I am trying to make the setup shown in this very common tutorial work:http://itp.nyu.edu/physcomp/Labs/DCMotorControl
You can see the setup attached.
I am using an external DC power supply, powering the Arduino Uno with 9V and with 12 V. With lower V it does not work. When I press the switch nothing happens. But when I randomly touch the wire from output 4 th motor runs for a second and slows down, runs and slows down and so on...
So i put the wire, currently in the output pin 4 in the nearby GND pin. Same behaviour as touching the wire.
So what is wrong with the setup? Why the switch doesnt cause any response?
Thanks, best regards