An NPK sensor nitrogen (N), phosphorus (P), and potassium (K)

 Nitrogen (N), phosphorus (P), and potassium (K)

An NPK sensor measures the nitrogen (N), phosphorus (P), and potassium (K) levels in soil. These are the primary nutrients essential for plant growth. NPK sensors are widely used in smart agriculture and soil monitoring systems to help farmers and gardeners optimize fertilization.

Types of NPK Sensors

1. Capacitive/Resistive Soil Sensors with NPK Estimation

   • Typically used in hobbyist/Arduino setups.

   • Estimate NPK indirectly based on soil conductivity and other inferred parameters.

   • Inexpensive, but less accurate.

2. Optical or Spectroscopic Sensors

   • Use light absorption/reflection to measure nutrient levels.

   • Often found in advanced agricultural equipment.

   • More accurate but expensive.

3. Electrochemical Sensors

   • Use ion-selective electrodes to directly detect N, P, K ions.

   • Moderate cost, decent accuracy.

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How It Works (General)

• The sensor is inserted into the soil.

• It reads values and often communicates via UART, I2C, or analog output.

• Values are processed to give N, P, and K levels—either as concentration (mg/kg) or a qualitative level (low/medium/high).

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Arduino-Compatible NPK Sensors

A popular model is the DFRobot NPK Soil Sensor, which:

• Works via UART (serial).

• Operates at 9–24V DC.

• Outputs values in mg/kg.

• Needs calibration and proper insertion depth.

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Sample Arduino Connection (for UART NPK sensor)

Wiring:

• Red: VCC (12V)

• Black: GND

• Yellow: TX → Arduino RX (via voltage divider)

• Blue: RX → Arduino TX

Here's a complete Arduino example that reads values from an NPK soil sensor via UART and displays the data on an I2C LCD (16x2 or 20x4).

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✅ What You Need

• Arduino Uno/Nano/Mega

• NPK Sensor (UART type like DFRobot)

• I2C LCD (1602 or 2004 with I2C backpack)

• Libraries:

  • LiquidCrystal_I2C (LCD)

• Power Supply: The sensor usually needs 9–24V DC

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✅ Wiring

NPK Sensor Pin	Arduino Uno/Nano	Notes
VCC (Red)	External 12V	Use external power (not 5V)
GND (Black)	GND	Shared ground
TX (Yellow)	D4	SoftwareSerial RX
RX (Blue)	D5	SoftwareSerial TX (optional)

I2C LCD Pin	Arduino Pin
VCC	5V
GND	GND
SDA	A4
SCL	A5

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✅ Arduino Code

cpp
#include <Wire.h>
#include <LiquidCrystal_I2C.h>
#include <SoftwareSerial.h>

// LCD setup: address 0x27 or 0x3F depending on your model
LiquidCrystal_I2C lcd(0x27, 16, 2);

// Sensor connected via SoftwareSerial
SoftwareSerial npkSerial(4, 5); // RX, TX

byte requestData[] = {0x01, 0x03, 0x00, 0x00, 0x00, 0x03, 0x05, 0xCB}; // Modbus RTU: Read 3 registers from address 0

void setup() {
  lcd.init();
  lcd.backlight();
  lcd.setCursor(0, 0);
  lcd.print("Initializing...");
  
  npkSerial.begin(9600);
  delay(2000);
  lcd.clear();
}

void loop() {
  npkSerial.write(requestData, sizeof(requestData));
  delay(500);  // Wait for sensor to respond

  if (npkSerial.available() >= 11) {
    byte response[11];
    npkSerial.readBytes(response, 11);

    int nitrogen = response[3] << 8 | response[4];
    int phosphorus = response[5] << 8 | response[6];
    int potassium = response[7] << 8 | response[8];

    lcd.setCursor(0, 0);
    lcd.print("N:");
    lcd.print(nitrogen);
    lcd.print(" P:");
    lcd.print(phosphorus);
    lcd.setCursor(0, 1);
    lcd.print("K:");
    lcd.print(potassium);
    lcd.print(" mg/kg");
  } else {
    lcd.setCursor(0, 0);
    lcd.print("Reading failed   ");
    lcd.setCursor(0, 1);
    lcd.print("Check sensor     ");
  }

  delay(3000);  // Wait before next reading
}

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🛠 Notes

• Adjust lcd address (0x27 or 0x3F) if nothing shows up.

• This uses Modbus RTU protocol to request data.

• You may need a voltage divider or logic level shifter if the sensor’s TX is 5V and Arduino RX is 3.3V (or vice versa).