Why does my ESP31B beta board not work at low temperature?

[johnlee]

The reason for this is a design change in ESP31B in the crystal oscillator to radically reduce the power consumption (during sleep), and add more tuning range to the crystal oscillator. This resulted in the crystal being sensitive to the type and brand of crystal used and somehow even the design of the board matters as well.

For this reason we did not manage to catch this bug in our first round of test because we were using internal test boards at even -40°C, which did not have this problem. Fortunately our beta testers (thanks Rudi) found this bug and reported this to us, and we manage to replicate this bug both with a beta board and in simulations.

The bug will be resolved in ESP32 with ample margins. For the time being, if you have a problem, you might consider changing the crystal, but it's a delicate operation. So far we only found 1 brand of crystal with this problem, but we haven't tried many brands either.

We thank our beta testers for the feedback.