HVAC Click as its foundation uses the SCD41, a Sensirion's next-generation miniature CO2 sensor. This carbon dioxide sensor builds on the photoacoustic sensing principle and Sensirion's patented PASens® and CMOSens® technology to offer high accuracy at a minor form factor. It operates within a specified range from 400 to 5'000 ppm, configurable through the I2C interface with a low-power single-shot mode supported to reduce noise levels, i.e., on-demand measurement.

The SCD41 features on-chip signal compensation to counteract pressure and temperature effects. Feeding the SCD41 with the pressure or altitude enables the highest accuracy of the CO2 output signal across an extensive pressure range. Setting the temperature offset improves the accuracy of the relative humidity and temperature output signal. Note that the temperature offset does not impact the accuracy of the CO2 output.

HVAC Click communicates with MCU using the standard I2C 2-Wire interface to read data and configure settings, supporting Standard mode operation with a clock frequency up to 100kHz. Furthermore, this Click board™ is suitable for indoor air quality applications using an additional SPS30, a Particulate Matter (PM) sensor from Sensirion, with the help of which the HVAC Click in the most energy-efficient and human-friendly way maintains a low CO2 concentration for a healthy, productive environment.

The measurement principle of the SPS30 is based on laser scattering, which, together with high-quality, enables precise measurements from its first operation and throughout its lifetime of more than ten years. In addition, the SPS30 provides the possibility of using both I2C and UART interfaces where the communication interface selection can be made by positioning SMD jumpers labeled COMM SEL to an appropriate position. Note that all the jumpers' positions must be on the same side, or else the Click board™ may become unresponsive. Also, to activate I2C communication, the JP4 jumper must be populated.

This Click board™ can operate with both 3.3V and 5V logic voltage levels selected via the VCC SEL jumper. This way, it allows both 3.3V and 5V capable MCUs to use the communication lines properly. In addition, however, the Click board™ comes equipped with a library containing easy-to-use functions and an example code that can be used, as a reference, for further development.