In my project I'm using 5v relay module (3pins: +,-,signal), as arduino uno 5v pin is used by another module, I've connected relay + and "signal" wires to digital pins, everything working good, but its a little bit unclear does powering relay from digital pin can somehow damage the pin itself?
Can you please provide a link to the relay module that you are using ?
Has it really only got 3 connections ?
I’m using this relay module SRD-05VDC-SL-C:
Relays should preferably have thier own power connection / external power.
The pins from the Arduino have a limited current and using them for items that usually need more current is a way to cause random unwanted actions.
These may not initially show but can happen at any time and may include random on / off or board shutdowns.
They could eventually lead to the voltage regulators on the board failing.
If using a seperate supply do not forget a common ground