Distance plays a role in modern electrical devices. EM noise is also an important consideration leading to sometimes twice as many wires as necessary to transmit a signal because the extra wires are used to dampen noise. Since the 1970s Xerox PARC has been studying how people communication information.
Chapter 14: How Data Gets Into Your PC
Although the mouse never replaced the keyboard, the pointer (mouse, eraserhead, trackpad, trackball) supplements it almost universally.
Keyboard and Scan Codes
Pressing a key changes current and a microprocessor detects the change: increased when the key is pressed, decreased when it is released. The scan for changes repeats several hundred times per second, but only acts on signals that are confirmed in 2+ concurrent scans. The microprocessor generates a number called a scan code associated with the key’s circuit. Each key has two codes: one for depressed, one for released. These data are stored in the keyboard buffer and loaded into a port where they are read by BIOS which sends code to delete them from the buffer once they have been received. Two bytes track when shift or special toggle keys have been depressed, so that the code that follows can be augmented to reflect the combination of keys strokes. There are two ways to construct a keyboard: capacitance (springy, clicky keys) or hard contact (rubber dome collapses to allow contact between two metal plates).
How Mice Obey Your Every Gesture
The rolling of the mouse ball moves two rollers that are positioned at 90 degrees relative to one another to capture movement on the X and Y axis. Rollers are attached to an encoder which has a series metal contact points that records distance based on the number of contact points recorded. Signals are sent to the PC through the “tail” (cable) and the cursor moves accordingly onscreen. The click buttons send information about the button clicked and the number of clicks.
The optical mouse uses an LED or laser to light the surface on which the mouse is placed. A small camera inside the mouse scans the surface at 100 fps and sends the results to the DSP which calculates movement based on the change in the relative position of identifiable structures.
How a Touchpad Works
How a Pointing Stick Works
How Speech Recognition Works
No comments:
Post a Comment