This circuit indicates the level of moisture in a place due to rain or spilling of water. Green LED lights when there is moisture and Red LED lights when there is no moisture.
IC1 (741) is used as a voltage comparator. Its non inverting input (pin3) receives half supply voltage through the potential divider R2 and R3. Its inverting input (pin2) gets a higher voltage only when the sensor connected to points A and B are shorted with moisture. When the sensor is dry, the output of IC1 will be high because its pin3 gets more current than pin2. This high output makes the transistor T1 conducting and Red LED lights. At the same time T2 remains off because its base is not getting current since T1 takes all the current. So Green LED remains off. When sensor gets moisture, current flows through the sensor to the pin2 of IC1.As a result, pin2 of IC1 gets more current than pin3 and its out put becomes low. T1 then turns off allowing T2 to conduct. Red LED turns off and Green LED turns on indicating the presence of moisture.
Moisture Sensor Circuit
Touch pad can be a small piece of Strip board. Connect the adjacent tracks of the touch pad to points A and B using thin wire. Keep the touch pad in the place that is to be monitored. To test the circuit, take moist cotton and place it on the sensor. Green LED lights if there is sufficient moisture.
Circuit in Word format – Print
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