RuuviTag Pro Erratic External TMP117 Sensor Readings

[Logonwheeler]

I have both the RuuviTag Pro w/ External Sensor from the Ruuvi store and my own DIY version in which I soldered my own TMP117 external sensor from Focusens to the board per this topic:

New project: External Ruuvi sensor boards

Hi everyone! We’re planning to build some tiny external sensor boards that could be used with RuuviTags. I’ll share more info about boards’ dimensions and pinouts later, but before that, would be great to hear if you’ve got some ideas about sensors you’d like to see available. Currently, following parts are on the list: 9-DoF (acc, magn, gyro) IAQ VOC air quality sensor Temperature Relative air humidity PIR Photodiode Buzzer High brightness LED IR LED Push button Not all the features will …

The RuuviTag Pro w/ External Sensor I purchased from the shop is working perfectly and reporting a range of temperatures correctly (on v3.33.0-RC1), but I am having issues with my DIY version… I need help diagnosing and fixing this issue.

For my DIY version, when the TMP117 external sensor is subjected to temperatures over 25.5-26 deg C, the tempurature in the Ruuvi app keeps reverting to 0 deg C for some strange reason. When the sensor is placed in ice water, the app seems to report right around 0 deg C as expected. When the sensor is at ambient (~23-24 deg C now), it shows a very similar reading to the official RuuviTag Pro w/ External Sensor that I have.

This same behavior is exhibited in the following firmware released that I tried after updating via nRF Connect app:
v3.31.1
v3.33.0-RC1
v3.34.1

Here is the spec sheet for the external sensor I purchased from Focusens:

And here is the soldering of the sensor to the board. Note I chose to leave the ALERT wire disconnected intentionally.

Anything obvious that is incorrect or something I should do to correctly troubleshoot this issue?

Thanks,

Logan

[otso]

If I recall correctly, TMP117 defaults to 0 C after reboot.

I’d check the connections, a glitch could cause reboot. If the reboot is consistently about temperature, the board might have something that does not work at higher temperature.