label: printed circuit board, electrical pcb
The mouse's "skin" is the outer, hard plastic body that the user guides across a flat surface. It's "tail" is the electrical cable leading out of one end of the mouse and finishing at the connection with the Central Processing Unit (CPU). At the tail end, one to three buttons are the external contacts to small electrical switches. The press of a button closes the switch with a click; electrically, the circuit is closed, and the computer has received a command.
On the underside of the mouse, a plastic hatch fits over a rubberized ball, exposing part of the ball. Inside, the ball is held in place by a support wheel and two shafts. As the ball rolls on a surface, one shaft turns with horizontal motion and the second responds to vertical motion. At one end of each of the two shafts, a spoked wheel also turns. As these spokes rotate, infrared light signals from a light-emitting diode (LED) flicker through the spokes and are intercepted by a light detector. The dark and light are translated by phototransistors into electrical pulses that go to the interface integrated circuit (IC) in the mouse. The pulses tell the IC that the ball has tracked left-right and up-down, and the IC instructs the cursor to move accordingly on the screen. The interface integrated circuit is mounted on the printed circuit board (pcb) that is the skeleton to which all the internal workings of the mouse are attached. The integrated circuit, or computer chip, collects the information from the switches and the signals from the phototransistors and sends a data stream to the computer.
The mouse's outer shell and most of its internal mechanical parts, including the shafts and spoked wheels, are made of acrylonitrile butadiene styrene (ABS) plastic that is injection-molded. The ball is metal that is coated in rubber; it is made by a specialty supplier. The electrical micro-switches (made of plastic and metal) are also off-the-shelf items supplied by subcontractors although mouse designers can specify force requirements for the switches to make them easier or firmer to click. Integrated circuits or chips can be standard items, although each manufacturer may have proprietary chips made for use in its complete line of products. Electrical cables and overmolds (end connectors) are also supplied by outside sources. The printed circuit board (pcb) on which the electrical pcb and mechanical components are mounted is custom-made to suit the mouse design. It is a flat, resin-coated sheet. Electrical resistors, capacitors, oscillators, integrated circuits (ICs), and other components are made of various types of metal, plastic, and silicon.
