Editing Opto-mechanical sensor (section)

==Construction==
The sensor comprises four main components:

;Ball
:In mice, a heavy ball able to move freely within a recess rolls across the mousing surface as the mouse is moved; in trackballs, the ball is rotated manually
;Rollers
:Three rollers make contact with the ball: the ''x'' and ''y'' motion axis rollers, and a 45° sprung pressure roller to keep the ball away from the inside walls of the recess and against the axis rollers; if this spring weakens, the ball can make contact with the recess and the mouse will seize up
;Opto-mechanical sensor
:The axis rollers turn shafts connected to slotted wheels. Light from [[light-emitting diode]]s shines through the wheel onto light sensors, and the motion of the wheels interrupting the passage of light from the LEDs to the light sensors allows the mouse to sense direction in each axis
;Controller
:A controller chip converts the signals from the sensors into motion, which is fed back to the computer