SmartElex BX404 Digital PIR Motion Sensor

🔹 Overview
The SmartElex BX404 Digital PIR Motion Sensor is a low-power intelligent passive infrared (PIR) sensor designed for accurate human motion detection.
Integrates pyroelectric sensing + digital processing
Provides direct digital output
Designed for energy-efficient embedded systems
Unlike basic PIR elements, the BX404 includes on-chip signal processing, making it a complete motion detection solution.
🔹 Working Principle
Detects infrared radiation changes from moving human bodies
Uses a pyroelectric sensing element
Internal circuit:
Amplifies signal
Filters noise
Converts analog → digital output
👉 Motion detected → output triggered (REL signal)
🔹 Internal Architecture
Pyroelectric IR sensing element
High-impedance differential input stage
Digital signal processing (DSP) circuit
Built-in filtering (band-pass filter)
Threshold detection logic
👉 Fully digital processing improves stability and reduces drift
🔹 Electrical Characteristics
Operating Voltage: 2.2V – 3.7V
Static Current Consumption: < 11 µA
Ultra-low power → ideal for battery-powered devices
🔹 Detection Characteristics
Detection Range: up to 12 meters
Detection Angle: ~120° (horizontal)
Sensing Window: ~4 × 4 mm
👉 Range depends on lens (e.g., Fresnel lens)
🔹 Output Characteristics
Output Type: Digital (HIGH / LOW)
Signal Name: REL output
Behavior:
HIGH → Motion detected
LOW → No motion
👉 Directly usable with microcontrollers
🔹 Functional Features
Supports connection to external PIR elements (up to 2 sensors)
Adjustable timing via external DC voltage inputs
Built-in:
Noise filtering
Interference suppression
Stable threshold detection
🔹 Performance Characteristics
No drift or aging effects (digital processing)
High noise immunity (RF interference resistant)
Stable operation even in noisy environments
🔹 Functional Behavior
Detects dynamic IR changes (motion only)
Best sensitivity when motion is:
Across the sensor field
Provides:
Clean digital pulse output
Internal processing removes need for external amplification
🔹 Key Technical Features
Ultra-low power (<11 µA)
Wide detection angle (120°)
Long detection range (~12 m)
Integrated digital processing
Adjustable timing parameters
High noise immunity
Direct digital interface
🔹 Advantages
No external signal conditioning required
Very low power consumption
Stable and reliable detection
Compact and lightweight design
Suitable for embedded and IoT systems
🔹 Limitations
Cannot detect stationary objects
Requires:
Proper lens for full range
Sensitive to:
Temperature variations
External heat sources
Requires correct placement for optimal detection
🔹 Technical Summary
The BX404 is an advanced digital PIR sensor IC/module that:
Combines IR sensing + signal processing
Outputs direct digital motion detection
Provides high stability with ultra-low power consumption
👉 Compared to simpler PIR sensors:
More stable (less noise & drift)
Better interference rejection
Flexible timing control