PS2 mouse and BASIC Stamp computer


Posted on Feb 4, 2014

A mouse has two axes: `X` and `Y`. When the mouse is moved `horizontally`, the `X` wheel inside the mouse rotates. When the mouse is moved `vertically` (upon a surface), the `Y` wheel inside the mouse rotates. For arbitrary mouse motion, the `X` and `Y` wheels move according to the `horizontal` and `vertical` components of the mouse motion. Notice


PS2 mouse and BASIC Stamp computer
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the holes in the wheels inside the mouse. When the wheel rotates, the infra-red (IR) light emitted by an IR Light Emitting Diode (LED) is interrupted repeatedly, at a rate proportional to the rate of wheel rotation. Thus, the mouse knows how many "increments" (also called "ticks") the mouse axis has moved in a particular time period. Determining the direction of movement involves the use of 2 light sensors, located very close together, along an axis parallel to the movement of the wheel. (Both sensors are in a single 3-pin component shown below. ) Let us name the two sensors in the package "A" and "B". Suppose the wheel is initially at a rotation angle such that the IR light is blocked from reaching both sensors. As the wheel rotates, the IR light from the emitter will eventually be able to pass through a hole in the wheel and reach one of the two sensors, such as sensor "A". If the wheel continues rotating in the same direction, eventually the second sensor, "B", will be able to received IR light. If the wheel continues rotating in the same direction, eventually the IR light will be blocked from reaching sensor "A". If the wheel continues rotating in the same direction, eventually the IR light will be blocked from reaching sensor "B". To understand more about how the mouse circuitry interprets the light sensors and communicates with the personal computer (PC) (via PS/2 signals), I studied the circuit board. A search of...




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