HC-SR501 PIR Motion Sensor (Passive Infrared) + IR Proximity Sensor Combo

HC-SR501 PIR sensor (passive infrared) + IR proximity sensor combo – motion detection based on body heat plus infrared proximity sensing.

1. HC-SR501 PIR Sensor (Motion Detection)

What it does

• Detects human/animal movement

• Works based on body heat (infrared radiation)

It does NOT detect objects, only motion of warm bodies

Key Specifications

• Voltage: 4.5V 20V

• Output: Digital HIGH (3.3V) when motion detected

• Range: ~3 to 7 meters

• Angle: ~110120

• Delay time: 5s 300s adjustable

Features

• Adjustable sensitivity + delay

• Two modes:

  • Repeatable (keeps detecting)

  • Non-repeatable

• p detection

Pinout

• VCC 5V

• GND GND

• OUT Digital pin

Applications

• Security systems

• Automatic lights

• Smart home automation

• Human presence detection

Important Notes

• Needs 3060 sec warm-up

• Cannot detect stationary person

• Sensitive to heat changes

2. IR Proximity Sensor (Obstacle Detection)

What it does

• Detects objects (any material)

• Works using IR reflection

Key Specifications

• Voltage: 3.3V 5V

• Range: ~2 cm 3093 comparator

Features

• Adjustable detection distance

• Fast response

• Works for any object (not just humans)

• Cheap & simple

Pinout

• VCC 3.3V / 5V

• GND GND

• OUT Digital pin

Applications

• Obstacle avoiding robot

• Object detection

• Line following robot

• Smart vehicles

PIR vs IR Sensor (VERY IMPORTANT)

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When to use which

Use PIR if:

• You want human detection

• Example: automatic light ON when someone enters

Use IR if:

• You want object detection

• Example: robot avoiding obstacles

Pro Tip (Very Useful)

Combine BOTH sensors:

• PIR detect human presence

• IR detect distance/obstacle

Used in:

• Smart robots

• Smart doors

• Advanced IoT systems

Common Beginner Mistakes

• PIR not working didn't wait warm-up time

• IR giving false output not adju/p