What I liked about the DHT11 is that it also measures humidity. Humidity is also an important aspect of in-house climate quality. Good indoor humidity lies between 40 and 60%. While looking for an alternative sensor to upgrade the DHT11 with, I stumbled upon the Adafruit BME680. The BME680 has an accuracy of ± 3% humidity, ± 1.0 degrees Celcius. Compared to the DHT11, which has an accuracy of 5% humidity and 2.0 degrees Celcius, it’s a nice improvement.
In addition to temperature and humidity, the BME680 also measures air pressure. With an accuracy of ± 1 hPa air pressure, it is also possible to measure altitude with an accuracy of ± 1 meter, since air pressure changes with height. To calibrate the sensor, the current sea level pressure for the location must be set. E.g. from https://knmi.nl/nederland-nu/weer/waarnemingen.
Last but not least, the BME680 also measures volatile organic compound (VOC) gas. This is a group of hydrocarbon gasses including SMOG, butane (used for cooking) carbon monoxide (very toxic to humans) etc. The sensor can’t tell which gasses it measures but it can be used to detect trends and for comparison. This also requires calibration against known sources. I haven’t looked into the detail but I’ve already detected some interesting trends with it. More about that later.
For the Pi Zero W in the rooms, I was looking for a cheaper sensor to keep the project within a reasonable budget but without compromising the accuracy. The Adafruit SHT31-D is a good candidate that suits my requirements quite nicely. It is even more accurate than the BME680, but only measures the temperature and humidity. It has an accuracy of ± 2% humidity and ± 0.3 degrees Celcius. The little white chip in the centre is the actual sensor.