We can use the logic of making an automatic light detector to make a simple water level indicator.We just need to remove LDR from the circuit and put the wires into water, then it simply works as water level indicator. There is a specific resistance between the wires that are dipped into water and conduction of electricity through water gives biasing voltage to base of transistor.
The sensitivity can be adjusted using VR1. Put 470K variable resistance in VR1.
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VEK2639 – Liquid Level Controller Kit
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