I am just trying to protect the Arduino board.
I had the idea that powerful servos had the same risk as gear reduction motors.
Hence the one-way diode. And thought the signal had to be strong, hence the transistor.
So there is no need for extra security when using a servo?
Just Arduino PIN to servo pulse,
Arduino GND to servo GND ,
servo positive to powersource positive,
servo GND to powersource GND,
and powersource GND to Arduino GND.
The website that made me confused: http://itp.nyu.edu/physcomp/Tutorials/HighCurrentLoads
Might as well explain what I am going to use this servo for:
A Combined 12xKeypad & RFID Door Unlocker - possibly with automatic opening.