Input Device

1. Input Device • The Keyboard is the most common input device • The most common keyboards are: • 101-key Enhanced keyboard • 104-key Windows keyboard • 82-key Apple standard keyboard • 108-key Apple Extended keyboard

2. kinds of switches • To understand a keyboard, one must first understand the kinds of switches that are used. Types of keyboard switches Mainly four technologies are used to make keyboard-switches. • Mechanical switches • Membrane key-switches • Capacitate key-switches • Hall effect key-switches:

3. Mechanical switches In mechanical switch keys two pieces of metals are pushed together when one presses the key. The metal switch elements are often made of a phosphor-bronze alloy with gold plating on contact areas. They contain a spring to return the key to the non-pressed positioned a form to damp bouncing. Mechanical switches are inexpensive but they suffer from contact bounce. A pressed key may make & break contact several times before it makes solid contact. In addition, the contacts may become oxidized or dirty with age. Results in an improper contact. They have a lifetime of 1 million keystrokes.

4. Mechanical switches

5. Membrane key-switches These are special types of mechanical switches. This consists of 3 layers of plastic or rubber sandwiched as shown below. When we press a key we push the top ink line through the hole to contact the bottom ink line. The advantage is that these types of key-switches can be made very thin and sealed units. Lifetime of these key-switches vary over a wide range.

6. Capacitate key-switches • This type has two small metal plates on the PCB and another metal plate on the bottom of a piece of foam. When we press a key the movable plate is pushed closer to the fixed plate & this changes the capacitance between the fixed plates. The sense amplifier detects this change in capacitance and produces a logic level signal indicating a key-press. The advantage is the absence of mechanical contacts to be oxidized or dirty and the only disadvantage is that a special circuitry is required to detect the change in capacitance. The lifetime is about 20 million keystrokes.

7. Hall effect key-switches This type also has no mechanical contacts. It uses the principle of deflection of a moving change by a magnetic field. A reference current is passed through a semiconductor crystal between two opposite faces. When a key is pressed, the crystal is moved into a magnetic field, this has its flux lines perpendicular to the direction of current flow in the crystal.  This causes a small voltage to be developed between two of other opposing faces of the crystal. This indicated a key-press. It is more expensive but they are very dependable and have a lifetime of 100 million or more Keystrokes.

8. Keyboard Matrix The architecture of most of the keyboards looks like a matrix. Key switches are connected in a matrix of columns & rows.   The rows of the matrix are connected to four output port lines and the column lines of the matrix are connected to four input lines. When no key is pressed, the column lines are held high by the pull-up resistors to +5v. The main principle here is that pressing a key connects a row to a column. If a low is output on a row and a key in that row is pressed, then the low will appear on the column, which contains that key and can be redetected at the input port. If one knows the row and the column of the pressed key, one then knows which key is pressed. Therefore, the keyboard controller has to do three steps for the detection of a key-press. (1) Scan the rows (2) Sense the columns and (3) detect the key-press.

9. Keyboard Matrix Scanning The process of finding out which key is pressed by reading the row and column value is called keyboard scanning. Scan Codes The keyboard sends a special code called as scan code to the computer. The computer converts this scan code as proper ASCII codes with the help of the BIOS program. Scan code generated when the key is closed (pressed) is called as ‘make code’ and the scan code released when the key is open (when not pressed) is called as ‘break code’.

10. Connector The most common keyboard connectors are: • 5-pin DIN (Deustche Industrie Norm) connector • 6-pin IBM PS/2mini-DIN connector • 4-pin USB (Universal Serial Bus) connector • Internal connector (for laptops)

11. Inside the Keyboard The processor in a keyboard has to understand several things that are important to the utility of the keyboard, such as: • Position of the key in the key matrix. • The amount of bounce and how to filter it. • The speed at which to transmit the typematics

12. Trouble Shooting BIOS Upgrade:This is a known problem with Toshiba 8500 desktop systems and the Microsoft Natural Keyboard. In virtually all cases (including the Toshiba 8500), the PC keyboard controller BIOS recognizes the keyboard during the Power-On Self Test (POST), but it does not recognize some of the keys—including certain function keys and Windows-specific keys. One will need to try a generic keyboard or upgrade the system’s keyboard controller BIOS One or more Windows-specific keys don’t work BIOS: This is almost always a limitation of the keyboard-controller BIOS. For example, a Jetkey keyboard controller BIOS (v.3.0) will not recognize the right Windows key on a Microsoft Natural Keyboard. One will need to try a generic keyboard or upgrade the system’s keyboard- controller BIOS.

13. Trouble Shooting Remote-control programs don’t work after installing Driver Software: keyboard drivers Many PC “remote-control” programs (e.g., PC Anywhere, ReachOut, and Carbon Copy) use keyboard and mouse drivers that are simply not compatible with the keyboard’s specific drivers. For example, the remote-control programs listed will not work when IntelliType software is installed for the Microsoft Natural Keyboard. One will need to disable the remote-control software, install patches for the remote-control software that will properly support the keyboard or replace the keyboard with a more generic model. Assigned key sounds do not work Software Problem: When one assign sounds to keystrokes (under the Options tab in the Keyboard tool in the Control panel), the sounds might play when one presses the assigned keys. This problem is known to occur with some programmable keyboards when HiJaak Pro or HiJaak 95 Graphics Suite installed on the computer. These products might load a device driver named “Runner” that disables programmable keyboard sounds. One might be able to work around the problem by closing the “Runner” task: n      Press <Ctrl>+<Alt>+<Del> to open the Close program dialog box. n      If “Runner” is listed, click Runner, then click End task.

14. Trouble Shooting One cannot use Windows-specific keys to start task switching Update SYSTEM.INI software other than TASKSW16.EXE One can start the desired task switching software using <Ctrl>+<Esc>, or by double clicking the desktop. Chances are that the Windows-specific key will not start any other task switching utility if TASKSW16.EXE can be found on the path. One will need to update the task switching program reference in SYSTEM.INI. Load SYSTEM.INI into any text editor, and modify the line that reads: TASKMAN=TASKSW16.EXE to read TASKMAN=<task manager> where <task manager> is the name of the executable file that one wants to start when one presses the Windows key. Rename the TASKSW16.EXE file (e.g., TASKSW16.OLD) or move it to a directory that is not in the path. Save and close the SYSTEM.INI file, then restart the computer.

15. Trouble Shooting Disable Pen: This can happen with some programmable keyboards when pen software is installed on the system. One should be able to correct the problem by disabling the pen device: The NumLock feature might not activate when the NumLock key is pressed 1 Click Start, select Settings, then click Control panel. 2 Doubleclick the System icon and select the Device manager tab. 3 Doubleclick the Ports entry to expand it. 4 Doubleclick the port to which the pen (or touch-screen) device is connected. 5 In the Device usage area on the General tab, click the Original configuration (current) check box to clear it (if one is using OSR2, click the Disable in this hardware profile check box to select it). 6. Click OK, then restart the system when prompted.