I have just created a DC-motor circuit with an external 8.4 volts battery supply to run it. Via puls-with-modulation over (pin 9, which applies at maximum 5 volts) the transistor (http://www.mouser.at/ProductDetail/ON-Semiconductor/P2N2222AG/?qs=ZXBb0xZ9WeAcMztsfBZpJQ%3D%3D) is controlled to adjust the level of current, which flows through the motor. The problem is that it doesn´t work and I can´t figure it out since I´m an electronics-starter. What basically happens is that when I use the Arduino 5 volts circuit the motor works perfectly but if I connect the external power-supply instead it does nothing, althought the data-sheet of the transistor allows the voltage. It seems like the transistor blocks for some reason.
Thanks for your help!