Interesting....
I read the letter, on letterhead, but that was some time ago.
I just searched and found two references about the data sheet.
#1) D I/O pins are.
#2) that has been removed on recent data sheets.
to that end, If the manufacture is not making the claim, then I have to agree with you, it is not substantiated. put another way, if it is not written, it is not true.
I'll modify my earlier post. leaving what I said, but ADDING the new (to me) information.
I think generally the idea around here should be to prevent people damaging themselves or their hardware. As i said, i heard about the letter, and i think it was online at some point, but has since been removed. What i recommend is to stay within the safe range and as close to 3.3v as possible on the GPIO's
There are nodeMCU's (most of them actually) that are 5v tolerant On the RX pin but on that pin only ! And for me that meant that dividing 5v logic with 3x 1K resistors as i normally do, stopped Serial reception. I removed the voltage divider and then it worked, so if that happens, that is an option, but as far as i know that is only on some nodeMCUs.
As i understood before, the issue is not so much when the GPIO's are in input state, But if they go HIGH as an output, not even a current limiting resistor is going to help. That it has been removed from the datasheet would actually indicate that there is proof somewhere that the pins just aren't 5v tolerant, usually it's ok, but eventually some of them break.
I have to agree with two points. the one above and that we should never put a noob in a position to damage stuff.
I did read about some sort of protection on the pins, since removed.
your point about datasheets being modified means either they changed the design and it no longer does that thing, or it only did that in special uses and not universally, they got bit, so withdrew the statement.
back to the relay....
5v to the OPTO bit, the OPTO, then the pin to ground, may be low enough voltage.
but, I would test it with 5V to the COIL input pull the jumper, put 3.3 on the OPTO side and try out the relay board. if that works, then the problem is sovled.
The OP hasn't responded for a while, but i think the relay was actually working but the Fan wasn't connected to it properly (reply #13)
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