Full Bathtub Indicator

Posted on Nov 30, 2012

Running a bath can end in a minor domestic disaster if you forget to turn off the taps in time. This indicator activ

Full Bathtub Indicator
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ates an active buzzer to provide an audible warning when a given water level is reached. Because the water sensor and the driver circuit for the buzzer are contained on one PC board, the indicator, together with the 9-V battery and the buzzer, can be built into a compact case. Obviously, the sensor, which is etched on the PC-board, must not be fitted in case-iron or steel bath, the indicator is secured to it with the aid of a magnet glued onto the case. To prevent scratching the bath, the magnet can be covered in plastic or rubber. If you have a polypropylene bath, the indicator can be stuck to it with blue tack or double-sided adhesive tape. When the water reaches the sensor, the base of T1 is connected to the positive supply line. As a result, T1 and T2 are switched on so that the buzzer B21, a self-oscillating type, is activated. The current drawn by the circuit in that condition is about 25 mA. In case the circuit is actuated by steam, its sensitivity can be reduced by increasing the value of R2. It is best to tin the PC board tracks to prevent corrosion. T1, T2 = BC548C BZ1 = active piezo-ceramic resonator

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