A Project ReportOn

“ASTABLE MULTIVIBRATOR AS A SQUARE WAVE OSCILLATOR”

BY

“SABALIYA AMITKUMAR.C.”(Roll No :__15_______)

(Semester: __5TH_______)

Department of Electronics & Communication EngineeringC. U. Shah College of Engineering & Technology

Wadhwan City - 363030

CERTIFICATE

This is to certify that the project report entitled “ASTABLE MULTIVIBRATOR

AS A SQUARE WAVE OSCILLATOR” submitted by

Mr. SABALIYA AMITKUMAR.C. (Roll No.__15____) of ___5TH_______ Semester is

the work carried out by him in the subject _INTEGRATED CIRCUITS &

APPLICATION______during semester term of year__2011_____________.

Staff Incharge

Date of Submission: _________________ Head of Department

ABSTRACT

The 555 IC is unique in that it simply, cheaply, and accurately serves as a free-running astable multivibrator, square-wave generator, or signal source, as well as being useful as a pulse generator

CONTENTS:

Chapter 1: INTRODUCTION

1.1 INTRODUCTION

1.2 FEATURES OF 555 TIMER

1.3 PIN DIAGRAM OF THE 555 TIMER & FUNCTION OF PINS

1.4 INTERNAL BLOCK DIAGRAM OF THE 555 TIMER

Chapter 2: CIRCUIT DIAGRAM & WAVEFORM

2.1 : CIRCUIT DIAGRAM

2.2 : WORKING PRICIPLE

2.3 : WAVEFORMS

Chapter 3: DATASHEETS

CONCLUSION

References Appendix

Chapter 1: INTRODUCTION

1.1 INTRODUCTION :

The 555 IC is unique in that it simply, cheaply, and accurately serves as a free-running astable multivibrator, square-wave generator, or signal source, as well as being useful as a pulse generator and serving as a solution to many special problems. It can be used with any power supply in the range 5-18 volts, thus it is useful in many analog circuits. When connected to a 5-volt supply, the circuit is directly compatible with TTL or CMOS digital devices. The 555 timer can be used as a monostable multivibrator (one-shot), as an astable multivibrator (oscillator), as a linear voltage ramp generator, as a missing pulse detector, as a pulse width modulator and in many other applications.

1.2 FEATURES OF 555 TIMER

1. The 555 Timer is a highly stable & inexpensive device for generating accurate time delay or oscillation.2. It can provide time delays ranging from microseconds to hours.3. It can be used with power supply voltage ranging from +5V to +18V.4. It can source or sink up to 200mA.5. It is compatible with both TTL & CMOS logic circuits.6. It has very high temperature stability & it is designed to operate in the temperature range -55o to +125oC(SE 555), whereas NE555 is a commercial grade IC (0 - 70 oC).

1.3 PIN DIAGRAM OF THE 555 TIMER & FUNCTION OF PINS

pin 1 is the ground pin

pin 2 is the trigger input when a negative-going pulse causes the voltage fit

this pin to drop below Vcc/3 volt, the comparator to which this pin is

connected causes the Flip-Flop to change state causing the output level

to switch from 16w to high.

pin 3 is the output pin . It is capable of sinking or sourcing 200mA

pin 4 is the reset pin . Ii is used to reset the flip-flop which will force the

output to go low. The pin is activated when a voltage level below 0.4V

is applied.

pin 5 is the control voltage input . By applying a voltage to this pin , it is

possible to vary the timing of the device independently of the RC

network.

pin 6 is the threshold input . It resets the Flip-Flop and consequently drives

the output low if the voltage applied to it rises above 2\3 Vcc volt

pin 7 is the discharge pin . Usually a timing capacitor is connected between

this pin and ground and is discharged when the transistor is turned oil.

pin 8 is the power supply pin . The voltage applied to this pin may vary from

5 to 15 volt.

1.4 INTERNAL BLOCK DIAGRAM OF THE 555 TIMER

OR

Chapter 2: CIRCUIT DIAGRAM & WAVEFORM

2.1 : CIRCUIT DIAGRAM :

2.2 : WORKING PRICIPLE :

In the above circuit, during the charging interval of the capacitor the diode is forward biased, it conducts & bypasses Rb.So the capacitor charges through Ra & diode D.Assuming the diode to be ideal ,The expression for ON time is:

TON=TC=0.693RAC------------------------------------------------------(1)

But, At During the discharging time (OFF time) TD ,The diode in reverseBiased and discharging take place through only Rb. Then assuming ideal diode D,the expression for OFF time is:

TOFF=TD=0.693RBC------------------------------------------------------(2)

Then Total time TT

TT = TON + TOFF = TC + TD

TT= 0.693(RA+RB) C-------------------------------------------------(3)

D= Duty cycle =TC/T = (RA)/ (RA+RB)--------------------------------------(4)

Where TC = Charging time TD = Dischaging time TT = Total time D=Duty cycleFor a perfect square wave output, TC= TD TON= TOFF

0.693RAC=0.693RBC Then RA=RB

If we set Ra=Rb, we get a duty cycle of 50% & a symmetrical square wave at the output.

2.3 : WAVEFORMS :

Waveforms of square wave oscillator (50% Duty cycle) :

Chapter 3: DATASHEETS:

3.1 555 Data Sheet

NE/SA/SE555/SE555C Timer

DESCRIPTIONThe 555 monolithic timing circuit is a highly stable controller capableof producing accurate time delays, or oscillation. In the time delaymode of operation, the time is precisely controlled by one externalresistor and capacitor. For a stable operation as an oscillator, thefree running frequency and the duty cycle are both accuratelycontrolled with two external resistors and one capacitor. The circuitmay be triggered and reset on falling waveforms, and the outputstructure can source or sink up to 200mA.FEATURESTurn-off time less than 2s

Max. operating frequency greater than 500kHz

Timing from microseconds to hours

Operates in both astable and monostable modes

High output current

Adjustable duty cycle

TTL compatible

Temperature stability of 0.005% per CAPPLICATIONSPrecision timing

Pulse generation

Sequential timing

Time delay generation

Pulse width modulation

ORDERING INFORMATION

DESCRIPTION TEMPERATURE RANGE ORDER CODE DWG #

8-Pin Plastic Small Outline (SO) Package 0 to +70C NE555D 0174C8-Pin Plastic Dual In-Line Package (DIP) 0 to +70C NE555N 0404B8-Pin Plastic Dual In-Line Package (DIP) -40C to +85C SA555N 0404B8-Pin Plastic Small Outline (SO) Package -40C to +85C SA555D 0174C8-Pin Hermetic Ceramic Dual In-Line Package (CERDIP) -55C to +125C SE555CFE

8-Pin Plastic Dual In-Line Package (DIP) -55C to +125C SE555CN 0404B14-Pin Plastic Dual In-Line Package (DIP) -55C to +125C SE555N 0405B8-Pin Hermetic Cerdip -55C to +125C SE555FE

14-Pin Ceramic Dual In-Line Package (CERDIP) 0 to +70C NE555F 0581B14-Pin Ceramic Dual In-Line Package (CERDIP) -55C to +125C SE555F 0581B14-Pin Ceramic Dual In-Line Package (CERDIP) -55C to +125C SE555CF 0581B

555 Data Sheet

NE/SA/SE555/SE555C Timer

BLOCK DIAGRAM

EQUIVALENT SCHEMATIC

NOTE: Pin numbers are for 8-Pin package

CONCLUSION :

We can generate square wave in astable mode using the timer IC NE555 with the help of diode.

REFERENCES

Linear Integrated Circuits:

By Ramakant Gaikwad

Peoples Publishing House, N. D.

Nomenclature of ICs and transistors:

S. RamabhadranS. Chand and Co. New Delhi, 1987.

Linear applications of integrated circuits

Millman & HawkinsEastern Economy Edition

In the above circuit, during the charging interval of the capacitor the diode is forward biased, it conducts & bypasses Rb.So the capacitor charges through Ra & diode D.Assuming the diode to be ideal ,The expression for ON time is:

4 8

7

62

5 1

3NE555

+VC

CC

=Vcc

Ra

bb

C

OutputRb

abbb

0.01µFRabbb

4 8

6

2 5 1

3

7

555

TON=TC=0.693RAC------------------------------------------------------(1)

But, At During the discharging time (OFF time) TD ,The diode in reverseBiased and discharging take place through only Rb. Then assuming ideal diode D,the expression for OFF time is:

TOFF=TD=0.693RBC------------------------------------------------------(2)

AND Total time TT

TT = TON + TOFF = TC + TD

TT= 0.693(RA+RB) C-------------------------------------------------(3)

D= Duty cycle =TC/T = (RA)/ (RA+RB)--------------------------------------(4)Where TC = Charging time TD = Dischaging time TT = Total time D=Duty cycleFor a perfect square wave output, TC= TD TON= TOFF

0.693RAC=0.693RBC Then RA=RB

If we set Ra=Rb, we get a duty cycle of 50% & a symmetrical square wave at the output.

Square Wave Generator:An astable multivibrator can be used as a square wave generator. To obtain a symmetrical square wave with 50% duty cycle the following circuit can be used.

Here the capacitor charges through Ra & the forward biased diode D & discharges through Rb.In order to make the charging & discharging times equal, the resistance Ra is constructed with a fixed resistance in series with a potentiometer as shown in figure, so that the potentiometer can be adjusted to get Ra+Rf =Rb in order to obtain an exact symmetrical square wave output where Rf is the forward resistance of the diode.

4 8

7

62

5 1

3NE555

+VC

CC

=Vcc

Ra

bb

C

OutputRb

abbb

0.01µFRabbb

4 8

6

2 5 1

3

7

555

555 TimerThe 555 is a highly stable device designed for generating accurate time delays or oscillations. Additional terminals are provided ' for triggering or resetting. In the time delay mode (monostable mode) the time is set by one external resistor and one capacitor. In the astable (free running) mode the frequency and duty cycle are set by two external resistors and one capacitor. The circuit can be both triggered and reset on falling waveforms. The output circuit can source or sink up to 200mA. TTL circuitry can be driven directly from the output.A dual version of this IC is available, the 556.

Features• Timing from microseconds to hours• Adjustable duty cycle• Sink & source 200mA• 4-15V operation• Temperature stability >0.005% per°C

Absolute maximum ratingsSupply +18VPower dissipation 600mW

SpecificationsTiming Error, monostable Temperature drift 50ppm/°CSupply Drift 0.1 %/VTiming Error, astable Temperature Drift 150ppm/°C Supply Drift 0.30%/VTrigger VoltageVcc 15V (Itrig = 0.5µA) 5VVcc 5V 1.67vControl Voltage VCC15V 10vVCC 5V 3.3v

555 IC

By connecting this diode, D1 between the trigger input and the discharge input, the

timing capacitor will now charge up directly through resistor R1 only, as resistor R2 is

effectively shorted out by the diode. The capacitor discharges as normal through resistor,

R2. Now the previous charging time of t1 = 0.693(R1 + R2)C is modified to take account

of this new charging circuit and is given as: 0.693(R1.C). The duty cycle is therefore

given as D = R1/(R1 + R2). Then to generate a duty cycle of less than 50%, resistor R1

needs to be less than resistor R2.

PIN DIAGRAM OF THE 555 TIMER

Functions of pins:1. Ground: All voltages are measured with respect to this terminal.2. Trigger: It is the external input that will be applied to the inverting input of the lower comparator & will be compared with Vcc/3 coming from the potential divider network.3. Output: Complement of the output of the flip-flop acts as the final output of timer as it passes through a power amplifier with inverter. Load can either be connected between pin 3 & ground or pin 3 & Vcc.4. Reset : This is an input to the timing device which provides a mechanism to reset the flip-flop in a manner which overrides the effect of any instruction coming to the FF from lower comparator. This is effective when the reset input is less than 0.4V.When not used it is returned to Vcc.5. Control Voltage input: Generally the fixed voltages of 1/3Vcc & 2/3Vcc also aid in determining the timing interval. The control voltage at 5 can be used when it is required to vary the time & also in such cases when the reference level at V- of the UC is other than 2/3Vcc.Generally when not used a capacitor of 0.01uF should be connected between 5 & ground to bypass noise or ripple from the supply.6. Threshold: An external voltage by means of a timing capacitor & resistor is applied to this pin. When this voltage is greater than 2/3Vccoutput of UC is 1 which is given to the set input of FF thereby setting the FF making Q=1 & Q=0.7. Discharge: This pin is connected to the collector of the discharge transistor Q1.When Q output of the FF is 1,then Transistor Q1 is on due to sufficient base drive hence driving transistor into saturation.When output of the FF is low Transistor Q1 is off hence acting as a open circuit to any external device connected to it.8. +Vcc (Power Supply): It can work with any supply voltage between 5 & 18V.

Threshold

Control voltage

Discharge

output

IC 555

+ VccGND

Trigger

Reset

555 Data Sheet

NE/SA/SE555/SE555C Timer

DESCRIPTIONThe 555 monolithic timing circuit is a highly stable controller capableof producing accurate time delays, or oscillation. In the time delaymode of operation, the time is precisely controlled by one externalresistor and capacitor. For a stable operation as an oscillator, thefree running frequency and the duty cycle are both accuratelycontrolled with two external resistors and one capacitor. The circuitmay be triggered and reset on falling waveforms, and the outputstructure can source or sink up to 200mA.FEATURESTurn-off time less than 2s

Max. operating frequency greater than 500kHz

Timing from microseconds to hours

Operates in both astable and monostable modes

High output current

Adjustable duty cycle

TTL compatible

Temperature stability of 0.005% per CAPPLICATIONSPrecision timing

Pulse generation

Sequential timing

Time delay generation

Pulse width modulation

ORDERING INFORMATION

DESCRIPTION TEMPERATURE RANGE ORDER CODE DWG #

8-Pin Plastic Small Outline (SO) Package 0 to +70C NE555D 0174C8-Pin Plastic Dual In-Line Package (DIP) 0 to +70C NE555N 0404B8-Pin Plastic Dual In-Line Package (DIP) -40C to +85C SA555N 0404B8-Pin Plastic Small Outline (SO) Package -40C to +85C SA555D 0174C8-Pin Hermetic Ceramic Dual In-Line Package (CERDIP) -55C to +125C SE555CFE

8-Pin Plastic Dual In-Line Package (DIP) -55C to +125C SE555CN 0404B14-Pin Plastic Dual In-Line Package (DIP) -55C to +125C SE555N 0405B8-Pin Hermetic Cerdip -55C to +125C SE555FE

14-Pin Ceramic Dual In-Line Package (CERDIP) 0 to +70C NE555F 0581B14-Pin Ceramic Dual In-Line Package (CERDIP) -55C to +125C SE555F 0581B14-Pin Ceramic Dual In-Line Package (CERDIP) -55C to +125C SE555CF 0581B

555 Data Sheet

NE/SA/SE555/SE555C Timer

BLOCK DIAGRAM

EQUIVALENT SCHEMATIC

NOTE: Pin numbers are for 8-Pin package

741 Datasheet

741 Datasheet

Details of IC 555 timerIt is basically an 8–pin timer IC, which can produce precise time delay. It works on wide range of power supply voltage from 3V to 18V. The function of each pin of the IC is given below –Pin–1: it is connected to ground (0V) terminal of power supply.Pin–2: It starts up timing cycle, when its voltage is less than ⅓Vcc, the output of IC becomes high (1). Pin–3: it is output pin which either source or sink current up to 200mA. Pin–4: it is reset pin. When it is +ve, IC works normally. However, when it is –ve, IC stops its working completely. Pin–5: control voltage pin. It may not be used in normal working. Pin–6: it is threshold pin. It finalizes the timing cycle of the IC, when its voltage is equal to or greater than ⅔Vcc, the output of IC becomes low (0). Pin–7: it is discharge pin. It discharges external capacitor into itself. Pin–8: it is connected to +ve terminal of battery, generally 3–18V.

Internal block diagram of IC 555

It consists of three resistors of 5k each, two comparators, one flip-flop and a transistor. When threshold voltage (at pin–6) is equal to or greater than ⅔Vcc, then it SETs the flip-flop. So we get Q = 1 and = 0. Similarly, when trigger voltage (at pin–2) is equal to or less than ⅓Vcc, then it RESETs the flip-flop. So we get Q = 0 and = 1. The transistor T1 is called discharge transistor. Its collector is internally connected to pin–7. So when it is forward biased, it discharges a capacitor (C) (connected externally) into itself. There is one more important device – the RS flip-flop. It has two inputs (S–Set & R–Reset) having two outputs (Q–active output & –inactive output). THESE OUTPUTS ARE ALWAYS COMPLEMENTARY i.e. when Q = 1, = 0 and vice versa. The output of the IC is available at pin–3. It is connected to output terminal of the RS flip-flop. Also, when pin–4 of the IC is connected to +ve (i.e. high), the IC works normally but when it is grounded (i.e. low), the IC is disabled and stops its working. Finally pin–1 is connected to –ve terminal and pin–8 to +ve terminal of battery respectively.

Applications of IC 555 This IC has a very large number of applications. Only some of the important applications (within the syllabus) are discussed below –

Astable Multivibrator (AMV), Monostable Multivibrator (MMV), Bistable Multivibrator (BMV), Pulse Position Modulator (PPM), Pulse Amplitude Modulator (PAM), Pulse Width Modulator (PWM), Ramp Generator, Frequency Shift Keying (FSK).

Astable Multivibrator (AMV) – when power supply is switched on, capacitor C starts charging through R1 + R2. At this instant, voltage at pin–2 is less than ⅓Vcc. So trigger comparator operates and pin–3 becomes high (i.e. 1) and pin–7 is cutoff. Hence, capacitor C starts charging. When voltage of capacitor C becomes equal to or greater than ⅔Vcc, the threshold comparator operates and pin–3 becomes low (i.e. 0). Now pin–7 becomes active and discharges the capacitor into itself through R2 only. In this way, capacitor C charges through R1 + R2 but discharges through R2 only. So charging time is greater than discharging time. In this process, the capacitor voltage rises and fall exponentially as shown in the wave diagram. Also, the output of IC becomes high during charging and becomes low during discharging. Hence, rectangular wave is obtained at the output. This wave is NOT symmetrical because charging time is longer than discharging time.Since charging time (t1) and discharging time (t2) are different, we have following equations to calculate the different values of the circuit –

A linear resistor is a linear, passive two-terminal electrical component that implements electrical resistance as a circuit element. The current through a resistor is in direct proportion to the voltage across the resistor's terminals. Thus, the ratio of the voltage applied across a resistor's terminals to the intensity of current through the circuit is called resistance. This relation is represented by Ohm's law:

Resistors are common elements of electrical networks and electronic circuits and are ubiquitous in most electronic equipment. Practical resistors can be made of various compounds and films, as well as resistance wire (wire made of a high-resistivity alloy,

such as nickel-chrome). Resistors are also implemented within integrated circuits, particularly analog devices, and can also be integrated into hybrid and printed circuits.

The electrical functionality of a resistor is specified by its resistance: common commercial resistors are manufactured over a range of more than nine orders of magnitude. When specifying that resistance in an electronic design, the required precision of the resistance may require attention to the manufacturing tolerance of the chosen resistor, according to its specific application. The temperature coefficient of the resistance may also be of concern in some precision applications. Practical resistors are also specified as having a maximum power rating which must exceed the anticipated power dissipation of that resistor in a particular circuit: this is mainly of concern in power electronics applications. Resistors with higher power ratings are physically larger and may require heat sinks. In a high-voltage circuit, attention must sometimes be paid to the rated maximum working voltage of the resistor.

Practical resistors have a series inductance and a small parallel capacitance; these specifications can be important in high-frequency applications. In a low-noise amplifier or pre-amp, the noise characteristics of a resistor may be an issue. The unwanted inductance, excess noise, and temperature coefficient are mainly dependent on the technology used in manufacturing the resistor. They are not normally specified individually for a particular family of resistors manufactured using a particular technology.[1] A family of discrete resistors is also characterized according to its form factor, that is, the size of the device and the position of its leads (or terminals) which is relevant in the practical manufacturing of circuits using them.

Type Passive Working principle Electrical resistance Invented Georg Ohm (1827)

Electronic symbol

or

Waveforms of square wave oscillator:

REFERENCES

Linear Integrated Circuits:

By Ramakant Gaikwad

Peoples Publishing House, N. D.

Nomenclature of ICs and transistors:

S. RamabhadranS. Chand and Co. New Delhi, 1987.

Linear applications of integrated circuits

Millman & HawkinsEastern Economy Edition