Example Code for Arduino-Read Soil NPK

Hardware Preparation

• DFRduino UNO R3 (or similar) x 1
• RS485 Shield for Arduino x 1
• RS485 Soil Sensor(N&P&K) x 1

Software Preparation

• Arduino IDE

Wiring Diagram

Other Preparation Work

Before uploading the program to the Arduino:

1. Switch the RS485 Shield's transceiver mode switch to AUTO
2. Switch the Shield's run/compile switch to OFF

After uploading the code:

1. Switch the run/compile switch to ON
2. Set the serial monitor baud rate to 9600

Sample Code

uint8_t Com[8] = { 0x01, 0x03, 0x00, 0x1E, 0x00, 0x01, 0xE4, 0x0C };   //N
uint8_t Com1[8] = { 0x01, 0x03, 0x00, 0x1F, 0x00, 0x01, 0xB5, 0xCC };  //P
uint8_t Com2[8] = { 0x01, 0x03, 0x00, 0x20, 0x00, 0x01, 0x85, 0xC0 };  //K
int N, P, K;
void setup() {
  Serial.begin(9600);  /
}
void loop() {
  int N = readN();
  Serial.print("N = ");
  Serial.print(N);
  Serial.print(" mg/kg  ");
  int P = readP();
  Serial.print("P = ");
  Serial.print(P);
  Serial.print(" mg/kg  ");
  int k = readK();
  Serial.print("K = ");
  Serial.print(K);
  Serial.println(" mg/kg  ");
  delay(1000);
}

int readN(void) {
  uint8_t Data[10] = { 0 };
  uint8_t ch = 0;
  bool flag = 1;
  while (flag) {
    delay(100);
    Serial.write(Com, 8);
    delay(10);
    if (readN(&ch, 1) == 1) {
      if (ch == 0x01) {
        Data[0] = ch;
        if (readN(&ch, 1) == 1) {
          if (ch == 0x03) {
            Data[1] = ch;
            if (readN(&ch, 1) == 1) {
              if (ch == 0x02) {
                Data[2] = ch;
                if (readN(&Data[3], 4) == 4) {
                  if (CRC16_2(Data, 5) == (Data[5] * 256 + Data[6])) {
                    N = Data[3] * 256 + Data[4];
                    flag = 0;
                  }
                }
              }
            }
          }
        }
      }
    }
    Serial.flush();
  }
  return N;
}

int readP(void) {
  uint8_t Data1[10] = { 0 };
  uint8_t ch1 = 0;
  bool flag1 = 1;
  while (flag1) {
    delay(100);
    Serial.write(Com1, 8);
    delay(10);
    if (readN(&ch1, 1) == 1) {
      if (ch1 == 0x01) {
        Data1[0] = ch1;
        if (readN(&ch1, 1) == 1) {
          if (ch1 == 0x03) {
            Data1[1] = ch1;
            if (readN(&ch1, 1) == 1) {
              if (ch1 == 0x02) {
                Data1[2] = ch1;
                if (readN(&Data1[3], 4) == 4) {
                  if (CRC16_2(Data1, 5) == (Data1[5] * 256 + Data1[6])) {
                    P = Data1[3] * 256 + Data1[4];
                    flag1 = 0;
                  }
                }
              }
            }
          }
        }
      }
    }
    Serial.flush();
  }
  return P;
}

int readK(void) {
  uint8_t Data2[10] = { 0 };
  uint8_t ch2 = 0;
  bool flag2 = 1;
  while (flag2) {
    delay(100);
    Serial.write(Com2, 8);
    delay(10);
    if (readN(&ch2, 1) == 1) {
      if (ch2 == 0x01) {
        Data2[0] = ch2;
        if (readN(&ch2, 1) == 1) {
          if (ch2 == 0x03) {
            Data2[1] = ch2;
            if (readN(&ch2, 1) == 1) {
              if (ch2 == 0x02) {
                Data2[2] = ch2;
                if (readN(&Data2[3], 4) == 4) {
                  if (CRC16_2(Data2, 5) == (Data2[5] * 256 + Data2[6])) {
                    K = Data2[3] * 256 + Data2[4];
                    flag2 = 0;
                  }
                }
              }
            }
          }
        }
      }
    }
    Serial.flush();
  }
  return K;
}


uint8_t readN(uint8_t *buf, size_t len) {
  size_t offset = 0, left = len;
  int16_t Tineout = 500;
  uint8_t *buffer = buf;
  long curr = millis();
  while (left) {
    if (Serial.available()) {
      buffer[offset] = Serial.read();
      offset++;
      left--;
    }
    if (millis() - curr > Tineout) {
      break;
    }
  }
  return offset;
}

unsigned int CRC16_2(unsigned char *buf, int len) {
  unsigned int crc = 0xFFFF;
  for (int pos = 0; pos < len; pos++) {
    crc ^= (unsigned int)buf[pos];
    for (int i = 8; i != 0; i--) {
      if ((crc & 0x0001) != 0) {
        crc >>= 1;
        crc ^= 0xA001;
      } else {
        crc >>= 1;
      }
    }
  }

  crc = ((crc & 0x00ff) << 8) | ((crc & 0xff00) >> 8);
  return crc;
}

Result

Insert the soil sensor into the soil. Open the Arduino Serial Monitor (set to 9600 baud) to view printed nitrogen (N), phosphorus (P), and potassium (K) values.

Nitrogen, phosphorus and potassium sensor data can only be used as a reference and cannot be as accurate as professional instruments.