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(Main)astable square wave generator
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(Main)astable square wave generator

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  • 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 MULTIVIBRATORAS A SQUARE WAVE OSCILLATOR” submitted byMr. SABALIYA AMITKUMAR.C. (Roll No.__15____) of ___5TH_______ Semester isthe work carried out by him in the subject _INTEGRATED CIRCUITS &APPLICATION______during semester term of year__2011_____________.Staff InchargeDate of Submission: _________________ Head of Department
  • 3. ABSTRACTThe 555 IC is unique in that it simply, cheaply, and accurately serves as a free-runningastable multivibrator, square-wave generator, or signal source, as well as beinguseful as a pulse generator
  • 4. CONTENTS:Chapter 1: INTRODUCTION1.1 INTRODUCTION1.2 FEATURES OF 555 TIMER1.3 PIN DIAGRAM OF THE 555 TIMER & FUNCTION OF PINS1.4 INTERNAL BLOCK DIAGRAM OF THE 555 TIMERChapter 2: CIRCUIT DIAGRAM & WAVEFORM 2.1 : CIRCUIT DIAGRAM 2.2 : WORKING PRICIPLE 2.3 : WAVEFORMSChapter 3: DATASHEETSCONCLUSIONReferences
  • 5. AppendixChapter 1: INTRODUCTION1.1 INTRODUCTION :The 555 IC is unique in that it simply, cheaply, and accurately serves as a free-runningastable multivibrator, square-wave generator, or signal source, as well as being useful asa pulse generator and serving as a solution to many special problems. It can be used withany power supply in the range 5-18 volts, thus it is useful in many analog circuits. Whenconnected to a 5-volt supply, the circuit is directly compatible with TTL or CMOS digitaldevices. The 555 timer can be used as a monostable multivibrator (one-shot), as anastable multivibrator (oscillator), as a linear voltage ramp generator, as a missing pulsedetector, as a pulse width modulator and in many other applications.1.2 FEATURES OF 555 TIMER1. The 555 Timer is a highly stable & inexpensive device for generating accurate timedelay 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 temperaturerange -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 TIMEROR
  • 8. Chapter 2: CIRCUIT DIAGRAM & WAVEFORM2.1 : CIRCUIT DIAGRAM :
  • 9. 2.2 : WORKING PRICIPLE :In the above circuit, during the charging interval of the capacitor the diode isforward biased, it conducts & bypasses Rb.So the capacitor charges throughRa & diode D.Assuming the diode to be ideal ,The expression for ON timeis: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 idealdiode D,the expression for OFF time is:TOFF=TD=0.693RBC------------------------------------------------------(2)Then Total time TT TT = TON + TOFF = TC + TDTT= 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=RBIf we set Ra=Rb, we get a duty cycle of 50% & a symmetrical square wave atthe 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 0174C8-Pin Plastic Dual In-Line Package (DIP) 0 to +70°C NE555N 0404B8-Pin Plastic Dual In-Line Package (DIP) -40°C to +85°C SA555N 0404B8-Pin Plastic Small Outline (SO) Package -40°C to +85°C SA555D 0174C8-Pin Hermetic Ceramic Dual In-Line Package (CERDIP) -55°C to +125°C SE555CFE8-Pin Plastic Dual In-Line Package (DIP) -55°C to +125°C SE555CN 0404B14-Pin Plastic Dual In-Line Package (DIP) -55°C to +125°C SE555N 0405B8-Pin Hermetic Cerdip -55°C to +125°C SE555FE14-Pin Ceramic Dual In-Line Package (CERDIP) 0 to +70°C NE555F 0581B14-Pin Ceramic Dual In-Line Package (CERDIP) -55°C to +125°C SE555F 0581B14-Pin Ceramic Dual In-Line Package (CERDIP) -55°C to +125°C SE555CF 0581B 555 Data Sheet
  • 12. NE/SA/SE555/SE555C TimerBLOCK DIAGRAMEQUIVALENT SCHEMATICNOTE: Pin numbers are for 8-Pin package
  • 13. CONCLUSION :We can generate square wave in astable mode using thetimer 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 RabbbIn the above circuit, during the charging interval of the capacitor the diode isforward biased, it conducts & bypasses Rb.So the capacitor charges throughRa & diode D.Assuming the diode to be ideal ,The expression for ON timeis:
  • 16. 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 idealdiode D,the expression for OFF time is:TOFF=TD=0.693RBC------------------------------------------------------(2)AND Total time TT TT = TON + TOFF = TC + TDTT= 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=RBIf we set Ra=Rb, we get a duty cycle of 50% & a symmetrical square wave atthe 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 RabbbHere the capacitor charges through Ra & the forward biased diode D &discharges through Rb.In order to make the charging & discharging timesequal, the resistance Ra is constructed with a fixed resistance in series with apotentiometer as shown in figure, so that the potentiometer can be adjustedto get Ra+Rf =Rb in order to obtain an exact symmetrical square wave outputwhere Rf is the forward resistance of the diode.
  • 18. 555 TimerThe 555 is a highly stable device designed for generating accurate time delays oroscillations. Additional terminals are provided for triggering or resetting. In the timedelay 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 externalresistors and one capacitor. The circuit can be both triggered and reset on fallingwaveforms. The output circuit can source or sink up to 200mA. TTL circuitry can bedriven 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 ICAbsolute maximum ratingsSupply +18VPower dissipation 600mWSpecificationsTiming Error, monostable Temperature drift 50ppm/°CSupply Drift 0.1 %/VTiming Error, astable Temperature Drift 150ppm/°CSupply Drift 0.30%/VTrigger VoltageVcc 15V (Itrig = 0.5µA) 5VVcc 5V 1.67vControl VoltageVCC15V 10vVCC 5V 3.3v
  • 19. By connecting this diode, D1 between the trigger input and the discharge input, thetiming capacitor will now charge up directly through resistor R1 only, as resistor R2 iseffectively 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 accountof this new charging circuit and is given as: 0.693(R1.C). The duty cycle is thereforegiven as D = R1/(R1 + R2). Then to generate a duty cycle of less than 50%, resistor R1needs to be less than resistor R2.
  • 20. PIN DIAGRAM OF THE 555 TIMER GND + Vcc Discharge Trigger IC 555 Threshold output Control voltage ResetFunctions 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 inputof the lower comparator & will be compared with Vcc/3 coming from thepotential divider network.3. Output: Complement of the output of the flip-flop acts as the final outputof timer as it passes through a power amplifier with inverter. Load can eitherbe connected between pin 3 & ground or pin 3 & Vcc.4. Reset : This is an input to the timing device which provides a mechanismto reset the flip-flop in a manner which overrides the effect of anyinstruction coming to the FF from lower comparator. This is effective whenthe 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 & 2/3Vccalso aid in determining the timing interval. The control voltage at 5 can beused when it is required to vary the time & also in such cases when thereference level at V- of the UC is other than 2/3Vcc.Generally when not used a capacitor of 0.01uF should be connected between5 & ground to bypass noise or ripple from the supply.6. Threshold: An external voltage by means of a timing capacitor & resistoris applied to this pin. When this voltage is greater than 2/3Vccoutput of UC is1 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 dischargetransistor Q1.When Q output of the FF is 1,then Transistor Q1 is on due tosufficient base drive hence driving transistor into saturation.When output of the FF is low Transistor Q1 is off hence acting as a opencircuit 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 SheetNE/SA/SE555/SE555C TimerDESCRIPTIONThe 555 monolithic timing circuit is a highlystable controller capableof producing accurate time delays, oroscillation. In the time delaymode of operation, the time is preciselycontrolled by one externalresistor and capacitor. For a stableoperation as an oscillator, thefree running frequency and the duty cycleare both accuratelycontrolled with two external resistors andone capacitor. The circuitmay be triggered and reset on fallingwaveforms, and the outputstructure can source or sink up to 200mA.FEATURES Turn-off time less than 2µs Max. operating frequency greater than500kHz Timing from microseconds to hours Operates in both astable and monostablemodes 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 0174C8-Pin Plastic Dual In-Line Package (DIP) 0 to +70°C NE555N 0404B8-Pin Plastic Dual In-Line Package (DIP) -40°C to +85°C SA555N 0404B8-Pin Plastic Small Outline (SO) Package -40°C to +85°C SA555D 0174C8-Pin Hermetic Ceramic Dual In-Line Package (CERDIP) -55°C to +125°C SE555CFE8-Pin Plastic Dual In-Line Package (DIP) -55°C to +125°C SE555CN 0404B14-Pin Plastic Dual In-Line Package (DIP) -55°C to +125°C SE555N 0405B8-Pin Hermetic Cerdip -55°C to +125°C SE555FE14-Pin Ceramic Dual In-Line Package (CERDIP) 0 to +70°C NE555F 0581B14-Pin Ceramic Dual In-Line Package (CERDIP) -55°C to +125°C SE555F 0581B14-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 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 than⅓Vcc, the output of IC becomes high (1). Pin–3: it is outputpin 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. Itfinalizes the timing cycle of the IC, when its voltage is equal to or greater than ⅔Vcc, theoutput of IC becomes low (0). Pin–7: it is discharge pin. It discharges external capacitorinto itself. Pin–8: it is connected to +ve terminal of battery, generally 3–18V.
  • 28. Internal block diagram of IC 555It 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 555This 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 followingequations 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 resistors terminals. Thus, the ratio of the voltage applied across a resistors terminals to the intensity of current through the circuit is called resistance. This relation is represented by Ohms law:Resistors are common elements of electrical networks and electronic circuits and areubiquitous in most electronic equipment. Practical resistors can be made of variouscompounds 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: commoncommercial resistors are manufactured over a range of more than nine orders ofmagnitude. When specifying that resistance in an electronic design, the required precisionof the resistance may require attention to the manufacturing tolerance of the chosenresistor, according to its specific application. The temperature coefficient of theresistance may also be of concern in some precision applications. Practical resistors arealso specified as having a maximum power rating which must exceed the anticipatedpower dissipation of that resistor in a particular circuit: this is mainly of concern in powerelectronics applications. Resistors with higher power ratings are physically larger andmay require heat sinks. In a high-voltage circuit, attention must sometimes be paid to therated maximum working voltage of the resistor.Practical resistors have a series inductance and a small parallel capacitance; thesespecifications can be important in high-frequency applications. In a low-noise amplifieror pre-amp, the noise characteristics of a resistor may be an issue. The unwantedinductance, excess noise, and temperature coefficient are mainly dependent on thetechnology used in manufacturing the resistor. They are not normally specifiedindividually for a particular family of resistors manufactured using a particulartechnology.[1] A family of discrete resistors is also characterized according to its formfactor, that is, the size of the device and the position of its leads (or terminals) which isrelevant 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:
  • 33. 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.
  • 34. • Linear applications of integrated circuits Millman & Hawkins Eastern Economy Edition