mini porject

8/8/2019 Mini Porject

1/38

1

A

MINI PROJECT

REPORT ON

MOBILE BUG

Submitted in partial fulfillment

of the requirement for

BACHELOR DEGREEIN

ELECTRONICS & COMMUNICATION

2010-2011

Guided by:-

Md. YUSUF

SUBMITTED BY:-1. KAUSHAL KR. SINGH -0701931040

2. KHUSHBU GUPTA - 0701931041

3. KM. ARTI TEOTIA- 0701931042


2/38

2

ACKNOWLEDGEMENT

A lot of effort has gone into the report and my thanks are due to many people

without whom this report wouldnt been possible. First of all, I gratefully

acknowledge the continuous assistance and inspiration given to me by my

college faculty. I would like to thank my family for providing me monetary and

non-monetary support, as and when required. My gratitude also goes to the

IEEE website, via internet, which gave me lots of fruitful information, about the

proposed topic. . Finally I would like to thanks Md. YUSUF, in charge

withoutwhom this would not have been completed in time.

- Kaushal kr. SinghKhushbu guptaKm. Arti teotia


3/38

3

Contents

S

no.

Description Page no.

1 Introduction 4

2 Circuit description 5-13

3 Definition of pin function 14-22

4 Operating modes 23-27

5 Comparison between 555 & 7555 timer 28

6 A stable operation 29-31

7 Required parts 32-36

s8 Precautions 37


4/38

4

INTORDUCTION

Q.1:- What is mobile bug????

Th is h andy, pocket-size mobile transmission detector can sense t h e presence of an activated mobile p h one from a distance of one and a- h alf meters.

Q.2:- Where is mobile bug used????

It can be used to prevent use of mobile p h ones in examination h alls, confidential

rooms, etc. It is also useful for detecting t h e use of mobile p h one for spying and

unaut h orized video transmission.

Th e circuit can detect bot h th e incoming and outgoing calls, SMS andvideo

transmission even if t h e mobile p h one is kept in t h e silent mode.

y Th e moment t h e bug detects RF transmission signal from an activated

mobile p h one, it starts sounding a beep alarm and t h e LED blinks.

y Th e alarm continues until t h e signal transmission ceases.

y An ordinary RF detector using tuned LC circuits is not suitable for detecting

signals in t h e GHz frequency band used in mobile p h ones.

y Th e transmission frequency of mobile p h ones ranges from 0.9 to 3 GHz

wit h a wavelengt h of 3.3 to 10 cm. So a circuit detecting giga h ertz signals is

required for a mobile bug.


5/38

5

Circuit description:-

y O P-amp IC CA3130 (IC1) is used in t h e circuit as a current-to-voltageconverter wit h capacitor C3 connected between its inverting and non-

inverting inputs.

y It is a CMOS version using gate-protected p-c h annel MOSFET transistors inth e input to provide very h igh input impedance, very low input current and

very h igh speed of performance.

y Th e output CMOS transistor is capable of swinging t h e output voltage towit h in 10 mV of eit h er supply voltage terminal.

y Capacitor C3 in conjunction wit h th e lead inductance acts as a transmissionline t h at intercepts t h e signals from t h e mobile p h one.

y Th is capacitor creates a field, stores energy and transfers t h e stored energyin t h e form of minute current to t h e inputs of IC1.

y Th is will upset t h e balanced input of IC1 and convert t h e current into t h ecorresponding output voltage.

y Capacitor C4 along wit h h igh -value resistor R1 keeps t h e non-invertinginput stable for easy swing of t h e output to h igh state.

y Resistor R2 provides t h e disc h arge pat h for capacitor C4. Feedback resistor

R3 makes t h e inverting input h igh wh en t h e output becomes h igh .

y Capacitor C5 (47p F) is connected across strobe (pin 8) and null inputs

(pin 1) of IC1 for p h ase compensation and gain control to optimize t h e

frequency response.


6/38

6

y Wh en t h e mobile p h one signal is detected by C3, t h e output of IC1

becomes h igh and low alternately according to t h e frequency of t h e signal

as indicated by LED1.

y Th is triggers mono-stable timer IC2 t h roug h capacitor C7 .

y Capacitor C6 maintains t h e base bias of transistor T1 for fast switc h ing

action.

y Th e low-value timing components R6 and C9 produce very s h ort time delay

to avoid audio nuisance.

y Assemble t h e circuit on a general purpose PCB as compact as possible and

enclose in a small box like junk mobile case.

y carefully solder t h e capacitor C3 in standing position wit h equal spacing of

th e leads.

y Th e response can be optimized by trimming t h e lead lengt h of C3 for t h e

desired frequency.

y You may use a sh ort telescopic type antenna .

y U se t h e miniature 12V battery of a remote control and a small buzzer to

make t h e gadget pocket-size.

y Th e unit will give t h e warning indication if someone uses mobile p h one

wit h in a radius of 1.5 meters.


7/38

7

CIRCUIT DIAGRAM


8/38

8

y Th e 555 timer IC was first introduced around 1971 by t h e Signe

tics Corporation as t h e SE555/NE555 and was called " Th e IC Time

Mac h ine " and was also t h e very first and only commercial timer IC

available.

y Th is device was first made commercially available.

y Th e past ten years some manufacturers stopped making t h ese

timers because of competition or ot h er reasons. Yet ot h er

companies, like NTE (a subdivision of P h ilips) picked up w h ere

some left off.

y Alth oug h th ese days t h e CMOS version of t h is IC, like t h e

Motorola MC1455, is mostly used, t h e regular type is still

available.

y But all types are pin-for-pin plug compatible. Every time we can

see t h is 555 timer used in advanced and h igh -tec h electronic

circuits. It is just incredible.

y Here we will s h ow you w h at exactly t h e 555 timer is.

y Th is timer uses a maze of transistors, diodes and resistors and for

th is complex reason we will use a more simplified (but accurate)

block diagram to explain t h e internal organizations of t h e 555.

y So, let s start slowly and build it up from t h ere.

y Th e first type-number represents t h e type w h ich was/is preferred for

military applications w h ich h ave somew h at improved electrical and t h ermal

ch aracteristics, but also a bit more expensive, and usually metal-can or

ceramic casing.


9/38

9

y Th is is analogous to t h e 5400/7400 series convention for TTL integrated

circuits.

y Th e 555 come in two packages, eit h er t h e round metal-can called t h e ' T '

package or t h e more familiar 8-pin DIP ' V' package . About 20-years ago t h e

metal-can type was pretty muc h th e standard (SE/NE types).

y Th e 556 timer is a dual 555 version and comes in a 14-pin DIP package, t h e

558 is a quad version wit h four 555's also in a 14 pin DIP case.


10/38

10

I nside the 555 timer, at fig. 3, are the equivalent of over 20 transistors, 15

resistors, and 2 diodes, depending of the manufacturer.


11/38

11

y Th e Th res h old current determine t h e maximum value of Ra + R b. For 15

volt operation t h e maximum total resistance for R (Ra +Rb) is 20 Mega-

oh m.

y Th e supply current, w h en t h e output is ' h igh ', is typically 1 milli-amp (mA)

or less.

y Th e initial mono-stable timing accuracy is typically wit h in 1% of its

calculated value, and

y Exh ibits negligible (0.1%/V) drift wit h supply voltage.

y Th e temperature variation is only 50ppm/C (0.005%/C).

Some of t h e more attractive features of t h e 555 timer are :-

Supply voltage between 4.5 and 18 volt,

Supply current 3 to 6 mA,

A rise/Fall time of 100 nSec.

It can also wit h stand quite a bit of abuse.


12/38

12

y it takes a finite period of time for a capacitor (C) to c h arge or disc h arge

th roug h a resistor (R).

y Th ose times are clearly defined and can be calculatedwit h th e given values

of resistance and capacitance.T h e basic RC c h arging circuit is sh own in fig.

4.

y Assume t h at t h e capacitor is initially disc h arged. Wh en t h e switc h is closed,

th e capacitor begins to c h arge t h roug h th e resistor. T h e voltage across t h e

capacitor rises from zero up to t h e value of t h e applied DC voltage.


13/38

13

y Th e c h arge curve for t h e circuit is s h own in fig.6. T h e time t h at it takes for

th e capacitor to c h arge to 63.7% of t h e applied voltage is known as t h e

time constant (t) .

y Th at time can be calculated wit h th e simple expression :

t = R X C

Assume a resistor value of 1 MegaO h m and a capacitor value of 1uF (micro-

Farad). T h e time constant in t h at case is :

t = 1,000,000 X 0.000001 = 1 second

y Assume furt h er t h at t h e applied voltage is 6 volts. T h at means t h at it will

take one time constant for t h e voltage across t h e capacitor to reac h

63.2% of t h e applied voltage. T h erefore, t h e capacitor c h arges to

approximately 3.8 volts in one second.

F ig. 4-1, Change in the input pulse frequency allows completion of thetiming cycle.


14/38

14

As a general rule, t h e mono-stable 'ON' time is set approximately 1/3

longer t h an t h e expected time between triggering pulses. Suc h a circuit is

also known as a Missing Pulse Detector .

Looking at t h e curve in fig. 6. You can see t h at it takes approximately 5

complete time constants for t h e capacitor to c h arge to almost t h e applied

voltage. It would take about 5 seconds for t h e voltage on t h e capacitor to

rise to approximately t h e full 6-volts.

Definition of Pin Functions:

Pin 1 (Ground):Th e ground (or common) pin is t h e most-negative supplypotential of t h e device, w h ich is normally connectedto circuit common (ground)

Wh en operated from positive supply voltages.

Pin 2 (Trigger): y Triggering is accomplis h ed by taking t h e pin from above to below a

voltage

y Sensitive, allowing slow rate-of-c h ange waveforms, as well as pulses, to

be used level of 1/3 V+ (or, in general, one- h alf t h e voltage appearing at

pin 5).

y Th e action of t h is pin is t h e input to t h e lower comparator and is used to

set t h e latc h , w h ich in turn causes t h e output to go h igh . Th is is t h e

beginning of t h e timing sequence in mono-stable operation.


15/38

15

y Trigger input is level-as trigger sources. T h e trigger pulse must be of

sh orter duration t h an t h e time interval determined by t h e external R and

C.

y If th is pin is h eld low longer t h an t h at, t h e output will remain h igh until

th e trigger input is driven h igh again. One precaution t h at s h ould be

observed wit h th e trigger input signal is t h at it must not remain lower

th an 1/3 V+ for a period of time longer th an t h e timing cycle.

y If th is is allowed to h appen, t h e timer will re-trigger itself upon

termination of t h e first output pulse. T h us, w h en t h e timer is driven in

th e mono-stable mode wit h input pulses longer t h an t h e desired output

pulse widt h , t h e input trigger s h ould effectively be s h ortened by

differentiation.

y If th e minimum-allowable pulse widt h for triggering is greater t h an t h e

1uS (micro-Second), triggering will be reliable.

y In practice, t h e minimum mono-stable output pulse widt h sh ould be in

th e order of 10uS to prevent possible double triggering due to t h is effect.

Th e voltage range t h at can safely be applied to t h e trigger pin is between

V+ and ground .

y For a-stable configuration operating at V+ = 5 volts, t h is resistance is 3

Mega-o h m; it can be current, termed t h e trigger current , must also flow

from t h is terminal into t h e external circuit. T h is current is typically

500nAgreater for h igh er V+ levels.


16/38

16

Pin 3 (Output):

y Th e output of t h e 555 comes from a h igh -current totem-pole stage

made up of transistors Q20 - Q24. Transistors Q21 and Q22 provide drive

for source-type loads, and t h eir Darlington connection provides a h igh -

state output voltage about 1.7 volts less t h an t h e V+ supply level used.

y Transistor Q24 h as a low saturation voltage, w h ich allows it to interface

directly, wit h good noise margin, w h en driving current-sinking logic.

y High -state level is typically 3.3 volts at V+ = 5 volts; 13.3 volts at V+ = 15

volts. Bot h th e rise and fall times of t h e output waveform are quite fast,

typical switc h ing times being 100nS. T h e state of t h e output pin will

always reflect t h e inverse of t h e logic state of t h e latc h , and t h is fact may

be seen by examining Fig. 3.

y To trigger t h e output to a h igh condition, t h e trigger input is

momentarily taken from a h igh er to a lower level. [see "Pin 2 - Trigger"].

Th is causes t h e latc h to be set and t h e output to go h igh .

y Actuation of t h e lower comparator is t h e only manner in w h ich th e

output can be placed in t h e h igh state.

y Th e output can be returned to a low state by causing t h e t h res h old to go

from a lower to a h igh er level [see "Pin 6 - T h res h old"], w h ich resets t h e

latc h .

y Th e output can also be made to go low by taking t h e reset to a low state

near ground [see "Pin 4 - Reset"]. T h e output voltage available at t h is pin

is approximately equal to t h e Vcc applied to pin 8 minus 1.7V.


17/38

17

Pin 4 (Reset):y Th is pin is also used to reset t h e latc h and return t h e output to a low

state. T h e reset voltage t h res h old level is 0.7 volt, and a sink current of

0.1mA from t h is pin is required to reset t h e device. T h ese levels are

relatively independent of operating V+ level; t h us t h e reset input is TTL

compatible for any supply voltage.

y Th e reset input is an overriding function; t h at is, it will force t h e output to

a low state regardless of t h e state of eit h er of t h e ot h er inputs. It mayth us be used to terminate an output pulse prematurely, to gate

oscillations from "on" to "off", etc.

y Delay time from reset to output is typically on t h e order of 0.5 S, and

th e minimum reset pulse widt h is 0.5 S. Neit h er of t h ese figures is

guaranteed, h owever, and may vary from one manufacturer to anot h er.

y In s h ort, t h e reset pin is used to reset t h e flip-flop t h at controls t h e stateof output pin 3. T h e pin is activated w h en a voltage level anyw h ere

between 0 and 0.4 volt is applied to t h e pin.

y Th e reset pin will force t h e output to go low no matter w h at state t h e

ot h er inputs to t h e flip-flop are in. Wh en not used, it is recommended

th at t h e reset input be tied toV+ to avoid any possibility of false resetting.


18/38

18

Pin 5 (Control Voltage):y Th is pin allows direct access to t h e 2/3 V+ voltage-divider point, t h e

reference level for t h e upper comparator. It also allows indirect access to

th e lower comparator, as t h ere is a 2 :1 divider (R8 - R9) from t h is point to

th e lower-comparator reference input, Q13.

y U se of t h is terminal is t h e option of t h e user, but it does allow extreme

flexibility by permitting modification of t h e timing period, resetting of t h e

comparator, etc. Wh en t h e 555 timer is used in a voltage-controlled

mode, its voltage-controlled operation ranges from about 1 volt less t h an

V+ down to wit h in 2 volts of ground (alt h oug h th is is not guaranteed).

Voltages can be safely applied outside t h ese limits, but t h ey s h ould be

confined wit h in t h e limits of V+ and ground for reliability.

y By applying a voltage to t h is pin, it is possible to vary t h e timing of t h e

device independently of t h e RC network.

Mono-stable mode

y Th e control voltage may be varied from 45 to 90% of t h e Vcc, making it

possible to control t h e widt h of t h e output pulse independently of RC.

A-stable mode

y Th e control voltage can be varied from 1.7V to t h e full Vcc. Varying t h e

voltage in th

e a-stable mode will produce a frequency modulated (FM)output.

y In t h e event t h e control-voltage pin is not used, it is recommended t h at it

be bypassed, to ground, wit h a capacitor of about 0.01uF (10nF) for

immunity to noise, since it is a comparator input.


19/38

19

y Th is fact is not obvious in many 555 circuits since I h ave seen many

circuits wit h 'no-pin-5' connected to anyt h ing, but t h is is t h e proper

procedure. T h e small ceramic cap may eliminate false triggering.

Pin 6 (Threshold): y Pin 6 is one input to t h e upper comparator (t h e ot h er being pin 5) and is

used to reset t h e latc h , wh ich causes t h e output to go low. Resetting via

th is terminal is accomplis h ed by taking t h e terminal from below to above

a voltage level of 2/3 V+ (t h e normal voltage on pin 5).

y Th e action of t h e t h res h old pin is level sensitive, allowing slow rate-of-

ch ange waveforms.

y Th e voltage range t h at can safely be applied to t h e t h res h old pin is

between V+ and ground. A dc current, termed t h e threshold current,

must also flow into t h is terminal from t h e external circuit.

y Th is current is typically 0.1A, and will define t h e upper limit of total

resistance allowable from pin 6 to V+.

y For eit h er timing configuration operating at V+ = 5 volts, t h is resistance is

16 Mega-o h m.

y For 15 volt operation, t h e maximum value of resistance is 20 MegaO h ms.

Pin 7 (Discharge): y Th is pin is connected to t h e open collector of a npn transistor (Q14), t h e

emitter of w h ich goes to ground, so t h at w h en t h e transistor is turned

"on", pin 7 is effectively s h orted to ground.


20/38

20

y U sually t h e timing capacitor is connected between pin 7 and ground and

is disc h arged w h en t h e transistor turns "on".

y Th e conduction state of t h is transistor is identical in timing to t h at of t h e

output stage. It is "on" (low resistance to ground) w h en t h e output is low

and "off" ( h igh resistance to ground) w h en t h e output is h igh .

y In bot h th e mono-stable and a-stable time modes, t h is transistor switc h

is used to clamp t h e appropriate nodes of t h e timing network to ground.

Pin 8 (V +) :

y Th e V+ pin (also referred to as V cc) is t h e positive supply voltage terminal of

th e 555 timer IC.

y Supply-voltage operating range for t h e 555 is +4.5 volts (minimum) to +16

volts (maximum), and it is specified for operation between +5 volts and +

15 volts.

y Actually, t h e most significant operational difference is t h e output drivecapability, w h ich increases for bot h current and voltage range as t h e supply

voltage is increased.

y Th ere are special and military devices available t h at operate at voltages as

h igh as 18 V.


21/38

21

T he simple 555 testing-circuit is shown in F ig. 5. to test all 555 timer ic's.

y U se as a trouble shooter in 555 based circuits. T his tester will quickly tell you

if the timer is functional or not. Although not foolproof, it will tell if the 555

is shorted or oscillating.

y If both Led's are flashing the timer is most likely in good working order. If

one or both Led's are either off or on solid the timer is defective.


22/38

22

T he capacitor slows down as it charges, and in actual fact never reaches the full

supply voltage. T hat being the case, the maximum charge it receives in the timing

circuit (66.6% of the supply voltage) is a little over the charge received after a time

constant (63.2%).


23/38

23

T he capacitor slows down as it discharges, and never quite reaches the ground

potential. T hat means the minimum voltage it operates at must be greater than

zero. T iming circuit is 63.2% of the supply voltage.

T he discharge of a capacitor also takes time and we can shorten the amount of

time by decreasing resistance (R) to the flow of current.

Operating Modes:

y Th e 555 timer h as two basic operational modes :

1 .One shot mode .

2. A-stablemode .

1.one-s h ot mode -- Th e 555 acts like a mono-stable multivibrator. A mono-

stable is said to h ave a single stable state--t h at is t h e off state. Wh enever it is


24/38

24

triggered by an input pulse, t h e mono-stable switc h es to its temporary state.

It remains in t h at state for a period of time determined by an RC network.It

th en returns to its stable state.

y In ot h er words, t h e mono-stable circuit generates a single pulse of a fixed

time duration eac h time it receives and input trigger pulse. T h us th e name

one-s h ot .

y One-s h ot multivibrators are used for turning some circuit or external

component on or off for a specific lengt h of time.

y It is also used to generate delays. Wh en multiple one-s h ots are cascaded, a

variety of sequential timing pulses can be generated.

2. A-stable mode-

y A-stable multivibrator is simply and oscillator. T h e a-stable multivibrator

generates a continuous stream of rectangular off-on pulses t h at switc h

between two voltage levels. T h e frequency of t h e pulses and t h eir duty

cycle are dependent upon t h e RC network values.

O ne-S h ot O peration :

y Fig. 4 s h ows t h e basic circuit of t h e 555 connected as a mono-stable

multivibrator. An external RC network is connected between t h e supply

voltage and ground. T h e junction of t h e resistor and capacitor is connected to

th e t h res h old input w h ich is t h e input to t h e upper comparator. T h e internal

disc h arge transistor is also connected to t h e junction of t h e resistor and t h e

capacitor.


25/38

25

y An input trigger pulse is applied to t h e trigger input, w h ich is t h e input to

th e lower comparator. W ith th at circuit configuration, t h e control flip-flop is

initially reset. T h erefore, t h e output voltage is near zero volts. T h e signal from

th e control flip-flop causes T1 to conduct and act as a s h ort circuit across t h e

external capacitor.

y For t h at reason, t h e capacitor cannot c h arge. During t h at time, t h e input to

th e upper comparator is near zero volts causing t h e comparator output to

keep t h e control flip-flop reset.

Mono-stable mode:

y Th e 555 in fig. 9a is s h own h ere in its utmost basic mode of operation;

as a triggered mono-stable. One immediate observation is t h e extreme

simplicity of t h is circuit. Only two components to make up a timer, a

capacitor and a resistor.

y And for noise immunity maybe a capacitor on pin 5.


26/38

26

y Wh at 'bounce' is: bounce is a type of fast, s h ort term noise caused by a

switc h , relay, etc. and t h en picked up by t h e input pin.

y Th e trigger input is initially h igh (about 1/3 of +V). Wh en a negative-

going trigger pulse is applied to t h e trigger input (see fig. 9a), t h e

th res h old on t h e lower comparator is exceeded.

y Th e lower comparator, t h erefore, sets t h e flip-flop. T h at causes T1 to

cut off, acting as an open circuit. T h e setting of t h e flip-flop also causes

a positive-going output level w h ich is t h e beginning of t h e output

timing pulse.

y Th e capacitor now begins to c h arge t h roug h t h e external resistor. As

soon as t h e c h arge on t h e capacitor equal 2/3 of t h e supply voltage, t h e

upper comparator triggers and resets t h e control flip-flop. T h at

terminates t h e output pulse w h ich switc h es back to zero.

y At t h is time, T1 again conducts t h ereby disc h arging t h e capacitor. If a

negative-going pulse is applied to t h e reset input w h ile t h e output pulse

is h igh , it will be terminated immediately as t h at pulse will reset t h e

flip-flop.

y Wh enever a trigger pulse is applied to t h e input, t h e 555 will generate

its single-duration output pulse. Depending upon t h e values of external

resistance and capacitance used, t h e output timing pulse may be

adjusted from approximately one millisecond to as h igh as on h undred

seconds.

y IC timers are normally used w h ere long output pulses are required.


27/38

27

y In t h is application, t h e duration of t h e output pulse in seconds is

approximately equal to :

T = 1.1 x R x C (in seconds)

y Th e output pulse widt h is defined by t h e above formula. T h ere isactually no t h eoretical upper limit on T (output pulse widt h ), only

practical ones. T h e lower limit is 10uS. You may consider t h e range of T

to be 10uS to infinity.

y A reasonable lower limit for R(t) is in t h e order of about 10Kilo o h mandt h e upper limit for R(t) is in t h e order of about 15 Mega o h m

y A practical minimum for C(t) is about 95pF.

y Th ere are several different types of 555 timers.

y Th e LM555 from National is t h e most common one t h ese days.

y Th e Exar XR-L555 timer is a micro-power version of t h e standard 555

offering a direct, pin-for-pin (also called plug-compatible) substitute

device with

an advantage of a lower power operation.y Maxim's ICM7555, and Sanyo's LC7555 models are a low-power,T h e

internal sc h ematic of t h e 7555 (not s h own) is h owever totally different

from t h e normal 555 version.

y Th is very versatile version s h ould be considered w h ere a wide range of

timing is desired, as well as low power operation appears to be

important in t h e particular design.y A couple years after Intersil, Texas Instruments came on t h e market

wit h anot h er cmos variation called t h e LINCMOS (LINear CMOS) or

Turbo 555.


28/38

28

y Th e cmos version is t h e c h oice for battery powered circuits.

y However, t h e negative side for t h e cmos 555's is t h e reduced outputcurrent, bot h for sink and source, but t h is problem can be solved by

adding a amplifier transistor on t h e output if so required.

Comparison between 555 and 7555 timer -- y Th e regular 555 can easily deliver a 200mA output versus 5 to 50mA for

th e 7555. y On t h e workbenc h th e regular 555 reac h ed a limited output frequency

of 180K h z wh ile t h e 7555 easily surpassed t h e 1.1M h z mark and t h e

TLC555 stopped at about 2.4M h z.


29/38

29

A- stable operation:

y Figure 9b s h ows t h e 555 connected as an a-stable multivibrator. Bot h t h e

trigger and t h res h old inputs (pins 2 and 6) to t h e two comparators are

connected toget h er and to t h e external capacitor. T h e capacitor c h arges

toward t h e supply voltage t h roug h t h e two resistors, R1 and R2. T h e

disc h arge pin (7) connected to t h e internal transistor is connected to t h e

junction of t h ose two resistors.

y Wh en power is first applied to t h e circuit, t h e capacitor will be unc h arged,

th erefore, bot h t h e trigger and t h res h old inputs will be near zero volts (see

Fig. 10). T h e lower comparator sets t h e control flip-flop causing t h e output

to switc h h igh . Th at also turns off transistor T1.

y Th at allows t h e capacitor to begin c h arging t h roug h R1 and R2. As soon as

th e c h arge on t h e capacitor reac h es 2/3 of t h e supply voltage, t h e


30/38


31/38

31

Th e frequency of operation of t h e a-stable circuit is dependent upon t h e

values of R1, R2, and C. T h e frequency can be calculated wit h th e formula :

f = 1/(.693 x C x (R1 + 2 x R2))

y Th e Frequency f is in Hz, R1 and R2 are in o h ms, and C is in farads.

Th e time duration between pulses is known as t h e 'period', and usually

designated wit h a 't'. T h e pulse is on for t1 seconds, t h en off for t2 seconds.

Th e total period (t) is t1 + t2 (see fig. 10).T h at time interval is related to t h e

frequency by t h e familiar relations h ip:

f = 1/tort = 1/f

y Th e time intervals for t h e on and off portions of t h e output depend upon

th e values of R1 and R2. T h e ratio of t h e time duration w h en t h e output

pulse is h igh to t h e total period is known as t h e duty-cycle. T h e duty-cycle

can be calculated wit h th e formula :

D = t1/t = (R1 + R2) / (R1 + 2R2)

You can calculate t1 and t2 times wit h th e formulas below :

t1 = .693(R1+R2)Ct2 = .693 x R2 x C

y Th e 555, w h en connected as s h own in Fig. 9b, can produce duty-cycles inth e range of approximately 55 to 95%. A duty-cycle of 80% means t h at t h e

output pulse is on or h igh for 80% of t h e total period. T h e duty-cycle can

beadjusted by varying t h e values of R1 and R2.


32/38


33/38

33

CAPACITOR:--

y Capacitance is t h e property of opposition to a c h ange in voltage.

Capacitance h as t h e same reaction to voltage as t h e inductance h as to t h ecurrent. T h at is t h e voltage across circuit increases. Capacitor will resist

th e c h ange and if t h e voltage applied to a circuit is decreased and try to

maintain t h e original voltage.

y Th e property of capacitor is to store c h arge and release. T h e storing

capacity of capacitor is depend upon t h e value of capacitor as defined in

micro farad.A basic capacitor consist of two conducting metalplatesseparated by a layer of air or ot h er insulating material. T h e insulating layer

is called dielectric layer. All capacitor h ave two plates and separating layer.

y In practice t h e dielectric layer are often staked and even rolled into

compact form.

y Th e capacitor areas classified by t h e name of dielectric used in t h e

particular.

1. Paper capacitor

2. Mica capacitor

3. Ceramic capacitor

4. Electrolytic capacitor

All electrolytic capacitors are above 1 micro farad. All electrolytic capacitor

h aving two legs one is positive and second is negative , bigger leg is positive and

smaller leg is negative.


34/38

34

RESISTANCE: -

Th e unit being o h m t h e greater t h e o h mic value t h e greater is t h e opposition to

th e flow of current causes. T h e h eating effect and causes a loss of electrical

energy in t h e form of h eat energy, greater t h e o h mic value greater t h e loss.

TYPES OF RESISTANCE :-

1. F ixed value

2. Variable value

Normally fixed type of resistance are carbon resistance value of resistance in o h m

printed on t h e body of resistance in color code.

TRANSISTOR :-

y Transistor are tiny semiconductor device t h at provide current amplification.

A transistor h as t h ree leads identified as emitter Base and collector. A small

current to say 1mA flowing between base and emitter produce a large

current of 100ma or more in t h e widely used as a current amplifier circuit

transistor are also very useful in switc h ing circuit.

y W e use normally two type of transistor one is NPN and second in PNP. InPNP transistor conduction is conducting between emitter and collector wit h

th e h elp of electron flow. In PNP transistor conduction is conducting

between emitter and collector wit h th e h elp of h oles.


35/38

35

y W e normally give a forward bias to t h e emitter point and reverse bias to

th e collector point wit h t h e h elp of load resistance and for t h e base point .

W e give a very low voltage by resistance or any ot h er circuit control

devices.

SPEAKER :-

y Th e simply speaker c h anges electric audio energy into sound. T h e speaker

is a transducer.One in a family of devices w h ich converts energy from one

from into anot h er.

y Th e speaker in greatest use today is t h e permanent-magnet(pm) dynamic

speaker.

y Electromagnetic dynamic - Speakers are no longer used ,alt h oug h th ey

were very popular early in t h e development of audio systems.Dynamic

speakers are similar in operation. T h ey differ in met h od used to obtain t h e

stationary or static magnet field.

y Permanent magnet speaker - A permanent magnet concentrates a

magnetic field at t h e pole pieces of a h igh ly permeable h ousing. T h e pole

pieces are very close toget h er to obtain an intense magnetic field. A voice

coil cemented to t h e speaker cone is freely suspended between t h e

magnetic poles.

y A flexible membrane called t h e spider is attracted to t h e voice-coil form

sand cemented to t h e speaker frame. T h e spider centers t h e voice coil form

between t h e speaker poles keep it from rubbing against t h em. T h e flared

end of t h e cone is flexibly attac h ed to t h e speaker frame.


36/38

36

y Th e permanent magnet of a pm speaker is made of a mixture of aluminum,

nickel and cobalt and is called an alnico magnet.T h e audio-signal currents

led to t h e voice coil set up a moving magnetic field about t h e voice coil.

Th is interacts wit h th e fixed magnetic field and result in a vibratory motion

of t h e voice coil and h ence ossf t h e speaker cone.

y Th e rate of vibration of t h e speaker cone is determined by t h e frequency of

th e audio current. T h e amplitude of vibration i.e. h ow far t h e cone depends

on t h e amplitude of audio current. T h e speaker cone moves t h e air mass

surrounding it producing sound.

y Connections from t h e voice coil ends are broug h t to insulated solder

terminals on t h e speaker frame. Wh en output transformer are used to

matc h t h e impedance of t h e last audio amplifier to t h at of t h e speaker t h e

transformer may be mounted on t h e amplified classis .Leads from t h e

secondary of t h e output transformer are t h en connected to t h e voice coil at

th e solder terminals on t h e frame.

y A continuity c h eck may be made on t h e voice coil of a dynamic speaker.

Th e resistance is very low, usually 3 or 4o h m alt h oug h in some solid state

amplifier driven speakera it may be as 32o h m.Th e continuous motion of

th e voice coil may be cause t h e coil wire to break,resulting in an open

voice coil .T h is would c h eck as an infinite.


37/38

37

PRECAUTIONS :---

1. Mount t h e components at t h e appropriate places before soldering. Follow t h e

circuit description and components details, leads identification etc.2. Do not start soldering before making it confirm t h at all t h e component are

mounted at t h e rig h t place.

3. Do not use a spread solder on t h e board, it may cause s h ort circuit.

3. Do not sit under t h e fan w h ile soldering.

4. Position t h e board so t h at gravity tends to keep t h e solder w h ere you want it.5. Do not over h eat t h e components at t h e board. Excess h eat may damage t h e

components or board.

6. Th e board s h ould not vibrate w h ile soldering ot h erwise you h ave a dry or a

cold joint.

7. Do not put t h e kit under or over voltage source. Be sure abort t h e voltage

eit h er do or ac w h ile operating t h e gadget.8. Do spare t h e bare ends of t h e components leads ot h erwise it may s h ort circuit

wit h th e ot h er components. To prevent t h is use sleeves at t h e components

leads or use sleeved wire for connections.

9. Do not use old dark color solder. It may give dry joint. Be sure t h at all t h e joints

are clean and well s h iny.

10 . Do make loose wire connections specially wit h cell h older, speaker, probes

etc. Put knots w h ile connections to t h e circuit board, ot h erwise it may get loose.


38/38

mini porject

Documents