I'm using Arduino to control 2 stepper motors via two l293D drivers. I'm using a separate power supply for the steppers (6V). I'm looking forward to expand the system to 3 up to 10 motors.
Now i have read that i should share the grounds so i have connected the ground of the Arduino (powered from the USB cable) with the ground of the secondary power supply. It works all right. I haven't tested disconnecting the grounds. Now i read in an answer here in this site which is selected as the correct one (albeit for a different question) "Never share grounds."
Can someone explain a bit what is the case?
Thanks for the answers. Now please a bit more so to get it, I'm a newbie.
Now in the l293D (2 of these) i have connected the grounds all together (4,5,13,12).
In one of the answers the author talks about opto-isolation of the 2 power supplies (control and load). This means that if i raise the voltage and the current of my load i.e. use more motors, the circuit in it's current stage may misbehave and i should opto-isolate the grounds for precaution?