A meteorological station.

We have 2 PCBs in our sensor collection for use in a meteorological station: The BMP180 atmospheric pressure sensor, which can also measure the ambient temperature and the DHT11 temperature and humidity sensor. The BMP180 comes with an access library provided by the manufacturer, which must however be adapted to the I2C driver used by the Raspberry Pi.

Again we use the 2-line display controlled by the HD44780 LCD display controller to show the results.

This is by far the most evolved of the Open Day demo projects. It takes a measurement every 60 s and can run for weeks. Not only does it show the temperature, humidity and air pressure on its LCD display it also keeps a log file with all values measured, which can be analyzed and plotted offline.

The small PCB on the left is the BMP180 temperature and atmospheric pressure sensor while the PCB, just left of the blue cobbler, is the DHT11 humidity and temperature sensor. Since the temperature measurement on the BMP180 is more precise than the one on the DHT11 we use this measurement for display and logging.

The following plot shows the temperature and the humidity measured in the computer lab over a few days. One can clearly see that at the beginning of the measurement period the air conditioner had broken down and the temperature rose up to
30 °C while the humidity rose to 70%. The temperature drop which happened when the air conditioner was repaired is clearly visible.

-- Uli Raich - 2017-10-06

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