This fluid level sensor circuit uses an ac sensing signal to eliminate electrolytic corrosion on the probes .The ac signal rectified is used to drive T1 transistor that drives a 12 volt relay , that can activate or stop some device . R2 resistor is used to modify the sensor sensitivity and can be replaced with a small variable resistor . MC104093B is a p channel quad 2 input NAND schmitt trigger and is pin to pin compatible with the CD4093. The unused inputs must be tied to an appropriate voltage level , either ground or 12 volts (8,9,12 and 13) and the unused outputs must be left open (10 and 11) .
The circuit can be powered with an input voltage between 3 and 18 volts dc , but in our case the circuit use a 12 volts DC power source .
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