It has a small reset button, and I want to use it in order to power on a little 3.3V DC motor that should take the energy from board itself but only when the button stay pushed in order to make it spin only till the button remains pressed and stop on release.
The motor is a simple DC motor with just wires for V+ and V-.
The 3V3 pin of the board is already used as Vin for a sensor and the only 3V3 pin free are those of the 2 programming interfaces.
I don't know well this board, but if the button really a RESET button, you won't achieve what you want.
Why do you not connect the button to the board GPIO pin and than read it in the your sketch?
Because the microcontroller has to intervene in other tasks according the button status as well, isn't meant to just make the motor spinning. This is the point of my question but not the only purpose of the whole project.
If could be used on board button it would be better I would save a button and related wiring keeping the project more compact taking advantage of a button that practically I have never used, in case this is not possible I will check alternatives...
(I'm not talking about desoldering the on board button but a way to use it directly)
So are you saying that to reset this button works interrupting the microcontroller power... Ok, got it, so I cannot use this button.
I hoped it acted at logical level and could have been assigned to different purpose from software.
In this case I have no other choice to use an external button.
You should power your motor from power source, not from board's pin. 3v3 pins on the board are works via voltage regulator and can provide very limited current.
You can try to power the motor from the board, but it will almost certainly work unstable and you will have to change the connections later