Hey guys, i was reading the Arduinos Servo Library Documentation and i came across this..
Note servos draw considerable power, so if you need to drive more than one or two, you'll probably need to power them from a separate supply (i.e. not the +5V pin on your Arduino). Be sure to connect the grounds of the Arduino and external power supply together.
now this is not the first time ive read about connecting the Arduinos ground to the external power source's ground, i just do not know, rather understand, why?
because as far as I understand, and i am just begging to self teach my self , in electronic engineering it is said that current flows from positive to negative, but in real life it actually flows from negative to positive, so if i am using lets say a 9v or even better a 12v battery and connect it to the Arduinos ground would'nt i in "real life" be sending 12v to the Arduino?