Changing the speed 

Now that we have understood how to change the direction of the motor using the motor driver, it's time to take it a step further and control the speed of the motor using the motor driver. To do this, we don't really have to do much. The motor drivers are built to understand the PWM signals. Once the PWM signal to the motor driver is provided, then the motor driver in turn adjusts the output voltage for the motor and hence changes the speed of the motor driver. The PWM has to be provided on the same input ports IN 1 and IN 2 for motor A, and IN 3 and IN 4 for motor B. It is obvious that the pin on which the PWM is provided will decide the direction in which the motor will move, and the duty cycle of the PWM will decide the speed at which the motor will be spinning. 

Now we have understood how speed control in motor driver works. It's time to do it by ourselves. To do so, we do not need to make any changes to the connections; all we need to do is to upload the following...