some divice can calculate the distance that it move

i want create some robot(like car)..that cam calculate the distance that it move,i have 2 ide about this..

1) first by using IR...my project work like 'roller' in the mouse(near the ball)..The rollers each connect to a shaft, and the shaft spins a disk with holes in it. When a roller rolls, its shaft and disk spin. On either side of the disk there is an infrared LED and an infrared sensor. The holes in the disk break the beam of light coming from the LED so that the infrared sensor sees pulses of light....from that pulse..i want use it to calculate haw much that roller spin,and i can get the distance...

2)may be this be usefull fr me...,in my computer mouse,my scroller beetwen left and right click...that scroller not using IR,it use something like potentiometer...it have 3 pin(leg)..and it can be rotate like potentiometer..when i rotate the scroller,that thing will generate some voltage pulse,i know that because i test using multimeter..can yu describe what it is??

can anybody give some idea to me..

fatal_error said:

2)may be this be usefull fr me...,in my computer mouse,my scroller beetwen left and right click...that scroller not using IR,it use something like potentiometer...it have 3 pin(leg)..and it can be rotate like potentiometer..when i rotate the scroller,that thing will generate some voltage pulse,i know that because i test using multimeter..can yu describe what it is??

Click to expand...

Sounds like an encoder to me. It returns pulses when rotated, a controller can then calculate the angle of rotation out of this (0 - 360°)

yeah..that right...when you rotate small degree.,.you can still get that pulse...can you give any detail about encoder..any link....thanx