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    WIRELESS DATA MODEMS

    BACHELOR OF ENGINEERINGELECTRONICS AND

    COMMUNICATION ENGINEERING

    EC2404

    ELECTRONICS SYSTEM DESIGN LAB

    SUBMITTED BY,

    R.MONIKA, 31708106074

    M.ATHITHYA, 31708106079

    C.MENAGA, 31708106068

    NAZAREINE, 31708106083

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    ABSTRACT

    A wireless modem is a type ofmodulator-demodulator which connects to a wireless

    network instead of using telephone ofcable television lines. A mobile Internet user

    can connect using a wireless modem to a wireless Internet Service Provider (ISP) to

    get Internet access.Mobile phones, smartphones, and PDAs can be employed as data

    modems to form a wireless access point connecting a personal computer to the

    Internet (or some proprietary network). Here we made an attempt to construct a simple

    wireless data modem using NE555 and NE565. Modulator is constructed using

    NE555. Using a IR led transmission of signals are being performed. Using NE565

    demodulator is constructed.

    http://en.wikipedia.org/wiki/Modemhttp://en.wikipedia.org/wiki/Cable_televisionhttp://en.wikipedia.org/wiki/Internet_Service_Providerhttp://en.wikipedia.org/wiki/Internet_accesshttp://en.wikipedia.org/wiki/Mobile_phonehttp://en.wikipedia.org/wiki/Smartphoneshttp://en.wikipedia.org/wiki/PDAhttp://en.wikipedia.org/wiki/Computer_networkinghttp://en.wikipedia.org/wiki/Computer_networkinghttp://en.wikipedia.org/wiki/PDAhttp://en.wikipedia.org/wiki/Smartphoneshttp://en.wikipedia.org/wiki/Mobile_phonehttp://en.wikipedia.org/wiki/Internet_accesshttp://en.wikipedia.org/wiki/Internet_Service_Providerhttp://en.wikipedia.org/wiki/Cable_televisionhttp://en.wikipedia.org/wiki/Modem
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    CONTENTS

    CHAPTER TITLE PAGE NO

    1 Wireless data modems- an introduction

    1.1An example wireless data modems used 5

    in desktops

    1.2Applications 6

    2 Fsk modulation using NE555

    2.1NE555 pin diagram 7

    2.1.1specifications 7

    2.1.2Fsk modulation 8

    2.1.3Fsk modulated waveforms 9

    2.2Filters 10-11

    2.3IR LED

    2.3.1pin diagram 12

    2.4Fsk demodulation using NE5652.4.1NE565 pin diagram 13

    2.4.2specifications 14

    2.4.3block diagram of NE565 15

    2.4.4description 15

    2.4.5demodulation 16

    2.5Pin diagram of other ICs

    2.5.1IC7404 17

    2.5.2IC741 17

    3 Conclusion , Reference 18

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    LIST OF FIGURES

    FIGURE NO NAME PAGE

    NO

    1.1 An Example wireless data modems used in desktops

    2.1 NE555 pin diagram

    2.2 Fsk modulation using ne555

    2.3 Fsk modulated waveforms

    2.4 Filter circuits

    2.5 IR led

    2.6 IR led pin diagram

    2.7 NE565 pin diagram

    2.8 565 block diagram

    2.9 Fsk demodulator

    2.10 IC 7404

    2.11 IC741

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    CHAPTER-1

    WIRELESS DATA MODEMS - AN INTRODUCTION

    A wireless modem is a type ofmodulator-demodulator which connects to a wireless

    network instead of using telephone ofcable television lines. A mobile Internet user

    can connect using a wireless modem to a wireless Internet Service Provider (ISP) to

    get Internet access.

    Mobile phones, smartphones, and PDAs can be employed as data modems to form a

    wireless access point connecting a personal computer to the Internet (or some

    proprietary network). In this use the mobile phone is providing a gateway between the

    cellular service provider's data network technology and Point-to-Point Protocol (PPP)

    spoken by PCs. Almost all current mobile phone models support the Hayes command

    set, a standard method of controlling modems. To the PC, the phone appears like an

    external modem when connected via serial cable, USB, IrDA infrared

    or Bluetooth wireless. Some cellular providers forbid this kind of usage, or charge an

    extra fee.

    Wireless FireWire, USB and Serial modems are also used in the Wi-

    Fi and WiMAX standards, operating at microwave frequencies, to give a

    laptop, PDA or desktop computer an access point to a network. The modems may be

    as large as a regular cable modem to as small as a dongle or USB-stick. If combined

    with Voice over IP (VoIP) technology, these computing devices can make and receive

    telephone calls.

    PCMCIA, ExpressCard and Compact Flash modems are also used. These card-

    modems can also have GPS included.

    http://en.wikipedia.org/wiki/Modemhttp://en.wikipedia.org/wiki/Cable_televisionhttp://en.wikipedia.org/wiki/Internet_Service_Providerhttp://en.wikipedia.org/wiki/Internet_accesshttp://en.wikipedia.org/wiki/Mobile_phonehttp://en.wikipedia.org/wiki/Smartphoneshttp://en.wikipedia.org/wiki/PDAhttp://en.wikipedia.org/wiki/Computer_networkinghttp://en.wikipedia.org/wiki/Gateway_(telecommunications)http://en.wikipedia.org/wiki/Hayes_command_sethttp://en.wikipedia.org/wiki/Hayes_command_sethttp://en.wikipedia.org/wiki/USBhttp://en.wikipedia.org/wiki/IrDAhttp://en.wikipedia.org/wiki/Bluetoothhttp://en.wikipedia.org/wiki/Wi-Fihttp://en.wikipedia.org/wiki/Wi-Fihttp://en.wikipedia.org/wiki/WiMAXhttp://en.wikipedia.org/wiki/Personal_digital_assistantshttp://en.wikipedia.org/wiki/Donglehttp://en.wikipedia.org/wiki/USB_flash_drivehttp://en.wikipedia.org/wiki/Voice_over_IPhttp://en.wikipedia.org/wiki/PCMCIAhttp://en.wikipedia.org/wiki/ExpressCardhttp://en.wikipedia.org/wiki/Compact_Flashhttp://en.wikipedia.org/wiki/Compact_Flashhttp://en.wikipedia.org/wiki/ExpressCardhttp://en.wikipedia.org/wiki/PCMCIAhttp://en.wikipedia.org/wiki/Voice_over_IPhttp://en.wikipedia.org/wiki/USB_flash_drivehttp://en.wikipedia.org/wiki/Donglehttp://en.wikipedia.org/wiki/Personal_digital_assistantshttp://en.wikipedia.org/wiki/WiMAXhttp://en.wikipedia.org/wiki/Wi-Fihttp://en.wikipedia.org/wiki/Wi-Fihttp://en.wikipedia.org/wiki/Bluetoothhttp://en.wikipedia.org/wiki/IrDAhttp://en.wikipedia.org/wiki/USBhttp://en.wikipedia.org/wiki/Hayes_command_sethttp://en.wikipedia.org/wiki/Hayes_command_sethttp://en.wikipedia.org/wiki/Gateway_(telecommunications)http://en.wikipedia.org/wiki/Computer_networkinghttp://en.wikipedia.org/wiki/PDAhttp://en.wikipedia.org/wiki/Smartphoneshttp://en.wikipedia.org/wiki/Mobile_phonehttp://en.wikipedia.org/wiki/Internet_accesshttp://en.wikipedia.org/wiki/Internet_Service_Providerhttp://en.wikipedia.org/wiki/Cable_televisionhttp://en.wikipedia.org/wiki/Modem
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    1.1 AN EXAMPLE WIRELESS DATA MODEM USED IN DESKTOPS:

    Fig1.1 an eg wireless data modem

    1.2APPLICATIONS:

    Smart phones PDAs Mobile phones Used in wi-max and wi-fi standards PCMCIA ExpressCard Compact Flash

    http://en.wikipedia.org/wiki/PCMCIAhttp://en.wikipedia.org/wiki/ExpressCardhttp://en.wikipedia.org/wiki/Compact_Flashhttp://en.wikipedia.org/wiki/File:IBurst-Kyocera-desktop-modem01.jpghttp://en.wikipedia.org/wiki/Compact_Flashhttp://en.wikipedia.org/wiki/ExpressCardhttp://en.wikipedia.org/wiki/PCMCIA
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    CHAPTER 2

    2.1FSK MODULATION USING NE555:

    2.1.1NE555 PIN DIAGRAM:

    Fig 2.1 NE555 pin diagram

    The connection of the pins for a DIP package is as follows:

    Pin Name Purpose

    1 GND Ground, low level (0 V)

    2 TRIG OUT rises, and interval starts, when this input falls below 1/3 VCC.

    3 OUT This output is driven to +VCCor GND.

    4 RESET A timing interval may be interrupted by driving this input to GND.

    5 CTRL "Control" access to the internal voltage divider (by default, 2/3 VCC).

    6 THR The interval ends when the voltage at THR is greater than at CTRL.

    http://en.wikipedia.org/wiki/Vcchttp://en.wikipedia.org/wiki/Vcchttp://en.wikipedia.org/wiki/Vcchttp://en.wikipedia.org/wiki/Vcchttp://en.wikipedia.org/wiki/File:555_Pinout.svghttp://en.wikipedia.org/wiki/Vcc
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    7 DIS Open collector output; may discharge a capacitor between intervals.

    8 V+, VCC Positive supply voltage is usually between 3 and 15 V.

    2.1.2SPECIFICATIONS:

    These specifications apply to the NE555. Other 555 timers can have different specifications

    depending on the grade (military, medical, etc).

    Supply voltage (VCC) 4.5 to 15 V

    Supply current (VCC = +15 V) 10 to 15 mA

    Output current (maximum) 200 mA

    Maximum Power dissipation 600 mW

    Power Consumption (minimum operating) 30 mW@5V, 225 mW@15V

    2.1.3FSK MODULATION USING NE555:

    Fig 2.2 circuit diagram for modulation

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    A digital-to-analog modulation technique. Data is transmitted by shifting between two close

    frequencies with ones represented by one frequency and zeroes by the other.

    Frequency-shift keying (FSK) is a method of transmitting digital signals. The two binary states, logic

    0 (low) and 1 (high), are each represented by an analog waveform. Logic 0 is represented by a wave

    at a specific frequency, and logic 1 is represented by a wave at a different frequency. A modem

    converts the binary data from a computer to FSK for transmission over telephone lines, cables,

    optical fiber, or wireless media. The modem also converts incoming FSK signals to digital low and

    high states, which the computer can understand. Whenever the message or information signal rides

    over the carrier it is called modulation. In electrical sense the operation of riding over the amplitude

    of carriermeans to alter the amplitude of carrier. This is called amplitude modulation of the carrier.

    Thus the message signal becomes the modulating signal and it is transmitted by variations in the

    amplitude of the carrier.

    The transmission media suffers three major problems

    A. Attenuation

    B. Distortion

    C. noise

    Due to these inherent problems, it is very difficult to have wide range of frequency in the signals that

    are transmitted. Therefore to transmit data over wireless medium, it is necessary to use a modulator

    which restore the number of frequency in the transmitted signal by employing digital modulation

    techniques like ASK, FSK or PSK. Also Binary PSK with non-coherent detection can also be

    employed. A modem is a device that takes the digital electrical pulses from a terminal or computer

    and converts them into continuous analog signal that is used for transmission. The binary FSK

    technique is employed for modulating the digital signals. IC 555 timer and transistor acting as

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    switch, when the device acts as transformer. PLL IC 565 can be used for demodulator. It consists of

    phase detection LPF amplifier.

    2.1.4FSK MODULATED WAVE FORMS:

    The wave forms produced due to modulation is as shown in the figure

    a) Binary datab) Modulated signalc) Frequency characteristic signal

    2.2FILTERS:

    Electronic filters are electronic circuits which perform signal processing functions, specifically to

    remove unwanted frequency components from the signal, to enhance wanted ones, or both.

    Electronic filters can be:

    http://en.wikipedia.org/wiki/Filter_(signal_processing)http://en.wikipedia.org/wiki/Electronic_circuithttp://en.wikipedia.org/wiki/Signal_processinghttp://en.wikipedia.org/wiki/Signal_processinghttp://en.wikipedia.org/wiki/Electronic_circuithttp://en.wikipedia.org/wiki/Filter_(signal_processing)
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    passive or active analog or digital high-pass, low-pass, bandpass, band-reject (band reject; notch), or all-pass. discrete-time (sampled) or continuous-time linear or non-linear infinite impulse response (IIR type) or finite impulse response (FIR type)

    The most common types of electronic filters are linear filters, regardless of other aspects of their

    design. See the article on linear filters for details on their design and analysis.

    Fig 2.4 filter circuits

    Passive implementations of linear filters are based on combinations ofresistors (R), inductors (L)

    and capacitors (C). These types are collectively known as passive filters, because they do not depend

    upon an external power supply and/or they do not contain active components such as transistors.

    Inductors block high-frequency signals and conduct low-frequency signals, while capacitors do the

    reverse. A filter in which the signal passes through an inductor, or in which a capacitor provides a

    path to ground, presents less attenuation to low-frequency signals than high-frequency signals and is

    a low-pass filter. If the signal passes through a capacitor, or has a path to ground through an

    inductor, then the filter presents less attenuation to high-frequency signals than low-frequency

    http://en.wikipedia.org/wiki/Passive_componenthttp://en.wikipedia.org/wiki/Active_filterhttp://en.wikipedia.org/wiki/Analog_circuithttp://en.wikipedia.org/wiki/Digital_filterhttp://en.wikipedia.org/wiki/High-pass_filterhttp://en.wikipedia.org/wiki/Low-pass_filterhttp://en.wikipedia.org/wiki/Band-pass_filterhttp://en.wikipedia.org/wiki/Band-stop_filterhttp://en.wikipedia.org/wiki/All-pass_filterhttp://en.wikipedia.org/wiki/Discrete-timehttp://en.wikipedia.org/wiki/Continuous-timehttp://en.wikipedia.org/wiki/Linear_filterhttp://en.wikipedia.org/wiki/Non-linear_filterhttp://en.wikipedia.org/wiki/Infinite_impulse_responsehttp://en.wikipedia.org/wiki/Finite_impulse_responsehttp://en.wikipedia.org/wiki/Linear_filtershttp://en.wikipedia.org/wiki/Resistorhttp://en.wikipedia.org/wiki/Inductorhttp://en.wikipedia.org/wiki/Capacitorhttp://en.wikipedia.org/wiki/Capacitorhttp://en.wikipedia.org/wiki/Inductorhttp://en.wikipedia.org/wiki/Low-pass_filterhttp://en.wikipedia.org/wiki/File:1st_Order_Lowpass_Filter_RC.svghttp://en.wikipedia.org/wiki/File:1st_Order_Lowpass_Filter_RC.svghttp://en.wikipedia.org/wiki/Low-pass_filterhttp://en.wikipedia.org/wiki/Inductorhttp://en.wikipedia.org/wiki/Capacitorhttp://en.wikipedia.org/wiki/Capacitorhttp://en.wikipedia.org/wiki/Inductorhttp://en.wikipedia.org/wiki/Resistorhttp://en.wikipedia.org/wiki/Linear_filtershttp://en.wikipedia.org/wiki/Finite_impulse_responsehttp://en.wikipedia.org/wiki/Infinite_impulse_responsehttp://en.wikipedia.org/wiki/Non-linear_filterhttp://en.wikipedia.org/wiki/Linear_filterhttp://en.wikipedia.org/wiki/Continuous-timehttp://en.wikipedia.org/wiki/Discrete-timehttp://en.wikipedia.org/wiki/All-pass_filterhttp://en.wikipedia.org/wiki/Band-stop_filterhttp://en.wikipedia.org/wiki/Band-pass_filterhttp://en.wikipedia.org/wiki/Low-pass_filterhttp://en.wikipedia.org/wiki/High-pass_filterhttp://en.wikipedia.org/wiki/Digital_filterhttp://en.wikipedia.org/wiki/Analog_circuithttp://en.wikipedia.org/wiki/Active_filterhttp://en.wikipedia.org/wiki/Passive_component
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    signals and is a high-pass filter. Resistors on their own have no frequency-selective properties, but

    are added to inductors and capacitors to determine the time-constants of the circuit, and therefore the

    frequencies to which it responds.

    The inductors and capacitors are the reactive elements of the filter. The number of elements

    determines the order of the filter. In this context, an LC tuned circuit being used in a band-pass or

    band-stop filter is considered a single element even though it consists of two components.

    At high frequencies (above about 100 megahertz), sometimes the inductors consist of single loops or

    strips of sheet metal, and the capacitors consist of adjacent strips of metal. These inductive or

    capacitive pieces of metal are called stubs

    2.3IR LED:

    Fig 2.5 IR LED

    An IR LED, also known as IR transmitter, is a special purpose LED that transmits infrared rays in

    the range of 760 nm wavelength. Such LEDs are usually made of gallium arsenide or aluminium

    gallium arsenide. They, along with IR receivers, are commonly used as sensors. The appearance is

    same as a common LED. Since the human eye cannot see the infrared radiations, it is not possible

    for a person to identify whether the IR LED is working or not, unlike a common LED. To overcome

    http://en.wikipedia.org/wiki/High-pass_filterhttp://en.wikipedia.org/wiki/Resistorhttp://en.wikipedia.org/wiki/Reactance_(electronics)http://en.wikipedia.org/wiki/LC_circuithttp://en.wikipedia.org/wiki/Hertzhttp://en.wikipedia.org/wiki/Stub_(electronics)http://www.engineersgarage.com/content/ledhttp://www.google.co.in/imgres?imgurl=http://www.solarbotics.com/assets/images/ir-led/ir-led_pl.jpg&imgrefurl=http://www.solarbotics.com/products/ir-led/&h=450&w=600&sz=19&tbnid=c3i5mzU5ahuUwM:&tbnh=90&tbnw=120&prev=/search?q=ir+led&tbm=isch&tbo=u&zoom=1&q=ir+led&docid=GR6EAqgMVEBgUM&hl=en&sa=X&ei=uj5vTvWjB4HjiALwkMm1Ag&ved=0CEYQ9QEwAg&dur=2600http://www.engineersgarage.com/content/ledhttp://en.wikipedia.org/wiki/Stub_(electronics)http://en.wikipedia.org/wiki/Hertzhttp://en.wikipedia.org/wiki/LC_circuithttp://en.wikipedia.org/wiki/Reactance_(electronics)http://en.wikipedia.org/wiki/Resistorhttp://en.wikipedia.org/wiki/High-pass_filter
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    this problem, the camera on a cellphone can be used. The camera can show us the IR rays being

    emanated from the IR LED in a circuit.

    2.3.1Pin Diagram:

    Fig 2.6 pin diagram

    2.4FSK DEMODULATION USING NE565:

    2.4.1NE 565 PIN DIAGRAM:

    Fig 2.7 NE565 pin diagram

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    2.4.2SPECIFICATIONS:

    1.Operating frequency range : 0.001 Hz to 500 kHz.

    2.Operating voltage range : 6 to 12 V.

    3.Input impedance : 10 k Q typically.

    4.Output sink current :1mA typically.

    5.Output source current : 10 m A typically.

    6.Drift in VCO centre frequency with temperature : 300 ppm/ C typically.

    7.Drift in VCO centre frequency with supply voltage : 1.5 %/V maximum.

    8.Input level required for tracking : 10 mVrms minimum to 3 V peak-to-peak maximum.

    9.Bandwidth adjustment range : < 1 to > 60 %.

    2.4.3BLOCK DIAGRAM OF NE565:

    Fig 2.8 block diagram of NE565

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    2.4.4DESCRIPTION:

    The NE/SE565 PhaseLocked Loop(PLL) is a self-contained, adaptable filter and demodulator for

    the frequency range from 0.001Hz to 500kHz. The circuit comprises of a voltage controlled

    oscillator of exceptional stability and linearity, a phase comparator, an amplifier and a low pass filter

    as shown in block diagram. The center frequency of the PLL is determined by the free

    Running frequency of VCO. This frequency can be adjusted externally with a resistor or capacitr.

    The LPF which determines the capture characteristics of the loop is formed by internal resistor and

    an external capacitor.

    2.4.5FSK DEMODULATION USIN PLL 565:

    Fig 2.9 an fsk demodulator

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    A very useful application of the 565 PLL is as a FSK demodulator. In the 565 PLL the frequency

    shift is usually accomplished by driving a VCO with the binary data signal so that the two resulting

    frequencies correspond to the logic 0 and logic 1 states of the binary data signal. The frequencies

    corresponding to logic 1 and logic 0 states are commonly called the mark and space frequencies.

    Several standards are used to set the mark and space frequencies.

    An FSK signal demodulator can be built as illustrated in figure. The demodulator receives a signal at

    one of the two distinct carrier frequencies, 1,270 Hz or 1,070 Hz representing the RS-232 C logic

    levels of mark (- 5 V) or space (+ 14 V), respectively. Capacitance coupling is used at the input to

    remove a dc level. As the signal appears at the input of 565 PLL, the PLL locks to the input

    frequency and tracks it between the two possible frequencies with a corresponding dc shift at the

    output. Resistor R1 and capacitor C1 determine the free-running frequency of the VCO. Capacitor

    C2 is a loop filter capacitor that establishes the dynamic characteristics of the demodulator.

    Capacitor C2 is chosen smaller than usual one to eliminate overshoot on the output pulse. A three-

    stage RC ladder filter is employed for removing the sum frequency component from the output. The

    VCO frequency is adjusted with R1 so that the dc voltage level at the output (pin 7) is the same as

    that at pin 6. An input at frequency 1,070 Hz drives the demodulator output voltage to a more

    positive voltage level, driving the digital output to the high level (space or + 14 V). An input at

    1,270 Hz correspondingly drives the 565 dc output less positive with the digital output, which then

    drops to the low level (mark or5 V).

    2.5PIN DIAGRAMS OF OTHER ICS USED IN MODULATION AND

    DEMODULATION:

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    2.5.1IC 7404:

    Fig 2.10 Ic 7404

    2.5.2IC 741:

    Fig 2.11 IC741

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    CHAPTER 3

    CONCLUSION:

    FSK signals take many different forms depending on their intended application. With the increasing

    sophistication of electronics and signal detection theory, it is clear that FSK demodulators, are

    required to optimally demodulate the many different signal formats.

    A modem is a device that takes the digital electrical pulses from a terminal or computer and converts

    them into continuous analog signal that is used for transmission. The binary FSK technique is

    employed for modulating the digital signals. IC 555 timer and transistor acting as switch, when the

    device acts as transformer. PLL IC 565 can be used for demodulator. It consists of phase detection

    LPF amplifier.