Can I connect two power supply GND togheter?
You have to connect them, otherwise your circuit will most probably not work. If you do not connect both grounds, the voltage between these two grounds is somewhat random (determined by surrounding air, environment,...) and your signals might not be what you intended.

The best method is to connect the two grounds at exactly one point. This is called the star point. Make sure the ground connection from your power board has low resistance (thick wire) to keep the voltage drop over it small.

If you want to dive deeper into grounding, you can read this article, but for first experiments this is not necessary.