Tag Archives: SKU101991029

nanoFramework RS485 Temperature, Humidity & CO2 Sensor

Posted on by

As part of this series of samples comparing Arduino to nanoFramework to .NET IoT Device “Proof of Concept (PoC) applications, the next couple of posts use a SenseCAP CO2, Temperature and Humidity Sensor SKU101991029.

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 5V ~ 24V 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 static void Main()
{
   Debug.WriteLine("Modbus Client for Seeedstudio Temperature Humidity and CO2 sensor SKU101991029");

   Configuration.SetPinFunction(Gpio.IO06, DeviceFunction.COM2_RX);
   Configuration.SetPinFunction(Gpio.IO05, DeviceFunction.COM2_TX);
   Configuration.SetPinFunction(Gpio.IO03, DeviceFunction.COM2_RTS);

   DateTime warmupCompleted = DateTime.UtcNow;

   // Modbus Client
   using (var client = new ModbusClient("COM2"))
   {
      try
      {
         Debug.WriteLine("Reading CO2 Sensor Warmup duration");

         // Read warm-up time (seconds) from 0x0021
         var warmupReg = client.ReadHoldingRegisters(SlaveAddress, RegWarmup, 1);
         ushort warmupSeconds = unchecked((ushort)warmupReg[0]);

         Debug.WriteLine($"Sensor warm-up:{warmupSeconds}sec");

         warmupCompleted += TimeSpan.FromSeconds(warmupSeconds);
      }
      catch (Exception ex)
      {
         Debug.WriteLine($"Warm-up read failed (continuing): {ex.Message}");
      }

      while (true)
      {
         try
         {
            var regs = client.ReadHoldingRegisters(SlaveAddress, RegCO2, 3);
            short rawTemp = regs[RegTemperature];
            double tempC = rawTemp / 100.0; // Signed 16 - bit, value = °C * 100

            // regs[2] = Humidity. Unsigned 16-bit, value = %RH * 100
            ushort rawRh = unchecked((ushort)regs[RegHumidity]);
            double rhPercent = rawRh / 100.0; // Humidity. Unsigned 16-bit, value = %RH * 100

            if (DateTime.UtcNow > warmupCompleted)
            {
               // regs[0] = CO2 (ppm)
               ushort rawCO2 = unchecked((ushort)regs[RegCO2]);

               int co2Ppm = rawCO2; // already ppm
               Debug.WriteLine($"T:{tempC:F2}°C, RH:{rhPercent:F2}%, CO2:{co2Ppm} ppm");
            }
            else
            {
               Debug.WriteLine($"T:{tempC:F2}°C, RH:{rhPercent:F2}%");
            }
         }
         catch (Exception ex)
         {
            Debug.WriteLine($"Read failed: {ex.Message}");
         }

         Thread.Sleep(60000);
      }
   }
}

The nanoFramework Modbus Library based application worked first time but implementing the CO2 Sensor warm-up time took a couple of attempts.

I did consider trying to fit the Seeed Studio XIAO ESP32-S3 inside the SenseCAP CO2, Temperature and Humidity Sensor but the electronics had been sprayed with a corrosion resistant coating. Connecting (rather than via a breakout board) the VCC+, VCC-, universal asynchronous receiver-transmitter(UART) and transmit enable would have been difficult.

I tried Copilot to clean up the image but it didn’t go well