A bit is the smallest unit of digital information, represented as a 0 or a 1. A byte is an eight bit word

Significant Figures We shall define significant figures by the following rules.3 1. The leftmost nonzero digit is the most significant digit. 2. If there is no decimal place, the rightmost nonzero digit is the least significant digit. 3. If there is a decimal point then the right most digit is the least significant digit even if it is a zero. 4. All digits between the least and most significant digits are counted as significant digits.

Analogue: LPs, cassette tapes. DIGITAL: hard disks, CDs, DVDs. Record player

λ/4 depth, so that the wave travels λ/2 further, and destructively interferes Pits and bumps

 The bump edges are read as ones (i.e. no light).  The flat bump tops and intervening flat plains are read as zeros. Destructive interference occurs when light is reflected from the edge of a pit. Calculate the wavelength of laser that must be used for a bump height of 125ηm. DVD’s use a laser of shorter wavelength. Bumps and pits are closer together, tighter spirals so more information can be stored.

QualityDepends on sampling rate, but can be indistinguishable from the input Virtually indistinguishable from the input, but liable to corruption. ReproducibilityEach retrieval almost identical Subject to wear and damage from each use. Retrieval speedEasy to search around within a film Hard to search through a video tape. PortabilityUsually smallLarger for the same data Discuss the implications for society of ever- increasing capability of data storage, consider the following: moral, ethical, social, economic and environmental implications. Cost, Privacy, Ownership of data, Accessibility

A CCD is a silicon chip divided into small areas called pixels. Each pixel can be considered to behave as a capacitor. A capacitor is a device that can store charge Capacitance is defined as “the charge stored per volt across the plates” and is measured in Farads:

1.Charge Generation is via the photoelectric effect 2.Each pixel “fills” with photoelectrons i.e. the charge across each capacitor increases. N.B. Charge produced is proportional to the intensity of the light

An electrode measures the potential difference developed across each pixel and this is then converted into a digital signal. The pixel position is also stored. Quantum efficiency is the ratio of the number of photoelectrons emitted to the number of photons incident on the pixel. Magnification is the ratio of the length of the image on the CCD to the length of the object. RESOLUTION: Two points on an object may be just resolved on a CCD if the images of the points are at least two pixels apart.

 Quantum efficiency – If this is low, then not all the photons will be recorded. Leads to a loss of detail. Different for different colours.  Magnification – As the magnification increases, the image is projected onto a smaller area. This will eventually force photons from different areas of the object onto the same pixel. A larger CCD decreases this problem.  Resolution- The greater the resolution, the more the detail that can be stored i.e. quality increases. But, more memory is needed.

1. The cost of each photo is cheaper. 2. The QE of film is typically less than 10%. Therefore CCDs can capture images in darker conditions. 3. The image can be enhanced electronically. 4. Immediate viewing of the image. 5. Easy to store a large number of photos, films etc… CCD’s are used for image capturing in a large range of the electromagnetic spectrum. Items such as digital cameras, video cameras, telescopes, including the Hubble Telescope, and medical X-ray imaging use ccds

1. A control circuit causes each capacitor to transfer its contents to its neighbour (and hence the name charge coupled device. The last capacitor in the array dumps its charge into a charge amplifier, which converts the charge into a voltage 2. Convert the analogue signal (i.e.the voltage from a given pixel) to a digital number. 3. This can be used to generate the intensity of that part.

 ELECTRONICS  An operational amplifier (op-amp) is a voltage amplifier which amplifies the difference between the voltages on its two input terminals. It is a high gain differential amplifier. Properties of an ideal op-amp:  infinite gain  zero current drawn on the inputs. Inverting amplifier Non-inverting amplifiers

For the inverting voltage amplifier the non-inverting input terminal is connected to 0V. This means that the inverting op-amp input is virtually at 0V, i.e. it is a Virtual Earth Point. Assuming that the input resistance of the op-amp is so large that no current passes into its input terminals, then the current passing through R1 must pass through Rf. Non-inverting voltage amplifier – both inputs are at the same pd

The circuit diagram below shows how the thermistor can be used with an op- amp comparator to sound an alarm if the temperature goes above a set temperature. Resistor R 1 forms a voltage divider with the thermistor. As the temperature of the thermistor increases, its resistance decreases, and so the voltage at the non- inverting input of the op- amp will increase. If V + <V -, then the output of the op- amp will be at –Vs. The diode prevents the buzzer being damaged. When V + >V -, the output of the op-amp will switch to +V s and the buzzer will switch on sounding the alarm. The temperature at which the alarm sounds can be altered by changing the value of any of the resistors, but the most convenient arrangement is to make R 2 equal to R 3, (e.g. 10k  ) and then use a variable resistor for R 1.

When any signal is transmitted from one place to another it will suffer attenuation, (become weaker), dispersion (spread out) and it will gather noise and interference. After amplification the original signal is therefore not restored. The Schmitt trigger circuit uses positive feedback to create two voltage switching levels instead of the single voltage switching level of a comparator. As a result the circuit can be set so that it will ignore the majority of the noise on the signal and so not produce stray pulses.

Each area is divided into a number of cells (each with its own base station) to which is allocated a range of frequencies - so as to avoid overlap between cells. The shading shows that adjacent base stations never use the same frequency groups. Cellular exchange is used in the selection and monitoring of base stations and the allocation of channels. When a mobile phone is switched on, it sends out a signal announcing to the nearest base station that it is available to receive calls. If the phone moves to another cell while the call is in progress, then the base station of the new cell will register the phone and allocate a new frequency channel. Each of the base stations are joined together with data links and are controlled by a computer network. They are also connected to the Public Switched Telephone Network (PSTN). The data links between the base stations allow them to exchange information, so that when a mobile user enters and leaves cell service areas, their calls stay connected.

As the bandwidth and memory available to each mobile phone increases so does the opportunity to use the mobile phone as a multimedia device. Many phones now have a camera integrated into the phone and so video as well as speech content can be exchanged. Most mobile phones can connect to the internet so enabling content to be down loaded, including music in the form of MP3 files and films in the form of MPEG4 files which can then be viewed on the screen of the mobile phone. RSS (Really Simple Syndication) streaming is available to phones from many web sites so that news items like weather, football results etc can be viewed continuously. CONSEQUENCES OF MOBILE PHONES – consider the following: The cost of calls. The environmental impact of mobile phone aerials and masts. The speed with which people can be contacted. The benefits of always being able to contact people. Phone related crime. Pressures caused by mobile phones on employees working in industry and commerce. Health issues of mobile phones Future developments of mobile phone