Has my RX pin just died?

[philippe76]

For a few months now, I'm using a Nano 33 BLE to communicate with a camera gimbal through UART Serial1 (pins 0 and 1). Today, suddenly, my system stopped working. After a few tests, it seemed to me that my Nano 33 BLE couldn't receive serial messages anymore (it could send them, though).

So I got another Nano 33 BLE and connected both of them like in this tutorial. I tried one Nano as the transmitter and the other one as a receiver, then the other way round (notice that I first needed to fix the bug around Serial1.available()).

And indeed, it seems the original Nano cannot receive messages (but can send them). Could it be that the RX pin is dead? Everything else seems to work. How is that possible? Do pins just die?

There is something more about this RX pin: it can power up the second Nano. What I mean is that when my original Nano is powered up by USB, there is no need to plug the second Nano to USB: the RX wire acts as a power line (if I unplug it, the second Nano shuts down). The reverse is not true: the original Nano cannot be powered up by the second Nano.

Any clue?

EDIT: in the above text, I sometimes used "Uno" instead of "Nano". I've just fixed that. I'm using two Nano 33 and my camera gimbal is also 3.3V.

[jremington]

@philippe76

There is something more about this RX pin: it can power up the second Uno.

That is a very bad sign. You should never connect an unpowered device to a powered one, as that can damage both of them. And probably did, in your case.

Also, do not connect a 5V (Uno) and 3.3V (Nano BLE) device together without using level shifters. Similar problem.

[philippe76]

Thanks @jremington .

I've just fixed some mistakes in my original post: there's no Uno involved, I'm only using Nanos.

You should never connect an unpowered device to a powered one

Never though about that, thank you very much. I will try to learn more about this.