This circuit uses a 555 timer configured as an astable multivibrator to generate a square wave that controls room lights and counts the number of visitors in a room. Infrared sensors detect when people enter or exit and send signals to the 555 timer. The timer then turns the lights on when people are detected and off when the count reaches zero. It can also display the visitor count on seven-segment displays. The circuit works by charging and discharging capacitors connected to the timer to switch its output state, controlling the lights and counting system.
The document proposes a low-cost, wireless remote health monitoring system using sensors to measure vital signs like temperature, heart rate, blood pressure, and lung capacity. The sensor data is sent to a monitoring system via wireless communication networks and the Internet of Things (IoT), allowing doctors to remotely monitor patients and reducing the need for frequent in-person visits. The proposed system aims to make healthcare more accessible and affordable for chronic disease patients.
This document presents a 2-digit object counter circuit designed by "The FJ group" consisting of 4 students. The circuit uses an IR sensor and comparator IC to detect objects, then a 555 timer IC to generate pulses that trigger 7-segment decoder ICs to display the increasing count on two 7-segment displays. As objects are detected, the timer pulse increments the displays from 00 to 99, providing an automatic count without a microcontroller. Components include ICs, resistors, capacitors, displays, and a power supply. Diagrams and explanations describe how the circuit detects objects and increments the display count with each detection.
Sequential logic circuits use a clock signal to control the timing of state changes in memory elements like flip-flops. A master-slave JK flip-flop allows both the J and K inputs to be simultaneously 1, toggling the output. When this occurs, the master section is reset if the clock is 1, and set if the clock is 0, preventing unstable oscillations between circuits.
The document describes the ADC0808 analog to digital converter chip. It has an 8-channel multiplexer that selects which analog input signal to convert to digital. The conversion process takes 64 clock cycles to complete. The chip outputs the digital conversion result on 8 pins and has control signal pins for start, clock, output enable and end of conversion notification. It converts analog voltages to 8-bit digital numbers for use by digital devices like microprocessors.
This was one of my Diploma in Engineering Projects.
It's a Voice controlled Home Automation System which works with the Internet. Which means you can control your home appliances from anywhere.
I did the Presentation for the Home Automation System. I was also one of the core team members who made it happen.
Here are the complete powerpoint slides.
Thank You
Bio-telemetry involves the remote measurement and transmission of biological data. It has two main elements - a measurement subsystem that detects physiological signals and converts them to electrical data, and a communication subsystem that transmits the data via wired or wireless methods to receiving devices. Common types of bio-telemetry systems include those using wired connections, short-range radio transmitters, or satellite transmission of patient medical data from sensors.
This document discusses interfacing digital-to-analog converters (DACs) and sensors with PIC microcontrollers. It introduces DACs and common DAC types like R-2R ladder and weighted resistor DACs. It then discusses interfacing a DAC0808 converter to a PIC microcontroller and sensing light intensity with an LDR light sensor. Finally, it describes interfacing the LM75 temperature sensor to a PIC, including the sensor's register structure and digital output representation of temperature readings.
The document proposes a low-cost, wireless remote health monitoring system using sensors to measure vital signs like temperature, heart rate, blood pressure, and lung capacity. The sensor data is sent to a monitoring system via wireless communication networks and the Internet of Things (IoT), allowing doctors to remotely monitor patients and reducing the need for frequent in-person visits. The proposed system aims to make healthcare more accessible and affordable for chronic disease patients.
This document presents a 2-digit object counter circuit designed by "The FJ group" consisting of 4 students. The circuit uses an IR sensor and comparator IC to detect objects, then a 555 timer IC to generate pulses that trigger 7-segment decoder ICs to display the increasing count on two 7-segment displays. As objects are detected, the timer pulse increments the displays from 00 to 99, providing an automatic count without a microcontroller. Components include ICs, resistors, capacitors, displays, and a power supply. Diagrams and explanations describe how the circuit detects objects and increments the display count with each detection.
Sequential logic circuits use a clock signal to control the timing of state changes in memory elements like flip-flops. A master-slave JK flip-flop allows both the J and K inputs to be simultaneously 1, toggling the output. When this occurs, the master section is reset if the clock is 1, and set if the clock is 0, preventing unstable oscillations between circuits.
The document describes the ADC0808 analog to digital converter chip. It has an 8-channel multiplexer that selects which analog input signal to convert to digital. The conversion process takes 64 clock cycles to complete. The chip outputs the digital conversion result on 8 pins and has control signal pins for start, clock, output enable and end of conversion notification. It converts analog voltages to 8-bit digital numbers for use by digital devices like microprocessors.
This was one of my Diploma in Engineering Projects.
It's a Voice controlled Home Automation System which works with the Internet. Which means you can control your home appliances from anywhere.
I did the Presentation for the Home Automation System. I was also one of the core team members who made it happen.
Here are the complete powerpoint slides.
Thank You
Bio-telemetry involves the remote measurement and transmission of biological data. It has two main elements - a measurement subsystem that detects physiological signals and converts them to electrical data, and a communication subsystem that transmits the data via wired or wireless methods to receiving devices. Common types of bio-telemetry systems include those using wired connections, short-range radio transmitters, or satellite transmission of patient medical data from sensors.
This document discusses interfacing digital-to-analog converters (DACs) and sensors with PIC microcontrollers. It introduces DACs and common DAC types like R-2R ladder and weighted resistor DACs. It then discusses interfacing a DAC0808 converter to a PIC microcontroller and sensing light intensity with an LDR light sensor. Finally, it describes interfacing the LM75 temperature sensor to a PIC, including the sensor's register structure and digital output representation of temperature readings.
This document discusses using a 4:1 multiplexer to create half adder and half subtractor combinational circuits. It defines half adders, half subtractors, and multiplexers. It then shows the logic diagrams and transistor-level implementations of half adders and half subtractors using a 4:1 multiplexer. The document concludes that combinational circuits like these produce outputs only based on present inputs and have no memory elements, resulting in no delay in producing outputs.
This document provides an overview of linear integrated circuits. It defines an integrated circuit as multiple interconnected electronic components on a single semiconductor chip. Analog integrated circuits are classified as either linear or non-linear, with linear ICs having a linear relationship between voltage and current, such as the op-amp IC 741. Digital ICs operate at discrete levels instead of continuous values. The document outlines the course objectives and units which will introduce operational amplifiers, applications, analog multipliers, analog-to-digital converters, waveform generators, and special function ICs.
Digital electronics deals with digital signals represented as 1s and 0s to perform tasks. It uses integrated circuits and logic gates on silicon chips. Digital systems are more accurate and faster than analog systems. Common digital devices include data servers, GPS systems, and security systems. Logic gates are basic building blocks, and CMOS is the most common integrated circuit type due to its low power usage. Digital systems have advantages over analog in applications like vehicle speedometers. Digital electronics has a wide future scope due to advantages like decreased size, accuracy, and secure data transmission.
The past decade has seen significant advancement in the field of consumer electronics. Various ‘intelligent’ appliances such as cellular phones, air-conditioners, home security devices, home theatres, etc. are set to realize the concept of a smart home. They have given rise to a Personal Area Network in home environment, where all these appliances can be interconnected and monitored using a single controller.
Busy families and individuals with physical limitation represent an attractive market for home automation and networking. A wireless home network that does not incur additional costs of wiring would be desirable. Bluetooth technology, which has emerged in late 1990s, is an ideal solution for this purpose.
Home automation involves introducing a degree of computerized or automatic control to
Certain electrical and electronic systems in a building. These include lighting, temperature
Control etc.
This project demonstrates a simple home automation system which contains a remote mobile host controller and several client modules (home appliances). The client modules communicate with the host controller through a wireless device such as a Bluetooth enabled mobile phone, in this case, an android based Smart phone.
23. serial and parallel data communicationsandip das
This document discusses serial and parallel data transfer modes in microprocessors. It focuses on the 8085 microprocessor. There are two main modes: parallel I/O mode where the 8085 communicates directly with I/O devices using its full data bus, and serial I/O mode where it uses a converter and single data line. Serial I/O involves asynchronous or synchronous transmission formats, with asynchronous using start and stop bits to delineate characters. The 8085 has two pins, SOD and SID, for software-controlled serial I/O using the SIM and RIM instructions to output and input single bits of serial data.
This document describes a mini project to build an electronic counter that can count up to 10,000 using an infrared light sensor and integrated circuits. It presents the motivation, objectives, introduction, components, block diagram, circuit diagram, working, applications, problems faced, and future scope of the electronic counter project. The counter automates manual counting and is designed using low power CMOS ICs. It uses a light dependent resistor, timer IC, decade counter, BCD to 7-segment display, and 7-segment display. The counter has applications in industries, parking areas, offices, and other areas to automate counting.
This document discusses the design of a floating point multiplier. It begins by explaining the representation of floating point numbers with sign, exponent, and significand. It then describes why floating point is used over fixed point for its wider range of values and greater precision over integers. The key steps for multiplying floating point numbers are described as adding the exponents and multiplying the significands, while XORing the signs. Block diagrams and techniques for partial product generation and accumulation are presented, including radix-4 Booth multiplication and use of carry save adders and ripple carry adders. Finally, floating point formats for single, double, and quadruple precision are shown along with using the divide and conquer technique for higher precision multiplication.
100 watt inverter using IC CD4047 and MOSFET IRF540
CD 4047 is a low power CMOS astable/monostable multivibrator IC. Here it is wired as an astable multivibrator producing two pulse trains of 0.01s which are 180 degrees out of phase at the pins 10 and 11 of the IC. Pin 10 is connected to the gate of Q1 and pin 11 is connected to the gate of Q2. Resistors R3 and R4 prevents the loading of the IC by the respective MOSFETs. When pin 10 is high Q1 conducts and current flows through the upper half of the transformer primary which accounts for the positive half of the output AC voltage. When pin 11 is high Q2 conducts and current flows through the lower half of the transformer primary in opposite direction and it accounts for the negative half of the output AC voltage.
Introduction to Embedded System I: Chapter 2 (5th portion)Moe Moe Myint
The document provides an introduction to embedded systems, outlining key components and concepts. It discusses the core of embedded systems including processors, programmable logic devices, and memory. Sensors, actuators, and communication interfaces are also reviewed. Embedded firmware, other system components like reset circuits and watchdogs, and printed circuit boards are examined. The objectives are to learn about the building blocks of embedded systems and factors in selecting components.
DTMF based home automation without using Microcontrollerprasanth nani
This document describes a DTMF-based home automation system that allows controlling home appliances wirelessly using a mobile phone. It works by using a DTMF decoder chip to decode tones from the phone dial pad and trigger relays connected to devices. The system has advantages like wireless control and energy savings but limitations like limited number of controllable devices and lack of feedback. It finds applications in homes and industries for remote control of electrical systems.
Electromechanical and solid state relays are used in industrial and commercial applications. Electromechanical relays consist of an electromagnet, armature, spring, and set of contacts. They operate by using a small electrical signal to energize an electromagnet, which pulls the armature and closes the contacts to allow current from another circuit to flow. Relays allow isolation between control and load circuits. They are useful for switching higher power loads than transistors and can switch both AC and DC. However, relays are larger than transistors and cannot switch as rapidly. Relay specifications include coil voltage and current and contact ratings. Relays are commonly used in machine control applications.
This document describes how to build a robot that can be controlled via Bluetooth from a mobile phone or PC. An HC-05 Bluetooth module connects to a microcontroller on the robot to receive commands from a Bluetooth-enabled device. The microcontroller then uses a motor driver IC to control the robot's motors to move forward, reverse, or turn based on the received commands.
This document discusses counters, which are digital circuits used for counting pulses. It describes asynchronous and synchronous counters, and different types including up/down counters, decade counters, ring counters, and Johnson counters. Examples of counter applications are given such as in kitchen appliances, washing machines, microwaves, and programmable logic controllers. Counters are used for tasks like time measurement, frequency division, and digital signal generation.
The document discusses the ICL8038 function generator integrated circuit. It can produce sine, square, triangular, sawtooth, and pulse waveforms using minimal external components. The frequency can be selected from 0.001Hz to over 300kHz using resistors or capacitors. It has features like low frequency drift with temperature, low distortion, high linearity, and wide frequency range. It can simultaneously output sine, square, and triangle waves.
This document provides a project report on an automatic room light controller with a bidirectional visitor counter. The report includes an abstract, introduction, list of components, schematic diagrams, hardware design and descriptions of the main components. The system uses an infrared sensor and microcontroller to sense when a person enters or exits a room and count the number of visitors. It controls a relay to turn the room light on or off depending on the visitor count. The report provides details of the circuit design and components used to realize this automatic light and visitor counting system.
Automatic Room Lock And Lights Off CircuitAmrish Tejas
This circuit automatically controls room lights and locks based on the number of people in the room. It uses 555 timers, a 74LS192 decade counter, 74LS47 7-segment display driver, and HEF4002B 4-input NOR gate. The counter tracks the number of people and displays it. When someone enters, it increases the count and turns on the lights. When empty, it turns off the lights. The NOR gate controls the relay for locking/unlocking the door based on the people count. It can be useful for monitoring room capacity and conserving energy by automatically turning lights off. Future improvements could include remote monitoring and voice alerts.
This document discusses using a 4:1 multiplexer to create half adder and half subtractor combinational circuits. It defines half adders, half subtractors, and multiplexers. It then shows the logic diagrams and transistor-level implementations of half adders and half subtractors using a 4:1 multiplexer. The document concludes that combinational circuits like these produce outputs only based on present inputs and have no memory elements, resulting in no delay in producing outputs.
This document provides an overview of linear integrated circuits. It defines an integrated circuit as multiple interconnected electronic components on a single semiconductor chip. Analog integrated circuits are classified as either linear or non-linear, with linear ICs having a linear relationship between voltage and current, such as the op-amp IC 741. Digital ICs operate at discrete levels instead of continuous values. The document outlines the course objectives and units which will introduce operational amplifiers, applications, analog multipliers, analog-to-digital converters, waveform generators, and special function ICs.
Digital electronics deals with digital signals represented as 1s and 0s to perform tasks. It uses integrated circuits and logic gates on silicon chips. Digital systems are more accurate and faster than analog systems. Common digital devices include data servers, GPS systems, and security systems. Logic gates are basic building blocks, and CMOS is the most common integrated circuit type due to its low power usage. Digital systems have advantages over analog in applications like vehicle speedometers. Digital electronics has a wide future scope due to advantages like decreased size, accuracy, and secure data transmission.
The past decade has seen significant advancement in the field of consumer electronics. Various ‘intelligent’ appliances such as cellular phones, air-conditioners, home security devices, home theatres, etc. are set to realize the concept of a smart home. They have given rise to a Personal Area Network in home environment, where all these appliances can be interconnected and monitored using a single controller.
Busy families and individuals with physical limitation represent an attractive market for home automation and networking. A wireless home network that does not incur additional costs of wiring would be desirable. Bluetooth technology, which has emerged in late 1990s, is an ideal solution for this purpose.
Home automation involves introducing a degree of computerized or automatic control to
Certain electrical and electronic systems in a building. These include lighting, temperature
Control etc.
This project demonstrates a simple home automation system which contains a remote mobile host controller and several client modules (home appliances). The client modules communicate with the host controller through a wireless device such as a Bluetooth enabled mobile phone, in this case, an android based Smart phone.
23. serial and parallel data communicationsandip das
This document discusses serial and parallel data transfer modes in microprocessors. It focuses on the 8085 microprocessor. There are two main modes: parallel I/O mode where the 8085 communicates directly with I/O devices using its full data bus, and serial I/O mode where it uses a converter and single data line. Serial I/O involves asynchronous or synchronous transmission formats, with asynchronous using start and stop bits to delineate characters. The 8085 has two pins, SOD and SID, for software-controlled serial I/O using the SIM and RIM instructions to output and input single bits of serial data.
This document describes a mini project to build an electronic counter that can count up to 10,000 using an infrared light sensor and integrated circuits. It presents the motivation, objectives, introduction, components, block diagram, circuit diagram, working, applications, problems faced, and future scope of the electronic counter project. The counter automates manual counting and is designed using low power CMOS ICs. It uses a light dependent resistor, timer IC, decade counter, BCD to 7-segment display, and 7-segment display. The counter has applications in industries, parking areas, offices, and other areas to automate counting.
This document discusses the design of a floating point multiplier. It begins by explaining the representation of floating point numbers with sign, exponent, and significand. It then describes why floating point is used over fixed point for its wider range of values and greater precision over integers. The key steps for multiplying floating point numbers are described as adding the exponents and multiplying the significands, while XORing the signs. Block diagrams and techniques for partial product generation and accumulation are presented, including radix-4 Booth multiplication and use of carry save adders and ripple carry adders. Finally, floating point formats for single, double, and quadruple precision are shown along with using the divide and conquer technique for higher precision multiplication.
100 watt inverter using IC CD4047 and MOSFET IRF540
CD 4047 is a low power CMOS astable/monostable multivibrator IC. Here it is wired as an astable multivibrator producing two pulse trains of 0.01s which are 180 degrees out of phase at the pins 10 and 11 of the IC. Pin 10 is connected to the gate of Q1 and pin 11 is connected to the gate of Q2. Resistors R3 and R4 prevents the loading of the IC by the respective MOSFETs. When pin 10 is high Q1 conducts and current flows through the upper half of the transformer primary which accounts for the positive half of the output AC voltage. When pin 11 is high Q2 conducts and current flows through the lower half of the transformer primary in opposite direction and it accounts for the negative half of the output AC voltage.
Introduction to Embedded System I: Chapter 2 (5th portion)Moe Moe Myint
The document provides an introduction to embedded systems, outlining key components and concepts. It discusses the core of embedded systems including processors, programmable logic devices, and memory. Sensors, actuators, and communication interfaces are also reviewed. Embedded firmware, other system components like reset circuits and watchdogs, and printed circuit boards are examined. The objectives are to learn about the building blocks of embedded systems and factors in selecting components.
DTMF based home automation without using Microcontrollerprasanth nani
This document describes a DTMF-based home automation system that allows controlling home appliances wirelessly using a mobile phone. It works by using a DTMF decoder chip to decode tones from the phone dial pad and trigger relays connected to devices. The system has advantages like wireless control and energy savings but limitations like limited number of controllable devices and lack of feedback. It finds applications in homes and industries for remote control of electrical systems.
Electromechanical and solid state relays are used in industrial and commercial applications. Electromechanical relays consist of an electromagnet, armature, spring, and set of contacts. They operate by using a small electrical signal to energize an electromagnet, which pulls the armature and closes the contacts to allow current from another circuit to flow. Relays allow isolation between control and load circuits. They are useful for switching higher power loads than transistors and can switch both AC and DC. However, relays are larger than transistors and cannot switch as rapidly. Relay specifications include coil voltage and current and contact ratings. Relays are commonly used in machine control applications.
This document describes how to build a robot that can be controlled via Bluetooth from a mobile phone or PC. An HC-05 Bluetooth module connects to a microcontroller on the robot to receive commands from a Bluetooth-enabled device. The microcontroller then uses a motor driver IC to control the robot's motors to move forward, reverse, or turn based on the received commands.
This document discusses counters, which are digital circuits used for counting pulses. It describes asynchronous and synchronous counters, and different types including up/down counters, decade counters, ring counters, and Johnson counters. Examples of counter applications are given such as in kitchen appliances, washing machines, microwaves, and programmable logic controllers. Counters are used for tasks like time measurement, frequency division, and digital signal generation.
The document discusses the ICL8038 function generator integrated circuit. It can produce sine, square, triangular, sawtooth, and pulse waveforms using minimal external components. The frequency can be selected from 0.001Hz to over 300kHz using resistors or capacitors. It has features like low frequency drift with temperature, low distortion, high linearity, and wide frequency range. It can simultaneously output sine, square, and triangle waves.
This document provides a project report on an automatic room light controller with a bidirectional visitor counter. The report includes an abstract, introduction, list of components, schematic diagrams, hardware design and descriptions of the main components. The system uses an infrared sensor and microcontroller to sense when a person enters or exits a room and count the number of visitors. It controls a relay to turn the room light on or off depending on the visitor count. The report provides details of the circuit design and components used to realize this automatic light and visitor counting system.
Automatic Room Lock And Lights Off CircuitAmrish Tejas
This circuit automatically controls room lights and locks based on the number of people in the room. It uses 555 timers, a 74LS192 decade counter, 74LS47 7-segment display driver, and HEF4002B 4-input NOR gate. The counter tracks the number of people and displays it. When someone enters, it increases the count and turns on the lights. When empty, it turns off the lights. The NOR gate controls the relay for locking/unlocking the door based on the people count. It can be useful for monitoring room capacity and conserving energy by automatically turning lights off. Future improvements could include remote monitoring and voice alerts.
This document outlines a project to design and construct an automatic room light controller with a bidirectional visitor counter. It aims to limit power waste by turning lights off when rooms are empty and automatically turning them on when people enter. The system will incorporate transmitters, receivers, and relays to detect presence and absence and control lights accordingly. It will also count the number of people in a room at a given time. The project scope includes use in schools, offices, and conference halls to conserve electricity without inconveniencing visitors.
Automatic room light controller using microcontroller and visitor countereSAT Journals
Abstract The Project ‘Automatic Room Light Controller Using microcontroller ATMEGA16A and bidirectional visitor counter’ controls a room light as well as count the number of individuals entering and leaving a room. When an individual enters into a room then one counter is incremented by one and one light in a room will be switched ON and when the individuals leaves a room then the counter is decremented by one. When the number of individuals in a room is greater than 5 then 2 lights will be switched ON. When the individuals in a room are more than 10 then 3 lights will be switched ON. Similarly on increase of every 5 individuals one more light will switched ON. Lights will turn OFF when all the individuals go out of a room. The total number of individuals present inside a room is also displayed on the LCD display. IR sensors and microcontroller does above job. IR sensors sense the obstruction and microcontroller receives the signals produced by the obstruction from the sensors. The received signal is operated via program stored in ROM of Microcontroller.. Keywords: Microcontroller ATMEGA16A, IR Sensors, LCD, Counters
Android is an open source software stack for mobile devices that includes an operating system, middleware and key applications. It was developed by Google and the Open Handset Alliance to advance open standards for mobile devices. When released in 2008, most of the Android platform was made available under the Apache free-software and open-source license. The unveiling of Android was announced with the founding of the Open Handset Alliance, a consortium of 34 hardware, software and telecom companies devoted to advancing open standards for mobile devices.
1. The document discusses prepaid energy meters as an alternative to traditional electricity billing systems. Prepaid energy meters allow customers to pay for a set amount of electricity units in advance before using them.
2. Traditional billing systems are time-consuming and error-prone, involving manual meter readings, bill production, and payment collection. Prepaid energy meters address these issues by automating the process.
3. Key advantages of prepaid energy meters include accuracy, reducing debt and electricity theft, enabling customers to better budget their electricity usage, and allowing suppliers to better monitor consumption and demand.
Faculty of Engineering & Technology , Gurukula Kangri University , Haridwarashwini kumar
Topic:- Tachometer
Description :- This is use to measure the speed of rotating machines in rpm....
Ashwini kumar
Electrical Engineering
ashwinikmr555@gmail.com
+919027134556
This document describes a prepaid electricity meter project aimed at minimizing power losses in India. The project involves developing an electronic meter that monitors electricity consumption, informs users of usage via SMS, and allows for prepaid payment of bills. When the prepaid balance reaches zero, the meter will automatically cut off power to loads like bulbs. Key components include a microcontroller, LCD display, GSM module, and relays to control loads. The goal is to shift from a postpaid billing system prone to losses to a prepaid system with automatic notifications and cutoffs to reduce theft.
Bidirectional visitor counter & home automation by Jitendra DhakaNIT srinagar
This document appears to be an industrial training report submitted by Jitendra Dhaka to the National Institute of Technology in Hazratbal, Srinagar, India. The report details Dhaka's winter training on embedded systems conducted at TATA CMC Jaipur. It includes an acknowledgements section thanking various individuals and organizations for their support. It also includes a preface describing the benefits of industrial training for engineering students and an overview of the project Dhaka completed - a bidirectional visitor counter and home automation system.
The document discusses various renewable energy sources in India, including their current usage and potential. It provides details on solar energy technologies and applications, the wind energy program in India, hydropower systems, bioenergy including biomass, biogas and biofuels, and emerging renewable options. It also outlines relevant policies and legislation in India to promote renewable energy.
Automatic room light controller with visible counterMafaz Ahmed
This project creates an automatic room light controller that also counts visitors bidirectionally. When someone enters the room, the counter increments and the light turns on. When someone leaves, the counter decrements and the light turns off once the room is empty. A password must be entered using a keypad to unlock the room. The system uses an ATmega16 microcontroller, infrared sensors, an LCD display, relays and other components. It provides functions like automatic lighting control, visitor counting and secured access with a password. The design aims to ease complexity and control room congestion.
This document is a project report for an automatic room light controller with a bidirectional visitor counter. It includes certificates signed by the project supervisors and head of department certifying the completion of the project by the students. It also includes an acknowledgment, abstract, preface, table of contents, and introduction describing the objective of the project to count the number of people entering and leaving a room and control the room lights accordingly. The block diagram and its description are provided, outlining the main components including a power supply, entry and exit sensors, microcontroller, and relay driver circuit.
The flywheel is a rotating mechanical device that stores rotational energy. It is typically made of steel and connects the engine's crankshaft to the transmission, smoothing out the power delivery from the engine. The flywheel's position is between the engine and clutch, and it is used to start the engine by providing rotational energy to the crankshaft when the starter is engaged. The principle of the flywheel has been known since Neolithic pottery wheels and spindles, and it was further developed during the Industrial Revolution for use in steam engines.
ppt of automatic room light controller and BI directional counterMannavapremkumar
This document is a project presentation for an automatic room light controller. It includes the objective, introduction, block diagram, circuit diagram, advantages, disadvantages, limitations and applications. The block diagram shows the components used including IR transmitters and receivers, timers, counters and a relay to control the room light. The circuit diagram provides more details of the electronic components and connections used to automatically turn the light on when motion is detected and off when the room is empty.
Automatic room light controller with bidirectional visitor counterNiladri Dutta
This document describes a student project to create an automatic room light controller with a bi-directional visitor counter. The project uses sensors to detect when people enter or exit a room and a microcontroller to count visitors and control the room lights accordingly. When the first person enters, the light turns on and the counter increments by one. When the last person exits, the light turns off and the counter resets to zero. The project aims to automatically control room lighting and count visitors to prevent wasted electricity in places like schools, offices, and homes. It discusses the components used, the circuit diagram, working principle, advantages like low cost and automatic operation, and potential applications.
1) A flywheel energy storage system consists of five main components: a flywheel, motor/generator, power electronics, magnetic bearings, and external inductor.
2) Flywheels store energy mechanically in the form of kinetic energy by rotating a steel or composite mass at high speeds.
3) Permanent magnet motors/generators are most suitable as they provide higher efficiency and smaller size compared to other types.
A Report on Bidirectional Visitor Counter using IR sensors and Arduino Uno R3Abhishekvb
The aim of our project is to make a controller which can sense if any person enters the room and it lights up the room automatically and also counts how many person are entering the room or going out of it.
Dimmers are devices used to vary the brightness of lights by changing the voltage waveform applied. Early dimmers used inefficient variable resistors or rheostats, but modern dimmers use silicon-controlled rectifiers for higher efficiency. Dimmers are used both in domestic and professional lighting installations, with professional dimmers often controlled digitally via protocols like DMX. Key developments included the first solid-state dimmer by Joel Spira and the introduction of thyristor dimmers which enabled remote analog control.
Design and Implementation of Astable Multivibrator using 555 Timer IOSRJEEE
The 555 timer is widely used as IC timer circuit and it is the most commonly used general purpose linear integrated circuit. It can run in either one of the two modes: Monostable (one stable state) or Astable (no stable state). In the Monostable mode it can produce accurate time delays from microseconds to hours. In the Astable mode it can produce rectangular waveforms with a variable Duty cycle. The simplicity and ease with which both the multivibrator circuits can be configured around this IC is one of the main reasons for its wide use. The state of the art presented in the paper is the design and implementation of an Astable multivibrator using 555 timer IC, generating non-sinusoidal waveform in the form of Rectangular waveform as well as capacitor voltage waveform in the form of ramp waveform.
This document discusses several integrated circuits used for filtering, timing, waveform generation, and phase locking. It describes the universal active filter IC, which can produce low-pass, high-pass, and band-pass filter responses from a single chip. It also summarizes timer ICs like the 555 and XR-2240, which can generate accurate time delays from microseconds to days. Finally, it covers function generator ICs like the 8038 and XR-2206, which can produce sine, square and triangular waveforms, and the 565 phase locked loop IC.
This document describes the design of a heat sensor circuit using an IC 555 timer. The circuit uses a diode as a temperature sensor whose resistance decreases with increasing temperature. When the temperature rises above a threshold, the 555 timer is triggered to produce a 2 minute alarm from a piezo buzzer. Key components include the 555 timer, resistor, capacitor, transistor, diode, LED, and piezo buzzer. The circuit operates in monostable mode to provide a timed output when the temperature rises above the threshold set by the variable resistor.
This document describes an automatic Mall elevator control system that uses an infrared sensor and microcontroller to automatically turn the elevator lights on when someone enters and off when they leave to save power. It includes block diagrams of the system components, detailed circuit diagrams and explanations of the infrared transmitter, receiver, microcontroller, and power supply circuits. The system aims to save electrical power by automatically controlling the elevator lights based on occupancy.
ELECTRONICS PROJECT REPORT OF HOME AUTOMATION CUM BUILDING SECUIRITYEldhose George
This document summarizes a home security and automation system that uses an intruder detection system and cameras for security, and controls lights, garden watering, and a water pump for automation. The security section uses IR sensors and cameras to detect intruders and monitor areas. The automation section controls lights, garden watering using a solenoid valve, and a water pump for an overhead tank. The system is controlled by a microcontroller and includes circuits for sensors, cameras, relays, and a power supply.
The document describes the design and development of a TV remote jammer circuit using an IC 555 timer. It begins with an introduction to remote controls and their operating principles. It then discusses the literature surveyed on remote jamming techniques. The system development section describes the use of an astable multivibrator using IC 555 to generate pulses that jam the IR receiver of the TV. It provides circuit diagrams and explanations of the power supply, astable multivibrator, and the overall TV remote jammer circuit. The document aims to jam the TV receiver at a particular frequency and channel to prevent changes using the remote control.
The document describes the design and development of a TV remote jammer circuit using an IC 555 timer. It begins with an introduction to remote controls and their operating principles. It then discusses the literature surveyed on remote jamming techniques. The system development section describes the use of an astable multivibrator using IC 555 to generate pulses that jam the IR receiver of the TV. It provides circuit diagrams and explanations of the power supply, astable multivibrator, and the overall TV remote jammer circuit. The document aims to jam the TV receiver at a particular frequency and channel to prevent changes using the remote control.
Microcontroller based multifunction_relayRajeev Kumar
This document discusses a microcontroller-based relay system for detecting faults in a power system. It describes how the microcontroller monitors electrical parameters in real-time, detects abnormal conditions, and sends a trip signal to circuit breakers. The microcontroller converts analog signals to digital using an ADC and detects faults based on programmed conditions. It also discusses using the system to implement overvoltage/undervoltage protection and the advantages of microcontroller-based relays over electromechanical relays.
Here is the code for an open loop speed controller:
#include <PWM.h>
#define ENABLE 5
#define DIR1 3
#define DIR2 4
void setup() {
pinMode(ENABLE, OUTPUT);
pinMode(DIR1, OUTPUT);
pinMode(DIR2, OUTPUT);
PWM.begin();
PWM.setPeriod(500); // Period in microseconds
}
void loop() {
// Run motor forward at half speed
digitalWrite(DIR1, HIGH);
digitalWrite(DIR2, LOW);
PWM.setDuty(ENABLE, 50); // Duty cycle in percent
delay(2000); // Run for 2 seconds
This document describes the components and construction of a digital heart beat counter circuit. The circuit uses a piezoelectric sensor to detect heart beats which are then amplified and filtered. A 555 timer chip creates pulses from the filtered signal which are counted by a 4026 decade counter. The count is displayed on 7-segment LED displays. Key components include operational amplifiers, logic gates, voltage regulators, and LED displays. The circuit automatically counts heart beats over a 10 second interval and displays the result.
Sensors are devices that measure physical quantities and convert them into signals that can be read by observers or instruments. The document discusses several common sensors: infrared (IR) sensors, sound sensors, temperature sensors, and discusses their working principles and applications. It also provides details on using timers and integrated circuits like the 555 timer IC to process sensor output signals.
Sensors are devices that measure physical quantities and convert them into signals that can be read by observers or instruments. The document discusses several common sensors: infrared (IR) sensors, sound sensors, temperature sensors. It provides details on how IR sensors, temperature sensors, and timer integrated circuits like the 555 timer work, including diagrams of common circuits. Applications of sensors include in cars, machines, medicine, manufacturing, and robotics.
Functional block, characteristics of 555 Timer and its PWM application – IC-566 voltage controlled oscillator IC; 565-phase locked loop IC, AD633 Analog multiplier ICs.
A report on ultrasonic distance measurementitfakash
The document describes an ultrasonic distance meter circuit. It consists of a microcontroller that encodes and transmits ultrasonic pulses via a transmitter. When the pulses reflect off an object, a receiver detects the echo and the microcontroller calculates the distance based on the time elapsed. It displays the measured distance on an LCD screen. The circuit uses various components like a voltage regulator, microcontroller, LCD, buzzer, and ultrasonic transducers to transmit pulses, receive echoes, and determine distances to objects.
The document describes a remote controlled fan regulator that allows controlling a fan's speed without moving. It uses an infrared receiver to receive signals from the remote control. A decade counter then controls the speed, varying the pulse width which changes the TRIAC firing angle and fan speed. The aim was to develop an affordable, reliable remote controlled fan system.
The 555 timer is a versatile integrated circuit that can be used to generate accurate timing signals. It works by using internal comparators and a flip-flop to accurately time an external resistor-capacitor circuit. The 555 timer can be used in various configurations (monostable, bistable, astable) to generate pulses or oscillations for applications like timers, flashing lights, and tone generation. It is an inexpensive and robust chip contained in an 8-pin package that can drive loads directly from its output.
early 1871 Belgian inventor Zénobe Gramme invented a generator powerful enough to produce power on a commercial scale for industry.[1]
In 1878, a hydroelectric power station was designed and built by William, Lord Armstrong at Cragside, England. It used water from lakes on his estate to power Siemens dynamos. The electricity supplied power to lights, heating, produced hot water, ran an elevator as well as labor-saving devices and farm buildings.[2]
In January 1882 the world's first public coal-fired power station, the Edison Electric Light Station, was built in London, a project of Thomas Edison organized by Edward Johnson. A Babcock & Wilcox boiler powered a 93 kW (125 horsepower) steam engine that drove a 27-tonne (27-long-ton) generator. This supplied electricity to premises in the area that could be reached through the culverts of the viaduct without digging up the road, which was the monopoly of the gas companies. The customers included the City Temple and the Old Bailey. Another important customer was the Telegraph Office of the General Post Office, but this could not be reached through the culverts. Johnson arranged for the supply cable to be run overhead, via Holborn Tavern and Newgate.[3]
In September 1882 in New York, the Pearl Street Station was established by Edison to provide electric lighting in the lower Manhattan Island area. The station ran until destroyed by fire in 1890. The station used reciprocating steam engines to turn direct-current generators. Because of the DC distribution, the service area was small, limited by voltage drop in the feeders. In 1886 George Westinghouse began building an alternating current system that used a transformer to step up voltage for long-distance transmission and then stepped it back down for indoor lighting, a more efficient and less expensive system which is similar to modern systems. The war of the currents eventually resolved in favor of AC distribution and utilization, although some DC systems persisted to the end of the 20th century. DC systems with a service radius of a mile (kilometer) or so were necessarily smaller, less efficient of fuel consumption, and more labor-intensive to operate than much larger central AC generating stations.early 1871 Belgian inventor Zénobe Gramme invented a generator powerful enough to produce power on a commercial scale for industry.[1]
In 1878, a hydroelectric power station was designed and built by William, Lord Armstrong at Cragside, England. It used water from lakes on his estate to power Siemens dynamos. The electricity supplied power to lights, heating, produced hot water, ran an elevator as well as labor-saving devices and farm buildings.[2]
In January 1882 the world's first public coal-fired power station, the Edison Electric Light Station, was built in London, a project of Thomas Edison organized by Edward Johnson. A Babcock & Wilcox boiler powered a 93 kW (125 horsepower) steam engine that drove a 27-tonne (27-long-ton) generator. This supplk
This document describes the design of a clap-activated switch circuit. The circuit uses a microphone to detect clapping sounds and convert them to electrical signals. These signals are amplified and used to trigger a timer integrated circuit (IC). The timer IC is configured as a monostable multivibrator and its output drives a decade counter IC that acts as a bistable switch to turn a relay on or off. The relay then switches power to an electrical device. The circuit only changes the output state when two claps are detected within a set time period determined by a resistor-capacitor component. The circuit provides a simple way to remotely control devices through hand clapping without risk of accidental triggering.
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Automatic room light contoller without microcontroller
1. 1. Introduction
Projet title is “Automatic Room Light Controller”. The objective of this project is
to make a model to count number of person visiting particular room and accordingly
light up the room. Here we can use sensonrs and can know present number of persons.
In today’s world, there is a continuous need for automatic appliances with the
increase in standard of living, there is a sense of urgency for developing circuits that
would ease the complexity of life.
Also if at all one wants to know the number of people present in room so as not
to have congestion. This circuit proves to be helpful. The project is a reliable circuit
that takes over the task of controlling the room lights as well as counting number of
persons/visitors in the room very accurately. When somebody enters in the room then
the counter is decremented by one. The light will be onlye switched OFF until all the
persons in the room go out. The total number of persons inside the room is also
displayed on the seven segment displays.
The 555 timer does the above job.It receives the signals from the sensors, and this
signal is operated under the control of software which is stored in 555 timer
continuously monitor the Infrared Receivers. When any object pass through the IR’s
Receivers then the IR rays falling on the receivers are obstructed, this obstraction is
sensed by the 555 timer.
2. Working Principle
2.1 Circuit Diagram
2. There are two main part of the circuits.
1. Transmission Circuit(Infrared Led’s)
2. Receiver Circuit
1. Transmission Circuit
This circuit diagram show how a 555 timer IC, configured to function as a basic
astable multivibrator. The astable multivibrator generates a square wave, the period of
which is determined by the circuit external to IC 555. The astable multivibrator does
not require any external trigger to change the state of the output. Hence the name free
running oscillator. The time during which the output is either high or low is
3. determined by the two resistors and a capacitor which are externally connected to the
555 timer.
IR Transmission circuit is used to generate the modulated 36 kHz IR signal. The
IC555 in the transmitter side is to generate 36 kHz square wave. Adjust the preset in
the transmitter to get a 38 kHz signal at the output. Then you point it over the sensors
and its output will go low when it senses the IR signal of 38 kHz.
2. Receiver Circuit
The IR transmitter will emit modulated 38 kHz IR signal and at the receiver we use
TSPO1738(Infrared Sensor). The output goes high when there is an interruption and it
return back to low after the time period determined by the capacitor and resistor in the
circuit i.e. around 1 Second. CL100 is to trigger the IC555 which is configured as
monostable multivibrator. Input is given to the port 1. Port 0 is user for the 7-Segment
4. display purpose. Port 2 is used for the relay Turn on and Turn off purpose. LTS
542(Common Anode) is used for 7-Segment display and that time relay will get
voltage and triggered, so light will get voltage and it will turn on and when counter
will be 00 and at that time relay turned off.
2.2 PCB Layout
2.3 Components Lists
2.4 Working
This system is designed by using two sets of IR transmitters and receivers. These IR
sensors are placed in such a way that they detect a person entering and leaving the
room to turn the home appliances. In this optimum energy management system, a
microcontroller is the central processing unit of this project which is of 89S51
5. controller from the 8051 family. This system facilitates a bidirectional visitor counter
for displaying the number of persons inside the room.
When a person enters into the room, an IR beam is obstructed between the IR
transmitter and the receiver. This IR obstruction from the sensor-1 gives the
corresponding signal to the microcontroller. The microcontroller in such a way that by
the reception of the signal from the sensor-1 it turns on the fans and lights inside the
room. Thus, the microcontroller gives command signals to a relay driver which turns
the rellays such that all these appliances turn on.
When the person leaves from this room, another set of IR sensors enable and give
control signals to the microcontroller. Furthermore, similar to the above process, this
system turns off the appliances like fans and lights. Apart from this, the system also
takes account of the number of persons inside the room so that this control operation
is varied depending on the persons’ availability in the room.
For every person entering and leaving the room, the microcontroller reads the digital
input from two receivers, and calculates the number of persons inside the room, and
then displays it on the LCD. When the persons’ count is greater than one, the
microcontroller turns on the room light and when the persons’ count is zero, it turns
off all the lights and fans.
3. DESIGN PROCEDURE
3.1 Multivator
A multivibrator circuit oscillates between a “HIGH” state and a “LOW” state
producing a continuous output. Astable multivibrators generally have an even 50%
duty cycle, that is that 50% of the cycle time the output is “HIGH” and the remaining
50% of the cycle time the output is “OFF”. In other words, the duty cycle for an
astable timing pulse is 1:1.
Sequential Logic Circuits that use the clock signal for synchronization are dependant
upon the frequency and and clock pulse width to activate there switching action.
Sequential circuits may also change their state on either the rising or falling edge, or
both of the actual clock signal as we have seen previously with the basic flip-flop
circuits. The following list are terms associated with a timing pulse or waveform.
Active HIGH - if the state change occurs from a “LOW” to a “HIGH” at the clock’s
pulse rising edge or during the clock width.
6. Clock Signal Waveform
Active LOW - if the state change occurs from a “HIGH” to a “LOW” at the clock’s
pulses falling edge.
Duty Cycle - this is the ratio of the clock width to the clock period.
Clock Width - this is the time during which the value of the clock signal is equal to a
logic “1”, or HIGH.
Clock Period - this is the time between successive transitions in the same direction,
ie, between two rising or two falling edges.
Clock Frequency - the clock frequency is the reciprocal of the clock period,
frequency = 1/clock period
Clock pulse generation circuits can be a combination of analogue and digital circuits
that produce a continuous series of pulses (these are called astable multivibrators) or a
pulse of a specific duration (these are called monostable multivibrators). Combining
two or more of multivibrators provides generation of a desired pattern of pulses
(including pulse width, time between pulses and frequency of pulses).
There are basically three types of clock pulse generation circuits:
· Astable – A free-running multivibrator that has NO stable states but
switches continuously between two states this action produces a train of square
wave pulses at a fixed frequency.
· Monostable – A one-shot multivibrator that has only ONE stable state and
is triggered externally with it returning back to its first stable state.
· Bistable – A flip-flop that has TWO stable states that produces a single
pulse either positive or negative in value.
One way of producing a very simple clock signal is by the interconnection of logic
gates. As NANDgates contains amplification, they can also be used to provide a clock
signal or timing pulse with the aid of a single Capacitor and a single Resistor to
provide the feedback and timing function.
These timing circuits are often used because of there simplicity and are also useful if a
logic circuit is designed that has unused gates which can be utilised to create the
monostable or astable oscillator. This simple type of RC Oscillator network is
sometimes called a “Relaxation Oscillator”.
7. 3.1 Operation:
Figure 1: Basic BJT astable multivibrator
The circuit has two astable (unstable) states that change alternatively with maximum
transition rate because of the "accelerating" positive feedback. It is implemented by
the coupling capacitors that instantly transfer voltage changes because the voltage
across a capacitor cannot suddenly change. In each state, one transistor is switched on
and the other is switched off. Accordingly, one fully charged capacitor discharges
(reverse charges) slowly thus converting the time into an exponentially changing
voltage. At the same time, the other empty capacitor quickly charges thus restoring its
charge (the first capacitor acts as a time-setting capacitor and the second prepares to
play this role in the next state). The circuit operation is based on the fact that the
forward-biased base-emitter junction of the switched-on bipolar transistor can provide
a path for the capacitor restoration.
3.2 State 1 (Q1 is switched on, Q2 is switched off):
In the beginning, the capacitor C1 is fully charged (in the previous State 2) to the
power supply voltage V with the polarity shown in Figure 1. Q1 is on and connects
the left-hand positive plate of C1 to ground. As its right-hand negative plate is
connected to Q2 base, a maximum negative voltage (-V) is applied to Q2 base that
keeps Q2 firmly off. C1 begins discharging (reverse charging) via the high-value base
resistor R2, so that the voltage of its right-hand plate (and at the base of Q2) is rising
from below ground (-V) toward +V. As Q2 base-emitter junction is backward-biased,
it does not conduct, so all the current from R2 goes into C1. Simultaneously, C2 that
is fully discharged and even slightly charged to 0.6 V (in the previous State 2) quickly
charges via the low-value collector resistor R4 and Q1 forward-biased base-emitter
junction (because R4 is less than R2, C2 charges faster than C1). Thus C2 restores its
charge and prepares for the next State C2 when it will act as a time-setting capacitor.
Q1 is firmly saturated in the beginning by the "forcing" C2 charging current added to
R3 current; in the end, only R3 provides the needed input base current. The resistance
R3 is chosen small enough to keep Q1 (not deeply) saturated after C2 is fully charged.
8. When the voltage of C1 right-hand plate (Q2 base voltage) becomes positive and
reaches 0.6 V, Q2 base-emitter junction begins diverting a part of R2 charging current.
Q2 begins conducting and this starts the avalanche-like positive feedback process as
follows. Q2 collector voltage begins falling; this change transfers through the fully
charged C2 to Q1 base and Q1 begins cutting off. Its collector voltage begins rising;
this change transfers back through the almost empty C1 to Q2 base and makes Q2
conduct more thus sustaining the initial input impact on Q2 base. Thus the initial
input change circulates along the feedback loop and grows in an avalanche-like
manner until finally Q1 switches off and Q2 switches on. The forward-biased Q2
base-emitter junction fixes the voltage of C1 right-hand plate at 0.6 V and does not
allow it to continue rising toward +V.
3.3 State 2 (Q1 is switched off, Q2 is switched on):
Now, the capacitor C2 is fully charged (in the previous State 1) to the power supply
voltage V with the polarity shown in Figure 1. Q2 is on and connects the right-hand
positive plate of C2 to ground. As its left-hand negative plate is connected to Q1 base,
a maximum negative voltage (-V) is applied to Q1 base that keeps Q1 firmly off. C2
begins discharging (reverse charging) via the high-value base resistor R3, so that the
voltage of its left-hand plate (and at the base of Q1) is rising from below ground (-V)
toward +V. Simultaneously, C1 that is fully discharged and even slightly charged to
0.6 V (in the previous State 1) quickly charges via the low-value collector resistor R1
and Q2 forward-biased base-emitter junction (because R1 is less than R3, C1 charges
faster than C2). Thus C1 restores its charge and prepares for the next State 1 when it
will act again as a time-setting capacitor...and so on...
3.4 Multivibrator frequency
Derivation
The duration of state 1 (low output) will be related to the time constant R2C1 as it
depends on the charging of C1, and the duration of state 2 (high output) will be
related to the time constant R3C2 as it depends on the charging of C2. Because they do
not need to be the same, an asymmetric duty cycle is easily achieved.
The voltage on a capacitor with non-zero initial charge is:
Looking at C2, just before Q2 turns on, the left terminal of C2 is at the base-emitter
voltage of Q1 (VBE_Q1) and the right terminal is at VCC ("VCC" is used here
9. instead of "+V" to ease notation). The voltage across C2 is VCC minus VBE_Q1 . The
moment after Q2 turns on, the right terminal of C2 is now at 0 V which drives the
left terminal of C2 to 0 V minus (VCC - VBE_Q1) or VBE_Q1 - VCC. From this instant in
time, the left terminal of C2 must be charged back up to VBE_Q1. How long this
takes is half our multivibrator switching time (the other half comes from C1). In
the charging capacitor equation above, substituting:
VBE_Q1 for
(VBE_Q1 - VCC) for
VCC for
results in:
Solving for t results in:
For this circuit to work, VCC>>VBE_Q1 (for example: VCC=5 V,
VBE_Q1=0.6 V), therefore the equation can be simplified to:
or
or
The period of each half of the multivibrator is therefore given by t = ln(2)RC.
The total period of oscillation is given by:
T = t1 + t2 = ln(2)R2 C1 + ln(2)R3 C2
where...
10. · f is frequency in hertz.
· R2 and R3 are resistor values in ohms.
· C1 and C2 are capacitor values in farads.
· T is the period (In this case, the sum of two period durations).
For the special case where
· t1 = t2 (50% duty cycle)
· R2 = R3
· C1 = C2
3.5 Output pulse shape
The output voltage has a shape that approximates a square waveform. It is considered
below for the transistor Q1.
During State 1, Q2 base-emitter junction is reverse-biased and the capacitor C1 is
"unhooked" from ground. The output voltage of the switched-on transistor Q1
changes rapidly from high to low since this low-resistive output is loaded by a high
impedance load (the series connected capacitor C1 and the high-resistive base resistor
R2).
During State 2, Q2 base-emitter junction is forward-biased and the capacitor C1 is
"hooked" to ground. The output voltage of the switched-off transistor Q1 changes
exponentially from low to high since this relatively high resistive output is loaded by
a low impedance load (the capacitance C1). This is the output voltage of
R1C1 integrating circuit.
To approach the needed square waveform, the collector resistors have to be low
resistance. The base resistors have to be low enough to make the transistors saturate in
the end of the restoration (RB < β.RC).
3.6 Initial power-up:
When the circuit is first powered up, neither transistor will be switched on. However,
this means that at this stage they will both have high base voltages and therefore a
tendency to switch on, and inevitable slight asymmetries will mean that one of the
transistors is first to switch on. This will quickly put the circuit into one of the above
states, and oscillation will ensue. In practice, oscillation always occurs for practical
values of R and C.
11. However, if the circuit is temporarily held with both bases high, for longer than it
takes for both capacitors to charge fully, then the circuit will remain in this stable
state, with both bases at 0.6 V, both collectors at 0 V, and both capacitors charged
backwards to −0.6 V. This can occur at startup without external intervention,
if R and C are both very small.
3.7 Frequency divider:
An astable multivibrator can be synchronized to an external chain of pulses. A single
pair of active devices can be used to divide a reference by a large ratio, however, the
stability of the technique is poor owing to the variability of the power supply and the
circuit elements; a division ratio of 10, for example, is easy to obtain but not
dependable. Chains of bistable flip-flops provide more predictable division, at the cost
of more active elements.
3.8 Protective components:
While not fundamental to circuit operation, diodes connected in series with the base
or emitter of the transistors are required to prevent the base-emitter junction being
driven into reverse breakdown when the supply voltage is in excess of
the Veb breakdown voltage, typically around 5-10 volts for general purpose silicon
transistors. In the monostable configuration, only one of the transistors requires
protection.
3.9 Astablemultivibrator:
Astable Multivibrators are the most commonly used type of multivibrator
circuit. An astable multivibrator is a free running oscillator that have no permanent
“meta” or “steady” state but are continually changing there output from one state
(LOW) to the other state (HIGH) and then back again. This continual switching action
from “HIGH” to “LOW” and “LOW” to “HIGH” produces a continuous and stable
square wave output that switches abruptly between the two logic levels making it
ideal for timing and clock pulse applications.
As with the previous monostable multivibrator circuit above, the timing cycle is
determined by the RC time constant of the resistor-capacitor, RC Network. Then the
output frequency can be varied by changing the value(s) of the resistors and capacitor
in the circuit.
12. NAND Gate Astable Multivibrator
The astable multivibrator circuit uses two CMOS NOT gates such as the CD4069 or
the 74HC04 hex inverter ICs, or as in our simple circuit below a pair of
CMOS NAND such as the CD4011 or the 74LS132 and an RC timing network. The
two NAND gates are connected as inverting NOT gates.
Suppose that initially the output from the NAND gate U2 is HIGH at logic level “1”,
then the input must therefore be LOW at logic level “0” (NAND gate principles) as
will be the output from the first NAND gate U1. Capacitor, C is connected between
the output of the second NAND gate U2 and its input via the timing resistor, R2. The
capacitor now charges up at a rate determined by the time constant of R2 and C.
As the capacitor, C charges up, the junction between the resistor R2 and the
capacitor, C, which is also connected to the input of the NAND gate U1 via the
stabilizing resistor, R2 decreases until the lower threshold value of U1 is reached at
which point U1 changes state and the output of U1 now becomes HIGH. This
causes NAND gate U2 to also change state as its input has now changed from logic
“0” to logic “1” resulting in the output of NAND gate U2 becoming LOW, logic level
“0”.
Capacitor C is now reverse biased and discharges itself through the input
of NAND gate U1. Capacitor, C charges up again in the opposite direction determined
by the time constant of both R2and C as before until it reaches the upper threshold
value of gate U1. This causes U1 to change state and the cycle repeats itself over
again.
Then, the time constant for a NAND gate Astable Multivibrator is given
as T = 2.2RC in seconds with the output frequency given as f = 1/T.
For example: if the resistor R2 = 10kΩ and the capacitor C = 45nF, the oscillation
frequency of the circuit would be given as:
13. Then the output frequency is calculated as being 1kHz, which equates to a time
constant of 1mS so the output waveform would look like:
3.10 Monostablemultivibrator Circuit
Monostable Multivibrators or “one-shot” pulse generators are generally used to
convert short sharp pulses into wider ones for timing applications. Monostable
multivibrators generate a single output pulse, either “HIGH” or “LOW”, when a
suitable external trigger signal or pulse T is applied.
This trigger pulse signal initiates a timing cycle which causes the output of the
monostable to change state at the start of the timing cycle, ( t1 ) and remain in this
second state until the end of the timing period, ( t2 ) which is determined by the time
constant of the timing capacitor, CT and the resistor, RT.
The monostable multivibrator now stays in this second timing state until the end of
the RC time constant and automatically resets or returns itself back to its original
(stable) state. Then, a monostable circuit has only one stable state. A more common
name for this type of circuit is simply a “Flip-Flop” as it can be made from two cross-coupled
NAND gates (or NOR gates) as we have seen previously. Consider the circuit
below.
14. Simple NAND Gate Monostable Circuit
Suppose that initially the trigger input T is held HIGH at logic level “1” by the
resistor R1 so that the output from the first NAND gate U1 is LOW at logic level “0”,
(NAND gate principals). The timing resistor, RT is connected to a voltage level equal
to logic level “0”, which will cause the capacitor, CT to be discharged. The output
of U1 is LOW, timing capacitor CT is completely discharged therefore junction V1 is
also equal to “0” resulting in the output from the second NAND gate U2, which is
connected as an inverting NOT gate will therefore be HIGH.
3.11 Bistable Circuit:
The Bistable Multivibrators circuit is basically a SR flip-flop that we look at in the
previous tutorials with the addition of an inverter or NOT gate to provide the
necessary switching function. As with flip-flops, both states of a bistable multivibrator
are stable, and the circuit will remain in either state indefinitely. This type of
multivibrator circuit passes from one state to the other “only” when a suitable external
trigger pulse T is applied and to go through a full “SET-RESET” cycle twotriggering
pulses are required. This type of circuit is also known as a “Bistable Latch“, “Toggle
Latch” or simply “T-latch“.
NAND Gate Bistable Multivibrator
15. The simplest way to make a Bistable Latch is to connect together a pair of
Schmitt NAND gates to form a SR latch as shown above. The
two NAND gates, U2 and U3 form the bistable which is triggered by the
input NAND gate, U1. This U1 NAND gate can be omitted and replaced by a single
toggle switch to make a switch debounce circuit as seen previously in the SR Flip-flop
tutorial.
When the input pulse goes “LOW” the bistable latches into its “SET” state, with its
output at logic level “1”, until the input goes “HIGH” causing the bistable to latch into
its “RESET” state, with its output at logic level “0”. The output of a bistable
multivibrator will stay in this “RESET” state until another input pulse is applied and
the whole sequence will start again.
Then a Bistable Latch or “Toggle Latch” is a two-state device in which both states
either positive or negative, (logic “1” or logic “0”) are stable.
Bistable Multivibrators have many applications such as frequency dividers, counters
or as a storage device in computer memories but they are best used in circuits such
as Latches and Counters.
4. 555 Timer
4.1 Introduction
Simple Monostable or Astable multivibrators can now be easily made using
standard commonly available waveform generator IC’s specially design to create
timing and oscillator circuits. Relaxation oscillators can be constructed simply by
connecting a few passive components to their input pins with the most commonly
used waveform generator type IC being the classic 555 timer.
The 555 Timer is a very versatile low cost timing IC that can produce a very accurate
timing periods with good stability of around 1% and which has a variable timing
period from between a few micro-seconds to many hours with the timing period being
controlled by a single RC network connected to a single positive supply of between
4.5 and 16 volts.
The NE555 timer and its successors, ICM7555, CMOS LM1455, DUAL NE556 etc,
are covered in the555 Oscillator tutorial and other good electronics based websites, so
are only included here for reference purposes as a clock pulse generator. The 555
connected as an Astable oscillator is given below.
16. NE555 Astable Multivibrator.
Here the 555 timer is connected as a basic Astable Multivibrator producing a
continuous output waveform. Pins 2 and 6 are connected together so that it will re-trigger
itself on each timing cycle, thereby functioning as an Astable oscillator.
Capacitor, C1 charges up through resistor, R1 and resistor, R2 but discharges only
through resistor, R2 as the other side of R2 is connected to the discharge terminal, pin
7. Then the timing period of t1 and t2 is given as:
· t1 = 0.693 (R1 + R2) C1
· t2 = 0.693 (R2) C1
· T = t1 + t2
The voltage across the capacitor, C1 ranges from between 1/3 Vcc to approximately
2/3 Vcc depending upon the RC timing period. This type of circuit is very stable as it
operates from a single supply rail resulting in an oscillation frequency which is
independent of the supply voltage Vcc.
In the next tutorial about Sequential Logic Circuits, we will look another type of clock
controlled flop-flop called a Data Latch. Data latches are very useful sequential
circuits which can be made from any standard gated SR flip-flop and used for
frequency division to produce various ripple counters, frequency dividers and latches.
4.2 Inputs of 555/556:
Trigger input: when < 1/3 Vs ('active low') this
17. makes the output high (+Vs). It monitors the discharging of the timing capacitor in an
astable circuit. It has a high input impedance > 2M .
Threshold input: when > 2/3 Vs ('active high') this makes the output low (0V)*. It
monitors the charging of the timing capacitor in astable and monostable circuits. It has
a high input impedance > 10M .
* providing the trigger input is > 1/3 Vs, otherwise the trigger input will override the
threshold input and hold the output high (+Vs).
Reset input: when less than about 0.7V ('active low') this makes the output low (0V),
overriding other inputs. When not required it should be connected to +Vs. It has an
input impedance of about 10k .
Control input: this can be used to adjust the threshold voltage which is set internally
to be 2/3 Vs. Usually this function is not required and the control input is connected to
0V with a 0.01μF capacitor to eliminate electrical noise. It can be left unconnected if
noise is not a problem.
The discharge pin is not an input, but it is listed here for convenience. It is connected
to 0V when the timer output is low and is used to discharge the timing capacitor in
astable and monostable circuits.
4.3 Output of 555/556:
The output of a standard 555 or 556 can sink and source up to 200mA. This is more
than most ICs and it is sufficient to supply many output transducers directly, including
LEDs (with a resistor in series), low current lamps, piezo transducers, loudspeakers
(with a capacitor in series), relay coils (with diode protection) and some motors (with
diode protection). The output voltage does not quite reach 0V and +Vs, especially if a
large current is flowing.
18. To switch larger currents you can connect a transistor.
The ability to both sink and source current means that two devices can be connected
to the output so that one is on when the output is low and the other is on when the
output is high. The top diagram shows two LEDs connected in this way. This
arrangement is used in the Level Crossing project to make the red LEDs flash
alternately.
4.4 Loudspeakers
A loudspeaker (minimum resistance 64 ) may be connected to the output of a 555 or
556 astable circuit but a capacitor (about 100μF) must be connected in series. The
output is equivalent to a steady DC of about ½Vs combined with a square wave AC
(audio) signal. The capacitor blocks the DC, but allows the AC to pass as explained in
capacitor coupling.
Piezo transducers may be connected directly to the output and do not require a
capacitor in series.
4.5 Duty Cycle of 555 Timer IC
The duty cycle in a 555 integrated circuit (IC) is the percentage of time that the
output is high for each cycle of the square wave. For example, if the total cycle time is
1 s and the output is high for the first 0.4 s of each cycle, the duty cycle is 40%.
With an astable circuit, the duty cycle must always be greater than 50%. In other
words, the duration for which the output is high must always be more than the
duration during which the output is low.
19. The explanation for this is pretty simple: For the duty cycle to be 50%, the capacitor
would have to charge and discharge through the same resistance. The only way to
accomplish that would be to omit R1 altogether, so that the capacitor charged and
discharged through R2 only.
But the problem with that is that you would end up connecting pin 7 directly to Vcc.
With no resistance between pin 7 and the voltage source, the current flowing through
pin 7 would exceed the maximum that can be handled by the circuitry inside the 555,
and the chip would be damaged.
There's a clever way around this limitation: Place a diode across R2. This diode
bypasses R2 when the capacitor is charged. That way, the capacitor charges through
R1 and discharges through R2.
When a diode is used in this way, you have complete control over the duration of both
the charge and discharge time. If R1 and R2 have the same value, the capacitor takes
the same amount of time to charge as it does to discharge, so the duty cycle will be
50%. If R2 is smaller than R1, the duty cycle is less than 50% because the capacitor
discharges faster than it charges.
If you use this approach, you must adjust the formulas for calculating the time
intervals as follows:
T = 0.7 (R1 + R2) C1
Thigh = 0.7 R1 C1
Tlow = 0.7 R2 C1
21. The relationships of the trigger signal, the voltage on C and the pulse width in monostable mode
In the monostable mode, the 555 timer acts as a "one-shot" pulse generator. The pulse
begins when the 555 timer receives a signal at the trigger input that falls below a third
of the voltage supply. The width of the output pulse is determined by the time
constant of an RC network, which consists of a capacitor (C) and a resistor (R). The
output pulse ends when the voltage on the capacitor equals 2/3 of the supply voltage.
The output pulse width can be lengthened or shortened to the need of the specific
application by adjusting the values of R and C.[5]
The output pulse width of time t, which is the time it takes to charge C to 2/3 of the
supply voltage, is given by
where t is in seconds, R is in ohms (resistance) and C is in farads (capacitance).
While using the timer IC in monostable mode, the main disadvantage is that the
time span between any two triggering pulses must be greater than the RC time
constant.
4.7 Bistable:
Schematic of a 555 in bistable mode
22. In bistable (also called Schmitt trigger) mode, the 555 timer acts as a basic flip-flop.
The trigger and reset inputs (pins 2 and 4 respectively on a 555) are held
high via pull-up resistors while the threshold input (pin 6) is simply floating. Thus
configured, pulling the trigger momentarily to ground acts as a 'set' and transitions
the output pin (pin 3) to Vcc (high state). Pulling the reset input to ground acts as
a 'reset' and transitions the output pin to ground (low state). No timing capacitors
are required in a bistable configuration. Pin 5 (control voltage) is connected to
ground via a small-value capacitor (usually 0.01 to 0.1 uF); pin 7 (discharge) is
left floating.
4.8 Astable:
Standard 555 astable circuit
In astable mode, the 555 timer puts out a continuous stream of rectangular pulses
having a specified frequency. Resistor R1 is connected between VCC and the discharge
pin (pin 7) and another resistor (R2) is connected between the discharge pin (pin 7),
and the trigger (pin 2) and threshold (pin 6) pins that share a common node. Hence the
capacitor is charged through R1 and R2, and discharged only through R2, since pin 7
has low impedance to ground during output low intervals of the cycle, therefore
discharging the capacitor.
In the astable mode, the frequency of the pulse stream depends on the values of R1,
R2 and C:
[8]
The high time from each pulse is given by:
23. and the low time from each pulse is given by:
where R1 and R2 are the values of the resistors in ohms and C is the value
of the capacitor in farads.
The power capability of R1 must be greater than .
Particularly with bipolar 555s, low values of must be avoided so that
the output stays saturated near zero volts during discharge, as assumed by
the above equation. Otherwise the output low time will be greater than
calculated above. The first cycle will take appreciably longer than the
calculated time, as the capacitor must charge from 0V to 2/3 of VCC from
power-up, but only from 1/3 of VCC to 2/3 of VCC on subsequent cycles.
To achieve a duty cycle of less than 50% a small diode (that is fast enough
for the application) can be placed in parallel with R2, with the cathode on
the capacitor side. This bypasses R2 during the high part of the cycle so
that the high interval depends approximately only on R1 and C. The
presence of the diode is a voltage drop that slows charging on the
capacitor so that the high time is longer than the expected and often-cited
ln(2)*R1C = 0.693 R1C. The low time will be the same as without the
diode as shown above. With a diode, the high time is
where Vdiode is when the diode has a current of 1/2 of Vcc/R1 which can
be determined from its datasheet or by testing. As an extreme
example, when Vcc= 5 and Vdiode= 0.7, high time = 1.00 R1C which is
45% longer than the "expected" 0.693 R1C. At the other extreme,
when Vcc= 15 and Vdiode= 0.3, the high time = 0.725 R1C which is
closer to the expected 0.693 R1C. The equation reduces to the
expected 0.693 R1C if Vdiode= 0.
The operation of RESET in this mode is not well defined, some
manufacturers' parts will hold the output state to what it was when
RESET is taken low, others will send the output either high or low.
4.9 Power on reset or Trigger:
24. In VLSI devices, the power-on reset (PoR) is an electronic device incorporated into
the integrated circuit that detects the power applied to the chip and generates a reset
impulse that goes to the entire circuit placing it into a known state.
A simple PoR uses the charging of a capacitor, in series with a resistor, to measure a
time period during which the rest of the circuit is held in a reset state. A Schmitt
trigger may be used to deassert the reset signal cleanly, once the rising voltage of
the RC network passes the threshold voltage of the Schmitt trigger. The resistor and
capacitor values should be determined so that the charging of the RC network takes
long enough that the supply voltage will have stabilised by the time the threshold is
reached.
One of the issues with using RC network to generate PoR pulse is the sensitivity of
the R and C values to the power-supply ramp characteristics. When the power supply
ramp is rapid, the R and C values can be calculated so that the time to reach the
switching threshold of the schmitt trigger is enough to apply a long enough reset
pulse. When the power supply ramp itself is slow, the RC network tends to get
charged up along with the power-supply ramp up. So when the input schmitt stage is
all powered up and ready, the input voltage from the RC network would already have
crossed the schmitt trigger point. This means that there might not be a reset pulse
supplied to the core of the VLSI.
4.10 Edge-triggering:
edge-triggering circuit
If the trigger input is still less than 1/3 Vs at the end of the time period the output will
remain high until the trigger is greater than 1/3 Vs. This situation can occur if the input
signal is from an on-off switch or sensor.
The monostable can be made edge triggered, responding only to changes of an input
signal, by connecting the trigger signal through a capacitor to the trigger input. The
capacitor passes sudden changes (AC) but blocks a constant (DC) signal. For further
information please see the page on capacitance. The circuit is 'negative edge triggered'
because it responds to a sudden fall in the input signal.
25. The resistor between the trigger (555 pin 2) and +Vs ensures that the trigger is
normally high (+Vs).
4.11 555/556 Inverting Buffer (Schmitt trigger) or NOT gate:
555 inverting buffer circuit
(a NOT gate)
NOT gate symbol
The buffer circuit's input has a very high impedance (about 1M ) so it requires only a
few μA, but the output can sink or source up to 200mA. This enables a high
impedance signal source (such as an LDR) to switch a low impedance output
transducer (such as a lamp).
It is an inverting buffer or NOT gate because the output logic state (low/high) is the
inverse of the input state:
· Input low (< 1/3 Vs) makes output high, +Vs
· Input high (> 2/3 Vs) makes output low, 0V
When the input voltage is between 1/3 and 2/3 Vs the output remains in its present state.
This intermediate input region is a deadspace where there is no response, a property
called hysteresis, it is like backlash in a mechanical linkage. This type of circuit is
called a Schmitt trigger.
If high sensitivity is required the hysteresis is a problem, but in many circuits it is a
helpful property. It gives the input a high immunity to noise because once the circuit
output has switched high or low the input must change back by at least 1/3 Vs to make
26. the output switch back.
4.12 Features
· Direct replacement for SE555/NE555
· Timing from microseconds through hours
· Operates in both astable and monostable modes
· Adjustable duty cycle
· Output can source or sink 200mA
· Output and supply TTL compatible
· Temperature and stability better than 0.005%
· Normally on and off output
4.13 Applications
· Precision timing
· Pulse generation
· Sequential timing
· Time delay generation
· Pulse width modulation
· Linear ramp generator
5. Diodes:
A diode is an electrical device allowing current to move through it in one direction
with far greater ease than in the other. The most common kind of diode in modern
circuit design is the semiconductor diode, although other diode technologies exist.
Semiconductor diodes are symbolized in schematic diagrams such as Figure. The term
“diode” is customarily reserved for small signal devices, I ≤ 1 A. The termrectifier is
used for power devices, I > 1 A.
Semiconductor diode schematic symbol: Arrows indicate the direction of electron
current flow.
27. When placed in a simple battery-lamp circuit, the diode will either allow or prevent
current through the lamp, depending on the polarity of the applied voltage.
Diode operation: (a) Current flow is permitted; the diode is forward biased. (b)
Current flow is prohibited; the diode is reversed biased.
When the polarity of the battery is such that electrons are allowed to flow through the
diode, the diode is said to be forward-biased. Conversely, when the battery is
“backward” and the diode blocks current, the diode is said to be reverse-biased. A
diode may be thought of as like a switch: “closed” when forward-biased and “open”
when reverse-biased.
Oddly enough, the direction of the diode symbol's “arrowhead” points against the
direction of electron flow. This is because the diode symbol was invented by
engineers, who predominantly use conventional flow notation in their schematics,
showing current as a flow of charge from the positive (+) side of the voltage source to
the negative (-). This convention holds true for all semiconductor symbols possessing
“arrowheads:” the arrow points in the permitted direction of conventional flow, and
against the permitted direction of electron flow.
Diode behavior is analogous to the behavior of a hydraulic device called a check
valve.
5.1 Thermionic and gaseous state diodes:
Thermionic diodes are thermionic-valve devices (also called as vacuum tubes, tubes,
or valves), which are arrangements of electrodes surrounded by the vacuum within a
glass envelope. Early examples were fairly alike in appearance to incandescent light
bulbs.
In the thermionic valve diodes, a current through heater filament indirectly heats
cathode, another internal electrode treated with the mixture of barium and strontium
oxides, which are the oxides of alkaline earth metals; these substances are taken
because they have a small work function. (Some valves make use of direct heating, in
which a tungsten filament acts as heater and cathode both.) The heat causes
thermionic emission of the electrons into vacuum. In forward operation, a
surrounding metal electrode known as anode is positively charged so that it
28. electrostatically attracts emitted electrons. But the electrons are not easily released
from unheated anode surface when the voltage polarity is reversed. Thus, any reverse
flow is negligible.
For much of 20th century, thermionic valve diodes were taken in use in analog signal
applications, and as rectifiers in many power supplies. Nowadays, valve diodes are
only used in niche applications like rectifiers in electric guitar and high-end audio
amplifiers also a specialized high- voltage equipment.
A thermionic diode is a thermionic-valve device (also known as a vacuum tube, tube,
or valve), consisting of a sealed evacuated glass envelope containing two electrodes:
a cathode heated by a filament, and a plate (anode). Early examples were fairly
similar in appearance to incandescent light bulbs.
In operation, a separate current through the filament (heater), a high resistance wire
made of nichrome, heats the cathode red hot (800–1000 °C), causing it to
release electrons into the vacuum, a process called thermionic emission. The cathode
is coated with oxides of alkaline earth metals such as barium and strontium oxides,
which have a low work function, to increase the number of electrons emitted. (Some
valves use direct heating, in which a tungsten filament acts as both heater and
cathode.) The alternating voltage to be rectified is applied between the cathode and
the concentric plate electrode. When the plate has a positive voltage with respect to
the cathode, itelectrostatically attracts the electrons from the cathode, so a current of
electrons flows through the tube from cathode to plate. However when the polarity is
reversed and the plate has a negative voltage, no current flows, because the cathode
electrons are not attracted to it. The unheated plate does not emit any electrons itself.
So electrons can only flow through the tube in one direction, from cathode to plate.
In a mercury-arc valve, an arc forms between a refractory conductive anode and a
pool of liquid mercury acting as cathode. Such units were made with ratings up to
hundreds of kilowatts, and were important in the development of HVDC power
transmission. Some types of smaller thermionic rectifiers sometimes had mercury
vapor fill to reduce their forward voltage drop and to increase current rating over
thermionic hard-vacuum devices.
Throughout the vacuum tube era, valve diodes were used in analog signal applications
and as rectifiers in DC power supplies in consumer electronics such as radios,
televisions, and sound systems. They were replaced in power supplies beginning in
the 1940s by selenium rectifiers and then by semiconductor diodes by the 1960s.
Today they are still used in a few high power applications where their ability to
withstand transients and their robustness gives them an advantage over semiconductor
devices. The recent (2012) resurgence of interest among audiophiles and recording
studios in old valve audio gear such as guitar amplifiers and home audio systems has
provided a market for the legacy consumer diode valves.
29. 5.2 I-V Characteristic Curves of Semiconductors:
Semiconductor devices such as diodes, transistors and thyristors are all constructed
using semiconductor PN junctions connected together and as such their I-V
characteristics curves will reflect the operation of these PN junctions. Then these
devices will have non-linear I-V characteristics, as opposed to resistors which have a
linear relationship between the current and voltage.
So for example, the primary function of a semiconductor diode is rectification of AC
to DC. When a diode is forward biased (the higher potential is connected to its
Anode), it will pass current. When the diode is reverse biased (the higher potential is
connected to its Cathode), the current is blocked. Then a PN junction needs a bias
voltage of a certain polarity and amplitude for current to flow. This bias voltage also
controls the resistance of the junction and therefore the flow of current through it.
Consider the diode circuit below. When the diode is forward biased, anode positive
with respect to the cathode, a forward or positive current passes through the diode and
operates in the top right quadrant of its I-V characteristics curves as shown. Starting at
the zero intersection, the curve increases gradually into the forward quadrant but the
forward current and voltage are extremely small.
When the forward voltage exceeds the diodes P-N junctions internal barrier voltage,
which for silicon is about 0.7 volts, avalanche occurs and the forward current
increases rapidly for a very small increase in voltage producing a non-linear curve.
The “knee” point on the forward curve.
30. Fig
Likewise, when the diode is reversed biased, cathode positive with respect to the
anode, the diode blocks current except for an extremely small leakage current, and
operates in the lower left quadrant of its I-V characteristic curves. The diode
continues to block current flow through it until the reverse voltage across the diode
becomes greater than its breakdown voltage point resulting in a sudden increase in
reverse current producing a fairly straight line downward curve as the voltage losses
control. This reverse breakdown voltage point is used to good effect with zener
diodes.
Then we can see that the I-V Characteristic Curves for a silicon diode are non-linear
and very different to that of the previous resistors linear I-V curves as their electrical
characteristics are different. Current-Voltage characteristics curves can be used to plot
the operation of any electrical or electronic component from resistors, to amplifiers, to
semiconductors and solar cells.
The current-voltage characteristics of an electronic component tells us much about its
operation and can be a very useful tool in determining the operating characteristics of
a particular device or component by showing its possible combinations of current and
voltage, and as a graphical aid can help visually understand better what is happening
within a circuit.
6. Relay
A relay is an electrically operated switch. Many relays use an electromagnet to
mechanically operate a switch, but other operating principles are also used, such
as solid-state relays. Relays are used where it is necessary to control a circuit by a
low-power signal (with complete electrical isolation between control and controlled
circuits), or where several circuits must be controlled by one signal. The first relays
were used in long distance telegraph circuits as amplifiers: they repeated the signal
coming in from one circuit and re-transmitted it on another circuit. Relays were used
extensively in telephone exchanges and early computers to perform logical
operations.
A type of relay that can handle the high power required to directly control an electric
motor or other loads is called a contactor. Solid-state relays control power circuits
with no moving parts, instead using a semiconductor device to perform switching.
Relays with calibrated operating characteristics and sometimes multiple operating
coils are used to protect electrical circuits from overload or faults; in modern electric
31. power systems these functions are performed by digital instruments still called
"protective relays".
Relay-lamp
A simple electromagnetic relay consists of a coil of wire wrapped around a soft iron
core, an iron yoke which provides a low reluctance path for magnetic flux, a movable
iron armature, and one or more sets of contacts (there are two in the relay pictured).
The armature is hinged to the yoke and mechanically linked to one or more sets of
moving contacts. It is held in place by a spring so that when the relay is de-energized
there is an air gap in the magnetic circuit. In this condition, one of the two sets of
contacts in the relay pictured is closed, and the other set is open. Other relays may
have more or fewer sets of contacts depending on their function. The relay in the
picture also has a wire connecting the armature to the yoke. This ensures continuity of
the circuit between the moving contacts on the armature, and the circuit track on
the printed circuit board (PCB) via the yoke, which is soldered to the PCB.
When an electric current is passed through the coil it generates a magnetic field that
activates the armature, and the consequent movement of the movable contact(s) either
makes or breaks (depending upon construction) a connection with a fixed contact. If
32. the set of contacts was closed when the relay was de-energized, then the movement
opens the contacts and breaks the connection, and vice versa if the contacts were
open. When the current to the coil is switched off, the armature is returned by a force,
approximately half as strong as the magnetic force, to its relaxed position. Usually
this force is provided by a spring, but gravity is also used commonly in industrial
motor starters. Most relays are manufactured to operate quickly. In a low-voltage
application this reduces noise; in a high voltage or current application it
reduces arcing.
When the coil is energized with direct current, a diode is often placed across the coil
to dissipate the energy from the collapsing magnetic field at deactivation, which
would otherwise generate a voltage spike dangerous to semiconductor circuit
components. Some automotive relays include a diode inside the relay case.
Alternatively, a contact protection network consisting of a capacitor and resistor in
series (snubber circuit) may absorb the surge. If the coil is designed to be energized
with alternating current (AC), a small copper "shading ring" can be crimped to the
end of the solenoid, creating a small out-of-phase current which increases the
minimum pull on the armature during the AC cycle
6.1 Types Of Relays
1. Latching Relay
Latching relays are also called impulse relays. They work in the bistable mode, and
thus have two relaxing states. They are also called keep relays or stay relays because
as soon as the current towards this relay is switched off, the relay continues the
process that it was doing in the last state. This can be achieved only with a solenoid
which is operating in a ratchet and cam mechanism. It can also be done by an over-centre
spring mechanism or a permanent magnet mechanism in which, when the coil
is kept in the relaxed point, the over-centre spring holds the armature and the contacts
in the right spot. This can also be done with the help of a remanent core.
In the ratchet and cam method, power consumption occurs only for a particular time.
Hence it is more advantageous than the others.
2. Reed Relay
These types of relays have been given more importance in the contacts. In order to
protect them from atmospheric protection they are safely kept inside a vacuum or
inert gas. Though these types of relays have a very low switching current and voltage
ratings, they are famous for their switching speeds.
33. 3. Polarized Relay
This type of relay has been given more importance on its sensitivity. These relays
have been used since the invention of telephones. They played very important roles in
early telephone exchanges and also in detecting telegraphic distortion. The sensitivity
of these relays are very easy to adjust as the armature of the relay is placed between
the poles of a permanent magnet.
4. Buchholz Relay
This relay is actually used as a safety device. They are used for knowing the amount
of gas present in large oil-filled transformers. They are designed in such a way that
they produce a warning if it senses either the slow production of gas or fast
production of gas in the transformer oil.
5. Overload protection Relay
As the name implies, these relays are used to prevent the electric motors from damage
by over current and short circuits. For this the heating element is kept in series with
the motor. Thus when over heat occurs the bi-metallic strip connected to the motor
heats up and in turn releases a spring to operate the contacts of the relay.
6. Mercury Wetted Relay
This relay is almost similar to the reed relay explained earlier. The only difference is
that instead of inert gases, the contacts are wetted with mercury. This makes them
more position sensitive and also expensive. They have to be vertically mounted for
any operation. They have very low contact resistance and so can be used for timing
applications. Due to these factors, this relay is not used frequently.
7. Machine Tool Relay
This is one of the most famous industrial relay. They are mainly used for the
controlling of all kinds of machines. They have a number of contacts with easily
replaceable coils. This enabkes them to be easily converted from NO contact to NC
contact. Many types of these relays can easily be setup in a control panel. Though
they are very useful in industrial applications, the invention of PLC has made them
farther away from industries.
8. Contacor Relay
This is one of the most heavy load relay ever used. They are mainly used in switching
electric motors. They have a wide range of current ratings from a few amps to
hundreds. The contacts of these relays are usually made with alloys containing a small
percentage of silver. This is done so as to avoid the hazardous effects of arcing. These
type of relays are mainly categorized in the rough use areas. So, they produce loud
noises while operated and hence cannot be used in places where noise is a problem.
34. 9. Solid State relay
SSR relays, as its name implies are designed with the help of solid state components.
As they do not have any moving objects in their design they are known for their high
reliability.
10. Solid State Contactor Relay
These relays combine both the features of solid state relays and contactor relays. As a
result they have a number of advantages. They have a very good heat sink and can be
designed for the correct on-off cycles. They are mainly controlled with the help of
PLC, micro-processors or microcontrollers.
7. Relay Applications
In general, the point of a relay is to use a small amount of power in the
electromagnet -- coming, say, from a small dashboard switch or a low-power
electronic circuit -- to move an armature that is able to switch a much larger amount
of power. For example, you might want the electromagnet to energize using 5 volts
and 50 milliamps (250 milliwatts), while the armature can support 120V AC at 2
amps (240 watts).
Relays are quite common in home appliances where there is an electronic control
turning on something like a motor or a light. They are also common in cars, where the
12V supply voltage means that just about everything needs a large amount of current.
In later model cars, manufacturers have started combining relay panels into the fuse
box to make maintenance easier. For example, the six gray boxes in this photo of a
Ford Windstar fuse box are all relays:
In places where a large amount of power needs to be switched, relays are
often cascaded. In this case, a small relay switches the power needed to drive a much
larger relay, and that second relay switches the power to drive the load.
Relays can also be used to implement Boolean logic. See How Boolean Logic
Works for more information.
Advantages
The major advantage of a automatic light control system over stand-alone lighting
controls or conventional manual switching is the ability to control individual lights or
groups of lights from a single user interface device. This ability to control multiple
light sources from a user device allows complex lighting scenes to be created. A room
35. may have multiple scenes pre-set, each one created for different activities in the room.
A major benefit of lighting control systems is reduced energy consumption. Longer
lamp life is also gained when dimming and switching off lights when not in use.
Wireless lighting control systems provide additional benefits including reduced
installation costs and increased flexibility over where switches and sensors may be
placed.