Input Devices And Peripherals

The major input devices, mainly being the keyboard and mouse.  It is important to know the basics of these pieces of equipment, their connectors, and their IRQ and I/O settings.

The Mouse (No, Not Mickey)

Almost every single computer in use today uses some form of a mouse.  Although digitizing pads and trackballs may look different, they are essentially the same equipment modified for some specific use.  In fact, a trackball is simply an upside-down mouse that you move the ball rather than the whole mouse.

There are three essential connectors that a mouse can use.  A serial mouse uses a DB 9 pin connector to connect to a serial port.  A PS/2 mouse uses a 6 pin mini-DIN connector to connect to a PS/2 port.  A bus mouse uses it's own proprietary adaptor card to connect to the computer.

There are combination PS/2-Serial mice out there, and these two formats make up the biggest chunk of the mouse market.  Most of the time combination PS/2-Serial mice use an adaptor to change the 6 pin mini-DIN connector to a serial-type connection.

Inside The Mouse

Most mice use a simple system where a rubber ball inside the mouse moves in relation to how the mouse moves on the table.  Rollers that touch the rubber ball move, and sensors attached to the rollers check for the distance traveled by the ball and the speed of the rollers to determine the movement of the pointer on the screen.

Newer mice are also coming out of the optical variety.  This means they have no rubber ball, but instead track movement of the mouse by scanning the surface below the mouse for movement.  As the mouse is moved, changes in the surface are detected and the mouse pointer moves accordingly.  This is not a new technology, but an improvement on an older form of optical mouse that required a special pad in order to work.

Optical mice are preferable over standard mice because they have no moving parts for their tracking systems.  This makes them less prone to failure.  Also, rubber mouse balls pick up dirt and debris and transfer it to the inside of the mouse.  Optical mice are sealed units, and do not suffer from this debris issue.  This makes optical mice more reliable, but also more expensive.

As stated before, a trackball is simply a mouse turned upside-down.  This means that instead of moving the mouse to move the rubber ball, you just move the ball.  They are no different from standard mice in their maintenance and function, with one minor difference.  Because their ball and roller mechanisms face up, they are more prone to dust and debris than other forms of mice.

Digitizing tablets are totally different from other types of mice, put are still categorized with them.  They use sensors in a pad to track the movement of a specialized pen across the top of their surface.  This pen system tends to be more accurate than normal mice, but is much more expensive and is harder to learn to use.  It is mainly meant for CAD work, graphic artists, and 3D motion programs.

Caring For Your Mice

Trackballs and mice require you to perform some regular maintenance on them.  As their balls collect dust and dirt, it transfers this dirt to the mechanisms inside the mouse, which can slow down their tracking speed and cause them to function erratically.  Maintenance on a mouse or trackball is limited mainly because they only cost around $15 for a standard mouse, making replacement cheaper than repair.  You can do some basic maintenance on a mouse to help correct slow tracking and skipping performance.

First of all, examine the access cover around the ball.  You'll notice that it turns on way or the other to release the ball.  Open the cover and take out the ball.  This ball can be washed in water, but don't use alcohol.  Alcohol is used extensively in computer cleaning because it cleans without leaving residues, but it can change the stickiness of a rubber ball causing it to pick up more debris.  

After you've cleaned the ball, take some compressed air and blow out the inside of the mouse.  This should loosen most of the debris inside the mouse.  Then examine the rollers.  If you use a material-covered mouse pad, you may notice that material building up on the rollers.  Take a set of tweezers and remove that buildup from around the rollers.  Be careful not to break the rollers, as you will be buying a new mouse if you do.

One of the oldest tricks in the technician's book is to clean a mouse ball by rolling it on a pant leg.  To be honest, it works fairly well and doesn't do much damage.  It may not get all the dirt off, but it's easier than waiting for a mouse ball to dry. You must use soap and water for cleaning.

Configuring Mice

With most of the current versions of windows, mice do not require any special drivers or configurations beyond personal settings. 

Generally, a mouse came with a set-up disk with a file called mouse.sys or something similar to that.  You simply copied that file to the hard drive, and then accessed it with the "Device=" command in the Config.sys file.

PS/2 mice use an IRQ of 12 and an I/O Address of 238h.  This is more because the port they plug in to uses this information.  A serial mouse will use the settings of the serial port it is attached to, as will the bus mouse.  Assume the IRQ 12 setting if you don't have a specified format of connector for the mouse.

Keyboards

There are 4 different standards of keyboards that have been used by computers over the last 15 or so years.  They are;

XT - 83 keys, including 10 function keys, a numeric keypad, and cursor control keys.  XT keyboards had a built-in processor.

AT - 84 keys, adding a SysRq key and a larger return key.  This format moved the keyboard processor onto the motherboard.

Enhanced - 101 keys, including 12 function keys, a numeric keypad, and cursor and screen controls.

Windows Enhanced - 104 keys.  It is essentially an enhanced keyboard with three new buttons.  Two access the start menu, and one brings up the file menu for the active window.  Every keyboard sold in the last 4 or 5 years is a Windows enhanced keyboard.

Although most keyboards are compatible with each other, there are two exceptions.  XT computers and AT computers use different keyboard processor placement, meaning they are incompatible with each other.  An enhanced keyboard will work on either an XT or AT system, but an AT keyboard won't work on an XT system and vice versa.  Also, in the mid 90's most major computer manufacturers made their keyboards proprietary, meaning their pin placement was specific to their computer.  That made running any other keyboard besides the manufacturer's keyboard impossible.  (I'm not sure if this is still true or not, but I'd assume that they got out of that habit a couple years ago)

How Keyboards Work

A keyboard is a map of characters on an electronic grid.  Each character produces a specialized electronic signal that can be converted by the keyboard processor.  When a key is pushed, it creates it's specific "make" code.  When it it released, it creates a "break" code.   These two signals produce a "scan" code that the keyboard processor uses to determine the appropriate character that is associated with different scan codes.  If you press the shift, alt, or control key, it shifts the scan code slightly to allow a different character to be produced.  The scan codes are decoded through the use of a character map, which is embedded in the BIOS or keyboard driver.  

There are two types of keyboards, although you'll never notice the difference without opening the keyboard and looking inside. 

The first type is a mechanical keyboard, or a keyswitch keyboard.  This uses metal contacts to determine when a key is pressed down.  When the user presses the key, it touches two metal contacts against each other to complete an electrical signal.  When the key is released, the signal is broken.

The other type of keyboard is a capacitive keyboard.  This use a membrane rather than electrical contacts to determine when a key is pushed.  Membranes are more reliable and use fewer moving parts than mechanical keyboards, but are expensive to produce.

Most of today's keyboards are capacitive, although some cheaper keyboards still use keyswitches.  Because capacitive keyboards use a membrane rather than contacts, their are generally non-repairable items.  

Maintenance For Your Keyboard

Most of the maintenance for a keyboard is simple.  First, don't spill anything in it.  Secondly, if something falls in, turn the keyboard over and shake it until it falls out. For dirt that won't come out through shaking, pry the ctrl key off of blow out the keyboard with compressed air.  

That's right, pry the key right off.  Use a slot screwdriver and lift from under the key.  It will pop off.  If it doesn't with a small bit of force, don't push too hard.  In most cases the keys will pry out giving you lots of room to blow out dirt.

**DON'T pry off the space bar.  It works on a spring system that is nigh-impossible for a beginner to re-attach.  I've done it, and it wasn't fun.  If you even have a keyboard with a space bar problem, examine the mechanical springs and such carefully before attempting to fix.  For $15, a new keyboard might be worth avoiding the aggravation.

Keyboards are durable enough that they can be immersed in water.  In fact, I've heard technicians talk about putting keyboards in the dishwasher.  I would suggest that the dishwasher is a little extreme, but as long as you dry the keyboard completely before you reattach it it can be dunked underwater to clean it.  No soap though, as it adds residue that can jam up a keyboard.

Keyboard Connectors And Assignments

Keyboards use either a 5 pin DIN or 6 pin mini-DIN connector.  If you see a keyboard with a phone-style RJ-11 connector, it's either fairly old or belongs to a WYSE (workstation) terminal.  

The keyboard is assigned IRQ 1 and I/O address 060h.  The keyboard's device driver is generally stored in the BIOS or in the ROM codes in the computer.  DOS and Windows 3.x could use additional device drivers to extend older BIOSes, but they aren't required in any new version of Windows.

Repair Vs. Replace

Keyboards and mice bring up an important topic in computer technology.  In most cases, you will never repair a mouse or keyboard.  They are called FRU's (Field Replaceable Units), and are meant to be throw-away technology.  FRU's basically are interchangeable parts that aren't worth trying to fix.  A technician simply goes to the computer, replaces the unit, and leaves after he's sure the new equipment solved the problem.

The deciding factor over whether to replace or repair a component is it's price.  Some companies set a lower threshold for replacing than others, so I won't make any specific statements about guidelines.  I can tell you that in the time I spent doing fieldwork about 80% of it was done replacing parts that we threw away after.

Ergonomics

This specifically relates to the mouse and keyboard because they are the two devices you will use the most.  Ergonomics refers to the design of the equipment to be safe to the user.  If you've ever looked at a mouse and wondered why it was shaped that way, you simply have to look at ergonomics.

The most common type of injury that a computer user can suffer is a repetitive stress injury.  This occurs when a certain task is performed over and over that requires the user to put part of their body in an awkward position.  Carpal Tunnel Syndrome is an example of an RSI.

Ergonomics looks at how these injuries occur and changes the style of the equipment to avoid the injury.  For example, wrist rests at the bottom of your keyboard avoid unnecessary bending of the wrists, a major contributor to Carpal Tunnel Syndrome.  I won't get into any more detail, but remember that ergonomics changes designs to avoid injuries.

Other Input Devices

There are more and more input devices showing up every day.  These include scanners, digital photography equipment, joysticks, and sound mixers.  These devices differ from keyboards and mice in that they are optional, where a keyboard and mouse is pretty much a requirement for every computer.  They also can use DMA channels, which keyboards and mice do not.

It's more important to know what an input device is than what it does.  Every camera and scanner is so different.  It takes years of experience to know most of the information, and it just isn't practical for the standard PC technician's job description.

Input devices are any device that sends information to the computer through the direct action of a user explaining the desire of a user.  A mouse is rolled to move a pointer on a screen.  A key is pressed to produce a character.  A photograph is up-loaded to be viewed on the screen.  Anything that sends user data from a piece of equipment a user manipulates is an input device

So why aren't bi-directional printers input devices?  I thought the same thing, seeing as they send information back to the computer.  Printers and other bi-directional output devices only send information about configuration and wait states; They aren't sending information that the user inputs.  So although they are sending data, they are not inputting user data into the computer, and therefore aren't input devices.

Remember that all input devices require an IRQ and an I/O address in order to work.  Some require DMA channels, but others don't.  Any time you see a reference to an IRQ, DMA, or I/O Address, remember that address.