🌱 Smart Plant Monitoring + Automatic Watering System

Using ESP32 + Soil Moisture Sensor + Relay + Water Pump

 ESP32 code + very detailed line-by-line explanation :

✅ Serial Monitor shows:

• Moisture %

• Status: DRY / OK

• Pump: ON / OFF

✅ Condition:

• Moisture < 10% → Pump ON

• Moisture ≥ 10% → Pump OFF

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✅ 1) ESP32 Auto Watering Code (Copy-Paste)

⚡ Connections used in this code:

• Soil Sensor AO → GPIO34

• Relay IN → GPIO26

 

/************************************************************
SMART PLANT MONITORING + AUTO WATERING SYSTEM
Board: ESP32
Sensor: Soil Moisture Sensor (Analog)
Relay: 1 Channel Relay
Pump: DC Water Pump

Condition:
Moisture < 10% -> Pump ON
Moisture >= 10% -> Pump OFF

Serial Monitor Output:
Moisture Value + Moisture Percentage + Pump Status
************************************************************/

// ----------- Pin Definitions -----------
#define SOIL_SENSOR_PIN 34 // Analog pin (ADC) for Soil Sensor AO
#define RELAY_PIN 26 // Digital pin for Relay IN

// ----------- Moisture Settings -----------
int dryValue = 3500; // ADC value when soil is fully DRY (you will calibrate)
int wetValue = 1500; // ADC value when soil is fully WET (you will calibrate)

int pumpThreshold = 10; // Moisture % threshold (10%)

// ----------- Pump Control Variables -----------
bool pumpState = false; // false = OFF, true = ON

void setup() 
{
Serial.begin(115200); // Start Serial Monitor at 115200 baud rate

pinMode(RELAY_PIN, OUTPUT); // Relay pin as output

digitalWrite(RELAY_PIN, HIGH); 
// Most relay modules are ACTIVE LOW:
// HIGH = OFF, LOW = ON

Serial.println("=======================================");
Serial.println("SMART PLANT MONITORING + AUTO WATERING");
Serial.println("ESP32 + Soil Sensor + Relay + Pump");
Serial.println("=======================================");
}

void loop() 
{
// ----------- Step 1: Read Soil Sensor ADC Value -----------
int sensorValue = analogRead(SOIL_SENSOR_PIN); // Reads 0 to 4095

// ----------- Step 2: Convert ADC Value to Moisture % -----------
// We map DRY ADC to 0% and WET ADC to 100%
int moisturePercent = map(sensorValue, dryValue, wetValue, 0, 100);

// ----------- Step 3: Limit the moisture value between 0 and 100 -----------
if (moisturePercent > 100) moisturePercent = 100;
if (moisturePercent < 0) moisturePercent = 0;

// ----------- Step 4: Print Sensor Values on Serial Monitor -----------
Serial.print("Sensor ADC Value: ");
Serial.print(sensorValue);
Serial.print(" | Moisture: ");
Serial.print(moisturePercent);
Serial.print("%");

// ----------- Step 5: Pump Control Logic -----------
if (moisturePercent < pumpThreshold) 
{
// Soil is DRY -> Pump ON
pumpState = true;
digitalWrite(RELAY_PIN, LOW); // ACTIVE LOW relay -> LOW = ON

Serial.print(" | Soil: DRY");
Serial.println(" | Pump: ON");
} 
else 
{
// Soil is OK -> Pump OFF
pumpState = false;
digitalWrite(RELAY_PIN, HIGH); // HIGH = OFF

Serial.print(" | Soil: OK");
Serial.println(" | Pump: OFF");
}

// ----------- Step 6: Delay -----------
delay(1000); // Update every 1 second
}

✅ 2) VERY IMPORTANT NOTE (Relay Active LOW / Active HIGH)

Most relay modules work like this:

That’s why I wrote:

If your relay is opposite, tell me I’ll change it.

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✅ 3) FULL DETAILED CODE EXPLANATION (Line by Line)

 

✅ Section A: Header Comment

This is just a comment block for project information.
It does not affect code.

---

✅ Section B: Pin Definitions

Meaning:

• Soil sensor AO connected to GPIO34

• Relay IN connected to GPIO26

GPIO34 is a good analog pin because it is input-only and stable.

---

✅ Section C: Calibration Values

Meaning:

These values depend on your sensor + soil.

• When sensor is in dry soil, ADC becomes high (~3500)

• When sensor is in wet soil, ADC becomes low (~1500)

⚠ These are sample values.

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✅ Section D: Threshold

This is your main condition:

If moisture < 10%

➡ Pump ON

If moisture >= 10%

➡ Pump OFF

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✅ Section E: Pump State Variable

This stores pump status.

• false = OFF

• true = ON

(Used for clarity)

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✅ setup() Function Explanation

1) Start Serial Monitor

This starts serial communication.

So we can see values in Serial Monitor.

---

2) Relay Pin Output

Relay is controlled by ESP32 output.

---

3) Pump OFF by Default

This turns relay OFF initially.

Because relay is Active LOW.

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4) Print Project Title

This prints project name on Serial Monitor.

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✅ loop() Function Explanation (Main Logic)

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✅ Step 1: Read Soil Sensor Value

This reads analog voltage from soil sensor.

ESP32 gives value between:

• 0 to 4095

---

✅ Step 2: Convert to Moisture %

This is most important line.

It converts ADC into percentage.

• dryValue → 0%

• wetValue → 100%

So it gives moisture percent.

---

✅ Step 3: Fix Moisture Range

Sometimes map() gives:

• negative value

• above 100 value

So we clamp it.

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✅ Step 4: Print on Serial Monitor

This prints:

Example:

---

✅ Step 5: Pump Control Logic

Main condition:

Means:

If moisture < 10%
➡ Soil is dry
➡ Pump ON

---

Pump ON Block

• LOW triggers relay

• Pump starts

---

Print ON Status

So output becomes:

---

Pump OFF Block

This turns pump OFF.

---

Print OFF Status

Output:

---

✅ Step 6: Delay

Updates serial monitor every 1 second.

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✅ 4) Serial Monitor Output Example

Dry soil:

Wet soil:

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✅ 5) IMPORTANT: Calibration (Must Do)

To get correct moisture %:

Step 1: Put sensor in dry soil

Note sensor ADC value → put in dryValue

Step 2: Put sensor in water / wet soil

Note sensor ADC value → put in wetValue