Generate a sound wave of certain duration (in my case 10 seconds) with high frequency (say 20000 Hz) using my Scilab toolbox for tone generation.
 Cut a wire from an old pc headphone including the TRS connector
 Connect one end of the dc motor with a diode and the other end of the diode with any wire out from the sound card.
 Connect the second wire with the motor
 Run the sound file with any media player and control the speed via volume control slider
Note: wave rectification is done by hardware (diode) and is not going to work when done by software
Note: when motor is connected without diode it is not going to rotate and it will behave as a speaker (you can hear songs from the motor!)