This simple water level indicator will activate an active buzzer (e.g. BeStar BPT-23CX ) in order to make a noise when a certain level of water is being reached. Because the water sensor and the command circuit are located on the same printed circuit board, indicator, together with its 9 V battery and the buzzer can be mounted in a compact case. Obviously the sensor, that is made by corossion, on the board, must not be mounted directly on iron or steel bathtubs but with a magnet atached on the case.
Check out the new water level sensor circuit.
In order to avoid the scratching of the bathtub, the magnet can be covered with plastic or rubber. If the bathtub is made of polypropylene, the water indicator must be attached to it with two clamps or double adhesive tape.
When the water reaches the sensor T1 base is connected to the positive terminal. In consequence, T1 and T2 are opening and the active buzzer makes a buzz. The current consumption is now around 25 mA.
In order that the water level sensor circuit will not be put into operation by steam it may be necessary the reduction of the sensibility by increasing the value of R2. Is recommended to tin the PCB in order to avoid corossion.