AT89RFD-11 User Guide
-7
7648A–USB–06/06
Figure 3-3.
Mouse Buttons
3.4
Z-Wheel
The motion of Z-wheel is detected using the quadrature signal generated by optical sen-
sors. Two phototransistors are connected in a source-follower configuration forming
Channel A and Channel B. An infrared LED shines, causing the phototransistors to turn
on. In between the phototransistors and LED is a pinwheel that turns on the mouse ball
rollers. The fan of this pinwheel is mechanically designed to block the infrared light such
that the phototransistors are turned on and off in a quadrature output pattern. Every
change in the phototransistor outputs represents a count of mouse movement. Compar-
ing the last state of the optics to the current state derives directional information. As
shown in the Figure below, rotating the wheel forward produces a unique set of state
transitions, and rotating the wheel backward produces another set of unique state
transitions.
Figure 3-4.
Optics Quadrature Signal Generation
Left Button
Middle Button
Right Button
AT89C5131A-M
P1_0
P1_2
P1_1
