Scanners, input devices and the peripherals that arrive with them

Why this matters

Peripherals are the part of the job that touches users most directly. A keyboard that does not work stops someone entirely, and a scanner producing files too large to email produces a complaint that sounds like a fault and is a settings question.

The exam covers these as installation, configuration and basic fault finding rather than in depth, but there is a real skill here: knowing which settings change the outcome, and knowing the small set of causes behind "the computer does not recognise it".

Accessibility belongs in this lesson too, because input devices are where it is configured and because a technician who knows those settings exist can solve problems that otherwise look like user error.

The lesson

Flatbed, sheet-fed and automatic document feeders, and where each one jams

• Flatbed scanners have a glass platen and a moving sensor bar. They handle books, fragile originals, odd sizes and photographs. One page at a time.
• Sheet-fed scanners pull the page past a fixed sensor. Faster for stacks, and unsuitable for anything creased, stapled, torn or bound.
• Automatic document feeders sit on top of a flatbed and combine the two: stacks go through the feeder, awkward originals go on the glass.

The mechanical faults, and what each looks like:

• Multi-feed — two sheets pulled at once, so a page is silently missing from the scan. Caused by worn separation rollers, static, or paper that is too light. This is the dangerous one, because nothing announces it; a page count at the end is the control.
• Skew — pages pulled at an angle. Guides not set, or a worn roller on one side.
• Jams — usually a torn page, a staple, or a sticky note. Staples are the single most common cause of a damaged feeder.
• Streaks down every page — a mark on the glass or the sensor strip. On a flatbed, a streak in the same place on every page from the feeder and not from the glass identifies which sensor path is dirty.

Maintenance is cleaning the glass and the sensor strip, and replacing the feeder's rollers and separation pad at their stated count — the same consumable discipline as lesson 24.

Resolution, colour depth and file size, and choosing settings for a stated purpose

Scanner resolution is in dots per inch, and it is the setting users get most wrong in both directions.

The relationship worth knowing: doubling the resolution multiplies the file size by roughly four, because it doubles in both dimensions. Going from 300 to 600 dpi quadruples the file; going to 1200 dpi multiplies it by sixteen.

Sensible settings for stated purposes:

• Text document for filing or email: 200 to 300 dpi, black and white or greyscale, as PDF. Small and perfectly readable.
• Text intended for optical character recognition: 300 dpi, greyscale. OCR accuracy improves up to 300 and gains little beyond it.
• Photograph for screen viewing: 300 dpi colour.
• Photograph for enlargement or archive: 600 dpi or higher, colour, in a lossless format.
• Line art or a diagram: higher resolution, bitonal.

Optical resolution is what the sensor actually captures; interpolated resolution is software inventing pixels between them. Only the optical figure is real, and a scanner advertising a very high interpolated number is advertising arithmetic.

The other size lever is format: PDF or JPEG for ordinary use, TIFF or PNG where lossless matters. A user complaining that scans are too large to email is usually scanning at 1200 dpi in colour and saving as TIFF, and the fix is three settings.

Keyboards, mice, trackpads and touchscreens, including calibration and accessibility

Connection is USB, Bluetooth, or a proprietary wireless receiver. The diagnostic order for a dead input device:

1. Battery or charge, on anything wireless. The most common cause by a wide margin.
2. Receiver present and in a working port, or pairing intact.
3. A different port, to separate device from port.
4. A different machine, to separate device from computer.
5. Wired, if possible, to remove the wireless variable entirely.

Configuration worth knowing:

• Pointer speed and acceleration, and scroll direction, which is the setting behind "my mouse scrolls the wrong way" after a platform change.
• Trackpad gestures and palm rejection; a cursor that jumps while typing is usually palm rejection needing adjustment rather than a faulty trackpad.
• Touchscreen calibration, where touches land consistently offset from where they are made. Distinguish this from a digitiser fault, which is inconsistent rather than offset.
• Keyboard layout, which explains the classic "the @ and the " are swapped" — a UK layout configured as US or the reverse, and not a hardware fault at all.

Accessibility settings a technician should know exist: sticky keys, filter keys, toggle keys, on-screen keyboards, magnifiers, screen readers, high contrast themes, and pointer size and colour. Some of these can also be enabled accidentally by keyboard shortcuts, which is why a machine that suddenly beeps at every keypress is usually sticky keys rather than a fault.

Cameras, headsets and capture devices, and the driver problems they share

Webcams, headsets, microphones and capture devices mostly use standard device classes, so they work without a driver download — and that is the source of their characteristic problems.

The shared failure patterns:

• Exclusive access. Most cameras and many audio devices can be held by one application at a time. A camera "not working" in a meeting application is frequently still held by the one used before it.
• Default device selection. The operating system has a default input and output, and applications may have their own overrides. A headset that works in one application and not another is a per-application setting.
• Privacy permissions. Both major desktop platforms gate camera and microphone access per application. A denied permission produces a black image or silence, with no error message that names the cause.
• Bandwidth on shared buses. Several cameras on one USB controller can exceed its capacity, which presents as one device failing when another is started — a genuine hardware limit rather than a fault.
• Physical mute switches on headsets and microphones, which nobody looks at first and should.

Capture cards, which bring an external video source into the machine, add one more: they often require the source to permit copying, and content protection on the source produces a black picture with working audio.

Installing a peripheral that the operating system does not recognise

When a device does not appear at all, the causes are few and the order is worth following:

1. Try another port and another cable. This is lesson 23's method and it resolves a large share of cases outright.
2. Check the device manager or equivalent for an unknown device or one with a warning. A device that appears with an error is a driver problem; a device that does not appear at all is usually power, cable or port.
3. Is it powered? Devices needing more than a port supplies need a powered hub or their own supply.
4. Install the manufacturer's driver, from the manufacturer, for the right operating system version and architecture. Not from a search result.
5. Check whether the device requires a specific mode — many devices have a switch that changes what they present as.
6. Try it on another machine. This separates device from computer definitively, and is the test worth doing before ordering anything.

Two habits that prevent repeat visits: read the installation instructions for the order of operations, because some devices must have their driver installed before being connected; and record what you installed, because a driver that needed a specific version is a fact that will be needed again after the next rebuild.