Hi everyone,
I'm currently working on a project that involves using an NPK sensor via RS485 Modbus communication. Based on the sensor's user manual, the calibration formula for the sensor is Y = AX + B,
where:
Y is the calibrated value (the output I need after calibration),
X is the raw reading from the sensor,
A is the coefficient (slope) for each parameter (N, P, K),
B is the calibration offset for each parameter (N, P, K).
Also, according to the manual, I can access the coefficient and calibration values from specific Modbus registers:
- Nitrogen coefficient (high byte: 0x04E8, low byte: 0x04E9),
- Nitrogen calibration value (0x04EA),
- Phosphorus and Potassium have similar registers for their coefficients and calibration values.
I am using an Arduino to read the raw sensor data and communicate with the sensor via Modbus. Iām a bit unsure about the best way to incorporate this calibration formula into my code. Could someone help me apply the calibration formula to adjust the sensor readings?
Code:
#include <SoftwareSerial.h>
#include <Wire.h>
// RE and DE Pins set the RS485 module
// to Receiver or Transmitter mode
#define RE 8
#define DE 7
// Modbus RTU requests for reading NPK values
const byte nitro[] = {0x01,0x03, 0x00, 0x1e, 0x00, 0x01, 0xe4, 0x0c};
const byte phos[] = {0x01,0x03, 0x00, 0x1f, 0x00, 0x01, 0xb5, 0xcc};
const byte pota[] = {0x01,0x03, 0x00, 0x20, 0x00, 0x01, 0x85, 0xc0};
// A variable used to store NPK values
byte values[11];
// Sets up a new SoftwareSerial object
// Digital pins 10 and 11 should be used with a Mega or Mega 2560
SoftwareSerial mod(2, 3);
//SoftwareSerial mod(10, 11);
void setup() {
// Set the baud rate for the Serial port
Serial.begin(9600);
// Set the baud rate for the SerialSoftware object
mod.begin(9600);
// Define pin modes for RE and DE
pinMode(RE, OUTPUT);
pinMode(DE, OUTPUT);
delay(500);
}
void loop() {
// Read values
byte val1,val2,val3;
val1 = nitrogen();
delay(250);
val2 = phosphorous();
delay(250);
val3 = potassium();
delay(250);
// Print values to the serial monitor
Serial.print("Nitrogen: ");
Serial.print(val1);
Serial.println(" mg/kg");
Serial.print("Phosphorous: ");
Serial.print(val2);
Serial.println(" mg/kg");
Serial.print("Potassium: ");
Serial.print(val3);
Serial.println(" mg/kg");
delay(2000);
}
byte nitrogen(){
digitalWrite(DE,HIGH);
digitalWrite(RE,HIGH);
delay(10);
if(mod.write(nitro,sizeof(nitro))==8){
digitalWrite(DE,LOW);
digitalWrite(RE,LOW);
for(byte i=0;i<7;i++){
//Serial.print(mod.read(),HEX);
values[i] = mod.read();
Serial.print(values[i],HEX);
}
Serial.println();
}
return values[4];
}
byte phosphorous(){
digitalWrite(DE,HIGH);
digitalWrite(RE,HIGH);
delay(10);
if(mod.write(phos,sizeof(phos))==8){
digitalWrite(DE,LOW);
digitalWrite(RE,LOW);
for(byte i=0;i<7;i++){
//Serial.print(mod.read(),HEX);
values[i] = mod.read();
Serial.print(values[i],HEX);
}
Serial.println();
}
return values[4];
}
byte potassium(){
digitalWrite(DE,HIGH);
digitalWrite(RE,HIGH);
delay(10);
if(mod.write(pota,sizeof(pota))==8){
digitalWrite(DE,LOW);
digitalWrite(RE,LOW);
for(byte i=0;i<7;i++){
//Serial.print(mod.read(),HEX);
values[i] = mod.read();
Serial.print(values[i],HEX);
}
Serial.println();
}
return values[4];
}
