// Define which pin to be used to communicate with Base pin of TIP120 transistor
int TIP120pin = 11; //Arduino's PMW pin 11
void setup()
{
pinMode(TIP120pin, OUTPUT); // Set pin for output to control TIP120 Base pin
}

void loop()
{
analogWrite(TIP120pin, 255); // By changing values from 0 to 255 you can control motor speed

}