External Hardware Devices

Question 1

Describe the 4 steps for a barcode reader to read a barcode

Answer 1

1. The mirror directs light from the laser onto a printed barcode
2. The light reflected by the barcode passes through the lens and is incident on the photodiode
3. The photodiode turns light into electrical charge
4. The electrical charge is measured and processed to form a digital signal representing the content of the barcode

Question 2

Describe the 4 steps for a digital camera to take a photo

Answer 2

1. The lens focuses light onto a sensor. The passage of the light is regulated by a shutter
2. CMOS and CCD sensors convert incident light into electrical charge
3. The charge builds up in cells which represent the pixels of the image
4. The charge in each of the cells is measured and converted into a digital value which is processed and stored as an image

Question 3

How do colour cameras record colour and what is used to replicate the human eye?

Answer 3

There are multiple cells for each pixels, each of which has a filter that only allows certain wavelengths of light. These let the camera build up separate images for each colour which are combined.
A Bayer filter had the same number of green filters as red and blue combined given the human eye is sensitive to green light

Question 4

Describe the 3 steps for a laser printer to print

Answer 4

1. The drum is positively charged and the laser is directed at it’s surface by the mirror. The laser discharges parts of the drum, leaving an impression of the page in electrical charge.
2. The toner roller dispenses negatively charged toner onto the drum. This is only attracted to the charged portion of the drum.
3. The toner is applied to the paper by the drum and the paper is heated by fusers, fixing the toner to it

Question 5

Describe the structure of a HHD

Answer 5

A Hard Disc Drive consists of a number of circular platters made from magnetic material.
Above each platter hovers an actuating arm with a read write head. The arm allows the read write head, which changes magnetic polarity of parts of the platter, to access all portions of the platter.
Data is written in concentric tracks, divided into sectors.

Question 6

Describe the structure a SSD

Answer 6

A solid-state drive consists of non-volatile NAND flash memory cells and a controller that manages the structure of data on the drive. The memory cells are formed of floating gate transistors that store information by trapping electrical charge.
Data is stored in pages which are combined to form blocks.

Question 7

Describe the structure of an optical disc

Answer 7

Optical discs have a continuous track that have pits burnt into it with a high-power laser that permanently deforms the surface. The area around the pits are lands.
When a laser is passed over the optical disc, the light is scattered differently over the pits and lands. This can be converted into a digital signal.