https://www.artronshop.co.th/c/131

WaterLevelSensor_RS485.ino

#include <ModbusMaster.h>

#define RS485_RX_PIN (27)
#define RS485_TX_PIN (26)

ModbusMaster sensor;

void setup() {
  Serial.begin(115200);

  // Modbus communication runs at 9600 baud
  Serial2.begin(9600, SERIAL_8N1, RS485_RX_PIN, RS485_TX_PIN); // AdapBit

  // Sensor init with Modbus slave ID 1
  sensor.begin(1, Serial2);
}

void loop() {
  // Read
  uint8_t result;
  result = sensor.readHoldingRegisters(0, 7); // Read Input Register start at 0 -> 7 word (0x0000 - 0x0006)
  if (result == sensor.ku8MBSuccess) {
    int unit = sensor.getResponseBuffer(2);
    int decimal = sensor.getResponseBuffer(3);
    float value = sensor.getResponseBuffer(4);
    value /= pow(10, decimal);

    Serial.print("Level: ");
    Serial.print(value);
    if (unit == 1) {
      Serial.print(" CM");
    } else if (unit == 2) {
      Serial.print(" MM");
    } else if (unit == 3) {
      Serial.print(" MPa");
    } else if (unit == 4) {
      Serial.print(" Pa");
    } else if (unit == 5) {
      Serial.print(" KPa");
    } else if (unit == 6) {
      Serial.print(" MA");
    }
    Serial.println();

    delay(1000);
  } else {
    Serial.println("Read sensor error, check your serial configs, wiring and power supply");
    delay(1000);
  }
}