Infrared sensor enhances motion detection

25th September 2023
Mick Elliott

The STHS34PF80 high-sensitivity infrared sensor from STMicroelectronics is now being shipped by distributor Mouser Electronics.

Designed specifically to address the limitations of existing passive infrared (PIR) sensors that miss the mark when detecting stationary objects, the STHS34PF80 is an economical, ultra-low power MEMS-based infrared (IR) Sensor that enables building and home automation to function consistently whether detected occupants are moving or not.

Utilising a more streamlined lens-free configuration, this uncooled, factory-calibrated proximity sensor features thermal MOSFETs (TMOS), sensitive to IR heating effects and can accurately sense objects' absolute temperature or IR radiation within its field of view (FOV). These capabilities make the STHS34PF80 a perfect solution for smart homes, smart buildings, and IoT applications that require precise detection of motion, presence or over-temperature conditions.

The sensor is built using thermal MOSFETs (TMOS), digital readout circuitry and ST's mature and reliable silicon-on-insulator (SOI) CMOS technology integrated efficiently on the same chip.

Multiple TMOS transistors provide IR detection, and each transistor is operated in the subthreshold region, making the drain-source current extremely temperature-dependent and ultra-sensitive.

This condition enables the measurement of IR radiation absorption at the transistor's gate, which helps reliably detect and measure an object's presence and motion using a smart algorithm embedded in the sensor. The STHS34PF80 infrared radiation sensing wavelength range is 5 µm to 20 µm, which is very suitable for collecting human peak radiation, rated at 9.8 µm.

The proximity sensor uses time-of-flight technology to detect objects within 4 m without needing an optical lens and features an 80-degree field of view that covers a large area in front of the sensor.

An optical band-pass filter at the input ensures that ambient light conditions will not impact detection ability.

For an even greater range or FOV, engineers can integrate custom or commercial Fresnel lenses to boost performance.

The operating current on the sensor is rated at 10 µA, much less than a traditional PIR, making it ideal for low-power and battery-powered devices.

The highly integrated, SMD-friendly STHS34PF80 infrared sensor is available in a small, 3.2 mm x 4.2 mm x 1.455 mm 10-lead organic LGA SMT package that is ECOPACK, RoHS and Green compliant and offers high immunity to electromagnetic interference (EMI).

For development, the STHS34PF80 is also supported by an evaluation kit (the STEVAL-MKI231KA), which is also available to order on the Mouser website and includes the STHS34PF80 industrial board, a Fresnel lens (to verify performance) and a standard DIL24 adapter.

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