Choosing input and output devices for a problem

Overview

Recall questions on choosing input and output devices for a problem, including barcode scanners, optical mark and character recognition, touchscreens, graphics tablets, devices for users who cannot use their hands or cannot see, printers and actuators.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   How should you decide which input device suits a particular problem?

   Model answer

   Match the characteristics of the device to the demands of the problem: how much data must be entered and how quickly, how accurate the entry has to be, the physical environment the device will live in, who the users are and what they can physically do, the cost and durability required, and what form the data is already in. A good justification always names the property of the device and links it to a stated requirement of the problem.

2. 2

   Which input device suits a supermarket checkout, and why?

   Model answer

   A barcode scanner. A laser or camera reads the pattern of bars and spaces, which is far quicker than typing a product code and removes typing errors entirely; the code is already printed on the goods so nothing has to be prepared; the scanners are cheap and hard-wearing enough for constant use. The till uses the code to look up the price and update the stock count automatically. A keypad is still needed as a fallback for damaged barcodes and for loose items.

3. 3

   A national testing organisation must mark twenty thousand multiple choice answer sheets. What input device, and what limitation does it have?

   Model answer

   Optical mark recognition. The reader detects the position of pencil marks in pre-printed boxes on the form, processing thousands of sheets an hour with almost no errors and no operator typing anything. The limitation is that it only works with specially designed forms, marks must be in the right place and made with the right kind of pencil, and it reads only the presence of a mark, not any handwriting.

4. 4

   A company wants to turn a filing cabinet of printed letters into searchable text. Which devices and techniques?

   Model answer

   A sheet-feed or flatbed scanner to capture each page as an image, followed by optical character recognition software to convert the shapes of the printed characters into character codes. Scanning alone gives only a picture, which cannot be searched or edited; OCR is what makes the text usable. Accuracy depends on the quality of the print, and OCR output has to be checked, unlike optical mark recognition which is essentially exact.

5. 5

   Why is a touchscreen the right input device for a self-service ticket machine at a railway station?

   Model answer

   It combines the display and the input in one sealed unit, so there is no separate keyboard or mouse to be stolen, vandalised or damaged by weather; it tolerates dirt and wet hands; it needs no training, because the user simply touches what they can see; and the controls can be redrawn at every step to show only the choices that are currently relevant. Its weaknesses are that it is slow for entering long text and that an alternative must be offered for users who cannot see or reach the screen.

6. 6

   Which input device would you specify for a professional digital illustrator?

   Model answer

   A graphics tablet with a pressure-sensitive stylus. Pressure and tilt are captured as well as position, so the software can vary line width and opacity as a real brush would; the absolute positioning and high resolution give far finer control than a mouse, which reports only relative movement. The illustrator draws with a hand movement they already have years of practice in.

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