7Semi SHT45 and SGP41 Environmental Sensor Breakout

Overview

This breakout combines two advanced sensors:

• Sensirion SHT45 temperature and humidity sensor

• Sensirion SGP41 VOC and NOx gas sensor

It is a multi-parameter environmental sensing module capable of measuring:

• Temperature

• Relative Humidity

• Volatile Organic Compounds (VOC)

• Nitrogen Oxides (NOx)

Working Principle

Temperature & Humidity (SHT45)

Temperature

• Uses bandgap temperature sensing

• Provides highly accurate temperature readings

Humidity

• Uses capacitive polymer sensing

• Moisture absorption changes capacitance

• Converted to digs are factory calibrated and digitally processed.

  Gas Sensing (SGP41)

  VOC / NOx Detection

  • Uses MOX (Metal-Oxide) gas sensing technology

  • Includes:

    • Micro-heater

    • Gas-sensitive layer

     

   

  Operation

  • Heater activates sensing layer

  • VOC/NOx gases interact with surface

  • Resistance changes

  • Converted into digital signal

   

  Provides air quality indices (raw signals + processed outputs).

  Measurement Characteristics

  SHT45

  • Temperature:

    • Range: 40C to +125C

    • Accuracy: 0.1C (typical)

     

  • Humidity:

    • Range: 0100% RH

    • Accurac

      SGP41

      • VOC index (relative scale)

      • NOx index (relative scale)

      • Requires humidity compensation for best accuracy

       

      Combined system provides complete indoor air quality monitoring.

      Electrical Characteristics

      • Supply voltage: 1.7V to 3.6V

      • Low power consumption overall

      • SGP41 consumes more due to heater cycles

       

      Communication Interface

      • Interface: I2C (shared bus)

      • Typical addresses:

        • SHT45: 0x44

        • SGP41: 0x59

         

       

      Both sensors operate independently but share the same I2C lines.

      Internal Features

      Environmental Compensation

      • SGP41 uses:

        • Temperature

        • Humidigas measurement accuracy

         

        Digital Output

        • Fully processed data:

          • C

          • %RH

          • VOC index

          • NOx index

           

        Integrated Heater (SGP41)

        • Enables gas sensing

        • Requires controlled operation cycles

         

        High Stability & Low Drift

        • Suitable for long-term monitoring

        Operating Behavior

        Multi-Sensor Coordination

        • Temperature & humidity readings:

          • Used to compensate gas sensor output

           

        Continuous Monitoring

        • Periodic measurement cycles:

          • Fast response for environmental changes

           

        Air Quality Trends

        • VOC/NOx values represent:

          • Relative air quality changes

           

        Wide operating range:

        • Temperature: 40C to +125C

        • Humidity: 0100% RH

         

      Limitations

      • VOC/NOx outputs are:

        • Relative indices (not exact ppm values)

         

      • Gas sensor sensitive to:

        • Humidity

        • Temperature

        • Airflow

         

      • Requires:

        • Calibration algorithms for best results

         

       

      Breakout Board Role (7Semi)

      The breakout board:

      • Integrates both sensors on one PCB

      • Provides:

        • I2C interface access

        • Power regulation support

         

      • Simplifies multi-parameter sensing

       

      Summary

      The 7Semi SHT45 + SGP41 breakout is a comprehensive environmental sensing module

    • Detects VOC and NOx gases using MOX technology

    • Uses sensor fusion for improved accuracy

    • Provides digital I2C output

    • Enables indoor air quality monitoring in a compact design

     

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