A BRIEF INTRODUCTION TO 8051 MICROCONTROLLER
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16-02-2011, 04:26 PM
mc in cb.doc (Size: 149 KB / Downloads: 144)
Microcontrollers (MCU) are complete computer systems on a chip. They combine an arithmetic logic unit (ALU), memory, timer/counters, serial port, input/output (I/O) ports and a clock oscillator
Circuit breakers are mechanical switching devices capable of breaking currents under specified abnormal circuitconditions
A circuit breaker is an automatically-operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow. Unlike a fuse, which operates once and then has to be replaced, acircuit breaker can be reset (either manually or automatically) to resume normal operation. Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits feeding an entire city.
This project and implimentation is the related with the automation of currently available circuit breakers.
SCOPE OF PROJECT
This device is very useful to protect any electrical appliance from breakdown caused by over current (or voltage).The overall system of electronics circuit breaker is more dynamic than other circuit breaker as a current can be controlled according to the need of the system.
The electronic circuit breaker is vastly used in:-
A BRIEF INTRODUCTION TO 8051 MICROCONTROLLER
When we have to learn about a new computer we have to familiarize about the machine capability we are using, and we can do it by studying the internal hardware design (devices architecture), and also to know about the size, number and the size of the registers.
A microcontroller is a single chip that contains the processor (the CPU), non-volatile memory for the program (ROM or flash), volatile memory for input and output (RAM), a clock and an I/O control unit. Also called a "computer on a chip," billions of microcontroller units (MCUs) are embedded each year in a myriad of products from toys to appliances to automobiles. For example, a single vehicle can use 70 or more microcontrollers. The following picture describes a general block diagram of microcontroller.89s52: The AT89S52 is a low-power, high-performance CMOS 8-bit microcontroller with 8K bytes of in-system programmable Flash memory. The device is manufactured using Atmel’s high-density nonvolatile memory technology and is compatible with the industry-standard 80C51 instruction set and pinout. The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory programmer. By combining a versatile 8-bit CPU with in-system programmable Flash on a monolithic chip, the Atmel's AT89S52 is a powerful microcontroller which provides a highly-flexible and cost-effective solution to many embedded control applications. The AT89S52 provides the following standard features: 8K bytes of Flash, 256 bytes of RAM, 32 I/O lines, Watchdog timer, two data pointers, three 16-bit timer/counters, a six-vector two-level interrupt architecture, a full duplex serial port, on-chip oscillator, and clock circuitry. In addition, the AT89S52 is designed with static logic for operation down to zero frequency and supports two software selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial port, and interrupt system to continue functioning. The Power-down mode saves the RAM con-tents but freezes the oscillator, disabling all other chip functions until the next interrupt.The hardware is driven by a set of program instructions, or software. Once familiar withhardware and software, the user can then apply the microcontroller to the problems easily.
The pin diagram of the 8051 shows all of the input/output pins unique to microcontrollers:
The following are some of the capabilities of 8051 microcontroller.
Internal ROM and RAM
I/O ports with programmable pins
Timers and counters
Serial data communication
The 8051 architecture consists of these specific features:
16 bit PC &data pointer (DPTR)
8 bit program status word (PSW)
8 bit stack pointer (SP)
Internal ROM 4k
Internal RAM of 128 bytes.
4 register banks, each containing 8 registers
80 bits of general purpose data memory
32 input/output pins arranged as four 8 bit ports0-P3
Two 16 bit timer/counters: T0-T1
Two external and three internal interrupt sources
Oscillator and clock circuits
For any electronics project and implimentation the power supply plays a very important role in its proper functioning.In this project and implimentation we are using external A.C supply (220 v) as input, this high voltage is converted into 12 Volts A.C by step down transformer, then we use voltage regulators and filters with bridge rectifier to convert the A.C into D.C voltage.For voltage regulation we are using LM 7805 and 7812 to produce ripple free 5 and 12 volts D.C constant supply.
A circuit breaker capable of microcontroller-based fault detection having a backup circuit for causing the circuit to trip in response to a microcontroller fault or a failure of a regulated power supply powering the microcontroller. The circuit breaker includes an RC circuit connected to an SCR. The resistor of the RC circuit is connected between the anode and gate of the SCR, and the capacitor is connected between the gate and cathode of the SCR. The microcontroller has a first pin coupled to the RC circuit, which is initially in a high input impedance state. In the event of a microcontroller fault or power supply failure, the capacitor will charge to a voltage sufficient to activate the SCR and trip the breaker. If the microcontroller startup routine is successful, the pin is configured as an output and is pulled low, shorting out the capacitor.
A circuit breaker capable of microcontroller-based fault detection having a backup circuit for causing the circuit breaker to trip in response to a microcontroller fault, including a timing circuit powered by a power supply and a microcontroller. The timing circuit is electrically coupled to an SCR that causes the circuit breaker to trip. The timing circuit includes a BJT coupled to the gate of the SCR. The microcontroller has a first output coupled to the timing circuit and a second output coupled to the SCR. The first output is coupled to a node between a resistor and a grounded capacitor in the timing circuit, and the node is coupled to a gate of the SCR and to a base of the transistor. A voltage develops at the node sufficient to cause the gate of the SCR to turn on unless the microcontroller pulls the first high-impedance output to a logic low state.
FIELD OF THE INVENTION
Aspects of the present invention relates generally to circuit breakers with microcontroller-based fault detection, and in particular, to a backup tripping function for a circuit breaker with microcontroller-based fault detection.
BACKGROUND OF THE INVENTION
In a circuit breaker with microcontroller-based fault detection, a failure in the power supply regulator circuit or the microcontroller itself can lead to an inability to detect faults on the circuit being protected, leaving the load to which the circuit breaker is connected unprotected and vulnerable. It is desirable to have a circuit breaker deny power to the protected circuit if the circuit breaker does not have the ability to detect faults by tripping as soon after power is applied as possible.
What is needed is a backup circuit that forces a microcontroller-based circuit breaker to trip if the microcontroller does not start up correctly either due to a failure in the regulated power supply or a fault in the microcontroller itself or both. Aspects and embodiments disclosed herein are directed to addressing/solving these and other needs.
SUMMARY OF THE INVENTION
Two different backup timing circuit implementations are described. These backup timing circuits ensure that an electronic circuit breaker will trip even if certain electronics within the circuit breaker are unresponsive. The electronic circuit breaker includes a microcontroller that analyzes current or voltage signals in a circuit and trips the circuit breaker when those signals exceed certain thresholds or criteria. If the microcontroller does not work at startup, the loads being protected by the circuit breaker become vulnerable to certain types of electrical faults. In essence, the microcontroller represents a “warning system” to detect certain types of faults which are not protected by the mechanical thermal or magnetic components within the circuit breaker. The microcontroller is powered by a separate power supply within the circuit breaker, and this power supply derives its power from the current on the line. If the power supply fails, the microcontroller will become unresponsive, so one of the backup timing circuit implementations also bypasses the microcontroller if the power supply fails to operate properly. The backup timing circuits disclosed herein bypass or override the “early warning system” provided by the microcontroller if the microcontroller is unresponsive at startup or because its power supply is unresponsive or both.
In a first implementation, a backup timing circuit is powered by a power supply in a microcontroller-based circuit breaker. The timing circuit includes a transistor whose gate is charged by a node that is also connected to a configurable pin of the microcontroller. When the microcontroller is initially powered on, it runs through various startup and diagnostic routines. During this startup process, the pin is initially in a high impedance state. As a result, the node can build up a voltage across a capacitor that eventually becomes sufficient to energize the transistor. If the microcontroller properly completes its diagnostic and startup routines, then the microcontroller configures the pin to an output and drives it low, shorting out the capacitor of the timing circuit and preventing the transistor from turning on.
In a second implementation, a backup timing circuit is powered directly off of a rectified line voltage. A microcontroller is powered by a separate power supply, but because the timing circuit in this implementation is positioned upstream of the power supply, the timing circuit can react even if the timing circuit is unresponsive. A pin of the microcontroller is connected to a node of the timing circuit, which is also connected to a gate of an electronic switching device that causes the electronic circuit breaker to trip. Upon successful completion of the startup and diagnostic routines, the pin, initially in a high impedance state, is driven low by the microcontroller, shorting out a capacitor of the timing circuit thereby preventing the electronic switching device from turning on. However, if the startup and diagnostic routines fail or if the power supply fails, the pin will remain in a high impedance state, allowing a voltage to build up across the capacitor of the timing circuit, until it is sufficient to energize the electronic switching device.
The foregoing and additional aspects and embodiments of the present invention will be apparent to those of ordinary skill in the art in view of the detailed description of various embodiments and/or aspects, which is made with reference to the drawings, a brief description of which is provided next.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings.
FIG. 1 is a functional block diagram of a microcontroller-based circuit breaker having a backing timing circuit that can trip the circuit breaker if the microcontroller is unresponsive;
FIG. 2 is a functional block diagram of a microprocessor-based circuit breaker having a timing circuit that can trip the circuit breaker if either the regulated power supply fails or the microcontroller is unresponsive; and
FIG. 3 is a functional block diagram of a circuit breaker similar to that shown in FIG. 2 except that a drop resistor is placed downstream of a timing circuit.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
Although the invention will be described in connection with certain aspects and/or embodiments, it will be understood that the invention is not limited to those particular aspects and/or embodiments. On the contrary, the invention is intended to cover all alternatives, modifications, and equivalent arrangements as may be included within the spirit and scope of the invention as defined by the appended claims.
This disclosure describes at least two backup circuits that are used in microcontroller-based circuit breakers for tripping the circuit breaker in the event of a regulated power supply fault or a microprocessor fault. FIG. 1 illustrates a backup circuit that is powered by a regulated power supply and is operable to trip the circuit breaker in the event that the microcontroller is unresponsive at startup. FIGS. 2 and 3 illustrate line-powered backup circuits that are operable to trip the circuit breaker in the event that either the regulated power supply is or becomes unresponsive or the microcontroller is initially unresponsive or both.
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07-04-2011, 10:52 AM
8051.ppt (Size: 3.3 MB / Downloads: 120)
8051 Basic Component
4K bytes internal ROM
128 bytes internal RAM
Four 8-bit I/O ports (P0 - P3).
Two 16-bit timers/counters
One serial interface
Other 8051 featurs
only 1 On chip oscillator (external crystal)
6 interrupt sources (2 external , 3 internal, Reset)
64K external code (program) memory(only read)PSEN
64K external data memory(can be read and write) by RD,WR
Code memory is selectable by EA (internal or external)
We may have External memory as data and code
Embedded System (8051 Application)
What is Embedded System?
An embedded system is closely integrated with the main system
It may not interact directly with the environment
For example – A microcomputer in a car ignition control
An embedded product uses a microprocessor or microcontroller to do one task only
There is only one application software that is typically burned into ROM
Examples of Embedded Systems
video game player
MP3 music players
Embedded memories to keep configuration information
Mobile phone units
Domestic (home) appliances
Three criteria in Choosing a Microcontroller
meeting the computing needs of the task efficiently and cost effectively
speed, the amount of ROM and RAM, the number of I/O ports and timers, size, packaging, power consumption
easy to upgrade
cost per unit
availability of software development tools
assemblers, debuggers, C compilers, emulator, simulator, technical support
wide availability and reliable sources of the microcontrollers
Comparison of the 8051 Family Members
8031 no ROM
80xx mask ROM
89xx Flash EEPROM
C = CMOS technology
LV= Low Power(3.0v)