Working principle of Membrane Key switch. It is a multi-layer plastic or rubber assembly.

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1 Course Code CM-4-G Subject CHM (17428) Subject Teacher Prof. Y. S. Modhe Topic-4- Input And Output Devices Name different types of key switches in keyboard. Explain the principle of working of any one in detail. (02-marks for types, 02-marks for diagram, 04-marks for explanation) The type of key switches are: a. Capacitive switch b. Membrane switch c. Mechanical switch d. Rubber dome switch. a. Working principle of Capacitive switch This is one of the most common keyboard switch type as shown. In this type of switches have two plates of the capacitor are closer when the key is pressed. When the plates are brought closer or moved away, the capacitance of the switch is changed can be detected by measuring the voltage change across the switch using some sense amplifier. The sense amplifier will receive one voltage when the switch is in open position. These voltages are converted into proper logic signals to inform the computer about the open or close position of the switch. These switches have a normal lifespan of about 20 million keystrokes. Working principle of Membrane Key switch It is a multi-layer plastic or rubber assembly. It is used as keyboard in video game machines, calculators, medical instruments, cash registers etc. 1 P a g e

2 Two rubber or plastic sheets are used as row conductor sheet and column conductor sheet. Row and column lines are made on the plastic or rubber sheet using silver or some other conductor ink. c) Working principle of Mechanical Key switch Two metal pieces or contacts are kept in open position and moved into closed position when switch is pressed. When the switch is in normal position the contact is open, when the switch is pushed the contact closes, and the closure is sensed by the keyboard interface. After some use contacts become oxidized or dirty and make the switch useless. Gold plating on these contacts is done to improve the life span of the switch. Normal life span of high quality switches is about 1 million keystrokes. d) Working principle of Rubber dome switch A dome like rubber structure keeps the key in up position. When the key is pressed, the dome collapses and joins the two contact points. When key is released, the dome goes back to its normal shape, pushing the key into normal up position and breaking the contact. 2 P a g e

3 Working principle of Mechanical Key switch (Diagram 3 marks Working 5 marks)(any one diagram either A or B) Two metal pieces or contacts are kept in open position and moved into closed position when switch is pressed. When the switch is in normal position the contact is open, when the switch is pushed the contact closes, and the closure is sensed by the keyboard interface. After some use contacts become oxidized or dirty and make the switch useless. Gold plating on these contacts is done to improve the life span of the switch. Normal life span of high quality switches is about 1 million keystrokes. With neat diagram explain the working of opto mechanical mouse. Only difference is in the sensing circuit used to detect the movement of the mouse. In a mechanical mouse a decoder is used to detect the distance mouse is moved on the tabletop, whereas in a opto-mechanical mouse a combination of LED (Light Emitting Diode) and Photo detectors is used to sense the distance traveled by the mouse. 3 P a g e

4 Operation of Opto-Mechanical mouse : 1. When the mouse is moved, the ball at the bottom of the mouse moves and it turns two separate rollers fixed at 90 degree to each other. 2. One of these rollers is associated with back-and-forth movement of the mouse, i.e., vertical movement of the cursor on the screen. 3. The other roller is associated with the side-to-side movement of the mouse, i.e., the horizontal movement of the cursor on the screen. 4. Each roller is further connected with a wheel. These wheels are rotated by the corresponding movement of the rollers. 5. There are small openings on the rim of each wheel. As the wheel rotates, a pair of LED and Photo detectors detect the number of openings passed between them. 6. Each opening on the wheel allow the light from the LED to fall on the Photo detector and generate an electrical signal. 7. The number of signals generated indicates the number of openings in the rim of wheel passed, i.e., the more is the number of signals, the farther has been the mouse moved. 8. These signals are passed to the PC through the wire connecting mouse to the main system. 9. The PC, in turn, passes them to the mouse driver software which then converts them into distance, direction and speed required for the movement of the screen cursor. 10. Depressing any of the mouse button also produces a signal. Depending upon the button being pressed, number of times the button being pressed and the present location of the cursor on the screen, the software accomplishes the task desired by the user. 4 P a g e

5 Explain the working of optical mouse. (Working 4 marks) Working of Optical mouse: Modern surface-independent optical mice work by using an optoelectronic sensor (essentially, a tiny low-resolution video camera) to take successive images of the surface on which the mouse operates. As computing power grew cheaper, it became possible to embed more powerful special-purpose image-processing chips in the mouse itself. This advance enabled the mouse to detect relative motion on a wide variety of surfaces, translating the movement of the mouse into the movement of the cursor and eliminating the need for a special mouse-pad. Optical mice capture one thousand successive images or more per second. Depending on how fast the mouse is moving, each image will be offset from the previous one by a fraction of a pixel or as many as several pixels. Optical mice mathematically process these images using cross correlation to calculate how much each successive image is offset from the previous one. List any four advantages of optical mouse. (Any 4 advantages 1 mark each) Advantages of Optical mouse:- 1) No moving parts: thus less wear & tear 2) Lower chance of failure due to dust: no interference with tracking sensors. 3) No requirement of special surface such as mouse pad. 4) More accuracy than the mechanical mouse: 5) Less maintenance, no cleaning needed. 5 P a g e

6 Explain the working of flat bed scanner with the help of neat diagram. (Diagram 2 M, Working 2 M) WORKING OF FLAT BED SCANNER Light Source illuminates a piece of paper placed face down on the glass window above the scanning mechanism. Motor moves the scan head beneath the page. As it moves the scan head captures light reflected from individual areas of the page. Reflection takes place through a system of mirrors. A lens focuses the beams of light on to light sensitive diodes that translate the amount of light into electrical current. The more the reflected light, the more is the voltage of the signal. White spaces reflect more light than black or colored images. ADC converts each analog signal of voltage into digital pixel representing the scanned area. For monochrome scanner 1 bit per pixel is stored either on or off representing black or white. For color scanner, the scan head makes three passes under the images and the light on each pass is directed through a red, green or blue filter before it strikes the original image. Signals from three passes are converted into digital information and stored to represent red, green, or blue color value of the scanned area on the page. This digital information is sent to the software in the PC, where data is stored in a format on which a graphics program or OCR can work. 6 P a g e

7 Characteristics of Scanner OCR Most OCR readers include a small optical scanner for reading characters and sophisticated OCR software for analyzing what is read. Advantages of OCR readers include _ Written data and printed data can be read at the same time. _ Hard copies of documents can be read directly into a computer without retyping. _ The characters converted can later be edited by word processing software. Disadvantages of OCR readers include _ OCR readers often do not work well with handwritten characters or those in unusual fonts. OMR Optical mark recognition (OMR) readers can sense hand-drawn marks such as small circles or rectangles made on pre-printed forms in certain places. The OMR reader first reads the answer key sheet to record the correct answers based on the patterns of light, and then reads the remaining documents and matches their patterns of light against the answer key sheet. OMR readers are often used for marking multiple choice answer sheets, capturing data from questionnaires, enrolment forms, and lottery tickets. Advantages of OMR readers include OMR has a better recognition rate than OCR because fewer mistakes are made by machines to read marks than by reading handwritten characters. Large volumes of data can be collected quickly and easily without the need for specially trained staff. The cost of inputting data and the chance of data input errors could be reduced because it is not necessary to type the details for data entry. Disadvantages of OMR readers include The OMR reader needs to be reprogrammed for each new document design. OMR readers are relatively slow. The person putting marks on the documents must follow the instructions precisely. Any folding or dirt on a form may prevent the form from being read correctly. TWAIN TWAIN is an applications programming interface (API) and communications protocol that regulates communication between software and digital imaging devices, such as image scanners and digital cameras. TWAIN is not a hardware-level protocol; it requires a driver called Data Source for each device. 7 P a g e

8 TWAIN is a widely-used program that lets you scan an image (using a scanner ) directly into the application (such as PhotoShop) where you want to work with the image. Without TWAIN, you would have to close an application that was open, open a special application to receive the image, and then move the image to the application where you wanted to work with it. The TWAIN driver runs between an application and the scanner hardware. TWAIN usually comes as part of the software package you get when you buy a scanner. It's also integrated into PhotoShop and similar image manipulation programs. Resolution Scanner Resolution is a representation of the scanner's enlargement capability. Scanner Resolution is the measurement of the resolving power of the scanner's optics and is expressed as dots per inch, but it is more accurately described as pixels per inch. Interpolation Interpolation is a process that the scanning software uses to increase the perceived resolution of an image. It does this by creating extra pixels in between the ones actually scanned by the CCD array. These extra pixels are an average of the adjacent pixels. For example, if the hardware resolution is 300x300 and the interpolated resolution is 600x300, then the software is adding a pixel between every one scanned by a CCD sensor in each row. With neat sketches explain internal and external modem. (02-marks for internal modem, 02- marks for external modem) Types of Modem: 1. Internal Modem 2. External modem Internal modem The internal modem is a stand-alone board that plugs directly into an ISA or PCI expansion slot It contains its own Universal Asynchronous Receiver/Transmitter (UART). 8 P a g e

9 A modulator Circuit converts the serial data from the computer into audio signals to be transmitted over telephone lines. This modulated audio is then coupled to the telephone line. The signal passes through telephone jack (RJ-11) connector at the rate of the modem to the telephone line. On the receiver side, signals received from the telephone line is translated into serial data. The telephone interface separates the received signals and passes them to the demodulator. After demodulation the resulting serial data is passed to UART, which in turn converts the serial bits into parallel words that are placed on the system s data bus. The telephone interface also generates Dual Tone multi Frequency (DTFM) dialing signals needed to reach a remote modem. When the remote modem dials in, the telephone interface detects the incoming signal and alerts the UART to begin negotiating a connection. The telephone interface drives a speaker. During the initial stages of modem operation the speaker is used to hear the dial tone, dialing signals, and audio negotiation between the two modems. Once the connection is established, the speaker is disabled. The controller circuit manages the overall operation of the modem. It switches the modem between the control and data operating modes. The controller accepts commands from the modulator that allow the modem characteristics and operating parameters to be changed. In the event of power loss or reset conditions default modem parameters can be loaded from NVRAM. Permanent changes to modem parameters are stored in the NVRAM. External Modem The external modem does not include built in UART. It uses existing serial port already configured in the PC. A 9 pin (DB9) or 25 pin serial cable connects the PC serial port to the modem. Thus CPU need not be opened during modem installation. 9 P a g e

10 External modems avoid hardware conflicts such as (conflict of I/O address lines and that of interrupt lines) the external modem setup is faster and easier than internal modems. In the external modem the status of serial communication can be checked from the signal status LEDs. Draw diagram of centronics interface and explain function of any four signals (02-marks for diagram, ½ mark each for any four signal) It provides a handshake protocol between a computer and a printer. The printer side of the interface is a 36 pin connector and the PC side is a 25 pin D-type connector. Fig: : signals of the Centronics Interface Signals from PC-Printer There are 12 signals from PC to Printer. Out of these, 8 signals are data bits and 4 signals are control signals. Signals from computer to printer There are 12 signals from the computer to the printer. Out of these, eight signals are data bits and four signals are control signals. The control signals are: /STROBE /INIT /SCLTIN /AUTOFDXT All the control signal are low-active. /STROBE The printer should take the data when this signal is low 10 P a g e

11 /INIT /SLCTIN When /INIT is low, the printer resets its electronic logic and clears the printer buffer /SLCTIN is an interface enable signal. When this signal is low, the printer responds signals from the controller /AUTOFDXT After printing a line, the printer will provide one line feed automatically if this signal is low. This type of line feed is known as hardware line feed Signals from printer to computer There are five status signals from the printer to the computer. Thease are: /ACK, BUSY, PAPER_END, SELECT and /ERROR /ACK /ACK-signal is an acknowledgement for /STROBE signal from the computer. When active, it indicates that printer has received data sent by the computer and is ready to accept next byte. BUSY When BUSY is high, it indicates that the printer is busy and it cannot receive data. This signal becomes high under any of the following four conditions 1: On Receiving /STROBE active 2: During printing operation 3: When the printer is in offline state 4: When the printer sense some error condition PAPER_END When this signal is high, it indicates that there is no paper in the printer. Either the paper is torn or the paper is over. SELECT SELECT signal indicates that there is some error condition in the printer. The three reasons for this signal are: 1: Mechanical fault or electronic fault in the printer 2: The printer is in offline state 3: There is no paper in the printer, i.e. paper-end state 1. On receiving Strobe active 2. During printing operation 3. When printer is in offline status. 4. When printer senses some error condition. PE: When PE signal is high, it indicates that there is no paper in printer. Wither torn or absence of paper. SLCT: Printer is selected and logically connected to the Pc. Error: This indicates that there is error in printer SLCT:. Following may be the reasons: 1. Mechanical fault or electronic fault. 11 P a g e

12 2. Printer is offline 3. Paper Out. List any four advantages of Laser Printer over Dot Matrix printer. (Any 4 points, 2 Marks) 1. It is a non impact printer. 2. It is not noisy. 3. Printing speed is fast. 4. Printing quality is very good. Give any four disadvantages of Ink-jet Printer. (Any 4 points, 2 Marks) 1. Inkjet printers require periodic maintenance or else the ink gets logged in the nozzle. 2. They require special paper with controlled absorbency for best results 3. Ink cartridges are costly than ribbon and don t last longer. 4. It is costly than dot matrix printer. Draw the interface diagram for centronics and timing waveforms. (Diagram 2 marks, Explanation 2 marks) The printer controller sends data to the printer. After a minimum gap of 0.5 μs, it makes the strobe signal low and keeps it low for a minimum duration of 0.5 μs. As soon as strobe signal becomes active low the printer makes the busy line high. The controller should retain the data on the data lines for a minimum interval of 0.5 μs from the trailing edge of the strobe signal. Thus the data should be kept on the data lines for a minimum duration of 1.5 μs. When the printer is ready to receive the next character of data it makes the acknowledge line low. When the acknowledge line is made high the printer also removes the busy signal. 12 P a g e

13 State any four printer characteristics.(for any 4 characteristics ½M) 1. Printer type : Impact or Non-impact, laser or Inkjet 2. Resolution : specified in dpi 3. Print direction : One directional or Bi directional 4. Input Buffer : size in KB or MB 5. Printer Speed : in cpm, lpm or ppm 6. Interface : Serial or parallel /USB 7. Cartridge type With the block diagram, explain the working of dot matrix printer. Block diagram 4marks, working 4 marks Principle of operation of Dot-Matrix printer. 13 P a g e

14 Working of dot matrix printer: Print head moves horizontally across the paper and the print pin strikes the paper through an inked ribbon. Pin s impact is precisely timed so that it strikes the right position in the character matrix at the right time. Major factor determining printing speed is the time required between the successive strikes of each print pins. The time needed to retract and reactivate each print pin puts a physical limit on how fast the pins can be fired. PC sends series of ASCII codes that represent characters, punctuation marks etc to be printed over serial or parallel cable along with some printer movement information such as tabs, carriage return etc, to control the position of print head and print carriage. The ASCII codes are stored in the buffer (RAM) as the printing speed is less than the speed at which the PC sends data to the printer. When the buffer becomes full the printer informs the PC to stop sending further characters until some of the characters in the buffer are printed. The controller inside the printer selects a particular dot pattern for the ASCII code received from the PC. The dot pattern is stored in the ROM. The selected dot pattern is sent to the print head. Based on this information the print head fires different pins on the print head. The controller also controls the movement of print head and the paper. Working of Inkjet Printer 14 P a g e

15 OR Inkjet printers are most popular printers for home and small scale offices as they have a reasonable cost and a good quality of printing as well. A typical inkjet printer can print with a resolution of more than 300 dpi and some good quality inkjet printers are able to produce full colored hard copies at 600 dpi. An inkjet printer is made of the following parts: Printhead It is the heart of the printer which holds a series a nozzles which sprays the ink drops over the paper. Ink cartridge It is the part that contains the ink for printing. Generally monochrome (black & white) printers contain a black colored ink cartridges and a color printer contains two cartridges one with black ink and other with primary colors (cyan, magenta and yellow). Stepper motor It is housed in the printer to move the printerhead and ink cartridges back and forth across the paper. Stabilizer bar A stabilizer bar is used in printer to ensure the movement of printhead is précised and controlled over the paper. Belt A belt is used to attach the printhead with the stepper motor. Paper Tray It is the place where papers are placed to be printed. Rollers Printers have a set of rollers that helps to pull paper from the tray for printing purpose.. Paper tray stepper motor- another stepper motor is used to rotate the rollers in order to pull the paper in the printer.. Control Circuitry The control circuit takes the input from the computer and by decoding the input controls all mechanical operation of the printer. Similar to other printers, inkjet printers have a printhead as a key element. The printhead has many tiny nozzles also called as jets. When the printer receives the command to print something, 15 P a g e

16 the printhead starts spraying ink over the paper to form the characters and images. There are mainly two technologies that are used to spray the ink by nozzles. These are: Thermal Bubble This technology is also known as bubble jet is used by various manufacturers like Canon and Hewlett Packard. When printer receives commands to print something, the current flows through a set of tiny resistors and they produce heat. This heat in turn vaporizes the ink to create a bubble. As the bubble expands, some of the ink moves out of the nozzle and gets deposited over the paper. Then the bubble collapses and due to the vacuum it pulls more ink from ink cartridge. There are generally 300 to 600 nozzles in a thermal printer head which can spray the ink simultaneously. Piezoelectric In the piezoelectric technology, a piezo crystal is situated at the end of the ink reservoir of a nozzle. When printer receives the command to print, an electric charge is applied to the crystal which in turn starts vibrating and a small amount of ink is pushed out of the nozzle. When the vibration stops the nozzle pulls some more ink from the cartridge to replace the ink sprayed out. This technology is patented by Seiko Epson Corporation. An inkjet printer can print 100 to several hundred papers depending on the nature of the hard copy before the ink cartridge need to be replaced. Give disadvantages of ink jet printer. (Any two points) Ans. Advantages Initial Cost Ink-Jet printers are one of the lowest cost products on the market. In the past, the quality of low inkjet printers have matched with its price. It means that when you buy an cheap inkjet printer, the quality of the images are not good. However, ink-jet technology has developed and improved so remarkably that the cheapest inkjet printers can create images with good quality. Quality Today you can create images or documents with high quality by Inkjet printers. They used to use blurry effect to the texts or images before but with the powerful technology now, you are able to create more effects so that your images are more vivid and have the best quality. Space Compare to laser printers, the ink jet printers have suitable size to put on the desk on your office or a small room in your home to serve to your work. Time Different from laser printer, the inkjet printer do not require time to heat the machine system before print. They have also shorter delay between the document being sent to print and the beginning of a print process. Give any four disadvantages of Ink-jet Printer. (Any 4 points, 2 Marks) 1. Inkjet printers require periodic maintenance or else the ink gets logged in the nozzle. 16 P a g e

17 2. They require special paper with controlled absorbency for best results 3. Ink cartridges are costly than ribbon and don t last longer. 4. It is costly than dot matrix printer. Block Diagram of Laser Printer OR 17 P a g e

18 Working of Laser Printer Laser printers are the most popular printers that are mainly used for large scale qualitative printing. They are among the most popularly used fastest printers available in the market. A laser printer uses a slight different approach for printing. It does not use ink like inkjet printers, instead it uses a very fine powder known as Toner. components of a laser printer. The control circuitry is the part of the printer that talks with the computer and receives the printing data. A Raster Image Processor (RIP) converts the text and images in to a virtual matrix of dots. The photo conducting drum which is the key component of the laser printer has a special coating which receives the positive and negative charge from a charging roller. A rapidly switching laser beam scans the charged drum line by line. When the beam flashes on, it reverses the charge of tiny spots on the drum, respecting to the dots that are to be printed black. As soon the laser scans a line, a stepper motor moves the drum in order to scan the next line by the laser. A developer roller plays the vital role to paste the tonner on the paper. It is coated with charged tonner particles. As the drum touches the developer roller, the charged tonner particles cling to the discharged areas of the drum, reproducing your images and text reversely. Meanwhile a paper is drawn from the paper tray with help of a belt. 18 P a g e

19 As the paper passes through a charging wire it applies a charge on it opposite to the toner s charge. When the paper meets the drum, due to the opposite charge between the paper and toner particles, the toner particles are transferred to the paper. A cleaning blade then cleans the drum and the whole process runs smoothly continuously. Finally paper passes through the fuser which is a heat and presser roller, melts the toner and fixes on the paper perfectly. Advantages of Laser Printer The main advantage of Laser printer is its speed & efficiency at which it prints high-quality quality graphics & text. Laser printers produce high-quality output as compared to other printers. Laser printers are quite and does not produce disturbing sounds. They are also capable to produce color prints. Disadvantages of Laser Printer The main disadvantage of Laser printer is its cost, they are relatively costly as compared to other printers. The maintenance, repair & servicing charges are also high of these printers. Laser printers emit small amount of ozone and are hazardous to health and the atmosphere. 19 P a g e