Manual input devices, applications and how they work
Introduction
We have seen a model of a computer system before. We know that for a computer to do useful things, we need to get data into it. We use input devices to do this.
Input devices are often divided into two categories, manual input devices and automatic input devices. We will discuss manual input devices here.
Keyboards
Practically all computers have QWERTY keyboards. These devices can be used to enter in data manually. They are very efficient in the right hands but not so efficient if a user has limited training. In fact, they can be very slow and mistakes are easy to make, although software tools can automatically fix many of them. A lot of work has been done to ensure that keyboards are designed 'ergonomically'. This means that they are designed in a way that takes into account the 'design limitations' of a human being. There is a health and safety problem known as Repetitive Strain Injury (RSI) for people who use keyboards all the time, such as secretaries. The joints in their fingers can become 'worn'.
How do keyboards work?
Keyboards are essentially lots of switches arranged in a grid or matrix.
The keyboard is managed by the keyboard's own processor. When you press any key, this closes a switch, which completes an electrical cicuit. When the keyboard's processor detects this, it works out what key has been pressed by comparing the circuit that has been completed with a table of character keys kept in its Read Only Memory. It can also detect special combinations of keys pressed, such as SHIFT G being a capital G. When it has worked out the key or special combination, it then sends this information to the computer.
Touch-sensitive keyboards and concept keyboards and how they work
An extension of manual data input into computer systems using keyboards is to use touch-sensitive keyboards and concept keyboards. These types of keyboard have 'keys' which are made up of touch-sensitive areas on a plastic cover. A user presses on the touch-sensitive area to input data into the computer. They have a wide range of applications. They can be used in fast food restaurants. Operators simply press on pictures on the keyboard. This speeds up data input and means that training needs are minimal. They can be used in areas where there is likely to be a lot of dirt such as in factories. Dirt can get into normal QWERTY keyboards and cause them to malfunction but the protective plastic cover on touch-sensitive keyboards stops this happening. They can be used to customise keyboards because some touch-sensitive keyboards (called 'concept keyboards') allow you to program what you want to happen when an area is pressed. You can imagine, for example, designing a concept keyboard for a two year old child, who may have limited co-ordination and cannot yet read. You could provide a keyboard with four big brightly coloured areas. When the child wants to make any selection at all, they just need to touch the right coloured area.
Touch screens and how they work
This is another manual data input method. A touch screen enables a user to touch their VDU screen to make selections. A plastic cover that has fine wires running through it can be placed over a VDU's screen. A user makes a selection by touching the screen with their finger. The exact position can be calculated from the signals sent back by the wires. Touch screens allow very fast selections from choices. They could be used in places where people need to find out information but may have zero computer skills, for example, an information system in a library or a museum. They would be of limited use if you had to type in a letter, for example.
Graphics tablets and how they work
Another manual data input method is the graphics tablet. These are touch-sensitive pads that allow you to 'draw' on them with a stylus. The pressure from the stylus on the pad is sent to the computer, which reproduces what was done on the pad in a drawing program or CAD program. These types of data input devices are far more natural for designers to use than trying to use a keyboard and mouse to draw with.
Optical mice and how they work
An optical mouse is a pointing and selecting device used with graphical user interfaces (GUI). There are different kinds of mice around, each with their own advantages and disadvantages although they all broadly do they same thing: point and select things on the screen. Optical mice are the most common type of mouse now as they aren't prone to collecting fluff and dirt and so don't need cleaning. They are also very accurate, don't need a special surface to work on and are very reliable because there are fewer moving parts than an old style roller ball mouse.
A small light emitting diode (LED) shines light onto the desk, which is reflected back to a photocell next to the LED. This has a lens, which magnifies the light signal for better accuracy. The reflected light signal is analysed by a processor inside the mouse, which can work out that your mouse is moving and where it has moved to.
Apart from the LED, there are also either two or three contact buttons that can be pressed to make a selection as well as a wheel, which allows you to scroll through a web page or document faster. The rotation of the wheel is detected either by another optical system or by using potentiometers, like those used on the volume control of a radio. This information is again passed to the mouse's processor, who then passes the information to the computer, to make the necessary adjustments.
Image capture
We will frequently want to capture images and get them into a computer. Images can be captured in a number of ways. We will look at web cams, scanners, video capture cards and digital cameras.
Web cams and microphones
Web cams and microphones are both input devices. Web cams capture the image in front of them whereas microphones capture sound. They are typically used for VOIP applications (Voice Over Internet Protocol) such as Skype, where two people can communicate over the Internet using a camera and a microphone. Microphones are increasingly integrated into the web cam. These kinds of devices are excellent for families and friends to keep in touch and for businesses to communicate instantly across the globe, saving the time, energy and expense of travelling.
How do microphones work?
When you speak or play music into a microphone, the microphone takes the sound waves and converts them into a voltage. As the sound waves vary, so the voltage varies. The microphone is connected to a computer's sound card. The sound card samples the microphone's voltage at intervals. How many times it does this in a second is known as the 'sample rate'. The time between samples is the 'sample interval'. The bigger the gap between taking a sample, (in other words the larger the sample interval), the lower the quality of the recording, although the benefit is a smaller file size. Each time the voltage is sampled, it is converted into a binary number by the sound card's Analogue to Digital Converter (ADC) and stored. If you store all of the digital samples, you end up with a sound file. This might be a song or a recording of your voice, for example.
To play back a sound file through some speakers, the sound file is passed back to the sound card, into which the speakers are connected. The Digital to Analogue Converter (DAC) on the sound card takes the digital signals that make up the sound file and converts them back into analogue signals. They are then passed out to the speakers and the sound is played.
Voice recognition
Voice recognition software is getting better every year! Using a microphone and some appropriate software, it is possible to input data into a computer or directly into a tablet PC or phone. The software is not perfect. You often have to teach it to recognise your voice accurately. If you have a cold or a throat problem, or a very strong accent, it may reduce the accuracy of input. Nevertheless, it is still a fast way of inputting data.
Scanners
Images from magazines or photographs, for example, can be captured using scanners.
- Typically, the image is placed on a flat screen or 'bed'.
- A cover is placed over the image.
- The image is divided up into sections or 'pixels' by the software. The user can tell the software what resolution to use (how many pixels per square centimetre to split the picture up into). The higher the resolution, the better the detail of the image but the bigger the file. Often, low resolution, smaller files will be perfectly adequate for most uses.
- A light is passed from one end of the flat bed to the other, so that it passes over the image and over each pixel.
- When the light hits each pixel, it gets reflected back. The intensity of the reflection depends on the colour at that pixel. Each pixel's information is stored.
- The information about all of the pixels is used by the software to reconstruct a bit map image of the whole picture.
- Because bit maps are large files, they are often compressed. This can be done by telling the software to save the image as a different file type that uses compression, such as GIF files or JPG files.
- Software tools either within the scanning software or within a drawing package allow the user to manipulate an image in various ways. These typically include allowing the user to 'crop' an image (select just a portion of an image), allowing the user to improve the detail of the image, allowing the adjustment of colours and allowing the user to add special effects such as making a photo image look antique.
Video capture cards
A video is made up of a series of pictures, or frames, that are played quickly enough to appear moving. A video capture card is a piece of hardware that is plugged into an expansion slot inside the computer. A user then attaches a video camera or TV, for example, to the video card. When the video or TV is played through the card, the analogue signals that make up the moving picture from these devices are converted into digital images, frame-by-frame and stored. Once you have captured each frame, you can then use the software to do all kinds of clever things. For example, you can edit out frames, reorganise them, save individual frames and transfer them to word processing documents, create your own presentations using presentation software and some of the images or add your own soundtrack.
Digital cameras
These cameras do not store images on film. They store images digitally in memory. The images are then transferred to the computer. There are many points that could be made about digital cameras.
- The price of digital cameras has been steadily falling over recent years.
- The amount of memory is a very important consideration with these cameras, as is the ability of a camera to add memory. This is because storing images is memory-intensive.
- Cameras often allow the user to select between high resolution and low resolution modes. If you use a high resolution mode, you will be able to take fewer pictures than low resolution mode.
- You can immediately view photos and re-take or overwrite them if they are not what you want.
- You can often add extra information easily, such as the date or information about the photo.
- Many cameras allow you to add special effects as you take the picture.
- Images can easily be combined into digital photo albums and distributed or emailed to friends.
- Once the picture has been taken and transferred to the computer, it can be opened in a drawing package and manipulated. Pictures can be cropped, colours changed and parts of the photo 'touched up', for example.
Camcorders
Video camera recorders, or camcorders, are cameras that store moving images. There is a wide range of types of camera. Some camcorders store the moving images as analogue signals. You may have heard of VHS, Super VHS or 8mm analogue camcorders. Analogue camcorder films lack really mint quality and lose quality if they are copied. Films made using digital camcorders, on the other hand, have much better quality and don't lose any quality if they are reproduced. This is because the films are stored digitally. Digital Video (DV) and Digital 8 are two of the common digital formats around. Typical features of digital camcorders include the ability to zoom in, record sound, view films through a viewfinder, some have night viewing capabilities, time-lapse photography, picture stability software and special effects.
Biometric devices
People are being increasingly identified using biometrics. This means using a unique part of your body to identify you. Typical examples include fingerprint scanning in canteens, libraries, phones and ATMS, retinal scanning for access to buildings and biometric data held in a chip in newer passports. Biometrics are very convenient as you can't lose or forget a finger or your eye like you can a library card! It also reduces the need for cash to be handled, which cuts down on costs and removes security issues. There are concerns about what happens to the data, how it is stored and who has access to it, however, and the ever-present problem of hackers stealing your data and using it for unauthorised or illegal activities.