIGH) {
        forward();  // Person in front
    } else if (digitalRead(leftPIR) == HIGH) {
        turnLeft();  // Person on left
    } else if (digitalRead(rightPIR) == HIGH) {
        turnRight(); // Person on right
    } else {
        stop();
    }
}

Case Study: Museum Guide Robot

A museum guide robot used four PIR sensors (front, left, right, rear) to detect visitors. When a person approached, the robot would stop and offer information. The system worked reliably for 2 years on a single battery charge.

Conclusion

PIR sensors are a valuable addition to a robot’s sensor suite for human detection. They are low-cost, low-power, and privacy-preserving, making them ideal for human-robot interaction applications.