project

1. A Project Report
On
“ASTABLE MULTIVIBRATOR AS A SQUARE
WAVE OSCILLATOR”
BY
“SABALIYA AMITKUMAR.C.”
(Roll No :__15_______)
(Semester: __5TH_______)
Department of Electronics & Communication Engineering
C. U. Shah College of Engineering & Technology
Wadhwan City - 363030

2. 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

3. 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

4. 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

5. 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).

6. 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 23 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.

7. 1.4 INTERNAL BLOCK DIAGRAM OF THE 555 TIMER
OR

8. Chapter 2: CIRCUIT DIAGRAM & WAVEFORM
2.1 : CIRCUIT DIAGRAM :

9. 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 reverse
Biased 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 cycle
For 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.

10. 2.3 : WAVEFORMS :
Waveforms of square wave oscillator (50% Duty cycle) :
Chapter 3: DATASHEETS:
3.1 555 Data Sheet

11. NE/SA/SE555/SE555C Timer
DESCRIPTION
The 555 monolithic timing circuit is a highly
stable controller capable
of producing accurate time delays, or
oscillation. In the time delay
mode of operation, the time is precisely
controlled by one external
resistor and capacitor. For a stable
operation as an oscillator, the
free running frequency and the duty cycle
are both accurately
controlled with two external resistors and
one capacitor. The circuit
may be triggered and reset on falling
waveforms, and the output
structure can source or sink up to 200mA.
FEATURES
Turn-off time less than 2µs
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 °C
APPLICATIONS
Precision 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 +70°C NE555D 0174C
8-Pin Plastic Dual In-Line Package (DIP) 0 to +70°C NE555N 0404B
8-Pin Plastic Dual In-Line Package (DIP) -40°C to +85°C SA555N 0404B
8-Pin Plastic Small Outline (SO) Package -40°C to +85°C SA555D 0174C
8-Pin Hermetic Ceramic Dual In-Line Package (CERDIP) -55°C to +125°C SE555CFE
8-Pin Plastic Dual In-Line Package (DIP) -55°C to +125°C SE555CN 0404B
14-Pin Plastic Dual In-Line Package (DIP) -55°C to +125°C SE555N 0405B
8-Pin Hermetic Cerdip -55°C to +125°C SE555FE
14-Pin Ceramic Dual In-Line Package (CERDIP) 0 to +70°C NE555F 0581B
14-Pin Ceramic Dual In-Line Package (CERDIP) -55°C to +125°C SE555F 0581B
14-Pin Ceramic Dual In-Line Package (CERDIP) -55°C to +125°C SE555CF 0581B
555 Data Sheet

12. NE/SA/SE555/SE555C Timer
BLOCK DIAGRAM
EQUIVALENT SCHEMATIC
NOTE: Pin numbers are for 8-Pin package

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

14. REFERENCES
• Linear Integrated Circuits:
By Ramakant Gaikwad
Peoples Publishing House, N. D.
• Nomenclature of ICs and transistors:
S. Ramabhadran
S. Chand and Co. New Delhi, 1987.
• Linear applications of integrated circuits
Millman & Hawkins
Eastern Economy Edition

15. +VC
Ra 44 8
8 CC
bb =Vcc
7
7 NE
Rb 555
55 3
3 Output
abb 66 5
C b 22 5 1
5 1
0.01µF
Rabbb
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:

16. TON=TC=0.693RAC------------------------------------------------------(1)
But, At During the discharging time (OFF time) TD ,The diode in reverse
Biased 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 cycle
For 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.

17. 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.
+VC
Ra 44 8
8 CC
bb =Vcc
7
7 NE
Rb 555
55 3 Output
abb 66 5
C b 22 5 1
5 1
0.01µF
Rabbb
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.

18. 555 Timer
The 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
555 IC
Absolute maximum ratings
Supply +18V
Power dissipation 600mW
Specifications
Timing Error, monostable Temperature drift 50ppm/°C
Supply Drift 0.1 %/V
Timing Error, astable Temperature Drift 150ppm/°C
Supply Drift 0.30%/V
Trigger Voltage
Vcc 15V (Itrig = 0.5µA) 5V
Vcc 5V 1.67v
Control Voltage
VCC15V 10v
VCC 5V 3.3v

19. 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.

20. PIN DIAGRAM OF THE 555 TIMER
GND + Vcc
Discharge
Trigger
IC 555
Threshold
output
Control voltage
Reset
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.

21. 8. +Vcc (Power Supply): It can work with any supply voltage between 5 &
18V.

22. 555 Data Sheet
NE/SA/SE555/SE555C Timer
DESCRIPTION
The 555 monolithic timing circuit is a highly
stable controller capable
of producing accurate time delays, or
oscillation. In the time delay
mode of operation, the time is precisely
controlled by one external
resistor and capacitor. For a stable
operation as an oscillator, the
free running frequency and the duty cycle
are both accurately
controlled with two external resistors and
one capacitor. The circuit
may be triggered and reset on falling
waveforms, and the output
structure can source or sink up to 200mA.
FEATURES
Turn-off time less than 2µs
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 °C

23. APPLICATIONS
Precision 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 +70°C NE555D 0174C
8-Pin Plastic Dual In-Line Package (DIP) 0 to +70°C NE555N 0404B
8-Pin Plastic Dual In-Line Package (DIP) -40°C to +85°C SA555N 0404B
8-Pin Plastic Small Outline (SO) Package -40°C to +85°C SA555D 0174C
8-Pin Hermetic Ceramic Dual In-Line Package (CERDIP) -55°C to +125°C SE555CFE
8-Pin Plastic Dual In-Line Package (DIP) -55°C to +125°C SE555CN 0404B
14-Pin Plastic Dual In-Line Package (DIP) -55°C to +125°C SE555N 0405B
8-Pin Hermetic Cerdip -55°C to +125°C SE555FE
14-Pin Ceramic Dual In-Line Package (CERDIP) 0 to +70°C NE555F 0581B
14-Pin Ceramic Dual In-Line Package (CERDIP) -55°C to +125°C SE555F 0581B
14-Pin Ceramic Dual In-Line Package (CERDIP) -55°C to +125°C SE555CF 0581B
555 Data Sheet
NE/SA/SE555/SE555C Timer
BLOCK DIAGRAM
EQUIVALENT SCHEMATIC

24. NOTE: Pin numbers are for 8-Pin package

25. 741 Datasheet

26. 741 Datasheet

27. Details of IC 555 timer
It 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.

28. Internal block diagram of IC 555
It consists of three resistors of 5kΩ 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 Q
= 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 Q
=
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 Q
output). THESE OUTPUTS ARE ALWAYS COMPLEMENTARY i.e. when Q = 1,
Q
= 0 and vice versa. The output of the IC is available at pin–3. It is connected to
output terminal Q
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).

29. 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 –
Let T = t1 + t 2
t1 = 0.693( R1 + R2 ) × C . . . . . charging time
t 2 = 0.693R2 C . . . . . discharging time
1 1.44
∴f = = . . . . . 1.44 is error constant
T ( R1 + 2 R2 ).C
And duty cycle is given by −
( R + R2 ) × 100%
DC = 1
( R1 + 2 R2 )
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,

30. 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.

31. Type Passive Working principle Electrical resistance Invented Georg Ohm (1827)
Electronic symbol
or

32. Waveforms of square wave oscillator:

34. REFERENCES
• Linear Integrated Circuits:
By Ramakant Gaikwad
Peoples Publishing House, N. D.
• Nomenclature of ICs and transistors:
S. Ramabhadran
S. Chand and Co. New Delhi, 1987.

35. • Linear applications of integrated circuits
Millman & Hawkins
Eastern Economy Edition