VCC rail rising at 4.6V in some code-specific conditions...

Hi guys,

I ordered a few days ago 2 Espruino Pico from Tindie, and yesterday I came accross some very strange behaviour/bug (?!?) : When I run this code on the Pico (revision 1v75), the VCC rail (usually 3.3V) raises up to ~4.6V, which seems to be approximately the same voltage as VBAT.

" Serial1.setup(4800);
Serial1.on('data', function (data) { print(" "+data); });
Serial1.print("hello"); "

I checked the hardware, no visual damage. The solder pad which is meant to control the battery Mosfet with B0 is NOT soldered.

Using Serial2 instead of Serial1 avoids this behaviour, therefore I suspect a software bug related to Serial1. Furthermore, this bug appears on both Picos.
Any ideas?

Thank you!

Hi - I think this is because you haven't updated the firmware to the latest release. Try upgrading to 1v79 and see if it still happens.

On the release they ship with, if you initialise Serial1 with no arguments it defaults to the lowest numbered port and pins available - A9 and A10. Unfortunately A9 is the USB VCC sense pin, so when it's set to 3.3v output it basically connects the 3.3v line to 5v. Obviously that's bad news - but it was fixed very soon after the boards were produced.

Oh I totally forgot to update to 1v79! Thank you Gordon for that fast reply.
Did you publish the schematic of the Pico? I didn't find it on Github.

Anyway, thank you for the support!

Not yet I'm afraid - there's the power supply circuit at http://www.espruino.com/Pico though.

It will get done, I'm just in the process of getting a new revision made so didn't want to post what will soon be out of date schematics :)

I totally agree with this approach.