Seeed-Studio-XIAO-SAMD21-Dual-Temperature-Sensor

This is a fork from Naata/Trinket-M0-liquid-temperature-sensor which I used as base, and modified to my particular use case, and needs. In my scenario, I wanted to monitor both Air/Ambient temperature and Water temperature, and have my radiator fan curves be a function of the air/water temperature difference, which ultimately helps tune for accoustics.

This also uses Newtonsoft.Json to handle json parsing. There is a .NET alternative "System.Text.Json" but I lack the knowledge required to understand why I could not make it work.

The Arduino code is derived from Naata's and Adafruit | Using a Thermistor page, essentially increasing the number of measurements and the delay between these in an effort to improve accuracy. Lastly, the output is JSON instead of a single temperature value to feed into FanControl.

PART 1. The Sensors

Most watercooling temp sensors are 10k Ohm thermistors. I used:

• Alphacool Eiszapfen inline temperature sensor | Part #17362
• Alphacool Eiszapfen temperature sensor plug | Part #17364

For both, Alphacool provides the same Thermistor Datasheet and this is useful to tune the calculated resistance values and improve accuracy. Also, means that the parts can be connected to either port in the pcb.

Another tip on improving the accuracy is: instead of assuming 10k are 10k resistors, measure their value and use that as a reference. It will very much near 10K but having a "truer" reference will help remove some of the variations in measurement.

PART 2. Microcontroller

I opted for the Seeed Studio XIAO SAMD21, and just like the Adafruit Trinket M0, it can:

• Natively output serial via USB (which is great since I wanted to use the internal USB2 header in the motherboard and splice the other end of the cable to a type-c interface)
• Be seen in Windows as a COM device. No RGB in this case, which I preferred, although do not deny the convenience of a color coded "alert"

PART 3. Assembly

• Solder gold pins to the Seeed Studio XIAO SAMD21
• Wire as per diagram below.

Wiring Diagram

Created with Circuit Diagram

Explanation

As this microcontroller (and many others) are unable to measure resistance directly, a voltage divider is used to instead measure the voltage and calculate the resistance at the junction between the resistor and the thermistor.

Use the 3.3V Pin and not the 5V PIN. This microcontroller's logic is 3.3V based. Using the 5V supply will result in skewed "measurements" which in my experience, turned into colder numbers than expected (water that was hot to the touch, around 50 °C would be represented in the range of 30 °C)

PART 4. Arduino IDE

Before this project, I'd tap into OpenWeather's Weather API, get temperature for my city via powershell, and update a .sensor file read from FanControl.

Code: Arduino I opted to output both sensor readings as a JSON formatted string, e.g.: {"temp1":22.66,"temp2":22.50} which then the DLL in the next section parses and turns into two sensors readable from FanControl.

PART 5. FanControl Plugin

• Download Fan Control. Arguably the best tool for the job, bar none.
• Download latest plugin DLL from Releases.
• Use instructions from FanControl Wiki.
• Set environment variable SENSOR_COM_PORT to whichever com port your Seeed Studio XIAO SAMD21 is connected to
• Profit.

PART 6. The Future

• Design and print a small case that protects the electronics, and helps place the controller inside the PC case (either double sided tape or proper mount with screws)