A simple and versatile 12-level water level indicator circuit

This is a simple yet versatile 12-level water level indicator circuit that will show you the current water level in the tank. This circuit can be used for general purposes. This circuit will sound an alarm when the water level falls below the lowest level at L1 and when the water level just touches the highest level at L12. This circuit is designed to display 12 different levels. However, the level display can be increased or decreased depending on the level of resolution required. This can be achieved by increasing or decreasing the number of layers of the metal strip detectors (L1 to L12) and related components.

In this water level indicator circuit, diodes D1, D2 and D13 act as half-wave rectifiers. The rectified outputs are filtered using capacitors C1 to C3 respectively.

Initially, when the water level is lower than the L1 bar, the supplied electrical oscillation frequency is not transmitted to the diode D1. Therefore, the output is low and the LED1 is not lit. In addition, since the base voltage of the transistor T1 is low and it is in the cut-off state, the collector voltage is high, which can generate the melody IC1 (UM66) and sound an alarm.

When water just touches the L1 level detection strip, the oscillating frequency of the power supply is transferred to the diode D1. This straightened power supply voltage forms capacitor C1 with the positive DC voltage, thus lighting up LED1. At the same time, the base voltage of transistor T1 becomes high, causing the forward bias and collector voltage to drop to nearly ground potential. IC1 (UM66) is disabled and the alarm is inhibited.

Depending on the amount of water in the tank, the water level display corresponding LED lights up. Thus, it shows the medium water level in the tank in the form of a bar graph.

When the water in the water tank just touches the highest water level detection line L12, a DC voltage is generated in the capacitor C2. This generates the melody IC1 (UM66) and the alarm sounds again.