[Arduino IDE demo source code for KC868-A8S]--#18-Read Modbus sensor by RS485

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KC868-A8S read KinCony TS modbus sensor by RS485.  USB print the temperature and humidity value.
   
   

Code:

/*
  Made by KinCony IoT
  https://www.kincony.com
*/

#include <HardwareSerial.h>

#define RS485_RX 32
#define RS485_TX 33

HardwareSerial RS485Serial(2);

// Read input register: ID=1, Function=04, Start=0000, Quantity=0002
uint8_t readCmd[] = {
  0x01, 0x04, 0x00, 0x00,
  0x00, 0x02, 0x71, 0xCB
};

uint16_t modbusCRC(uint8_t *buf, int len)
{
  uint16_t crc = 0xFFFF;

  for (int pos = 0; pos < len; pos++) {
    crc ^= buf[pos];

    for (int i = 0; i < 8; i++) {
      if (crc & 0x0001) {
        crc >>= 1;
        crc ^= 0xA001;
      } else {
        crc >>= 1;
      }
    }
  }

  return crc;
}

float decodeTemperature(uint16_t value)
{
  if (value >= 10000) {
    return -1.0 * (value - 10000) * 0.1;
  } else {
    return value * 0.1;
  }
}

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

  RS485Serial.begin(
    9600,
    SERIAL_8N1,
    RS485_RX,
    RS485_TX
  );

  delay(1000);

  Serial.println();
  Serial.println("RS485 Modbus Temperature & Humidity Sensor");
}

void loop()
{
  while (RS485Serial.available()) {
    RS485Serial.read();   // clear old data
  }

  RS485Serial.write(readCmd, sizeof(readCmd));
  RS485Serial.flush();

  delay(200);

  uint8_t buf[32];
  int len = 0;

  while (RS485Serial.available()) {
    buf[len++] = RS485Serial.read();
    if (len >= sizeof(buf)) break;
  }

  if (len == 9) {
    Serial.print("RX: ");
    for (int i = 0; i < len; i++) {
      if (buf[i] < 0x10) Serial.print("0");
      Serial.print(buf[i], HEX);
      Serial.print(" ");
    }
    Serial.println();

    uint16_t crc_recv = buf[7] | (buf[8] << 8);
    uint16_t crc_calc = modbusCRC(buf, 7);

    if (crc_recv == crc_calc) {
      uint16_t temp_raw = (buf[3] << 8) | buf[4];
      uint16_t hum_raw  = (buf[5] << 8) | buf[6];

      float temperature = decodeTemperature(temp_raw);
      float humidity = hum_raw * 0.1;

      Serial.print("Temperature: ");
      Serial.print(temperature, 1);
      Serial.print(" C   ");

      Serial.print("Humidity: ");
      Serial.print(humidity, 1);
      Serial.println(" %RH");
    } else {
      Serial.println("CRC Error");
    }
  } else {
    Serial.print("Response length error, len=");
    Serial.println(len);
  }

  delay(1000);
}

arduino source code download:

  rs485-sensor.zip (Size: 1.02 KB / Downloads: 8)
ESP32 BIN file download (just download to ESP32 module begin 0x0 address):

  rs485-sensor.ino.merged.zip (Size: 169.79 KB / Downloads: 7)