Feedback from DC motor help

[rextor]

hi, so far i have designed and drive the DC motor through DAC(digital 2 analogue converter) and a transistor(3904) as an amplifier to give the proper voltage and current to DC motor. now im in the pahse of taking feedback from DC motor, then put this feedback information to LPT port from where i have to control the RPM's of motor,using c++.
can any one help me in designing this pahse of my project.... i cant figure out how shall i'll be doing this.... plz it's very urgent... any type of material or if any one has done this type of feedback through LPT port using c++, will b very very helpy for me.. thankssssss , im waiting.....

 

[throwaway18]

You need to start by desciding how you are going to measure the speed of the motor.

One way is to use a sensor with an infrared light beam. You have a disc with a hole in it on the shaft of your motor. The sensor has a slot with an infrared led on one side and a phottransistor on the other. The hole in the disc allows the light through once per revolution.