Tag Archives: Dew point

nanoFramework RS485 Temperature, Humidity & Dewpoint Sensor

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As part of this series of samples comparing Arduino to nanoFramework to .NET IoT Device “Proof of Concept (PoC) applications, several posts use an SenseCap Air Temperature and Humidity Sensor SKU 101990882

I cut one of the cables of a spare Industrial IP68 Modbus RS485 1-to-4 Splitter/Hub to connect the sensor to the breakout board. This sensor has an operating voltage of 3.6-30V/DC so it can be powered by the 5V output of a RS485 Breakout Board for Seeed Studio XIAO (SKU 113991354)

The red wire is for powering the sensor with a 12V power supply so was tied back so it didn’t touch any of the other electronics.

public class Program
{
   // === Sensor Modbus params (from Seeed datasheet and label on cable) ===
   const byte SlaveAddress = 0x2A;   // default
   const ushort RegTemperature = 0x00; // int16 (twos-comp), value = °C * 100
   const ushort RegHumidity = 0x01; // uint16, value = %RH * 100
   const ushort RegDewPointTemperature = 0x02; // int16 (twos-comp), value = °C * 100

   public static void Main()
   {
      Console.WriteLine("Modbus Client for Seeedstudio Temperature Humidity and Dew point sensor SKU101990882");

#if ESP32_XIAO_ESP32_S3
      Configuration.SetPinFunction(Gpio.IO06, DeviceFunction.COM2_RX);
      Configuration.SetPinFunction(Gpio.IO05, DeviceFunction.COM2_TX);
      Configuration.SetPinFunction(Gpio.IO03, DeviceFunction.COM2_RTS);
#endif 
      var ports = SerialPort.GetPortNames();

      Console.WriteLine("Available ports: ");
      foreach (string port in ports)
      {
         Console.WriteLine($" {port}");
      }

      // Modbus Client
      using (var _client = new ModbusClient("COM2"))
      {
#if DEBUG_LOGGER
         _client.Logger = new DebugLogger("ModbusClient") 
         { 
            MinLogLevel = LogLevel.Debug 
         };
#endif

         while (true)
         {
            try
            {
               // regs[0] = Temperature.
               var regs = _client.ReadHoldingRegisters(SlaveAddress, RegTemperature, 3);
               short rawTemperature = regs[RegTemperature];
               double temperature = rawTemperature / 100.0; // Signed 16 - bit, value = °C * 100

               // regs[1] = Humidity.
               ushort rawRelativeHumidity = unchecked((ushort)regs[RegHumidity]);
               double relativeHumidity = rawRelativeHumidity / 100.0; // Humidity. Unsigned 16-bit, value = %RH * 100

               // regs[2] = Dewpoint.
               short rawDewPointTemperature = regs[RegDewPointTemperature];
               double dewPointTemperature = rawDewPointTemperature / 100.0; // Signed 16 - bit, value = °C * 100

               Console.WriteLine($"Temperature: {temperature:F1}°C, RH: {relativeHumidity:F0}%, Dewpoint:{dewPointTemperature:F1} °C");
            }
            catch (Exception ex)
            {
               Console.WriteLine($"Read failed: {ex.Message}");
            }

            Thread.Sleep(60000);
         }
      }
   }
}

The nanoFramework Modbus Library based application worked second attempt because initially I had the RegDewPointTemperature register value 0x021

Arduino RS485 Temperature, Dewpoint & Humidity Sensor

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As part of this series of samples comparing Arduino to nanoFramework to .NET IoT Device “Proof of Concept (PoC) applications, and a couple of posts use a SenseCAP Temperature dewpoint, and humidity Sensor SKU101990882.

I cut up a spare Industrial IP68 Modbus RS485 1-to-4 Splitter/Hub to connect the sensor to the breakout board as I find this much easier than soldering connectors

This sensor has an operating voltage of 3.6-30V/DC so it can be powered by the 5V output of a RS485 Breakout Board for Seeed Studio XIAO (SKU 113991354). The red wire is for powering the breakout and device with a 12V power supply so was tied back so it didn’t touch any of the other electronics.

HardwareSerial RS485Serial(1);
ModbusMaster node;

// -----------------------------
// RS485 Pin Assignments (Corrected)
// -----------------------------
const int RS485_RX = 6;  // UART1 RX
const int RS485_TX = 5;  // UART1 TX
const int RS485_EN = D2;

// Sensor/Modbus parameters (from datasheet)
#define MODBUS_SLAVE_ID 0x2A
#define REG_TEMPERATURE 0x0000
#define REG_HUMIDITY 0x0001
#define REG_DEWPOINT 0x0002

// Forward declarations for ModbusMaster callbacks
void preTransmission();
void postTransmission();

void setup() {
  Serial.begin(9600);
  delay(5000);

  Serial.println("ModbusMaster: Seeed SKU101990882 starting");

  // Wait for the hardware serial to be ready
  while (!Serial)
    ;
  Serial.println("Serial done");

  pinMode(RS485_EN, OUTPUT);
  digitalWrite(RS485_EN, LOW);  // Start in RX mode

  // Datasheet: 9600 baud, 8N1
  RS485Serial.begin(9600, SERIAL_8N1, RS485_RX, RS485_TX);
  while (!RS485Serial)
    ;
  Serial.println("RS485 done");

  // Tie ModbusMaster to the UART we just configured
  node.begin(MODBUS_SLAVE_ID, RS485Serial);

  // Register callbacks for half-duplex direction control
  node.preTransmission(preTransmission);
  node.postTransmission(postTransmission);
}
...
void loop() {
  float temperature;
  uint16_t humidity;
  uint16_t dewPoint;

  uint8_t result = node.readInputRegisters(0x0000, 3);

  if (result == node.ku8MBSuccess) {
    // --- Read Temperature ---
    uint16_t rawTemperature = node.getResponseBuffer(REG_TEMPERATURE);
    temperature = (int16_t)rawTemperature / 100.0;

    // --- Read Humidity ---
    humidity = node.getResponseBuffer(REG_HUMIDITY);
    humidity = humidity / 100;

    // --- Read DewPoint ---
    dewPoint = node.getResponseBuffer(REG_DEWPOINT);
    dewPoint = dewPoint / 100;

    Serial.printf("Temperature: %.1f°C Humidity: %u%%RH Dewpoint: %u°C\n", temperature, humidity, dewPoint);
  } else {
    Serial.printf("Modbus error: %d\n", result);
  }

  delay(60000);
}

The Arduino ModbusMaster based application worked first time I forgot to scale the dewpoint.

I have order an Industrial Soil Moisture & Temperature Sensor MODBUS-RS485 sensor from Mouser which will be my next project.