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What is Moisture Sensor Circuit? Construction, Working & Advantages

The soil moisture or moisture sensor mainly refers to a type of device that senses the moisture percentage in the soil. It is widely used in the frame, agriculture, and field projects. Other than farmers or engineers, hobbyists also use them in a wide range. 

The moisture sensor contains two main parts. One refers to the main circuit or board, while the other refers to the sensor plate. It contains probes half-buried in the soil which makes them vulnerable to rusting. Therefore, they need extra caution and care to work. For this, you can also use another customized probe that has better durability. 

Moreover, moisture sensors give output in two types; digital form and analog form. However, the type of output solely depends on the user and how they want their output values. Furthermore, the longer use of these sensors creates a layer of salt over the probes. Therefore, keep them clean and moisture free now and then.

Construction of a Moisture Sensor Circuit

Moisture sensors can have different types of schematics depending upon the type of sensor. However, this simple schematic diagram of the moisture sensor of soil contains various types of basic electronic components. It includes an LM393 Integrated circuit, a double voltage comparator that can be seen in other types of sensors too. It is considered the sensor’s heart, along with half-buried probes in the ground. Furthermore, it contains an onboarding status led and a potentiometer incorporated over the PCB. Both support moisture soil sensors to detect and find the moisture present in the soil. Besides this, it also helps the sensor maintain microcontroller values.

Make sure to keep soil and PCB away from each other so that they won’t cause any type of error in the values of the sensor. Also, this protects the probe’s pin header from corrosion while exposing it to moisture. Moreover, this sensor contains a high voltage range which makes it ideal to use with any type of microcontroller. But it gives altered values as per the type of microcontroller.

Working on a Moisture Sensor Circuit

A soil moisture detector follows a similar working principle as the LM393 IC sensor. However, they only differ in terms of the outputs they produce. Probes play an important role in detecting soil moisture. They are buried half in a field or ground and sense the amount of moisture present in the soil. However, if we see at the facts, the probe does not sense moisture. It measures the level of voltage, which refers to the analog sensor value that a microcontroller gives out. The probe is linked with the ground from one side and with a first comparator non-inverting input from the other side. Senor contains one capacitor of 0.1µF and one pull-up resistor parallel to the probe. In the last, the comparator comes in and decides the value of the output.

Fertilizers, pesticides, or any type of insecticides can alter the actual value of a moisture sensor. Therefore, use some kind of algorithm or PID to get the correct value of the moisture.

Advantages of Moisture Sensor Circuit

This type of moisture sensor comes with great features and advantages. It comes at affordable prices and is available easily in the market. Therefore, you won’t find a shortage of these sensors. It provides outputs in both types, including potentiometer and onboarding status led to adjust the values. Moreover, the PCB quality seems much better than the probes. Furthermore, this sensor can mount on any type of PCB surface because the circuit board uses a mid-hole to screw the PCB over any type of surface.

Disadvantages of Moisture Sensor Circuit

Regardless of its amazing benefits and features, soil moisture circuit sensor also comes with drawbacks. The biggest drawback is the Probes’ PCB quality. Many engineers and users do not seem to like the quality of these probes much. Because due to the moisture, probes start covered with a salt layer. Moreover, moisture also causes corrosion in the headers of pins and the connected wires, as they need checking now and then.

Applications of Moisture Sensor Circuit

Because of its easy usage, amazing features, and benefits, it’s widely used in various types of projects. Many engineers and agricultures tend to use this sensor and get better results.

FAQ about Moisture Sensor Circuit

What Is The Voltage Level Of The Moisture Sensor Circuit?

The LM393 Integrated circuit datasheet shows that it operates on a voltage of 36 volts. Therefore, it’s safe to connect the sensor to any level of voltage despite any logic level of voltage.

How To Dodge or Prevent the Depositing Coatings Of Salt Over The Moisture Sensor Circuit Probes?


The usage of commonly available probes or even copper probes can help in measuring the moisture value in soil. Thus, it gives better durability.

Can I use the wire with Long connections Between Main Board & Probes?

You may increase the length of the wires that connect probes and the mainboard. However, it may increase the wire’s resistance more than the conventional jumper wires. Thus resulting in altering the values.

Is there any effect of Fertilizers on the values Of Moisture Sensor circuits?

Yes, pesticides and fertilizers can have an impact on the values because they enhance the free ions content present in the soil. Thus, resulting in improved voltage signal conduction. Therefore, those extra free ions act as moisture and alter the values of soil moisture.

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