Hi I'm new to arduino and would like to control the speed of the dc motor by using a npn transister and the pwm output pin. I have a arduino uno (freetronics clone)
Here is my schematic: http://postimage.org/image/by96x8v13/ The NPN transitor i'm using is the TIP122 NPN Transistor http://www.jaycar.com.au/products_uploaded/TIP120-7.pdf
The motor is a 12v dc motor, i cant find the link for the specifcations for it but i know it uses 12v, has 2.7kg/cm torque and spins at about 11000 rpm
the problem is, when i hook this up, nothing happens, the motor does not spin at all. I have made sure i uploaded the sketch to my arduino uno, Im using pin 10 which is a pwm output pin. I am stumped here, many guides for controlling motor speed with arduino have similar schematics to this. I have used analogWrite(255) etc and even digitalWrite(10, HIGH) but the motor does not run at all. I have checked and the transistor is capable of much more current than required and the motor is being supplied with a 12v battery which should be enough.
So i am asking anyone out there, what am i doing wrong? thanks alot