Soil moisture sensor in Arduino - Mini Project: Build & Apply

Soil moisture sensor

📖 Scenario: You want to monitor the moisture level of your garden soil using an Arduino and a soil moisture sensor. This helps you know when to water your plants.

🎯 Goal: Build a simple Arduino program that reads the soil moisture sensor value and prints it to the Serial Monitor.

📋 What You'll Learn

Create a variable to store the analog pin number connected to the soil moisture sensor.

Create a variable to store the moisture sensor reading.

Read the sensor value from the analog pin.

Print the sensor value to the Serial Monitor.

💡 Why This Matters

🌍 Real World

Gardeners and farmers use soil moisture sensors to know when plants need watering, saving water and improving plant health.

💼 Career

Understanding sensor reading and Arduino programming is useful for jobs in electronics, IoT, and environmental monitoring.

1

Set up the sensor pin

Create an integer variable called sensorPin and set it to A0 to represent the analog pin connected to the soil moisture sensor.

Arduino

// Create an integer variable called sensorPin and set it to A0
// Your code here

Hint

The soil moisture sensor is connected to analog pin A0. Use int sensorPin = A0; to store this.

2

Prepare to read sensor values

Create an integer variable called sensorValue to store the reading from the soil moisture sensor.

Arduino

int sensorPin = A0;
// Create an integer variable called sensorValue
// Your code here

Hint

You need a variable to hold the sensor reading. Initialize it to 0.

3

Read the sensor value

In the loop() function, read the analog value from sensorPin using analogRead() and store it in sensorValue.

Arduino

int sensorPin = A0;
int sensorValue = 0;

void setup() {
  Serial.begin(9600);
}

void loop() {
  // Read the sensor value from sensorPin
  // Your code here
}

Hint

Use sensorValue = analogRead(sensorPin); inside the loop to get the sensor reading.

4

Print the sensor value

Use Serial.println(sensorValue); inside the loop() function to print the soil moisture sensor value to the Serial Monitor.

Arduino

int sensorPin = A0;
int sensorValue = 0;

void setup() {
  Serial.begin(9600);
}

void loop() {
  sensorValue = analogRead(sensorPin);
  // Print the sensorValue to Serial Monitor
  // Your code here
}

Hint

Use Serial.println(sensorValue); to print the value. Add delay(1000); to wait 1 second between readings.

Practice

1.

What does the analogRead() function do when using a soil moisture sensor with Arduino?

easy

A. It prints the sensor value to the serial monitor.

B. It reads the sensor's analog voltage value representing soil moisture.

C. It sends power to the soil moisture sensor.

D. It converts the sensor value to a digital HIGH or LOW.

Solution

1. Step 1: Understand the purpose of analogRead()

   The analogRead() function reads the voltage from an analog pin and returns a value between 0 and 1023.

2. Step 2: Connect to soil moisture sensor output

   The soil moisture sensor outputs an analog voltage that changes with moisture level, which analogRead() captures.

3. Final Answer:

   It reads the sensor's analog voltage value representing soil moisture. -> Option B

4. Quick Check:

   analogRead() reads analog sensor value [OK]

Hint: analogRead() always reads voltage from analog pins [OK]

Common Mistakes:

• Thinking analogRead() sends power to sensor
• Confusing analogRead() with Serial.println()
• Assuming analogRead() returns digital HIGH or LOW

2.

Which of the following is the correct way to read a soil moisture sensor connected to analog pin A0 and print its value?

void setup() {
  Serial.begin(9600);
}

void loop() {
  int moisture = ?;
  Serial.println(moisture);
  delay(1000);
}

easy

A. moisture = analogRead(A0);

B. moisture = digitalRead(A0);

C. moisture = Serial.read(A0);

D. moisture = analogWrite(A0);

Solution

1. Step 1: Identify correct function to read analog sensor

   Use analogRead() to read analog pin A0 for sensor value.

2. Step 2: Confirm syntax matches Arduino standards

   The correct syntax is moisture = analogRead(A0); to store the sensor value.

3. Final Answer:

   moisture = analogRead(A0); -> Option A

4. Quick Check:

   Use analogRead() for analog sensor input [OK]

Hint: Use analogRead() for analog sensors, not digitalRead() [OK]

Common Mistakes:

• Using digitalRead() for analog sensor
• Trying to use Serial.read() to get sensor value
• Using analogWrite() which outputs voltage, not reads

3.

What will be printed to the Serial Monitor when this Arduino code runs if the soil moisture sensor reads 512?

void setup() {
  Serial.begin(9600);
}

void loop() {
  int moisture = analogRead(A0);
  Serial.println(moisture);
  delay(1000);
}

medium

A. 0

B. 1023

C. 512

D. AnalogRead Error

Solution

1. Step 1: Understand analogRead() output

   analogRead() returns a value between 0 and 1023 based on sensor voltage. Here it reads 512.

2. Step 2: Serial.println() prints the value

   The code prints the value stored in moisture, which is 512.

3. Final Answer:

   512 -> Option C

4. Quick Check:

   analogRead() value printed = 512 [OK]

Hint: Serial.println() prints the sensor value read by analogRead() [OK]

Common Mistakes:

• Expecting maximum 1023 always printed
• Thinking analogRead() returns 0 or error
• Confusing analogRead() with digitalRead() output

4.

Identify the error in this Arduino code snippet for reading a soil moisture sensor and printing its value:

void setup() {
  Serial.begin(9600);
}

void loop() {
  int moisture = analogRead(0);
  Serial.print(moisture);
  delay(1000);
}

medium

A. Serial.print() should be Serial.println() to add a new line.

B. Serial.begin() must be called inside loop().

C. delay() cannot be used inside loop().

D. analogRead() should use A0 instead of 0.

Solution

1. Step 1: Check analogRead() argument

   Using analogRead(0) reads digital pin 0, which is incorrect for analog input.

2. Step 2: Use A0 for analog pin 0

   The correct syntax is analogRead(A0) to read analog pin A0.

3. Final Answer:

   analogRead() should use A0 instead of 0. -> Option D

4. Quick Check:

   Use A0 constant for analog pins [OK]

Hint: Use A0, A1, etc. for analogRead() pins [OK]

Common Mistakes:

• Using integer 0 instead of A0 in analogRead()
• Thinking Serial.print() must be println() always
• Believing delay() is not allowed in loop()
• Calling Serial.begin() inside loop()

5.

You want to turn on a water pump when the soil moisture is below 300. Which code snippet correctly implements this using a soil moisture sensor on A0 and a pump connected to digital pin 7?

void setup() {
  Serial.begin(9600);
  pinMode(7, OUTPUT);
}

void loop() {
  int moisture = analogRead(A0);
  if (?) {
    digitalWrite(7, HIGH);
  } else {
    digitalWrite(7, LOW);
  }
  delay(1000);
}

hard

A. moisture < 300

B. moisture > 300

C. moisture == 300

D. moisture != 300

Solution

1. Step 1: Understand the condition for watering

   The pump should turn on when soil is dry, meaning moisture value is less than 300.

2. Step 2: Write the correct if condition

   The condition moisture < 300 triggers the pump ON with digitalWrite(7, HIGH);.

3. Final Answer:

   moisture < 300 -> Option A

4. Quick Check:

   Turn pump ON if moisture below threshold [OK]

Hint: Use if moisture < threshold to activate pump [OK]

Common Mistakes:

• Using > instead of < for dry soil condition
• Checking equality instead of range
• Forgetting to set pinMode for pump pin