Building a Water Level Detector: Introduction
Creating a water level detector for applications like monitoring bath or water tank fillings, or indicating overflowing gullies, is remarkably straightforward. This design utilizes a CD4011 CMOS quad gates IC1. Sections A and B of IC1 are configured as an astable multivibrator, generating the necessary oscillations. The frequency of the oscillator is dictated by the values of C1, R2, and the adjustable preset P1.
Water Level Detector Circuit: Operating Principle
Resistor R1 plays a crucial role in the quiescent state by pulling the input to gate IC1.A down to logic low. This action effectively blocks the oscillator’s operation when there’s no water detected. The presence of water between the e+ and e− electrodes elevates the voltage at IC1.A, allowing the oscillator to function. The resulting output signal from gate IC1.B is shaped into a rectangular waveform using IC1.C. IC1.D inverts this signal, ensuring that transistor T1 remains off when there is no water. This prevents current flow in the transformer TR1’s primary winding during system inactivity.
Utilizing the Transformer and Piezo Sounder
Transformer TR1, a 12 V 1.5 VA AC power transformer, is configured as a step-up transformer with its low-voltage winding connected to T1. This arrangement amplifies the signal present at the drain of T1 passively. The high-voltage winding of the transformer is linked to the piezo sounder BZ1 (e.g., Murata with a diameter marked as ’28’), producing the audible warning when activated.
Optimizing Sound Output and Housing the System
To optimize the sound output, P1 needs adjustment to set the oscillator frequency to match the resonant frequency of the piezo transducer. This fine-tuning can be done by ear. The entire circuitry, along with the batteries, can be accommodated within a salvaged case, such as the oval box commonly found inside large chocolate ‘surprise’ eggs. For the electrodes, simple rigid copper wires are used, passing through the case. A watertight seal at the junction is achieved using epoxy adhesive.