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Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
@Gordon
When you use the external USB-TTL, do you ever see that
,rst cause:1appearing?Also, what if you disable the flow control you'd added? If you're not writing to the SD card you won't need it I guess, and I'd be interested to see if that is making it worse somehow.
It'll be fine to power by USB and use an external 3.3v regulator - the one on there will still do its job, but if another regulator is on there too then it'll take up the slack if the volts on the 3.3v line drops.
There's a 47uF capacitor (and a 0.1uF as well) on the 3.3v line next to the regulator in the circuit diagram - they're physically very close to the ESP8266 so should do pretty well. 47uF should do a pretty good job at soaking up any short-term power requirements.
Also, the ESP8266 itself only needs 1.7v (less than the STM32 I think?) so if that's browning out then I'd be very surprised if the STM32 is still working fine. I guess it could be your board in particular has a bad connection to the ESP8266?