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  • 8/8/2019 Prjct Report




    The primary purpose of switch is to provide means for connecting two or more terminals in order

    to permit the flow of current across them, so as to allow for interaction between electrical

    components, and to easily isolate circuits so as to terminate this communication flow when need

    be. The motivating force behind this design is based on the desire to alleviate the problem faced

    by the aged and physically challenged persons in trying to control some household appliances. It

    also takes into considerations the illiterates that may have problems operating some complex

    hand-held Remote Control Units (RCUs)

    Therefore this paper provides an introductory study on the basic principles involved in utilizing

    acoustic energy to control switching process. This is achieved by converting the energy

    generated by the handclap into electrical pulse, which is in turn used to drive an electronic

    circuitry that includes a relay , which in turn switches ON/OFF any appliance connected through

    it to the main.

    The device is activated by clapping twice within a set time period that is determined by a time

    constant (RC) component value in the circuit.

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    Introduction to Workshop

    1. Soldering:

    What is solder?

    Solder is an alloy (mixture) of tin and lead, typically 60% tin and 40% lead. It melts at a

    temperature of about 200C. Coating a surface with solder is called tinning because of

    the tin content of solder.

    Lead is poisonous and you should always wash your hands after using solder.

    Solder for electronics use contains tiny cores of flux, like the wires inside a mains flex.

    The flux is corrosive, like an acid, and it cleans the metal surfaces as the solder melts.

    This is why you must melt the solder actually on the joint, not on the iron tip.

    Without flux most joints would fail because metals

    quickly oxidise and the solder itself will not flow properly onto a dirty, oxidised, metal


    The best size of solder for electronic circuit boards is 22swg (swg = standard wire

    gauge).For plugs, component holders and other larger joints you may prefer to use 18swg


    Making soldered joints:

    Hold the soldering iron like a pen, near the base of the handle.

    Imagine you are going to write your name!

    Remember to never touch the hot element or tip.

    Touch the soldering iron onto the joint to be made.

    Make sure it touches both the component lead and the track.

    Hold the tip there for a few seconds.

    Feed a little solder onto the joint.

    It should flow smoothly onto the lead and track to form a volcano shape as shown in the

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    diagram below. Make sure you apply the solder to the joint, not the iron.

    Remove the solder, then the iron, while keeping the joint still.

    Allow the joint a few seconds to cool before you move the circuit board.

    Inspect the joint closely. It should look shiny and have a volcano shape. If not, you will need to reheat it and

    feed in a little more solder. This time ensure that both the lead and track are heated fully

    before applying solder.


    Soldering advice for components:

    Some components require special care when soldering.

    Many must be placed the correct way round and a few

    are easily damaged by the heat from soldering.

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  • 8/8/2019 Prjct Report



    Solder and Flux:

    Solder is a metal or metallic alloy used, when melted, to join metallic surfaces together. Themost common alloy is some combination of tin and lead. Certain tin-lead alloys have a lower

    melting point than the parent metals by themselves. The most common alloys used for

    electronics work are 60/40 and 63/37. The chart below shows the differences in melting points ofsome common solder alloys.

    Tin/Lead Melting Point

    40/60 460 degrees F (230 degrees C)

    50/50 418 degrees F (214 degrees C)

    60/40 374 degrees F (190 degrees C)

    63/37 364 degrees F (183 degrees C)

    95/5 434 degrees F (224 degrees C)

    Most soldering jobs can be done with fluxcored solder (solder wire with the flux in a "core")

    when the surfaces to be joined are already clean or can be cleaned of rust, dirt and grease. Flux

    an also be applied by other means. Flux only cleans oxides off the surfaces to be soldered. It does

    not remove dirt, soot, oils, silicone, etc.


    Objective: Rectifiers convert alternating currents (AC) into direct current (DC).

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    Fig .(A)

    The Bridge rectifier circuit is shown in the figure A. The circuit has four diodes connected to

    form a bridge. The ac input voltage is applied to the diagonally opposite ends of the bridge. Theload resistance is connected between the other two ends of the bridge.For the positive half cycle

    of the input ac voltage, diodes D1 and D3 conduct, whereas diodes D2 and D4 remain in the OFF

    state. The conducting diodes will be in series with the load resistance RL and hence the load

    current flows through RL.

    For the negative half cycle of the input ac voltage, diodes D2 and D4 conduct whereas, D1 and

    D3 remain OFF. The conducting diodes D2 and D4 will be in series with the load resistance RLand hence the current flows through RL in the same direction as in the previous half cycle. Thus a

    bi-directional wave is converted into a unidirectional wave.

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    A resistor is a two-terminal electrical orelectronic component that resists an electric currentby

    producing a voltage drop between its terminals in accordance with Ohm's law: R=V/I Theelectrical resistanceis equal to the voltage drop across the resistor divided by the current through

    the resistor. Resistors are used as part ofelectrical networks and electronic circuits.


    An electric circuit element used to store charge temporarily, consisting in general of two metallic

    plates separated and insulated from each other by a dielectric. Also called condenser.


    An electronic device that restricts current flow chiefly to one direction . An electron tube havinga cathode and an anode . A two-terminal semiconductor device used chiefly as a rectifier .


    A device used to transfer electric energy from one circuit to another, especially a pair of multiply

    wound, inductively coupled wire coils that effect such a transfer with a change in voltage,

    current, phase, or other electric characteristic.


    A relay is an electrical switchthat opens and closes under the control of anotherelectrical circuit.

    In the original form, the switch is operated by an electromagnet to open or close one or many

    sets of contacts. It was invented byJoseph Henryin 1835. Because a relay is able to control anoutput circuit of higher power than the input circuit, it can be considered, in a broad sense, to be

    a form of an electrical amplifier.


    Condenser means capacitor, an electronic component which stores energy in the form of anelectrostatic field. The term condenser is actually obsolete but has stuck as the name for this type

    of microphone, which uses a capacitor to convert acoustical energy into electrical energy.

    Condenser microphones require power from a battery or external source. The resulting audio

    signal is stronger signal than that from a dynamic. Condensers also tend to be more sensitive andresponsive than dynamics, making them well-suited to capturing subtle nuances in a sound. They

    are not ideal for high-volume work, as their sensitivity makes them prone to distort.'s_law's_law
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    Transistor :

    A 'transistor' is a semiconductor device, commonly used as an amplifier or an electrically

    controlled switch. The transistor is the fundamental building block of the circuitry in computers,cellular phones, and all other modernelectronic devices.

    The bipolar NPN transistors used in this design are basically used as switch, to trigger the relay

    and as amplifier to boost the mic level to line level. When a transistor is used as switch, it must

    be either OFF or fully ON. In the fully ON state, the voltage VCE across the transistor is almostzero and the transistor is said to be saturated because it cannot pass any more collector current

    IC. The transistor is off when VIN is less than 0.7 V, because the base current will be zero. The

    power developed in a switching transistor is very small

    In the OFF statePower = VD *IC but IC = 0 (3.3.1)

    P = 0

    In the ON state

    Power = VC * IC but VCE O (almost) (3.3.2)P 0

    So, the power is very small.

    The 555 Timer :

    The 555 timer is a very versatile 8-pin, which can be configured with a few external components

    and to build many circuits involving timing. The NE 555, used in this design is a popular versionthat is suitable in most cases where a 555 timer is needed. It is a dual-In -line (DIL) package.

    The 555 timer configuration can be done in three modes but for the purpose of this design, twoof them are required namely: astable and Monostable mode. An astable circuit produces a square

    wave with sharp transitions between low and high. It is called astable because it is not stable inany state since the output is continually changing between low and high.

    A monostable circuit produces a single output pulse when triggered. It is stable in just one state;

    the output low state. This is also known as the triggered pulse producer. Once triggered by aninput voltage, it gives a fixed length output pulse. It will do this for even short input pulse. The

    output high state is temporary. The duration of the pulse is called the time period (T), which is

    determined by resistor R8 and capacitor C3. The time period T, which is the time taken for thecapacitor to change to 2/3 of the supply voltage is given as

    T = 1.1 * R8 * C3

    Decade Counter :

    Counters are electronic circuits that count in binary and give outputs that changes every time an

    input signal changes from high to low (i.e. at every falling edge of the signal). A counter requires
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    a square wave input signal to make it count. This wave is a digital waveform with sharp

    transition between low (0 V) and high (+Vs), such as the output from a 555 timer circuit.

    In this design, the output of a decade counter is used for a transistor switch that enables the

    switching of the relay. The decade counter, CD4017BC, used in this design is a 5 stage divide-

    by-10 counter with 10 decoded outputs and a carry out bit. Counters are cleared to their zero contby a logical 1 on their reset line, and are advanced in their counts on the positive edge of the

    clock signal only when the clock enable is in the logical 0 state. The decade counter is a 16 pinDual-in-Line (DIL) package. The decade counter IC CD4017B, used in this design is wired as a

    bistable, by connecting its decoded output 2 (Pin 4) to its reset (Pin 15).

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    Here is a circuit that can switch on & off a light, Fan, Radio etc. by the sound of clap . clap

    switch free from false triggering. To turn on/off any appliance, you just have to clap twice. Thecir-cuit changes its output state only when you clap twice within the set time period. Here,

    youve to clap within 3 seconds. The clap sound sensed by condenser microphone is amplified

    by transistor T1.The amplified signal provides negative pulseto pin 2 of IC1 and IC2, triggeringboth the ICs. IC1, commonly used as a timer, is wired here as a monostable multivibrator.

    Trigging of IC1 causes pin 3 to go high and it remains high for a certain time period depending

    on the selected values of R7 and C3. This on time (T) of IC1 can be calculated using thefollowing relationship:



    where R7 is in ohms and C3 in microfarads.

    On first clap, output pin 3 of IC1 goes high and remains in this standby position for the preset

    time. Also, LED1 glows for this period. The output of IC1 provides supply voltage to IC2 at its

    pins 8 and 4.

    Now IC2 is ready to receive the triggering signal. Resistor R10 and capacitor C7 connectedto pin 4 of IC2 prevent false triggering when IC1 provides the supply voltage to IC2 at first clap.

    On second clap, a negative pulse triggers IC2 and its output pin 3 goes high for a time period

    depending on R9 and C5. This provides a positive pulse at clock pin 14 of decade counter IC4017 (IC3). Decade counter IC3 is wired here as a bistable. Each pulse applied at clock pin 14

    changes the output state at pin 2 (Q1) of IC3 because Q2 is connected to reset pin 15. The high

    output at pin 2 drives transistor T2 and also energises relay RL1. LED2 indicates activation of

    relay RL1 and on/off status of the appliance. A free-wheeling diode (D1) prevents damage of T2when relay de-energises.

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  • 8/8/2019 Prjct Report




    This circuit is used for easy switching purpose.


    R1 ,R5 3.3K

    R2 4.7KR3 2.2MR4,R7 270K

    R8,R12 1K

    R9 100KR6,R10,R13 10K

    R11 470K


    C1,C4,C5,C6 0.01 UF

    C2 0.1 UF

    C3 10 UF/25 VC7 2.2 UF/15 V


    Q1,2,3,4 BC 149

    D1 IN 4002

    D2,3,4,5 IN 4148


    CONDENSER MICRELAY 12V single charge over relay:

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    This circuit can be used to switch on and off a light, a fan, a radio or a t.v. by the sound of a



    The clap activated switching device function properly by responding to both hand claps at aboutthree to four meter away and finger tap sound at very close range, since both are low frequency

    sounds and produce the same pulse wave features. The resulting device is realizable, has good

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    reliability and its relatively inexpensive. This circuit turns on and off a light, a fan, a radio, a t.v.

    etc using this converted electrical energy which is used to turn on relay (an electronic switch).


    1.Timer (NE555)

    2.Counter IC (HCF4017B)

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    3.NPN Transistor



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