water detector

7-22 elektor july/august 1980 The level of water in a water tank can be measured in various ways, some of which can of course be more complicated than others. The circuit published here lights a LED when- ever the level of water drops below the electrodes. With a high water level, the FET hardly conducts or not at all, because the gate is then connected to earth and there is no voltage difference between gate and source. When the water level drops, the gate/source connection is inter- rupted. The gate is then at a positive potential by means of the 820 k resistor, thereby causing the FET to conduct. The LED will now light. If the reverse operation is needed, that 12V VN66AF VN46AF 27 water detector IIII is the LED lights when the electrodes are short circuited by the water, just connect the "earthy" electrode in the circuit to the positive and wire R2 between gate and source. R2 RI 80557 ITT Applications DI VN46AF VN66AF BS170 BS170