Water is a vital but scarce natural resource. To prevent water wastage, this water-tank overflow indicator comes in handy. It gives audio as well visual alarm whenever the water tank overflows.
Fig. 1 shows the water-tank overflow indicator circuit and Fig. 2 shows the power supply circuit.
In the power supply unit, mains AC is stepped down by transformer X1 to deliver secondary output of 9V-0-9V AC at 300 mA. The transformer output is rectified by a full-wave bridge rectifier comprising diodes D1 through D4 and filtered by capacitors C1 and C2 to provide +9V at ‘+B’ point and –9V at ‘–B’ point. Connect ‘+B,’ ‘–B’ and ‘GND’ terminals of the power supply unit to the respective terminals of the water-tank overflow indicator circuit.
The circuit is built around op-amp LM741 (IC1), which is used as a comparator. The pin configuration of melody generator IC1(UM66) is shown in Fig. 3.
When water in the tank is below the metal plate sensors, inverting pin 2 of IC1 is at a higher potential than non-inverting pin 3. Output pin 6 of the op-amp is low and there is no music from programmable melody generator IC UM66 (IC2). Transistor BC547 (T1) remains cut-off and therefore LED1 doesn’t glow and the loudspeaker remains silent.
When water in the tank touches the metal plate sensors, it extends ground to pin 2 of IC1. Now pin 3 of IC1 is at a higher potential than pin 2. The high output of the op-amp generates 3.1V across zener diode ZD1. Melody generator IC2produces a melody, which drives the transistor to light up LED1 and sound an alarm from the loudspeaker. Rectifier diode D5 is used to prevent negative polarity to the cathode of the zener diode.