How to Read Soil EC, Temperature and Humidity with Arduino and PR-3000-ECTH-N01 Sensor

This guide covers how to use the PR-3000-ECTH-N01 soil sensor with an Arduino UNO. The sensor measures three values in a single probe: Electrical Conductivity (EC), temperature, and soil moisture. It communicates over RS485 using the Modbus RTU protocol, which is stable and well-suited for outdoor agricultural environments.

Key Features of the PR-3000-ECTH-N01

• 3-in-1 measurement: Moisture, temperature, and EC from one probe
• RS485 protocol: Supports up to 1,200 meters cable length, immune to noise in field conditions
• Modbus RTU: Industrial standard, registers are straightforward to read
• 12V DC power: Powers the entire probe without needing multiple voltage sources

Why Measure EC Alongside Temperature

Electrical Conductivity (EC) in soil indicates the amount of dissolved salts or fertilizer concentration. However, EC is directly influenced by temperature. When temperature rises, EC rises too, even if the actual salt content in the soil has not changed. This sensor solves that problem by reporting temperature alongside EC, allowing you to correct EC values based on actual field conditions.

Required Components

Component	Quantity	Notes
Arduino UNO R3	1
MAX485 Module RS485 to TTL	1	Signal converter
PR-3000-ECTH-N01 Soil Sensor	1	Main probe
Power Adapter 12V DC	1	Sensor power supply
OLED 128x64 I2C Display	1	Optional readout
Breadboard MB-102	1	Circuit assembly
Jumper Wires Set	-	M-M, M-F, F-F

Wiring Diagram: Arduino with PR-3000-ECTH-N01

The circuit has three main sections: power supply, RS485 communication, and optional display output.

Part 1: MAX485 Connected to Arduino UNO

Arduino UNO	MAX485 Module	Role
5V	VCC	Power
GND	GND	Ground
Pin 2 (RX)	RO	Receive Output
Pin 3 (TX)	DI	Driver Input
Pin 7	DE	Driver Enable
Pin 8	RE	Receiver Enable

Part 2: PR-3000-ECTH-N01 Connected to MAX485 and Power

Sensor Wire	Connection	Notes
Blue Wire (B)	MAX485 B	RS485 B line
Yellow Wire (A)	MAX485 A	RS485 A line
Brown Wire	12V DC (+)	Positive power
Black Wire	12V DC (-)	Ground

Critical: The GND of Arduino, MAX485, and the 12V power supply must share a common ground. Without a shared ground, RS485 signals cannot be read correctly.

Part 3: OLED Display (Optional)

Arduino UNO	OLED I2C	Notes
5V	VCC
GND	GND
A4	SDA
A5	SCL

Modbus Registers of PR-3000-ECTH-N01

This sensor uses Modbus RTU Function Code 0x04 (Read Input Registers). Three registers are available:

Register	Data	Unit
0x0000	Soil Moisture	%
0x0001	Temperature	°C
0x0002	Electrical Conductivity (EC)	mS/cm

Installing Required Libraries

1. Download the library bundle from MediaFire — OLED and SoftwareSerial Libraries
2. Extract the archive with WinRAR or WinZip
3. Copy the library folders into Documents/Arduino/libraries/
4. Restart Arduino IDE

Arduino Code: Reading PR-3000-ECTH-N01 via Modbus RTU

#include <SoftwareSerial.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

#define SENSOR_SERIAL_RX 2
#define SENSOR_SERIAL_TX 3
#define MAX485_DE_RE 7
#define MAX485_RE 8

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_RESET -1
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

SoftwareSerial sensorSerial(SENSOR_SERIAL_RX, SENSOR_SERIAL_TX);

// Modbus RTU Function Code 0x04 (Read Input Registers)
byte readCommand[8] = {
  0x01,       // Slave Address
  0x04,       // Function Code: Read Input Registers
  0x00, 0x00, // Starting Address: 0x0000 (Moisture)
  0x00, 0x03, // Quantity: 3 registers (moisture, temp, EC)
  0x00, 0x00  // CRC (calculated below)
};

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

  pinMode(MAX485_DE_RE, OUTPUT);
  pinMode(MAX485_RE, OUTPUT);
  digitalWrite(MAX485_DE_RE, LOW);   // Receive mode
  digitalWrite(MAX485_RE, LOW);

  // Calculate CRC16 for Modbus command
  unsigned int crc = modbusCrc16(readCommand, 6);
  readCommand[6] = lowByte(crc);
  readCommand[7] = highByte(crc);

  // Initialize OLED
  if (!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println(F("OLED init failed"));
    for (;;);
  }
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(SSD1306_WHITE);
  display.display();
}

void loop() {
  // Send read command to sensor
  digitalWrite(MAX485_DE_RE, HIGH);
  digitalWrite(MAX485_RE, HIGH);
  sensorSerial.write(readCommand, 8);
  sensorSerial.flush();
  digitalWrite(MAX485_DE_RE, LOW);
  digitalWrite(MAX485_RE, LOW);

  // Wait for response (expected: 11 bytes)
  delay(100);

  byte response[20];
  int bytesReceived = 0;
  unsigned long startTime = millis();

  while (sensorSerial.available() && bytesReceived < 20) {
    if (millis() - startTime > 1000) break;
    response[bytesReceived++] = sensorSerial.read();
  }

  if (bytesReceived >= 9) {
    // Response format: [addr][func][bytecount][reg1_H][reg1_L][reg2_H][reg2_L][reg3_H][reg3_L][CRC_L][CRC_H]
    int moisture = (response[3] << 8) | response[4];
    int temperature = (response[5] << 8) | response[6];
    int ecRaw = (response[7] << 8) | response[8];


    float tempC = temperature / 10.0;
    float ecValue = ecRaw / 1000.0;  // Convert to mS/cm

    // Print to Serial Monitor
    Serial.print("Moisture: ");
    Serial.print(moisture);
    Serial.print("% | Temp: ");
    Serial.print(tempC);
    Serial.print("C | EC: ");
    Serial.print(ecValue, 3);
    Serial.println(" mS/cm");

    // Display on OLED
    display.clearDisplay();
    display.setCursor(0, 0);
    display.print("Moisture: ");
    display.print(moisture);
    display.println("%");
    display.print("Temp: ");
    display.print(tempC, 1);
    display.println("C");
    display.print("EC: ");
    display.print(ecValue, 3);
    display.println(" mS/cm");
    display.display();
  }

  delay(1000);
}

// CRC16 calculation for Modbus RTU
unsigned int modbusCrc16(byte *data, int length) {
  unsigned int crc = 0xFFFF;
  for (int i = 0; i < length; i++) {
    crc ^= data[i];
    for (int j = 0; j < 8; j++) {
      if (crc & 0x0001) {
        crc = (crc >> 1) ^ 0xA001;
      } else {
        crc >>= 1;
      }
    }
  }
  return crc;
}

How to Use This Code

1. Wire the circuit as shown in the diagram above
2. Open Arduino IDE, paste the code, and select Board → Arduino UNO
3. Select the correct Port and click Upload
4. Open Serial Monitor and set Baud Rate to 9600
5. Insert the probe into soil and observe the readings

Note: If readings show 0 or no response, check that GND is shared across Arduino, MAX485, and the 12V power supply. Also verify that the A (yellow) and B (blue) wires are connected to the correct terminals on the MAX485 module.

Reference Video

• https://youtu.be/-TtcgUAp76o

Soil EC Values and Practical Field Use

Soil EC is a critical indicator for crop management:

EC Value (mS/cm)	Interpretation	Action
0 – 1.0	Nutrient-poor soil	Add fertilizer
1.0 – 3.0	Normal for agriculture	Maintain current condition
3.0 – 4.0	Moderately high	Reduce fertilizer application
> 4.0	Excessively high — salt risk	Cut fertilizer, increase irrigation

Summary

The PR-3000-ECTH-N01 is a practical sensor for smart agriculture systems, combining EC, temperature, and moisture in one probe. Communication happens over RS485 using standard Modbus RTU, making the code relatively straightforward to write. The most important wiring detail is establishing a common ground across the entire system and providing 12V DC power to the sensor separately from the 5V logic used by Arduino.