SmartElex BS312 PIR Motion Sensor

Overview

The BS312 is a low-power passive infrared (PIR) motion sensor designed to detect human movement by sensing changes in infrared radiation emitted by warm bodies. It integrates sensing, signal processing, and output circuitry into a compact unit.

Working Principle

• Uses a pyroelectric infrared sensing element to detect variations in IR radiation.

• When a human body moves across the sensor's field, the IR level changes.

• An internal analog-to-digital conversion (ADC) and control circuit processes this signal.

• Output is converted into a digital HIGH/LOW signal for motion detection.

Internal Architecture

• Pyroelectric sensing element

• Integrated signal conditioning circuit

• On-chip ADC and digital processing

• Electromagnetic shielding enclosure (reduces noise/interference)

edli>Operating voltage: 2.2 V to 3.7 V

Static current consumption: < 12 A (very low power) Designed for battery-powered systems due to ultra-low standby current

Detection Characteristics

• Sensing range: up to 12 meters (with proper Fresnel lens)

• Detection angle: ~120 (horizontal field of view)

• Sensing window size: 3 4 mm

Output Characteristics

• Type: Digital output

• Signal levels:

  • HIGH Motion detected

  • LOW No motion

   

• Direct interface with digital systems without analog processing

Functional Behavior

• Detects dynamic changes in infrared radiation (movement), not static presence

• Best response when motion is across the fensor

• Processing is handled internally, so no external filtering required

Physical Characteristics

• Compact size (~28 20 11 mm)

• Small sensing window suitable for integration into embedded devices

Key Technical Features

• Fully integrated PIR + digital processing

• Ultra-low power consumption

• Wide-angle detection

• Medium-to-long detection distance

• Noise-resistant design (shielded housing)

• Simple digital interface

Limitations (Important Technical Points)

• Cannot detect stationary objects (only motion-based IR change)

• Performance depends on:

  • Ambient temperature

  • Lens quality and placement

  • Speed and direction of movement

• Sensitive to sudden environmental IR changes (h