The EC-Meter shows the reciprocal resistance (Ohm^-1 = Siemens), or conductance, of water normalized to a distance of 1 cm. The plug-jacks are 1,4 cm appart.

The input voltage from those two sensors is also on the ADC, so Vinput can change without messing up the callibration.

Temperature is meassured too, but I'm not normalizing the EC to a, so called, EC25(°C) value at the moment.



I meassured four different types of water:

#1 - Aquadest. (destilled water)
#2 - filtered tap water (through a new britta filter)
#3 - normal tap water (in Berlin/Ger.)
#4 - tap water with a pinch of salt

Results:

#1 EC = 110 µS/cm
#2 EC = 850 µS/cm
#3 EC = 930 µS/cm
#4 EC = 4.2 mS/cm

Based on:https://hackaday.io/project/7008-fly-wars-a-h