NPK Sensor working on arduino uno but on on arduino mega

Other Hardware Sensors
1

Heya, I've been having trouble making with using my NPK and pH sensor on the arduino mega.
At first i believed it was an issue with the pins, but switching the DI and RO pins didn't seem to fix it.
Right know, everything the sensor says that everything is at 255, while the uno works just fine...

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


// Pines para RS485
#define RE 30
#define DE 31


// Comandos Modbus RTU
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};
const byte ec[] = {0x01, 0x03, 0x00, 0x15, 0x00, 0x01, 0x95, 0xCE};
const byte salinity[] = {0x01, 0x03, 0x00, 0x14, 0x00, 0x01, 0xC4, 0x0E};
const byte ph[] = {0x01, 0x03, 0x00, 0x00, 0x00, 0x01, 0x84, 0x0A};


// Variables para almacenar lecturas
byte values[11];
SoftwareSerial mod(2, 3); // Pines para RS485

void setup() {
  Serial.begin(9600);
  mod.begin(9600); // Comunicación RS485
  pinMode(RE, OUTPUT);
  pinMode(DE, OUTPUT);

}


void loop() {
  // Leer valores de sensores
  Serial.print("Nitrogeno (mg/kg): ");
  Serial.println(readSensor(nitro));
  delay(250);


  Serial.print("Fosforo (mg/kg): ");
  Serial.println(readSensor(phos));
  delay(250);


  Serial.print("Potasio (mg/kg): ");
  Serial.println(readSensor(pota));
  delay(250);


  Serial.print("Conductividad eléctrica (EC): ");
  Serial.println(readSensorInt(ec));
  delay(250);


  Serial.print("Salinidad: ");
  Serial.println(readSensor(salinity));
  delay(250);


  float soil_ph = readSensorPH();
  Serial.print("pH del suelo: ");
  Serial.println(soil_ph, 1);



  delay(3000);
}


// Función para leer valores en formato byte
byte readSensor(const byte *command) {
  digitalWrite(DE, HIGH);
  digitalWrite(RE, HIGH);
  delay(10);


  if (mod.write(command, 8) == 8) {
    digitalWrite(DE, LOW);
    digitalWrite(RE, LOW);
    for (byte i = 0; i < 7; i++) {
      values[i] = mod.read();
    }
  }
  return values[4];
}


// Función para leer valores en formato entero (16 bits)
int readSensorInt(const byte *command) {
  digitalWrite(DE, HIGH);
  digitalWrite(RE, HIGH);
  delay(10);


  if (mod.write(command, 8) == 8) {
    digitalWrite(DE, LOW);
    digitalWrite(RE, LOW);
    for (byte i = 0; i < 7; i++) {
      values[i] = mod.read();
    }
  }
  return int(values[3] << 8 | values[4]);
}


// Función para leer el pH y convertirlo en flotante
float readSensorPH() {
  digitalWrite(DE, HIGH);
  digitalWrite(RE, HIGH);
  delay(10);


  if (mod.write(ph, 8) == 8) {
    digitalWrite(DE, LOW);
    digitalWrite(RE, LOW);
    for (byte i = 0; i < 11; i++) {
      values[i] = mod.read();
    }
  }
  return float(values[4]) / 10.0; // Conversión a pH real
}
2

What you need to understand is that the sensor you are using may be a scam. We have had a lot of people here asking questions. It can NEVER work. Anything you see is just random noise. I am just referring to the NPK sensors.

3

Are you using D20, D21 - for SDA, SCL (resp.) ?

4

Why use SoftwareSerial on a Mega with 3 free UARTs for communication?

Did you read the reference for SoftwareSerial? https://docs.arduino.cc/learn/built-in-libraries/software-serial/

5

Please rephrase; it might be a scam. You do not know what the OP exactly bought. Personally I find it unlikely that a scam would work on an Uno and not on a Mega.

Although a valid concern, the Wire library is not used in the code except for the include.

Additional information, on the Mega the I2C pins are usually also available on the dedicated pins near the USB connector.

6

Then why have that? I figured it was wrapped up with the readsensor() calls.

7

That's the million dollar question :slight_smile:

readSensor() uses mod which is a SoftwareSerial instance.

9

You're the scientist :wink: If they all are crap, I do apologise to @sonofcy.

1 Like
10

Most of the owners here are totally satisfied when they finally get some response from the sensor. I mentioned in another topic that op was only reading the low byte of each register, but it didn't bother him to get just a fraction of the whole value.
Not that it changes anything though.... :grinning:

11

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