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Abstract
The Silicon Labs Si7021 temperature and humidity sensor was used widely in embedded hardware for many years. In January 2025, it was discontinued. The discontinuation was not caused by weak measurement performance, aging design, or ordinary market decline. It came from material compliance issues linked to Polybenzoxazole insulation and PFAS-related regulatory pressure. There was no direct replacement from the manufacturer when this happened. That made a sudden disruption ans collapse for existing designs. Boards, firmware,
and structural plans had already been built around the sensor. This report uses that event as a case study. It also describes the Differential Temporal Derivative Soft Sensing framework, abbreviated here as DTDSS, as a way to keep practical measurement capability after this kind of part loss. Under this framework, lower-cost replacement sensors such as the Aosong AHT20 can still be used for useful environmental
measurement, including estimation of solar radiation and surface heat flux without a pyranometer.
Supplementary materials
Title
Sensor data obtained from the Department of Meteorology, Sri Lanka, using Class A pyranometers during the month of December. Content licensed under the MIT License.
Description
These datasets were used to compare and validate measurements from the FIAPhy device. The data includes solar radiation, heat flux, temperature, humidity, and other meteorological measurements collected from professional sensing equipment. The CSV files act as reference or ground-truth data for comparison with measurements reconstructed by the FIAPhy system and the DTDSS method. Comparing both datasets helps evaluate how closely the FIAPhy measurements follow the recorded environmental conditions and the data was obtained from Class A pyranometer systems operated by the Department of Meteorology, Colombo 7, Sri Lanka
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Title
These datasets were obtained using the FIAPhy device. They contain the measurements produced by our system.
Description
Please compare these values with the previously provided reference datasets for solar radiation and heat flux monitoring. Using the matching dates and times, the datasets can be checked to see how closely the FIAPhy measurements follow the recorded reference measurements.
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Supplementary weblinks
Title
Free, Open-source Data Repository of FIA Operating Systems, FiaPhy device network
Description
A large dataset of FiaPhy global environmental monitoring systems has been combined.
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Additional Meterial on FIA Operating Systems Platform
Description
This hyperlink points to the official main information platform of the research organization, FIA Operating Systems
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Use DTDSS and FiaPhy technology in your project/research
Description
This hyperlink points to the official download page and resource portal for the library. Documentation, research material, and usage information are available through this link.
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