ASTABLEAND MONOSTABLE MODE 555 TIMER APPLICATION CIRCUIT RAHMAH BINTI KHAMIS MAISARAH BINTI MAHIZAN SURAYAHANI BINTI MD SAHARI C IRCUI T THEORY AND E X ERC I S E POLITEKNIK IBRAHIM SULTAN
ASTABLEAND MONOSTABLE MODE 555 TIMER APPLICATION CIRCUIT RAHMAH BINTI KHAMIS MAISARAH BINTI MAHIZAN SURAYAHANI BINTI MD SAHARI C IRCUI T THEORY AND E X ERC I S E POLITEKNIK IBRAHIM SULTAN
Published by: POLITEKNIK IBRAHIM SULTAN KM10, JALAN KONG KONG, 81700 PASIR GUDANG, JOHOR DARUL TAKZIM COPYRIGHT@ 2022, Politeknik Ibrahim Sultan This work is subject to copyright. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or translated, in any form or by any means, electronics, mechanical, photocopying, recording or otherwise, without the prior written permission from publisher. The program listings (if any) may be entered, stored and executed in a computer system, but they may not be reproduced for publication. Perpustakaan Negara Malaysia Cataloguing-in-Publication Data Rahmah Khamis, 1981- 555 TIMER APPLICATION CIRCUIT : ASTABLE AND MONOSTABLE MODE : CIRCUIT THEORY AND EXERCISE / RAHMAH BINTI KHAMIS, MAISARAH BINTI MAHIZAN, SURAYAHANI BINTI MD SAHARI. Mode of access: Internet eISBN 978-967-2065-91-3 1. Electric circuits. 2. Government publications--Malaysia. 3. Electronic books. I. Maisarah Mahizan, 1985-. II. Surayahani Md Sahari, 1977-. III. Title. 621.3192 Printed and Published in Malaysia by: POLITEKNIK IBRAHIM SULTAN KM10, Jalan Kong Kong, 81700 Pasir Gudang, Johor. Tel: +607-2612488 Faks: +607-2612402 www.pis.edu.my Module eBook Development Chief Editor : Dr. Arfah binti Ahmad Hasbollah Authors : Rahmah binti Khamis, Maisarah binti Mahizan, Surayahani binti Md Sahari, Proof-Reader : Siti Noraini binti Hamzah
Infinite thanks to my very hardworking teammates, Maisarah and Surayahani who worked hard together to prepare this eBook. It brings a proud achievement to our writing journey. My team would not be able to get our work done without continual support and vision from our Chief Editor Dr. Arfah , e-learning facilitator Mrs Yuzi and our proof reader, Ms Siti Noraini. Special thanks to Mr. Sarawanan who gave the inspiration and opportunity to my team to develop this eBook. Not to forget to the e-learning and CDeC committee that gave us a lot of guidance during the eBook development workshop. Hopefully this eBook will be beneficial for all students and lecturers. Team Leader Rahmah acknowledgment acknowledgment acknowledgment
This eBook is contains three main topics. Topic 1 is intended to provide the basic introduction and applications of the 555 timer. Topic 2 provides the schematic circuits, waveforms, operation and the formula for the 555 Timer in Monostable Mode. It also states the effect of varying values of components to the output of timer. Topic 3 provides the schematic circuits, waveforms, operation and the formula for the 555 Timer in Astable Mode. It also states the method to generate a duty cycle of less/more than 50%. All topics also contains examples and exercises for selfassessment. [email protected] preface preface preface
TOPIC 2: MONOSTABLE MODE Schematic circuit 16 Output waveform 17 Circuit operations 18 Effect of varying the values of components. 20 Examples 21 Test Yourself 22 TOPIC 3: ASTABLE MODE Introduction to Astable Mode 23 Schematic circuit 24 Output waveform 25 Circuit operations 26 What is Duty Cycle? 27 Formula for generating delay time 28 Examples 30 Generate a duty cycle of less/more than 50%. 32 How does the circuit work? 33 Examples 34 Test Yourself 35 T A B L E O F C O N T E N T S TOPIC 1: INTRODUCTION TO 555 TIMER Overview 1 What is 555 Timer? 3 Internal circuitry of 555 Timer 4 What inside in 555 Timer? 5 Pin configuration 7 Pin Assignment 8 Application of 555 Timer 11 Examples 12 Test Yourself 14 E B O O K 2 0 2 2 CONTENTS
1 C H A P T E R INTRODUCTION TO 555 TIMER
The 555 timer, is an extremely popular IC for timing-related applications. They are robust and versatile, as they can be used in any circuit which requires some sort of time control. It can be used to generate various types of pulses, to create time delays, and also for Pulse Width Modulation (PWM). The most common use of 555 timers is to generate clock signals for circuits. TOPIC 1: INTRODUCTION TO 555 TIMER 01 OVERVIEW
TOPIC 1: INTRODUCTION TO 555 TIMER 02 Hans Camenzind created the 555 Timer in 1971, and it may be used in a wide variety of electronic equipment, including toys, kitchen appliances, and even spacecraft. It is an extremely stable integrated circuit that can generate precise oscillations and time delays. The 555 Timer can operate in a variety of ways, including Schmitt trigger, bistable, monostable, and astable. Source:ebay.co.uk Figure 1.1: 555 Monostable Printed Circuit Board (PCB)
Source:NE555 Bipolar Single Timer TI - Irish Electronics.ie IC 555 is named after the three 5kΩ resistance that act as the voltage divider inside the IC circuitry. WHAT IS 555 TIMER? TOPIC 1: INTRODUCTION TO 555 TIMER 03 Figure 1.2: 555 timer integrated circuit (IC)
INTERNAL CIRCUITRY OF 555 TIMER It consists of voltage divider circuit, two comparators, a flip flop, a discharge transistor, and an output circuit. TOPIC 1: INTRODUCTION TO 555 TIMER 04 Source:www.CircuitsToday.com Figure 1.3: Internal Circuitry of 555 timer
TOPIC 1: INTRODUCTION TO 555 TIMER The voltage divider is made using three 5k resistors. The voltages across these resistors are given as reference voltages to the 1 comparators. voltage divider 2 comparator Upper comparator: The inputs to the upper comparator or the threshold comparator are the threshold pin connected to the non-inverting input (+), and a reference voltage of 2/3 Vcc is connected to the inverting input (-) of the comparator. Lower comparator: For the lower comparator or the trigger comparator, 1/3 Vcc reference voltage is given to the non-inverting input (+) and the trigger pin is connected to the inverting input (-) of the comparator. WHAT'S IN A 555 TIMER? 05
TOPIC 1: INTRODUCTION TO 555 TIMER S R Q Q' 0 0 Memory Memory 1 0 1 0 0 1 0 1 1 1 Invalid Invalid The outputs of the comparators are given as inputs to a flip flop. An SR flip-flop is a memory element that can store and output a logic “0” or logic “1” depending on the two inputs SET 3 and RESET or S and R, respectively. flip flop WHAT'S IN A 555 TIMER? 06
TOPIC 1: INTRODUCTION TO 555 TIMER The figure above shows pinouts of the 555 timers. 555 ICs generally come in an 8-pin DIP package. Note: To identify which pin is on top of an integrated circuit, there is typically a little notch in the packaging. The IC numbers are then counted counterclockwise, beginning with the upper-left pin PIN CONFIGURATION 07 Figure 1.3: Pin configuration of 555 timer
TOPIC 1: INTRODUCTION TO 555 TIMER OUTPUT pin 3 Connects to the 0V power supply. TRIGGER • th T a h t i i s s p r i e n sp is on a s n ib in le ve fo rt r in t g ra i n n s p it u io t n to o a f f c l o ip m -f p lo ar p at f o ro r m 2 pin 2 set to reset. • The output of the timer depends on the amplitude of the external trigger pulse applied to this pin. • When < 1/3 Vcc ('active low') this makes the output high (+Vcc). GROUND pin 1 Output of the timer. PIN ASSIGNMENTS 08
TOPIC 1: INTRODUCTION TO 555 TIMER CONTROL VOLTAGE pin 5 RESET pin 4 • To disable or reset the timer, a negative pulse is applied to this pin. •When this pin is not to be used for reset purpose, it should be connected to + Vcc to avoid any possibility of false triggering. • The function of this terminal is to control the threshold and trigger levels which is set internally to be 2/3 Vcc. •When this pin is not used, it should be connected to ground through a 0.01 µF to eliminate electrical noise. •It can be left unconnected if noise is not a problem. PIN ASSIGNMENTS 09
TOPIC 1: INTRODUCTION TO 555 TIMER DISCHARGE pin 7 THRESHOLD pin 6 Pin 7 is not an input. It is called discharge terminal because when transistor Q1 ON, capacitor discharges through the transistor Q1. When the transistor Q1 is OFF, the capacitor charges at a rate determined by the external resistor and capacitor. • This is the non-inverting input terminal of comparator 1, which compares the voltage applied to the terminal with a reference voltage of 2/3 Vcc. •The amplitude of voltage applied to this terminal is responsible for the set state of flipflop. •When > 2/3 Vcc ('active high') this makes the output low (0V)* only if pin 2 is HIGH. SUPPLY pin 8 • A supply voltage of + 5 V to + 18 V is applied to this terminal with respect to ground . PIN ASSIGNMENTS 10
TOPIC 1: INTRODUCTION TO 555 TIMER The 555 timer IC is an integrated circuit (chip). The part is still in widely used, easy to use, affordable and has good stability. Precision timing Oscillator (Pulse generation) Sequential timing Time delay generation Pulse width modulation (PWM) signals Pulse position modulation Linear ramp generator Accurate clock signals APPLICATION OF TIMERS 11
TOPIC 1: INTRODUCTION TO 555 TIMER EXAMPLES 1.Identify the name of pin configuration of 555 timer IC in figure below. a b c d e f g h Answer: a- control voltage b- reset c- threshold d- output e- discharge f- trigger g-power supply h- ground 12
TOPIC 1: INTRODUCTION TO 555 TIMER 2. State the function for Comparator 1 and Comparator 2 in figure below: Comparator 1 Comparator 2 Answer: Comparator 1 : The inputs to the upper comparator or the threshold comparator are the threshold pin connected to the non-inverting input (+), and a reference voltage of 2/3 Vcc is connected to the inverting input (-) of the comparator. Comparator 2: For the lower comparator or the trigger comparator, 1/3 Vcc reference voltage is given to the non-inverting input (+) and the trigger pin is connected to the inverting input (-) of the comparator. 13
TOPIC 1: INTRODUCTION TO 555 TIMER 1.Based on Figure 1.4, state the pin configuration for 'f'. A. threshold B. output C. trigger D. discharge 2. By referring to Figure 1.4, pin _______ is the output of the timer. A. a B. b C. c D. d Figure 1.4: Pin configuration of 555 timer a b c d e f g h YOURSELF test 14
3. ' This pin is an inverting input to a comparator 2 that is responsible for transition of flip-flop from set to reset.' This statement refer to pin ________ A. output B. threshold C. trigger D. reset 4. State the function of voltage divider in internal circuit of 555 timer. A. as a memory element that can store and output a logic “0” or logic “1” B. as a supply voltage . C. as reference voltages to the comparators. D. as a output of the timer . 5. Choose a TRUE application of a timer. A. Switch mode power supply B. Linear ramp generator C. Harmonic control D. Inverter A B C C B ANSWER: 1. 2. 3. 4. 5. TOPIC 1: INTRODUCTION TO 555 TIMER 15
C H 2A P T E R MONOSTABLE MODE
SCHEMATIC CIRCUIT TOPIC 2: MONOSTABLE MODE Monostable multivibrator (MMV) mode of 555 timer IC is also called Single shot mode. Only one state, as the names indicate, is stable, and the other is known as an unstable or quasi-stable condition. 555 timer IC remains in stable state until the external triggering is applied. 16 MONOSTABLE MODE TIMER CIRCUIT A BRIEF INTRODUCTION OF THE TIMER CIRCUIT Source: Writer Figure 2.1 : Schematic circuit of Monostable Mode
OUTPUT WAVEFORM TOPIC 2: MONOSTABLE MODE 17 Figure 2.2 : Output waveforms of Monostable Mode
Monostable mode has a stable state at LOW. Initially, when the output at pin 3 is low, the discharge transistor Q1 is ON and capacitor, C is shorted to ground. When a negative pulse is applied to pin 2, the trigger input falls below 1/3Vcc, the output of comparator 2 goes high which resets the flip-flop and the transistor Q1 turns OFF and the output at pin 3 goes high. This is the transition of the output from a stable to an unstable state. As the discharge transistor Q1 is OFF, the capacitor C begins charging toward Vcc through resistance R. 01 02 03 When a negative pulse is applied to pin 2, the trigger input falls below 1/3Vcc, the output of comparator 2 goes high which resets the flip-flop and the transistor Q1 turns OFF and the output at pin 3 goes high. 04 TOPIC 2: MONOSTABLE MODE CIRCUIT OPERATIONS 18
Thus the output returns back to a stable state from unstable state. The output of the Monostable Multivibrator remains low until a trigger pulse is again applied. The capacitor C has to charge through resistance R. The larger the time constant RC, the longer it takes for the capacitor voltage to reach 2/3 Vcc. The time during which the timer output remains high, Tw: Tw ≈ 1.1 RC 05 06 07 TOPIC 2: MONOSTABLE MODE 19
EFFECT OF VARYING VALUE OF COMPONENTS 01 The time constant of Monostable Multivibrators can be changed by varying the values of the capacitor, C the resistor, R or both. Generally used to increase the width of a pulse or to produce a time delay TOPIC 2: MONOSTABLE MODE 02 20 Source:https://www.electronics-tutorials.ws Figure 2.3 : Different values of the time constant affect the output time delay
EXAMPLES TOPIC 2: MONOSTABLE MODE 1. Draw a timer circuit in monostable operating modes. Answer: 2. Calculate the pulse width if R=1.2kΩ and C=0.1µF. Answer: Tw = 1.1RC Tw = 1.1 (1.2k)(0.1µ) Tw = 132µs 21
TOPIC 2: MONOSTABLE MODE 1. Determine the time period of a monostable 555 multivibrator. 2. A monostable multivibrator has R = 120kΩ and the time delay T= 1000ms, calculate the value of C? 3. A Monostable 555 Timer is required to produce a time delay within a circuit. If a 10uF timing capacitor is used, calculate the value of the resistor required to produce a minimum output time delay of 500ms. 4. 555 Timer is connected in monostable multivibrator mode. What is the output if no input trigger is given? YOURSELF test 22 Tw =1.1RC 7.5µF 45.5kΩ Low ANSWER: 1. 2. 3. 4.
C H 3A P T E R ASTABLE MODE
Timing components consists of two resistors, RA and RB with a capacitor, C that controls the delay time of output timer. ASTABLE MODE TIMER CIRCUIT The output continually switches between the high and low states, producing a square wave. An astable circuit has NO STABLE state. A BRIEF INTRODUCTION OF THE TIMER CIRCUIT In the Astable Mode, the 555 becomes an oscillator producing continuous pulses at frequencies up to 2 MHz. The capacitor C is periodically charged and discharged between the trigger level VL = 1/3 VCC and the threshold level VH = 2/3 VCC. TOPIC 3: ASTABLE MODE 23
Figure 3.1 shows the schematic circuit of Astable Mode. Reset pin (pin 4) is not to be used for reset purpose in this mode. Hence, it should be connected to pin 8 to avoid any possibility of false triggering. Astable continually triggers itself without any external trigger pulses at pin 2. Pin 2 is connected together with Pin 6. SCHEMATIC CIRCUIT Figure 3.1 : Schematic circuit of Astable Mode TOPIC 3: ASTABLE MODE TIMIN G C O M P O NEN T 24 Source: Writer
OUTPUT WAVEFORM Figure 3.2 : Output waveforms of Astable Mode TOPIC 3: ASTABLE MODE 25 Figure 3.2 shows the Astable Mode output waveform at pin 3 in a square wave. The capacitor voltage waveform is shown at pin 2. During the output timer is in Time Low (TL) state, the capacitor, C is discharging through resistor RB starting from 2/3 Vcc to 1/3 Vcc. Meanwhile, during the output timer is in Time High (TH) state, the capacitor, C is charging through resistor RA and RB from 1/3 Vcc to 2/3 Vcc.
With the discharging of capacitor, trigger voltage at inverting input of comparator 2 decreases. When it drops below 1/3 Vcc at TL, the output of comparator 2 goes high and this reset the flip-flop so that Q is low and the timer output is high. When the threshold voltage exceeds 2/3 Vcc at TH, the comparator 1 has a high output and triggers the flip-flop to set so that its Q is high and the timer output is low. When output flip flop, Q is low, timer output is high. The discharging transistor Q1 is OFF and the capacitor C begins charging toward Vcc through resistances RA and RB. CIRCUIT OPERATION With Q high, the discharge transistor Q1 ON and pin 7 grounds so that the capacitor C discharges through resistance RB. This proves the auto-transition in output from low to high and then to low continuously. TOPIC 3: ASTABLE MODE 26
The duty cycle is the duration of the output timer in the ON state in a period of the cycle. Typically, it is expressed in percentages. If the duty cycle is 70%, the timer is ON for 70% in a cycle. Hence, the timer will be in an OFF state for 30%. Here are several types of output timer in different duty cycles. Duty cycle 70%: Duty cycle of 50%: Duty cycle of 30%: 50% OFF 50% ON 100% 30% OFF 70% ON 100% 30% ON 70% OFF 100% TOPIC 3: ASTABLE MODE WHAT IS DUTY CYCLE ? 27
TIME HIGH, TH Output of the astable circuit is high during the charge time, TH: TH = 0.693(RA + RB) C FORMULA FOR GENERATING DELAY TIME TIME LOW, TL The output is low during the discharge time, TL: TL = 0.693(RB) C DUTY CYCLE, D The ratio of RA and RB precisely sets the duty cycle, D: D= TH/(TH+TL ) TOPIC 3: ASTABLE MODE 28
PERIOD, T The total period: T = TH + TL = 0.693 (RA + 2RB) C FREQUENCY, F The astable circuit’s frequency of oscillation: F = 1/T = (1.44) / [ (RA+ 2RB)C ] MARK TO SPACE RATIO Timing resistors and capacitors in the circuit control when the time output is high (the mark time) and when the time output is low (the space time). Mark to space ratio = Time High (TH)/Time Low (TL) = TH : TL TOPIC 3: ASTABLE MODE 29
The output of the 555 Timer for a Astable multivibrator mode __________. A C D 1. A. constantly switching between two states. B. is low until a trigger is received C. is high until a trigger is received D. floats until triggered 2. _______________ is defined as the active output time devided by the total period of the output signal. A. Time High B. Time Low C. Duty Cycle D. Frequency 3. The period for LOW and HIGH of Astable Multivibrator can be calculated based on _________ values to outside of timer. A. Capacitor and inductor B. Resistor and inductor C. Transistor and inductor D. Capacitor and resistor ANSWER: 1. 2. 3. TOPIC 3: ASTABLE MODE EXAMPLES 30
4. Calculate the time high (TH), time low (TL) and frequency of output from Astable mode timer. Answer: TH = 0.693 (RA + RB) C1 = 0.693 (5KΩ + 2KΩ) (10uF) = 48.51ms TL= 0.693 (RB)(C1) = 0.693 (2KΩ) (10uF) = 13.86ms Frequency = 1 / (TH + TL) = 1 / (48.51ms + 13.86ms) = 16.03Hz TOPIC 3: ASTABLE MODE 31
GENERATE A DUTY CYCLE OF LESS/MORE THAN 50% With the diode D1 in place parallel with resistor RB, the output waveform's duty cycle may be adjusted to less/more than 50% if desired. TOPIC 3: ASTABLE MODE Figure 3.3 : Schematic circuit of Astable Mode with diode 32 Source: Writer
TOPIC 3: ASTABLE MODE When capacitor C is charging, the current flows from supply voltage, Vcc. The current flow through RA and diode D1 towards capacitor C. Note that, the current does not flow through RB. In this case, diode D1 is forward bias has resistance much lower than resistor RB. TH = 0.693 RA C When capacitor C is discharging, the current flows through RB towards pin 7. Note that, the current does not flow through diode D1. In this case, diode D1 is reverse bias and has high resistance than resistor RB. TL = 0.693 RB C HOW DOES THE CIRCUIT WORK? 33
TOPIC 3: ASTABLE MODE Resistor RA and RB plays an important role to determine the percentage of duty cycle. HOW TO ADJUST THE DUTY CYCLE TO LESS/MORE THAN 50% Refer to Figure 3.4: In this case, value of RA < RB: TH = 0.693 RA C = 0.693 (1kΩ)(10uF) = 6.93ms TL = 0.693 RB C = 0.693 (2kΩ) (10uF) = 13.86ms Duty cycle = TH/(TH+TL) = 6.93ms/(6.93ms + 13.86ms) = 0.33 % Duty cycle = 0.33 X 100 = 33% Therefore, RA value must be less than RB to generate an output waveform with duty cycle less than 50%. 10uF 1k 2k You should try find the duty cycle value if RA > RB and RA = RB. What do you get? Figure 3.4 : Schematic circuit of Astable Mode with diode EXAMPLES 34
1. An integrated circuit of 555 timer is connected in Astable mode and the desired frequency is 10kHz with a duty cycle of 60%. Find the required resistors value if capacitor is 0.1µF. 2. A 555 timer for an Astable mode produce a square wave output. Based on the output waveform given in Figure 3.5, calculate the value of RA and RB if C=1µF. 3. Draw a 555 astable multivibrator completely with a frequency of 1KHz and a mark to space ratio of 2:1. A 10nF capacitor is used in the circuit. Show all the calculations to construct the multivibrator. TOPIC 3: ASTABLE MODE Figure 3.5 : Astable Mode circuit with output waveform YOURSELF test 35
4. RA = 16.03kΩ RB = 10.69kΩ 5. f = 641Hz C1 = 37.97nF D = 0.56 4. An LED is the output of timer. The LED will light up for 5 second and light off for 2 seconds. Find the suitable value for the timing components if the capacitor value is 270uF. 5. Figure 3.6 shows a circuit of Astable multivibrator. Calculate the frequency and sketch the output waveform with value of R1=R2=7.5kΩ and C1=0.1µF. If this circuit operates at 5KHz and the value of R1=1.0kΩ, R2=3.3kΩ, calculate the value of capacitor C1 and duty cycle. 3. RB = 48.05kΩ RA = 48.15kΩ ANSWER: 1. RA = 288.6 Ω RB = 577.2 Ω 2. RA = 7.2KΩ RB = 7.2KΩ TOPIC 3: ASTABLE MODE Figure 3.6 : Astable Multivibrator 36
REFERENCES https://circuitdigest.com/electronic-circuits/555-timer-monostable-circuit-diagram https://www.electronics-tutorials.ws/waveforms/monostable.html https://www.electronics-tutorials.ws/waveforms/555_timer.html https://www.CircuitsToday 1. 2. 3. 4.
Author 1 Polytechnic Lecturer Rahmah binti Khamis is a lecturer at Department of Electrical Engineering, Politeknik Ibrahim Sultan who has more than 10 years experience in Electronic Circuits subject. She also experienced in teaching Semiconductor Devices and Electronic Computer Aided Design. Author 2 Polytechnic Lecturer Maisarah binti Mahizan is a lecturer at Department of Electrical Engineering, Politeknik Ibrahim Sultan who has more than 10 years experience in Electronic Circuits subject. She also experienced in teaching Power Electronics and Electrical Circuits subject. Author 3 Polytechnic Lecturer Surayahani binti Md Sahari is a lecturer at Department of Electrical Engineering, Politeknik Ibrahim Sultan who has more than 10 years experience in Electronic Circuits subject. She also experienced in teaching Basic Control System and Electronic Computer Aided Design. RAHMAH BINTI KHAMIS MAISARAH BINTI MAHIZAN SURAYAHANI BINTI MD SAHARI MEETTHETEAM AUTHORS BIOGRAPHY
ELECTRONIC CIRCUITS This book is suitable for students who are majoring engineering field. It introduces students to the basic concept of 555 Timer. Upon this book, students should be able to apply the concept and principles of electronic circuits in various type of circuits engineering applications. PENERBIT POLITEKNIK IBRAHIM SULTAN www.pis.edu.my