Modbus sensor is not responding

Yassk · October 31, 2023, 12:06pm

Hello,

I got the Dissolved Oxygen sensor and I am working with ESP32 so I used a TTL RS845 converter and wrote two codes with two libraries but I still did not get an outcome.

First code:
#include <ModbusMaster.h>

ModbusMaster node;
uint8_t request[] = {0x01, 0x03, 0x00, 0x00, 0x00, 0x04, 0x45, 0xBE};
uint8_t result;
uint16_t response[28];

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

  // Modbus device ID (Slave Address)
  node.begin(1, Serial);
  Serial.println(" test setup ");
}

void loop() {
  Serial.println(" test loop1 ");

  Serial.println("******************************************* ");
  Serial.println(" ** Start Code ** ");
  Serial.println("test loop2 ");

// Send the Modbus request with the CRC16 checksum
uint16_t crc16_update(uint16_t crc, uint8_t a);

// This function calculates the CRC16 checksum for a byte.
uint16_t crc = 0;
crc = crc16_update(crc, 0xAB);

// The following code prints the CRC16 checksum to the serial port:

Serial.println(crc);


for (int i = 0; i < sizeof(request); i++) {
  for (int j = 0; j < 8; j++) {
    node.sendBit((request[i] >> j) & 1);
  }
}

    // Receive the Modbus response
    node.receive();

    Serial.println("---  **Error part**  ---");

    // Check for errors
    if (response[0] == 0x80) {
      if (response[1] == 0x03) {
        Serial.println("Data error");
      } else {
        Serial.println("Wrong function code");
      }
    }

    Serial.println("---   after receiving  ---");

    // Print the response
    for (int i = 0; i <28; i++) {
      Serial.print("--> ");
      Serial.println(response[i]);
    }

    // Interpret the data
    uint16_t dissolvedOxygen = (response[7] << 8) | response[8];
    uint16_t temperature = (response[11] << 8) | response[12];

    int dissolvedOxygenDecimalPlaces = response[9] >> 4;
    int temperatureDecimalPlaces = response[13] >> 4;

    // Calculate the divisor based on the number of decimal places
    float dissolvedOxygenValue = static_cast<float>(dissolvedOxygen) / pow(10, dissolvedOxygenDecimalPlaces);
    float temperatureValue = static_cast<float>(temperature) / pow(10, temperatureDecimalPlaces);

    // Print the results
    Serial.print("Temperature: ");
    Serial.print(temperatureValue);
    Serial.println(" °C");

    Serial.print("Dissolved oxygen: ");
    Serial.print(dissolvedOxygenValue);
    Serial.println(" mg/L");
/*  } else {
    Serial.print("probbb ");
    Serial.print("Failed to read registers! Error code: ");
    Serial.println(result);
  }*/

  delay(5000); // Adjust the delay according to your needs
}

--------------------------------------------------result

test loop2

48961

— Error part —

— after receiving —

→ 0

Temperature: 0.00 °C

Dissolved oxygen: 0.00 mg/L

and the second code with SoftwareSerial library, the result is unkown characters:
�������������//�

I didn't understand whether the problem is in the code, the wiring or the sensor. Can someone help me please ?