Fluid level sensor circuit using 741 op amp
This fluid level sensor circuit is based on a simple common 741 op amp IC used as an comparator . When that two fluid level sensor are not placed in liquid the output voltage from the 741 op amp is negative and the T1 is blocked resulting a 0 volts voltage on the R5 resistor .
If the fluid level sensor are placed in the liquid the output voltage from the 741 operational amplifier is around few hundred mili-volts and the T1 transistor conducts , resulting an output voltage on the R5 resistor around 4 volts .
With this voltage you can command another device which can do an visual or audio information about the state of the recipient .