From looking at the User Guide and the layout file, the location of the sensor on the pcb is not ideal for an ambient temperature sensor. The proximity of the sensor relative to the other components and especially the power input are not advised.

The ideal location would have been one of the top corners. Then push down all the other components as far as possible so that they are not close in proximity to the temp sensor. Using the corner of the PCB, you can optimize the paddle design. Maintaining a minimal pcb thickness is also recommended to reduce the thermal mass. 

Hi Yef,

The si7021.c/h files can be found in the thunderboard bsp folder in simplicity studio:

C:\SiliconLabs\SimplicityStudio\v5_3\developer\sdks\gecko_sdk_suite\v3.0\hardware\kit\common\bsp\thunderboard

The Si7053 and Si7055 are compatible. They have the same i2c commands.

There's also a driver file located in Simplicity Studio that works with the Si7013. The read RH and Temperature commands are compatible with the Si705x Temperature Sensors. The driver file is Si7013.c/h 

C:\SiliconLabs\SimplicityStudio\v4\developer\sdks\gecko_sdk_suite\v2.7\hardware\kit\common\drivers

Simplicity Studio has example projects which utilize the Si7021 RHT Sensor on the STK. Those projects have example driver files for the RHT Sensor. You can open the example project for your STK, or you can reference the drive files in simplicity studio. When you download Studio v5, the Si7013.c/h files can be found here:

C:\SiliconLabs\SimplicityStudio\v5\developer\sdks\gecko_sdk_suite\v3.0\hardware\kit\common\drivers

Simplicity Studio has example projects which utilize the Si7021 RHT Sensor on the STK. Those projects have example driver files for the RHT Sensor. You can open the example project for your STK, or you can reference the drive files in simplicity studio. When you download Studio v5, the Si7013.c/h files can be found here:

C:\SiliconLabs\SimplicityStudio\v5\developer\sdks\gecko_sdk_suite\v3.0\hardware\kit\common\drivers

Hi Yef,

The conversion time for the %RH measurement takes 10msec typical while the temperature measurements take 7msec typical. You can't achieve a 1msec sample rate due to the limitation of the sensor.

Hi Yef,

The conversion time for the %RH measurement takes 10msec typical while the temperature measurements take 7msec typical. You can't achieve a 1msec sample rate due to the limitation of the sensor.

It isn't a known problem. How are you measuring the >7degF difference?  

That said, the Thunderboard Sense wasnt designed to be a temperature sensing reference design. It is designed to show off the capability of our wireless devices as a development tool. A 7degF difference equates to about 3.9degC. That could be a reasonable temperature difference considering the design and how the boards might be used prior to the temperature measurements being made. 

The Si7021 on the SLTB004A isn't ideally located with respect to the other components for temperature sensing. It's located near a LED which could understandably contribute to heat. It is also located near the power input on both designs. Neither of these are recommended for ambient temperature sensing for high accuracy applications.

I invite you to please read our app note, AN1026 (link here), which covers temperature sensor design guidelines. The document references our temperature sensors specifically (Si705x), but the rules apply to the temperature sensor in our RHT sensors (Si7021) as well. The app note covers PCB design guidelines that should be followed. The section covers why the PCB uses a "paddle" design. 

It isn't a known problem. How are you measuring the >7degF difference?  

That said, the Thunderboard Sense wasnt designed to be a temperature sensing reference design. It is designed to show off the capability of our wireless devices as a development tool. A 7degF difference equates to about 3.8degC. That could be a reasonable temperature difference considering the design and how the boards might be used prior to the temperature measurements being made. 

The Si7021 on the SLTB004A isn't ideally located with respect to the other components for temperature sensing. It's located near a LED which could understandably contribute to heat. It is also located near the power input on both designs. Neither of these are recommended for ambient temperature sensing for high accuracy applications.

I invite you to please read our app note, AN1026 (link here), which covers temperature sensor design guidelines. The document references our temperature sensors specifically (Si705x), but the rules apply to the temperature sensor in our RHT sensors (Si7021) as well. The app note covers PCB design guidelines that should be followed. The section covers why the PCB uses a "paddle" design.