Custom RTD Board

A significant priority with the BU Weather Station is that it needs to measure temperature accuratley. For most users, the temperature alone is the most important piece of information, thus reporting and logging said temperature correctly is paramount.

During development, we used both a BME680 and BME280 environment sensor from Bosch-Sensortec. Both of these sensors have an accuracy of +- 0.5-1 degree Celsius.

To solve these issues, and as a learning expereince, the BU Weather Station team decided to make a custom printed circuit board (PCB) to carry a sensor capable of turning an RTD (Resistive Temperature Device) signal into a high-accuracy temperature. This board is shown below.

This board includes:

• An Analog Devices MAX31865 RTD to digital converter
• A NCP1117 3.3V fixed output voltage regulator
• A Texas Instruments TXB0108PWR Level Translator

The RTD to digital converter converts a RTD signal to a temperature that the microcontroller can read through SPI. This board can be used with 2, 3, or 4 wire RTDs by jumping the corresponding pads. The voltage regulator and level translator allow the board to be used with either 3v3 or 5v supplies and logic.

Manufacturing

The BU Weather Station team needed to assemble the board themselves due to the board and components arriving seperately. Most similar boards are either hand-soldered or reflow-soldered in an oven. The BU Weather Station team opted to manufacture our board with reflow-soldering. This was done using an off-the-shelf toaster oven with a custom software/hardware solution as well as a stencil from OshStencils.

Custom reflow-oven