Soil moisture sensor in Arduino - Step-by-Step Execution

Concept Flow - Soil moisture sensor

Start

↓

Initialize sensor pin

↓

Read sensor value

↓

Convert value to moisture level

↓

Print moisture level

↓

Wait some time

↓

Read sensor value

The program starts by setting up the sensor pin, then repeatedly reads the sensor, converts the reading to moisture level, prints it, waits, and repeats.

Execution Sample

Arduino

const int sensorPin = A0;
int sensorValue = 0;

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

void loop() {
  sensorValue = analogRead(sensorPin);
  Serial.println(sensorValue);
  delay(1000);
}

This code reads the soil moisture sensor value from analog pin A0 every second and prints it to the serial monitor.

Execution Table

Step	Action	sensorValue	Output	Delay(ms)
1	Initialize sensorPin to A0	-	-	-
2	Start Serial communication	-	-	-
3	Read sensor value from A0	523	Print 523	1000
4	Read sensor value from A0	510	Print 510	1000
5	Read sensor value from A0	498	Print 498	1000
6	Read sensor value from A0	505	Print 505	1000
7	Read sensor value from A0	495	Print 495	1000
...	Loop continues reading and printing	...	...	...

💡 The loop runs forever, reading and printing sensor values every 1000 ms.

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	...final
sensorValue	0	523	510	498	505	495	...

Key Moments - 3 Insights

Why does sensorValue change each time in the loop?

Because analogRead reads the current moisture level from the sensor each time (see execution_table steps 3-7), so sensorValue updates with new readings.

Why do we use delay(1000) after printing?

delay(1000) pauses the program for 1000 milliseconds (1 second) to avoid flooding the serial monitor with too many readings too fast (see execution_table Delay column).

What does Serial.begin(9600) do in setup()?

It starts serial communication at 9600 bits per second so the Arduino can send data to the computer (see execution_table step 2).

Visual Quiz - 3 Questions

Look at the execution_table, what is the sensorValue at step 4?

A 523

B 510

C 498

D 505

💡 Hint

Check the sensorValue column in execution_table row with Step 4.

At which step does the program first print the sensor value?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the Output column in execution_table to find when printing starts.

If delay(1000) was removed, how would the execution_table change?

A Output would print faster without delay

B Program would stop after first reading

C sensorValue would not change

D sensorPin would change

💡 Hint

Consider the Delay column and what delay(1000) controls in execution_table.

Concept Snapshot

Soil moisture sensor reads analog values from pin A0.
Use analogRead(sensorPin) to get moisture level.
Print values with Serial.println().
Use delay() to wait between readings.
Loop repeats to monitor moisture continuously.

Full Transcript

This Arduino program reads a soil moisture sensor connected to analog pin A0. It starts by setting sensorPin to A0 and begins serial communication at 9600 baud in setup(). In the loop(), it reads the sensor value using analogRead(sensorPin), stores it in sensorValue, and prints it to the serial monitor. Then it waits 1000 milliseconds before repeating. The sensorValue changes each loop because the sensor measures current moisture. The delay prevents flooding the output. This cycle repeats forever, giving continuous moisture readings.