IO devices

Question 1

[PPQ] Describe the principles of operation of an optical disk drive

Answer 1

Data is stored as grooves in the surface of the disk. The grooves are called pits and the raised areas are called lands. The data is separated into tracks. Lands reflect light while pits do not. The optical disk drive shines a laser beam at a certain track on the disk, which spinning at a constant linear velocity. When light is reflected by a land, a 1 is recorded, and when no light is reflected, a 0 is recorded.

Question 2

Describe the principles of operation of a digital camera

Answer 2

When a photograph is taken, the shutter opens and light hits the lens. The light is focused onto a CCD or CMOS sensor. There are either 3 sensors (for R, G, and B), or 3 filters. The sensors convert the light into electrons, and the charge in the sensors is recorded and converted into a .png or .jpg image

Question 3

Describe the principles of operation of a barcode reader

Answer 3

A laser is passed over an image. A light sensor is used to measure the intensity of the light being reflected, and the data is converted into a waveform. The waveform is used to distinguish the patterns of black and white bars. The waveform is converted to binary using a ADC. Types of barcodes include QR codes and UPCs

Question 4

What is RFID?

Answer 4

A microscopic device that stores data and transmits it using radio waves

Question 5

Describe the principles of operation of RFID

Answer 5

The tag contains a chip which contains data about the item, and a modem to modulate and demodulate the radio signals. It also contains an antenna. Tags can either be active (have a battery) or passive (pick up electromagnetic power from an RFID reader). The chip can therefore transmit data back to the reader.

Question 6

What are the uses of RFID?

Answer 6

Tracking people, electronic passports, contactless payment, supermarket anti-theft devices

Question 7

[PPQ] Describe the principles of operation of a laser printer

Answer 7

A heated wire positively charges a drum, and a laser then passes over this drum, reversing the charge on the areas it hits. The negatively charged areas on the drum represent the image stored in the printer’s memory. A toner roller is then passed over the
drum, and the positively charged toner particles stick to the negatively charged areas of
the drum. A piece of paper is then rolled under the drum and the toner is pressed onto its
surface. This is repeated for cyan, magenta, yellow and black.

Question 8

Describe the principles of operation of a HDD

Answer 8

A HDD is made of a stack of spinning magnetic disks inside a metal box. A head hovers over each magnetic disk in the stack. Each disk is split into sectors (areas of the same storage capacity). Files may be stored across multiple sectors.

Question 9

Describe the principles of operation of solid state storage

Answer 9

Semiconductors are used to store data. The data storage is split up into blocks, which are allocated to particular semiconductors. The advantage is that all of a file’s data can be stored in one block, reducing read/write times. Floating gate transistors are used, which are capable of trapping and storing charge using an oxide layer.

Question 10

[PPQ] Compare cameras, RFID readers and barcodes (see AS Paper 2 2016)

Answer 10

Cameras: Don’t require a tag, high data storage requirements

Barcodes: Very cheap, less cumbersome than RFID tags, easily obscured, requires the reader to be close to the barcode, barcode can be damaged

RFID: Can be read faster than other two, reusable tags, no line-of-sight issues or issues with barcodes/faces being obscured