A water level sensor is a device that detects the height of water in a container and converts this measurement into an electrical signal.�These sensors work through detecting changes in resistance as the water level changes.They are used in many applications, from home water tanks to industrial systems for monitoring and managing water resources.��
At the heart of this sensor is an S8050 NPN transistor, which works like a switch.
Operating voltage: DC 3-5V
Operating current < 20mA
Operating Temp: 10 to 30 degree Celsius
Judge the water level through with a series of exposed parallel wires stitch to measure the water droplet/water size
Simply, The more water the sensor is immersed in, the higher the output voltage in the signal pin is.
The sensor has a series of ten exposed copper traces. Five are power traces and five are sense traces. These traces are interlaced in parallel so that there is one sense trace between every two power traces. These traces are not connected unless they are bridged by water when submerged. When water touches the sensor, it connects these two sets of traces, allowing a small electric current to flow into the transistor’s base. This turns the transistor on, allowing a larger current to flow through it and produce a voltage at the output pin.
The traces act as a variable resistor (just like a potentiometer) whose resistance varies according to the water level.
The change in resistance corresponds to the distance from the top of the sensor to the surface of the water.
When the sensor is dry, the copper traces are separated from each other by air. This means no electric current flows between the traces. As a result, no current flows into the base of the NPN transistor, and the transistor remains switched off, similar to an open switch. Because the transistor is off, electricity cannot flow from its collector (connected to +5 volts) to its emitter (which is connected to ground through a 100-ohm resistor). Since the emitter is also connected to the sensor’s output pin (OUT), the output reads 0 volts (LOW). However, when water touches the copper traces, it creates a conductive bridge between them because water, especially with dissolved minerals and impurities, can conduct a small electric current. This tiny current from the traces flows into the base of the transistor. This turns the transistor on. Once the transistor is activated, it allows a much larger current to flow from the +5 volts through the transistor to the emitter and finally to ground through a 100-ohm resistor. Because the OUT pin is connected between the transistor’s emitter and this resistor, the OUT pin voltage rises towards +5 volts. Importantly, the sensor doesn’t just turn fully on or fully off—it provides different output voltages depending on how much water touches the sensor. If there’s just a little water, the transistor partially activates, causing a small increase in the output voltage. More water increases conductivity, allowing more current into the transistor’s base, and raising the output voltage even higher. Thus, the sensor generates an analog voltage signal directly proportional to the water level.
The module also has a power indicator LED. This LED is not involved in the sensing process – it just lights up when the module is powered, letting you know the sensor is turned on and ready to work.
The resistance is inversely proportional to the height of the water:
The more water the sensor is immersed in, the better the conductivity is, the lower the resistance is.
The less water the sensor is immersed in, the worse the conductivity is, the higher the resistance is.
The sensor produces an output voltage according to the resistance.
The water level sensor has 3 pins:
S (Signal) pin: is an analog output that will be connected to one of the analog inputs on your ESP32.
(VCC) pin: supplies power for the sensor. It is recommended to power the sensor with between 3.3V – 5V.
