The Sensirion SHT75 is a digital temperature and humidity sensor. Adaption speed is not perfect but the sensor has proven to work even in very low temperatures. It is the standard humidity sensor for the SUMO.
The communication happens through an I2C-like communication bus. As it is not exactly I2C the communication is done through dedicated GPIO pins by pulling the pins in software. The SHT75 is sold with four connectors. A 10k pull-up resistor is needed for the data line. There will be an adapter board available in the Paparazzi hardware repository.
To use the humidity sensor add:
<modules> <load name="humid_sht.xml"/> </modules>
The standard GPIO pins for Clock/Data is the ADC1 connector (P0.4/P030) for the Tiny/TWOG. The GPIO pins can be configured through defines, for the Umarim lite v2.0 they should be set to P0.13/P0.15 for AUX1/AUX2:
<modules> <load name="humid_sht.xml"> <define name="DAT_PIN" value="15"/> <define name="SCK_PIN" value="13"/> </load> </modules>
The location of the sensor on the aircraft does matter. There are various papers that analyze the best location. So far we have installed them within tubes (to protect from sunlight/heating) on the wings. That might not be the optimum place. The SHT75 is preferred over the SHT15 as it does have holes on the back that allows the air to flow through.