This Simple circuit can monitor overflow of water from the Overhead tank. The sensor placed close to the lid of the overhead tank always monitor the presence of water coming through the lid and gives a music tone when it senses the over flow. ROM IC UM66 is used to generate melody tone.
The circuit is easy to construct. Sensor can be a small piece of common PCB with line tracks. Points A and B are connected to two adjacent tracks using thin plastic wire. Normally T1 is not conducting and no current flows through it. This keeps T2 also non conducting. When water falls on the sensor, electrical conductivity occurs between points A and B though water. This gives base bias to T1 and it conducts to charge C1. When the voltage level in C1 increases, T2 gets base bias and conducts. It gives power to the melody generator IC UM66. Since UM 66 requires 3 volts, Zener diode ZD is used to regulate the supply of UM 66 to 3 volts. Output pulses from UM 66 are amplified by T3 and the Speaker gives Music tone. The music tone continues till the overflow water ceases.
The unit can be placed in the room for easy monitoring. Fix the sensor close to the lid of the overhead tank. Connect the sensor with the points A and B using long plastic wire. Since the copper tracts in the sensor may corrode due to weathering, periodic cleaning or replacement is necessary. To avoid this two brass pins or screws can be used. But these should be arranged closely with minimum spacing of 2mm between them. Then only current passes through water and the brass pins.
Power supply can be 9 volt battery or a 9 volt 500 mA DC adapter. Use a small 2 inch 4 ohms speaker. To get loud voice, use AC 187 or an NPN Darlington transistor in the place of T3 (BC547).