Digital technology• Contents:• Base 2 and base 10 number system• Bits and bytes• PN diodes• Boolean logic• Logic gates• Digital and analog basics• Storing devices for digital• Changing Analog to digital• How cds store in 1 and 0• What are CCDs?• Image capturing • Sampling for analog to digital conversion• Work cited pages

What are binary digits?

Computers use binary numbers, and therefore use binary digits in place of

decimal digits. The word bit is a shortening of the words "Binary digIT." Whereas decimal digits have 10 possible values ranging from 0 to 9, bits have only two

possible values: 0 and 1.

Decimal and binary numbers.• You can see that in binary numbers, each bit holds the value of increasing

powers of 2. That makes counting in binary pretty easy • E.g 1011 means • 1 * 23) + (0 * 22) + (1 * 21) + (1 * 20) = 8 + 0 + 2 + 1 = 11 • Some more examples

• 10 = 101011 = 101112 = 110013 = 110114 = 111015 = 111116 = 10000

Bits and bytes.• Bits are rarely seen alone in computers. They are

almost always bundled together into 8-bit collections, and these collections are called bytes.

• With 8 bits in a byte, you can represent 256 values ranging from 0 to 255, as shown here:

• 0 = 000000001 = 000000012 = 00000010

...254 = 11111110255 = 11111111

Bits and bytes continued

• CD uses 2 bytes, or 16 bits, per sample. That gives each sample a range from 0 to 65,535, like this:

• 0 = 00000000000000001 = 00000000000000012 = 0000000000000010...65534 = 111111111111111065535 = 1111111111111111

Analog at a glance

As a technology, analog is the process of taking an audio or video signal (in most cases, the

human voice) and translating it into electronic pulses. Digital on the other hand is breaking

the signal into a binary format where the audio or video data is represented by a series

of "1"s and "0"s.

A to D

• Digital technology breaks your voice (or television) signal into binary code—a series of 1s and 0s—transfers it to the other end where another device (phone, modem or TV) takes all the numbers and reassembles them into the original signal. The beauty of digital is that it knows what it should be when it reaches the end of the transmission.

Is the duplication perfect?

• But like any tansferred technology, digital has a few shortcomings. Since devices are constantly translating, coding, and reassembling your voice, you won't get the same rich sound quality as you do with analog.

Can we use the digital phone using an analog line?

• There are digital-to-analog adapters that not only let you use analog equipment in a digital environment, but also safeguard against frying the internal circuitry of your phone, fax, modem, or laptop. Some adapters manufactured by Konexx come designed to work with one specific piece of office equipment: phone, modem, laptop, or teleconferencer. Simply connect the adapter in between your digital line and your analog device.

Comparing Analog Vs. Digital

• http://telecom.hellodirect.com/docs/Tutorials/AnalogVsDigital.1.051501.asp

Visit the above site for more details of Analog Vs. Digital

Ancient way of recording the analog way

• In the Beginning: Etching Tin• Thomas Edison is credited with creating the first

device for recording and playing back sounds in 1877. His approach used a very simple mechanism to store an analog wave mechanically. In Edison's original phonograph, a diaphragm directly controlled a needle, and the needle scratched an analog signal onto a tinfoil cylinder . (see the clip in the link below)

• http://communication.howstuffworks.com/analog-digital1.htm

An analog wave

Analog WaveWhat is it that the needle in Edison's phonograph is scratching onto the tin cylinder? It is an analog wave representing the vibrations created by your voice. For example, here is a graph showing the analog wave created by saying the word "hello":

Image from www.howstuffworks.com

Analog recording contd….

• The waveform was recorded electronically rather than on tinfoil, but the principle is the same. What this graph is showing is, essentially, the position of the microphone's diaphragm (Y axis) over time (X axis). The vibrations are very quick -- the diaphragm is vibrating on the order of 1,000 oscillations per second. This is the sort of wave scratched onto the tinfoil in Edison's device. Notice that the waveform for the word "hello" is fairly complex.

Getting in to the digital world• In a CD (and any other digital recording technology), the goal

is to create a recording with very high fidelity (very high similarity between the original signal and the reproduced

signal) and perfect reproduction (the recording sounds the same every single time you play it no matter how many times you play it). To accomplish these two goals, digital recording

converts the analog wave into a stream of numbers and records the numbers instead of the wave. The conversion is

done by a device called an analog-to-digital converter (ADC). To play back the music, the stream of numbers is converted

back to an analog wave by a digital-to-analog converter (DAC). The analog wave produced by the DAC is amplified

and fed to the speakers to produce the sound.

Converting an analog wave to digital wave

• http://communication.howstuffworks.com/analog-digital3.htm

Here is a typical wave (assume here that each tick on the horizontal axis represents one-thousandth of a second):

……………..contd…

• When you sample the wave with an analog-to-digital converter, you have control over two variables:

• The sampling rate - Controls how many samples are taken per second

• The sampling precision - Controls how many different gradations (quantization levels) are possible when taking the sample

Convert the curve to numbers• In the following figure, let's assume that the sampling rate is

1,000 per second and the precision is 10:

The green rectangles represent samples. Every one-thousandth of a second, the ADC looks at the wave and picks the closest number between 0 and 9. The number chosen is shown along the bottom of the figure. These numbers are a digital representation of the original wave. Want to know the digital form of this curve? 7 8 9 5 3 4 0 3 7 5

Binary form? For individual digit

7 8 9 and so on

111 1000 1001 …………..

• When the DAC recreates the wave from these numbers, you get the blue line shown in the following figure:

You can see that the blue line lost quite a bit of the detail originally found in the red line, and that means the fidelity of the reproduced wave is not very good. This is the sampling error. You reduce sampling error by increasing both the sampling rate and the precision

In the following figure, both the rate and the precision have been improved by a factor of 2 (20 gradations at a rate of 2,000 samples per second) and then 4000 samples/sec.:

CDs and DVDs.

• http://electronics.howstuffworks.com/cd.htm• Exploring Sound: Digital Sound

– Laser discs such as CDs and DVDs carry digital information, which is represented by the binary code -- combinations of 1s and 0s. Any number can be represented in binary code. Learn how this information is encoded in the clip in the above link

CD’s and DVD’s

• Data is stored digitally– A series of ones and zeros read by laser light reflected

from the disk• Strong reflections correspond to constructive

interference– These reflections are chosen to represent zeros

• Weak reflections correspond to destructive interference– These reflections are chosen to represent ones

CD’s and Thin Film Interference

• A CD has multiple tracks – The tracks consist of a sequence of pits of varying

length formed in a reflecting information layer• The laser beam shines on a metallic layer

through a clear plastic coating

A CD’s pits and bumps

www.physics.byu.edu/faculty/rees/106/PPT/Class26.ppt

Reading a CD

• As the disk rotates, the laser reflects off the sequence of bumps and lower areas into a photodector– The photodector converts the

fluctuating reflected light intensity into an electrical string of zeros and ones

• The pit depth is made equal to one-quarter of the wavelength of the light

www.physics.byu.edu/faculty/rees/106/PPT/Class26.ppt

Reading a CD

• When the laser beam hits a rising or falling bump edge, part of the beam reflects from the top of the bump and part from the lower adjacent area

• Light reflecting from the top and bottom of the pit is a half-wavelength out of phase, so the intensity drops.

www.physics.byu.edu/faculty/rees/106/PPT/Class26.ppt

Reading a CD

• The bump edges are read as ones• The flat bump tops and intervening flat

plains are read as zeros

DVD’s

• DVD’s use shorter wavelength lasers– The track separation, pit depth and minimum pit

length are all smaller– Therefore, the DVD can store about 30 times more

information than a CD

• In the case of CD sound, fidelity (the similarity between the original wave and the DAC's output ) is an important goal, so the sampling rate is 44,100 samples per second and the number of gradations is 65,536. At this level, the output of the DAC so closely matches the original waveform that the sound is essentially "perfect" to most human ears .

Why is a CD’s capacity approximately 750 mb?

• One thing about the CD's sampling rate and precision is that it produces a lot of data. On a CD, the digital numbers produced by the ADC are stored as bytes, and it takes 2 bytes to represent 65,536 gradations. There are two sound streams being recorded (one for each of the speakers on a stereo system). A CD can store up to 74 minutes of music, so the total amount of digital data that must be stored on a CD is:

44,100 samples/(channel*second) * 2 bytes/sample * 2 channels * 74 minutes * 60 seconds/minute = 783,216,000 bytes (Convert to kbs and then Mbs.)

What is a digital image?• Essentially, a digital image is just a long string of 1s and 0s that

represent all the tiny colored dots -- or pixels -- that collectively make up the image. If you want to get a picture into this form, you have two options:

• You can take a photograph using a conventional film camera, process the film chemically, print it onto photographic paper and then use a digital scanner to sample the print (record the pattern of light as a series of pixel values).

• You can directly sample the original light that bounces off your subject, immediately breaking that light pattern down into a series of pixel values -- in other words, you can use a digital camera

•

Capturing image• The image sensor employed by most

digital cameras is a charge coupled device (CCD). Some cameras use complementary metal oxide semiconductor (CMOS) technology instead. Both CCD and CMOS image sensors convert light into electrons.

• A simplified way to think about these sensors is to think of a 2-D array of thousands or millions of tiny solar cells.

A CMOS sensor

Digitisation of the light

• http://www.olympusmicro.com/primer/digitalimaging/concepts/concepts.html

http://electronics.howstuffworks.com/digital-camera1.htm

The above site has a video clip to explain the digitisation of the light .

Digital Camera Resolution

• The amount of detail that the camera can capture is called the resolution, and it is measured in pixels. The more pixels a camera has, the more detail it can capture and the larger pictures can be without becoming blurry or "grainy." Photo courtesy Morguefile

The size of an image taken at different resolutions

Capturing Color

• Unfortunately, each photosite is colorblind. It only keeps track of the total intensity of the light that strikes its surface. In order to get a full color image, most sensors use filtering to look at the light in its three primary colors. Once the camera records all three colors, it combines them to create the full spectrum

For illustrations and explanations visit: http://electronics.howstuffworks.com/digital-camera3.htm

Work cited pages• Complete binary mathematics.• http://www.binarymath.info/• convert binary numbers to decimals• http://www.bellaonline.com/articles/art48652.asp• Basic principles of magnetic recording using digital data in HDD.• http://www.usbyte.com/common/HDD.htm#top• storage types • http://www.jegsworks.com/Lessons/lesson6/lesson6-2.htm• Details of DVDs.• http://electronics.howstuffworks.com/dvd3.htm• Optical recording in a CD.• http://physicsworld.com/cws/article/print/1383/1/world-11-10-7-2• Detailed study of dvds and cds comparison. More emphasis on technology of data capture.• http://www.iti.uni-stuttgart.de/~ghermanv/Lehre/Seminar/material/Presentation4/talk.pdf• For complete know how on CCDs and image capture in a digital camera • www.howstuffworks.com