4 hours and 40 posts later and you have not posted the complete schematic I asked for. You waste your time, and worse, you waste the forum's time. I am muting this thread and your account and I advise other forum members to do the same.
I have already placed this under trolling.
I am back to all.
It works with new resistors values 680K and 100K.
But the main: I found the problem... All Arduino I "burned" came from the same batch buying... they were clones.
After I took a normal Arduino one (I don't know if the changing resistor impacted or not) it worked.
I noted this because instead of starting to connect, I wanted to load the stretch... and it burned under the USB also!
Sorry, for the time. It's the first time I have had such a kind of problem directly caused by Arduino pcb...so I couldn't imagine it could depend on this.
I still don't understand what was wrong with my schematic (2 resistors and 2 pins connected but tons of polemics).
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Glad you found the problem!
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Thank you for the update.
For what it's worth I have a PCB with a D1 mini (3V3) and AT Mega 4809 (5V), with voltage dividers to take the 5V signals down to 3V3 between the two. The resistor values were a bit off, meaning the voltage presented to the D1 Mini was sometimes a bit too high, but this depended on what I was powering from. Using USB there wasn't a problem as the supply was a bit less than 5V, using the on-board power supply there was 5V and various weird problems. It took me ages to realise the problems were caused by the slightly high voltages on some of the D1 Mini pins. Nothing got damaged, but a whole load of problems went away once I fixed the resistor values.
The lesson is that the cause of a problem is not always obvious, and not what you first think it is.
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If the current is limited to less than 1mA, it is safe.
This was not the case in post#35 @PerryBebbington Bebbington
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The Nano Every has a 5V regulator with a body diode in the switching mosfet.
If the Nano is powered by USB or via the 5V pin, and the power to the Vin pin is switched off, the other circuitry fed by the line that is connected to Vin may draw current, possibly more than that body diode can handle.
Thank you for pointing that out. I don't find the description on the data sheet particularly clear as to what they are referring to, but if that means into the protection diodes then okay.
FWIW:
When calculating voltage dividers, I make R1 at least (external V - 0.6) / 0.0009. That would limit protection diode current to < 1mA in case of circuit failure between divider junction and GND.
Example, external V = 24V:
(24 - 0.6) / 0.0009 = 26k, use 27k resistor.
(24 - 0.6) / 27000 = 0.87mA.
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