Introduction
Thermal camera arrays (e.g., MLX90640, AMG8833) are becoming popular for occupancy sensing. This article compares them with traditional PIR sensors to help you choose the right technology.
How Thermal Camera Arrays Work
Thermopile arrays consist of multiple thermopile sensors arranged in a grid (e.g., 8×8, 32×24). Each pixel measures the temperature of the object in its field of view, creating a low-resolution thermal image.
Comparison Table
| Aspect | PIR Sensor | Thermal Camera Array |
|---|---|---|
| Output | Single motion event | Temperature matrix (image) |
| Resolution | N/A (binary or simple analog) | 8×8 to 32×24 pixels |
| Stationary Detection | No (unless special high-sensitivity) | Yes (detects warm objects regardless of motion) |
| People Counting | Requires multiple sensors/ML | Possible with image processing |
| Privacy | Excellent (no image) | Good (no facial features at low res) |
| Cost | $2-10 | $20-100 |
| Power Consumption | µA | mA (10-50 mA) |
| Complexity | Simple | Requires microcontroller with I2C and processing |
| Field of View | Defined by lens (90-180°) | Defined by optics (typically 50-110°) |
Applications Comparison
When PIR is Better
- Battery-powered devices (low power).
- Simple motion detection (lights, alarms).
- Low-cost applications.
- Privacy-critical where even low-res imaging is undesirable.
When Thermal Arrays are Better
- Presence detection (stationary people).
- People counting with direction.
- Occupancy estimation (how many people).
- Temperature screening.
- Applications where you need more than motion/no-motion.
Case Study: Office Occupancy
An office needed to know if desks were occupied (people sitting). PIR sensors failed because people sat still. Thermal arrays (MLX90640) mounted above each desk detected body heat reliably, regardless of motion.
Hybrid Approach
A power-optimized solution: use PIR to wake the thermal array only when motion is detected. The thermal array then confirms presence and counts people, then goes back to sleep.
Popular Thermal Array Models
- Melexis MLX90640 (32×24, $40-50)
- Panasonic AMG8833 (8×8, $30-40)
- Melexis MLX90641 (16×12, $30-40)
Conclusion
PIR and thermal arrays are complementary. PIR excels at low-power motion detection; thermal arrays provide richer information at higher cost and power. Choose based on your application’s requirements.