555 Astable Monostable multivibrator

8/11/2019 555 Astable Monostable multivibrator

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Experiment No. 9 555 timer and its Applications

Aim: To design and study the 555 timer in astable and monostable modesTo study the application of 555 timer as FS generator and pulse !idth

modulator

E"uipments and components re"uired: 555 timer# resistors# capacitors# breadboard#function generator# $%&. 'o!er supply

Theory:

ASTA()E *+)T,-,(%AT&%Figure shows the circuit diagram of a 555 Timer connected in Astable Mode. The pin number 8

and 4 th pin are shorted and given to power supply. The reset pin is connected to power supply toavoid accidental resets. The pin number 1 is grounded. ince the control pin !5" is not used it isgrounded through #.#1 $F to avoid high fre%uency noises. A resistance

A R is connected between

reset and discharge pins and resistance B R is connected between the pins discharge andthreshold. ince no e&ternal trigger is re%uired the trigger pin is connected to threshold and acapacitor which determines the output of the timer is connected to threshold pin. The other end of the capacitor is grounded. .. ince the 'ontrol (oltage pin !pin 5" is not used the comparator reference voltages will be )*+ (cc and 1*+ (cc respectively. o the output of the 555 will set!goes high" when the capacitor voltage goes below 1*+ (cc and output will reset !goes low" whenthe capacitor voltage goes above )*+ (cc

Figure shows the circuit diagram of a 555 Timer wired in Astable Mode. 8th pin and 1st pin of the,' are used to give power- (cc and /0 respectively. The 4th pin is 2 2T pin which is activelow and is connected to (cc to avoid accidental resets. 5th pin is the 'ontrol (oltage pin which isnot used. o to avoid high fre%uency noises it is connected to a capacitor '3 whose other end isconnected to ground. sually '3 #.#1$F. The Trigger !pin )" and Threshold !pin 6" inputs areconnected to the capacitor which determines the output of the timer. 0ischarge pin !pin 7" isconnected to the resistor B R such that the capacitor can discharge through b. 0iode 0

connected in parallel to B R is only used when an output of duty cycle less than or e%ual to 5#is re%uired. For the sa9e of e&plaing the wor9ing 'ircuit 0iagram with ,nternal :loc9 diagram isshown below. ince the 'ontrol (oltage !pin 5" is not used the comparator reference voltages will

be )*+ (cc and 1*+ (cc respectively. o the output of the 555 will goes high when the capacitor voltage goes below 1*+ (cc and output will goes low when the capacitor voltage goes above )*+(cc


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;hen the circuit is switched


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The time period of the rectangular waveform is e%ual to the sum of charging and discharging timeof the capacitor. >et the charging time of capacitor is ct and the discharging time of the capacitor

is d t . Then c d T t t = +0uring charging time the initial voltage across capacitor is * +ccV . The capacitor starts charging

to applied voltage ccV through A B R R+ . :ut at time ct where the voltage across capacitor ise%ual to ) * +ccV the change of state occurs.0uring charging the voltage across capacitor is given by

( ) * !1"

B

+)+

t RC c f i f

CC i f CC

CC c c

V V V V e

V V V V

V V at t t

= +

= =

= =

( )*! "

*! "

1

)+ +

)+ +

#.6C+! "

c A B

c A B

t R R C CC CC CC CC

t R R C CC CC

c A B

Substituting the value in the above equation

V V V V e

V V e

t R R C

+

+

= +

=

= +

imilarly during discharging time the initial voltage across capacitor is ) * +ccV . The capacitor starts discharging to ero voltage through B R . :ut at time d t where the voltage across capacitor

is e%ual to * +ccV the change of state occurs


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1## 1##

1##

)

c on d off

c on

A B

A B

if t T and t T

t T Duty cycle

T T R R

R R

= =

= =

+= + ( )

*! "

*! "

1

)# #

+ +)

+ +#.6C+! "

d B

d B

t R C CC CC

t R C CC CC

d B


V V e

V V e

t R C

= +

=

=c d T t t = +

#.6C+! " #.6C+

#.6C+! ) "1 1 1.44

#.6C+! ) " ! ) "

A B B

A B

A B A B

T R R C R C

R R C

f T R R C R R C

= + += += = =+ +

The duty cycle is given by

1## 1##

1##)

c on d off

c on

A B

A B

if t T and t T

t T Duty cycle

T T R R

R R

= =

= =

+= +

esign:0esign an astable multivibrator that generates a rectangular waveform of 1 D= fre%uency with6# duty cycle.

iven 0 6#

1## 6#)

#.6)

)

A B

A B

A B

A B

B A

R R D

R R

R R R R

R R

+= =++ =+

=

1.441

! ) "

1.441

!5 "

#.1

A B

A

f KHz R R C

KHz R C

let C f

= =+

=

=Then


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).88 - 5.76 A B R k R k = =

'rocedure:1. 0esign the astable multivibrator circuit for the given fre%uency and duty cycle

). Elace 555 timer on the bread board and 'onnect e&ternal component as per the circuitdiagram.+. Apply power supply and chec9 the output and voltage across capacitor 4. Find the duty cycle and fre%uency of the wave form5. 'ompare with theoretical values6. plot the output and voltage across capacitor on graph sheet

FS generator

/ote replace 5#D with variable resistors

Frequency Shift Keying plays a great role in wide range of applications in the field of communication and was considered efficient one in data transmission of wirelessmodems.This above circuit uses a simple IC N !!! in order to produce FSK signal withrespect to the given input signal.In this circuit it was wired as a simple "stable multivibrator

and in addition a transistor was connected through which input signal was given into thebase of the transistor.The resistors #a$#b and C determines the frequency of the FSKmodulated signal in the astable mode of operation. "lso chec% out the matching FSK&emodulator using IC !'! circuit. (ets move into the wor%ing of this circuit.

WORKING OF CIRCUIT:The output frequency of the signal was based on the input digital signal given to the base of the transistor.)hen the given input was high that is of logic * the +N+ transistor was , is off and IC !!! timer wor%s in the normal "stable mode of operation giving out the series of
http://gadgetronicx.blogspot.in/2013/08/fsk-demodulator-using-ic-pll-565.htmlhttp://gadgetronicx.blogspot.in/2013/08/fsk-demodulator-using-ic-pll-565.htmlhttp://gadgetronicx.blogspot.in/2013/08/fsk-demodulator-using-ic-pll-565.htmlhttp://gadgetronicx.blogspot.in/2013/08/fsk-demodulator-using-ic-pll-565.html


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square wave pulses thus there will be no change in the frequency of the output signal.-erethe resistors #a$ #b and Capacitor C was selected in such a way to obtain output frequencyof * / -0.The output frequency when the input was high was given by the equation

f1 *.2!34#a 5 #b6C

)hen the input binary data if logic $ the +N+ transistor is on and its connects the resistance#c across resistance #a.The resistors #c is selected in such a way that the value of *7/ -0.-ere the value of #c added in addition to the #a$ #b and C to contribute the wor%ingof the N !!!.This ma%es the charging and discharging quic%er resulting in high frequencywaves as output.The #a$ #b$ #c and C values was selected in such a way to obtain outputfrequency of *7/ -0.This was given by the equation

f1*.2!344#a 88 #c65 7#b6C

Thus the resultant output FSK will give frequency of * / -0 when input is high andfrequency of *7/ when input is low.Thus by this way the FSK signal was obtained usingN !!!.

'rocedure:1. Elace 555 timer on the bread board and 'onnect e&ternal component as per the circuit

diagram.). Apply power supply.+.Apply logic # at input and chec9 the output. Measure the fre%uency4. 'onnect logic 1 at input and chec9 the output. Measure the fre%uency.4. Apply a s%uare wave at input and note down the output wave form

*& N&STA()E *+)T,-,(%AT&%

Figure shows the circuit diagram of a 555 Timer connected in monostable Mode. The pin number 8 and 4 th pin are shorted and given to power supply. The reset pin is connected to power supply toavoid accidental resets. The pin number 1 is grounded. ince the control pin !5" is not used it isgrounded through #.#1 $F to avoid high fre%uency noises. A resistance R is connected betweenreset and discharge pins. The discharge and threshold pins are shorted and a capacitor whichdetermines the width of the pulse is connected to threshold pin. The other end of the capacitor isgrounded.

;hen the circuit is switched


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monostable multivibrator since the output does not change its state until

a negative trigger is applied at trigger input. When a negative pulse is applied to

the trigger input 4pin 76 the inverting terminal of lower comparator goes below * +ccV . As a result the

output of lower comparator becomes 1 which results #Q = . =ence output becomes high andthe transistor ?1 switches to off condition thereby removing the short circuit across the e9ternal timing

capacitor$ C. Now the capacitor starts charging towards Vcc. through the

resistor R with a time constant RC. When the capacitor voltage exceeds

2/3 Vcc the output of upper comparator !R" becomes high which results

#$% and 1Q = .. The output goes to ero and the transistor switches on shorting the capacitor

to ground.

Thus the output goes bac& to its stable state from #uasi stable state

/ote The triggering portion of the circuit is not included


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.

0uring charging the voltage across capacitor is given by

( ) * !1"#B

)+

t RC c f i f

i f CC

CC c

V V V V e

V V V

V V at t T

= + = =

= =

( )

( )

( )

*

*

1

)#

+)

1

+ ln!+" 1.1

T RC CC CC CC

T RC


V V V e

e

T RC RC

= +

=

= =

esign:0esign a mono@stable multivibrator that generates a pulse having width of 1 msec.

+

6

1.1

1 sec

#.1

1#C.#C1.1 #.1 1#

T RC

iven T !

let C uf

then R k

=

=

=

= =

'rocedure:1. 0esign the monostable multivibrator circuit for the pulse width). Elace 555 timer on the bread board and 'onnect e&ternal component as per the circuit

diagram.+. Apply power supply and chec9 the output and voltage across capacitor 4. Find the pulse width5. 'ompare with theoretical values


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6. plot the output and voltage across capacitor on graph sheet

'ulse !idth modulator

/ote The triggering portion of the circuit is not included


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In this mode the output is (:) 4 ;6 when there is no triggering$ when itis triggered via 7nd pin the output goes -Is$ transmitting servo signals for remote controlapplications etc.

'rocedure:

1. Elace 555 timer on the bread board and 'onnect e&ternal component as per the circuitdiagram.

)- 'onnect power supply+. Apply a low fre%uency sinusoid wave form! between 5#= and 1## = " as modulating

signal at pin 5.


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4.Apply a trigger wave form at pin ) !high fre%uency s%uare wave" power5. plot the output wave form on graph sheet

#esult? The !!! and its applications in astable and monostable modes were studied

%e/ie! "uestions0. 1rite a short note on multi/ibrators and their types2. Explain the function of reset pin of 555 timer.3. !hat are the modes of operation of 555 timer4

. 1hat are the applications of 555 timer in monostable mode45. 1hat are the applications of 555 timer in astable mode46. efine duty cycle.7. 1hat is the use of control pin in 555 timer48. 1hy pin number 5 is grounded through . 0uf !hen it is not used4

555 Astable Monostable multivibrator

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