A PROJECT REPORT ONSCADA (SUPERVISORY CONTROL AND DATA ACQUISTION) FOR REMOTE INDUSTRIAL PLANT OPERATIONSubmitted in partial fulfillment of the requirementsFor the award of the degreeBACHELOR OF ENGINEERINGINELECTRONICS AND COMMUNICATION ENGINEERINGSUBMITTED BY

___________ (_______)____________ (_______)____________ (_______)

DEPARTMENT OF ______________ ENGINEERING________ COLLEGE OF ENGINEERINGAFFILIATED TO ___________ UNIVERSITY

CERTIFICATE

This is to certify that the dissertation work entitled SCADA(SUPERVISORY CONTROL AND DATA ACQUISTION)FOR REMOTE INDUSTRIAL PLANT ORIENTATION is the work done by _________________________________________________________ submitted in partial fulfillment for the award of BACHELOR OF ENGINEERING (B.E) in ____________________________ Engineering from ___________ College of Engineering affiliated to _________ University , Hyderabad .

___________________ _____________(Head of the department, ECE) (Assistant Professor)

EXTERNAL EXAMINER

99

ACKNOWLEDGEMENT

The satisfaction and euphoria that accompany the successful completion of any task would be incomplete without the mentioning of the people whose constant guidance and encouragement made it possible. We take pleasure in presenting before you, our project, which is result of studied blend of both research and knowledge.

We express our earnest gratitude to our internal guide, Assistant Professor ___________, Department of ECE, our project guide, for his constant support, encouragement and guidance. We are grateful for his cooperation and his valuable suggestions.

DECLARATION

We, the undersigned, declare that the project entitled SCADA(SUPERVISORY CONTROL AND DATA ACQUISTION)FOR REMOTE INDUSTRIAL PLANT ORIENTATION, being submitted in partial fulfillment for the award of Bachelor of Engineering Degree in Electronics and Communication Engineering, affiliated to __________ University, is the work carried out by us.

___________ ___________ __________ ___________ ____________ ___________

CONTENTS PAGE NO. 1. ABSTRACT 13 2. INTRODUCTION TO EMBEDDED SYSTEMS 13 3. BLOCK DIAGRAM 154. HARDWARE REQUIREMENTS 4.1 TRANSFORMERS 17 4.2 VOLTAGE REGULATOR (LM7805) 19 4.3 RECTIFIER 4.4 FILTER 4.5 MICROCONTROLLER (AT89S52/C51) 224.6 ADC0808 4.7MAX2324.8 ULN20034.9 RELAY DRIVER4.10DB9 CONNECTOR4.11 LM35 TEMPERATURE SENSOR4.12 LED 4.13IN40074.14 RESISTORS4.15CAPACITORS 5. SOFTWARE REQUIREMENTS 5.1 IDE575.2 CONCEPT OF COMPILER575.3 CONCEPT OF CROSS COMPILER585.4 KEIL C CROSS COMPILER595.5 BUILDING AN APPLICATION IN UVISION2595.6 CREATING YOUR OWN APPLICATION IN UVISION2595.7 DEBUGGING AN APPLICATION IN UVISION2605.8 STARTING UVISION2 & CREATING A PROJECT615.9 WINDOWS_ FILES615.10 BUILDING PROJECTS & CREATING HEX FILES615.11 CPU SIMULATION625.12 DATABASE SELECTION625.13 START DEBUGGING635.14 DISASSEMBLY WINDOW635.15 EMBEDDED C64 6. SCHEMATIC DIAGRAM66 6.1 DESCRIPTION67 7. LAYOUT DIAGRAM71 8. BILL OF MATERIALS729. CODING759.1 COMPILER769.2 SOURCE CODE8410. HARDWARE TESTING 8810.1 CONTINUITY TEST8810.2 POWER ON TEST8911. RESULTS 6912. CONCLUSION 9313. BIBLIOGRAPHY94

LIST OF FIGURES PAGE NO.

2(a) EMBEDDED DESIGN CALLS2(b) V DIAGRAM3. BLOCK DIAGRAM OF THE PROJECT 4.1 A TYPICAL TRANSFORMER174.2 BLOCK DIAGRAM OF VOLTAGE REGULATOR 204.2(a) PERFORMANCE CHARACTERISTICS OF VOLTAGE REGULATOR214.5 BLOCK DIAGRAM OF AT89S52244.5(b) PIN DIAGRAM OF AT89S52254.5(c) OSCILLATOR CONNECTIONS 294.5(d) EXTERNAL CLOCK DRIVE CONFIG.304.6 ADC0808 314.8(a) LOGIC DIAGRAM OF ULN2003374.8(b) SCHEMATIC DIAGRAM OF ULN2003384.8(c) RELAY SHOWING COIL & SWITCH CONTACTS396. SCHEMATIC DIAGRAM OF THE PROJECT 427. PROJECT LAYOUT8.1 CONTINUITY TEST648.2 POWER ON TEST66

ABSTRACT

This is a temperature logging System. Here 8 temperature sensors in multiplexing mode are connected to the microcontroller through ADC 0808. Then the values of all the sensors are sent serially by AT89C51 through Max 232 to the com port of the PC. A Software "DAQ System loaded on the PC takes these values and show them on its front panel, and also logs them to the data base "daq.mdb" .One can set by interactive way some parameters like set point , low limit ,and high limit on the computer screen . When temperature of some sensor increases beyond set point, the microcontroller sends commands to relay driver IC ULN 2003. The heaters connected through relay contacts are (specific for that sensor) turned OFF (or ON in opposite case). High limit and low limits are for alarm. When temperature goes above high limit or below low limit the alarm will be turned on.

Hardware

The complete hardware schematic for the SCADA board consists of microcontroller 89C51, the temperature sensor (LM335), ADC 0808, relay driver ULN 2003, relays and Max232 for the serial interface. The on chip firmware controls reading the ADC converter, receives commands from PC and sends the reading to PC. We use LM335 temperature sensor. It can measure the temperature using two wires remotely. The chip produces an output signal that is proportional to the Celsius temperature scale. The trimmer POT is used to calibrate the correct output voltage at known temperature, for example 2.98V @ 25 C.

2. INTRODUCTION TO EMBEDDED SYSTEMS

What is Embedded system?An Embedded System is a combination of computer hardware and software, and perhaps additional mechanical or other parts, designed to perform a specific function. An embedded system is a microcontroller-based, software driven, reliable, real-time control system, autonomous, or human or network interactive, operating on diverse physical variables and in diverse environments and sold into a competitive and cost conscious market.An embedded system is not a computer system that is used primarily for processing, not a software system on PC or UNIX, not a traditional business or scientific application. High-end embedded & lower end embedded systems. High-end embedded system - Generally 32, 64 Bit Controllers used with OS. Examples Personal Digital Assistant and Mobile phones etc .Lower end embedded systems - Generally 8,16 Bit Controllers used with an minimal operating systems and hardware layout designed for the specific purpose. Examples Small controllers and devices in our everyday life like Washing Machine, Microwave Ovens, where they are embedded in.

SYSTEM DESIGN CALLS:

Figure 2.1(a) Embedded System design calls

EMBEDDED SYSTEM DESIGN CYCLE

Figure 2.1(b): V Diagram

Characteristics of Embedded System1. An embedded system is any computer system hidden inside a product other than a computer.1. They will encounter a number of difficulties when writing embedded system software in addition to those we encounter when we write applications.1. Throughput Our system may need to handle a lot of data in a short period of time.1. ResponseOur system may need to react to events quickly.1. TestabilitySetting up equipment to test embedded software can be difficult.1. DebugabilityWithout a screen or a keyboard, finding out what the software is doing wrong (other than not working) is a troublesome problem.0. Reliability embedded systems must be able to handle any situation without human intervention.0. Memory space Memory is limited on embedded systems, and you must make the software and the data fit into whatever memory exists.0. Program installation you will need special tools to get your software into embedded systems.0. Power consumption Portable systems must run on battery power, and the software in these systems must conserve power.0. Processor hogs computing that requires large amounts of CPU time can complicate the response problem.0. Cost Reducing the cost of the hardware is a concern in many embedded system projects; software often operates on hardware that is barely adequate for the job.

1. Embedded systems have a microprocessor/ microcontroller and a memory. Some have a serial port or a network connection. They usually do not have keyboards, screens or disk drives.

APPLICATIONS1) Military and aerospace embedded software applications2) Communication Applications3) Industrial automation and process control software4) Mastering the complexity of applications.5) Reduction of product design time.6) Real time processing of ever increasing amounts of data.7) Intelligent, autonomous sensors.

CLASSIFICATION1. Real Time Systems.1. RTS is one which has to respond to events within a specified deadline.1. A right answer after the dead line is a wrong answer

RTS CLASSIFICATION1. Hard Real Time Systems1. Soft Real Time SystemHARD REAL TIME SYSTEM "Hard" real-time systems have very narrow response time. Example: Nuclear power system, Cardiac pacemaker.

SOFT REAL TIME SYSTEM "Soft" real-time systems have reduced constrains on "lateness" but still must operate very quickly and repeatable. Example: Railway reservation system takes a few extra seconds the data remains valid.

3. BLOCK DIAGRAM

Fig 3.1 Block diagram of the project

4. HARDWARE REQUIREMENTS

HARDWARE COMPONENTS:

1. TRANSFORMER (230 12 V AC)2. VOLTAGE REGULATOR (LM 7805)3. FILTER4. RECTIFIER5. MICROCONTROLLER (AT89S52/AT89C51)6. ADC0808 7. MAX2328. RELAYS9. DB9 CONNECTOR10. LM35 TEMPERATURE SENSOR11. ULN200312. LED 13. IN400714. RESISTORS15. CAPACITORS

4.1 TRANSFORMER

Transformers convert AC electricity from one voltage to another with a little loss of power. Step-up transformers increase voltage, step-down transformers reduce voltage. Most power supplies use a step-down transformer to reduce the dangerously high voltage to a safer low voltage.

FIG 4.1: A TYPICAL TRANSFORMER

The input coil is called the primary and the output coil is called the secondary. There is no electrical connection between the two coils; instead they are linked by an alternating magnetic field created in the soft-iron core of the transformer. The two lines in the middle of the circuit symbol represent the core. Transformers waste very little power so the power out is (almost) equal to the power in. Note that as voltage is stepped down and current is stepped up. The ratio of the number of turns on each coil, called the turns ratio, determines the ratio of the voltages. A step-down transformer has a large number of turns on its primary (input) coil which is connected to the high voltage mains supply, and a small number of turns on its secondary (output) coil to give a low output voltage. TURNS RATIO = (Vp / Vs) = ( Np / Ns )Where,

Vp = primary (input) voltage.Vs = secondary (output) voltageNp = number of turns on primary coilNs = number of turns on secondary coil Ip = primary (input) current Is= secondary (output) current.Ideal power equation

The ideal transformer as a circuit elementIf the secondary coil is attached to a load that allows current to flow, electrical power is transmitted from the primary circuit to the secondary circuit. Ideally, the transformer is perfectly efficient; all the incoming energy is transformed from the primary circuit to the magnetic field and into the secondary circuit. If this condition is met, the incoming electric power must equal the outgoing power:

giving the ideal transformer equation

Transformers normally have high efficiency, so this formula is a reasonable approximation.If the voltage is increased, then the current is decreased by the same factor. The impedance in one circuit is transformed by the square of the turns ratio. For example, if an impedance Zs is attached across the terminals of the secondary coil, it appears to the primary circuit to have an impedance of (Np/Ns)2Zs. This relationship is reciprocal, so that the impedance Zp of the primary circuit appears to the secondary to be (Ns/Np)2Zp.

4.2 VOLTAGE REGULATOR 7805 Features Output Current up to 1A. Output Voltages of 5, 6, 8, 9, 10, 12, 15, 18, 24V. Thermal Overload Protection. Short Circuit Protection. Output Transistor Safe Operating Area Protection.

DescriptionThe LM78XX/LM78XXA series of three-terminal positive regulators are available in the TO-220/D-PAK package and with several fixed output voltages, making them useful in a Wide range of applications. Each type employs internal current limiting, thermal shutdown and safe operating area protection, making it essentially indestructible. If adequate heat sinking is provided, they can deliver over 1A output Current. Although designed primarily as fixed voltage regulators, these devices can be used with external components to obtain adjustable voltages and currents.

Internal Block Diagram

FIG 4.2(a): BLOCK DIAGRAM OF VOLTAGE REGULATOR

Absolute Maximum Ratings

TABLE 4.2(b): RATINGS OF THE VOLTAGE REGULATOR

4.3 RECTIFIERA rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), current that flows in only one direction, a process known as rectification. Rectifiers have many uses including as components of power supplies and as detectors of radio signals. Rectifiers may be made of solid state diodes, vacuum tube diodes, mercury arc valves, and other components. The output from the transformer is fed to the rectifier. It converts A.C. into pulsating D.C. The rectifier may be a half wave or a full wave rectifier. In this project, a bridge rectifier is used because of its merits like good stability and full wave rectification. In positive half cycle only two diodes( 1 set of parallel diodes) will conduct, in negative half cycle remaining two diodes will conduct and they will conduct only in forward bias only.

4.4 FILTER

Capacitive filter is used in this project. It removes the ripples from the output of rectifier and smoothens the D.C. Output received from this filter is constant until the mains voltage and load is maintained constant. However, if either of the two is varied, D.C. voltage received at this point changes. Therefore a regulator is applied at the output stage.The simple capacitor filter is the most basic type of power supply filter. The use of this filter is very limited. It is sometimes used on extremely high-voltage, low-current power supplies for cathode-ray and similar electron tubes that require very little load current from the supply. This filter is also used in circuits where the power-supply ripple frequency is not critical and can be relatively high. Below figure can show how the capacitor charges and discharges.

4.5 MICROCONTROLLER AT89S52The 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 Atmels high-density non volatile memory technology and is compatible with the industry standard 80C51 instruction set and pin out. The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional non volatile memory programmer. By combining a versatile 8-bit CPU with in-system programmable Flash on a monolithic chip, the Atmel 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 contents but freezes the oscillator, disabling all other chip functions until the next interrupt or hardware reset.

Features: Compatible with MCS-51 Products 8K Bytes of In-System Programmable (ISP) Flash Memory Endurance: 10,000 Write/Erase Cycles 4.0V to 5.5V Operating Range Fully Static Operation: 0 Hz to 33 MHz Three-level Program Memory Lock 256 x 8-bit Internal RAM 32 Programmable I/O Lines Three 16-bit Timer/Counters Eight Interrupt Sources Full Duplex UART Serial Channel Low-power Idle and Power-down Modes Interrupt Recovery from Power-down Mode Watchdog Timer Dual Data Pointer Power-off Flag Fast Programming Time Flexible ISP Programming (Byte and Page Mode) Green (Pb/Halide-free) Packaging Option

Block Diagram of AT89S52:

Fig 4.5: Block Diagram Of AT89S52Pin Configurations of AT89S52

FIG 4.2.5(b): PIN DIAGRAM OF AT89S52Pin Description:VCC: Supply voltage.GND: GroundPort 0:Port 0 is an 8-bit open drain bidirectional I/O port. As an output port, each pin can sink eight TTL inputs. When 1s are written to port 0 pins, the pins can be used as high-impedance inputs. Port 0 can also be configured to be the multiplexed low-order address/data bus during accesses to external program and data memory. In this mode, P0 has internal pull-ups. Port 0 also receives the code bytes during Flash programming and outputs the code bytes during program verification. External pull-ups are required during program verification.Port 1:Port 1 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 1 output buffers can sink/source four TTL inputs. When 1s are written to Port 1 pins, they are pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 1 pins that are externally being pulled low will source current (IIL) because of the internal pull-ups. In addition, P1.0 and P1.1 can be configured to be the timer/counter 2 external count input (P1.0/T2) and the timer/counter 2 trigger input (P1.1/T2EX).Port 2:Port 2 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 2 output buffers can sink/source four TTL inputs. When 1s are written to Port 2 pins, they are pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 2 pins that are externally being pulled low will source current (IIL) because of the internal pull-ups. Port 2 emits the high-order address byte during fetches from external program memory and during accesses to external data memory that use 16-bit addresses (MOVX @ DPTR). In this application, Port 2 uses strong internal pull-ups when emitting 1s. During accesses to external data memory that use 8-bit addresses (MOVX @ RI), Port 2 emits the contents of the P2 Special Function Register.Port 3:Port 3 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 3 output buffers can sink/source four TTL inputs. When 1s are written to Port 3 pins, they are pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 3 pins that are externally being pulled low will source current (IIL) because of the pull-ups.RST:Reset input. A high on this pin for two machine cycles while the oscillator is running resets the device. This pin drives high for 98 oscillator periods after the Watchdog times out. The DISRTO bit in SFR AUXR (address 8EH) can be used to disable this feature. In the default state of bit DISRTO, the RESET HIGH out feature is enabled.ALE/PROG:Address Latch Enable (ALE) is an output pulse for latching the low byte of the address during accesses to external memory. This pin is also the program pulse input (PROG) during Flash programming.In normal operation, ALE is emitted at a constant rate of 1/6 the oscillator frequency and may be used for external timing or clocking purposes. Note, however, that one ALE pulse is skipped during each access to external data memory.

PSEN:Program Store Enable (PSEN) is the read strobe to external program memory. When the AT89S52 is executing code from external program memory, PSEN is activated twice each machine cycle, except that two PSEN activations are skipped during each access to external data memory.EA/VPP:External Access Enable. EA must be strapped to GND in order to enable the device to fetch code from external program memory locations starting at 0000H up to FFFFH. Note, however, that if lock bit 1 is programmed, EA will be internally latched on reset. EA should be strapped to VCC for internal program executions. This pin also receives the 12-volt programming enable voltage (VPP) during Flash programming.

XTAL1:Input to the inverting oscillator amplifier and input to the internal clock operating circuit.XTAL2:Output from the inverting oscillator amplifier

Oscillator Characteristics: XTAL1 and XTAL2 are the input and output, respectively, of an inverting amplifier which can be configured for use as an on-chip oscillator, as shown in Figure 1. Either a quartz crystal or ceramic resonator may be used. To drive the device from an external clock source, XTAL2 should be left unconnected while XTAL1 is driven as shown in Figure 6.2. There are no requirements on the duty cycle of the external clock signal, since the input to the internal clocking circuitry is through a divide-by-two flip-flop, but minimum and maximum voltage high and low time specifications must be observed. FIG 4.5(c): Oscillator Connections FIG 4.5(d): External Clock Drive Configuration

Idle ModeIn idle mode, the CPU puts itself to sleep while all the on chip peripherals remain active. The mode is invoked by software. The content of the on-chip RAM and all the special functions registers remain unchanged during this mode. The idle mode can be terminated by any enabled interrupt or by a hardware reset.Power down Mode In the power down mode the oscillator is stopped, and the instruction that invokes power down is the last instruction executed. The on-chip RAM and Special Function Registers retain their values until the power down mode is terminated. The only exit from power down is a hardware reset. Reset redefines the SFRs but does not change the on-chip RAM. The reset should not be activated before VCC is restored to its normal operating level and must be held active long enough to allow the oscillator to restart and stabilize.

4.6 ADC0808Features Easy interface to all microprocessors Operates ratio metrically or with 5 VDC or analog span adjusted voltage reference No zero or full-scale adjust required 8-channel multiplexer with address logic 0V to 5V input range with single 5V power supply Outputs meet TTL voltage level specifications Standard hermetic or molded 28-pin DIP package 28-pin molded chip carrier package ADC0808 equivalent to MM74C949 ADC0809 equivalent to MM74C949-1

FIG: ADC0808 PIN CONFIGURATION

Key Specifications Resolution 8 Bits Total Unadjusted Error 12 LSB and 1 LSB Single Supply 5 VDC Low Power 15 mW Conversion Time 100 s

The ADC0808, ADC0809 data acquisition component is a monolithic CMOS device with an 8-bit analog-to-digital converter, 8-channel multiplexer and microprocessor compatible control logic. The 8-bit A/D converter uses successive approximation as the conversion technique. The converter features a high impedance chopper stabilized comparator, a 256R voltage divider with analog switch tree and a successive approximation register.

Fig 4.6 ADC0808The 8-channel multiplexer can directly access any of 8-single-ended analog signals. The device eliminates the need for external zero and full-scale adjustments. Easy interfacing to microprocessors is provided by the latched and decoded multiplexer address inputs and latched TTL TRI-STATE outputs. The design of the ADC0808, ADC0809 has been optimized by incorporating the most desirable aspects of several A/D conversion techniques. The ADC0808, ADC0809 offers high speed, high accuracy, minimal temperature dependence, excellent long-term accuracy and repeatability, and consumes minimal power. These features make this device ideally suited to applications from process and machine control to consumer and automotive applications. The ADC0808/ADC0809 Data Acquisition Devices (DAD) implement on a single chip most the elements of the standard data acquisition system. They contain an 8-bit A/D Converter, 8-channel multiplexer with an address input latch, and associated control logic. These devices provide most of the logic to interface to a variety of microcontrollers with the addition of a minimum number of parts. These circuits are implemented using a standard metal-gate CMOS process. This process is particularly suitable to applications. Where both analog and digital functions must be implemented on the same chip. These two converters, the ADC0808 and ADC0809, are functionally identical except that the ADC0808 has a total unadjusted error of 12 LSB and the ADC0809 has an unadjusted error of 1 LSB. All these converters will typically do a conversion in100 s when using a 640 kHz clock, but can convert a single input in as little as 50 s. 4.6(b): FUNCTIONAL BLOCK DIAGRAM OF ADC0808/ADC0809

Functional DescriptionThe ADC0808/ADC0809, shown in the above figure, can be functionally divided into 2 basic sub circuits. These two sub circuits are an analog multiplexer and an A/D converter. The multiplexer uses 8 standard CMOS analog switches to provide for up to 8 analog inputs. The switches are selectively turned on, depending on the data latched into a 3-bit multiplexer address register. The second function block, the successive approximation A/D converter, transforms the analog output of the multiplexer to an 8-bit digital word. The output of the multiplexer goes to one of two comparator inputs. The other input is derived from a 256R resistor ladder, which is tapped by a MOSFET transistor switch tree. The converter control logic controls the switch tree, funneling a particular tap voltage to the comparator. Based on the result of this comparison, the control logic and the successive approximation register (SAR) will decide whether the next tap to be selected should be higher or lower than the present tap on the resistor ladder. This algorithm is executed 8 times per conversion, once every 8 clock periods, yielding a total conversion time of 64 clock periods.When the conversion cycle is complete the resulting data is loaded into the TRI-STATE output latch. The data in the output latch can then be read by the host system any time before the end of the next conversion. The TRI-STATE capability of the latch allows easy interface to bus oriented systems. The operation of these converters by a microprocessor or some control logic is very simple. The controlling device first selects the desired input channel. To do this, a 3-bit channel address is placed on the A, B, C input pins; and the ALE input is pulsed positively, clocking the address into the multiplexer address register. To begin the conversion, the START pin is pulsed. On the rising edge of this pulse the internal registers are cleared and on the falling edge the start conversion initiated. There are 8 clock periods per approximation. Even though there is no conversion in progress the ADC0808/ADC0809 is still internally cycling through these 8 clock periods. A start pulse can occur any time during this cycle but the conversion will not actually begin until the converter internally cycles to the beginning of the next 8 clock period sequence. As long as the start pin is held high no conversion begins, but when the start pin is taken low the conversion will start within 8 clock periods. The EOC output is triggered on the rising edge of the start pulse. It, too, is controlled by the 8 clock period cycle, so it will go low within 8 clock periods of the rising edge of the start pulse. One can see that it is entirely possible for EOC to go low before the conversion starts internally, but this is not important, since the positive transition of EOC, which occurs at the end of a conversion, is what the control logic is looking for. Once EOC does go high this signals the interface logic that the data resulting from the conversion is ready to be read. The output enable (OE) is then raised high. This enables the TRI-STATE outputs, allowing the data to be read.

4.7 MAX 232

The MAX232 is an integrated circuit that converts signals from an RS-232 serial port to signals suitable for use in TTL compatible digital logic circuits. The MAX232 is a dual driver/receiver and typically converts the RX, TX, CTS and RTS signals.The drivers provide RS-232 voltage level outputs (approx. 7.5V) from a single +5V supply via on-chip charge pumps and external capacitors. This makes it useful for implementing RS-232 in devices that otherwise do not need any voltages outside the 0V to +5V range, as power supply design does not need to be made more complicated just for driving the RS-232 in this case. The receivers reduce RS-232 inputs (which may be as high as 25V), to standard 5V TTL levels. These receivers have a typical threshold of 1.3V, and a typical hysteresis of 0.5V.The later MAX232A is backwards compatible with the original MAX232 but may operate at higher baud rates and can use smaller external capacitors (0.1F) in place of the 1.0F capacitors used with the original device. The newer MAX3232 is also backwards compatible, but operates at a broader voltage range, from 3 to 5.5V.

Voltage levels:It is helpful to understand what occurs to the voltage levels. When a MAX232 IC receives a TTL level to convert, it changes a TTL Logic 0 to between +3 and +15V, and changes TTL Logic 1 to between -3 to -15V, and vice versa for converting from RS232 to TTL. This can be confusing when you realize that the RS232 Data Transmission voltages at a certain logic state are opposite from the RS232 Control Line voltages at the same logic state. To clarify the matter, see the table below. For more information see RS-232 Voltage Levels.

Pin Description:

Application:The MAX232 has two receivers (converts from RS-232 to TTL voltage levels) and two drivers (converts from TTL logic to RS-232 voltage levels). This means only two of the RS-232 signals can be converted in each direction.

Typically a pair of a driver/receiver of the MAX232 is used for TX and RX And the second one for CTS and RTS. There are not enough drivers/receivers in the MAX232 to also connect the DTR, DSR, and DCD signals. Usually these signals can be omitted when e.g. communicating with a PC's serial interface. If the DTE really requires these signals either a second MAX232 is needed, or some other IC from the MAX232 family can be used.4.8 DB9 CONNECTOR

The DB9 (originally DE-9) connector is an analog 9-pin plug of the D-Sub miniature connector family (D-Sub or Sub-D). The DB9 connector is mainly used for serial connections, allowing for the asynchronous transmission of data as provided for by standard RS-232 (RS-232C).

Fig 4.10: DB9 CONNECTOR

Pins:

This is a common connector used in many computer, audio/video, and data applications. The official name is D-sub miniature, but many people call it D-sub or just DB. The connector gets its name from its trapezoidal shape that resembles the letter D. Most DB connectors have two rows of pins. Common types of D-sub connectors are DB9 and DB25, used on PCs for serial and parallel ports.One special type of D-sub connectors is the High-Density DB style, which looks just like a regular DB connector, only with pins that are slightly smaller and placed closer together. This is typically referred to as an HD connector. HD connectors often have three rows of pins instead of two. The most common HD connector is the HD15, which is found on PC video cards and monitors. DB- and HD-connectors use thumbscrews to secure the connector in place.Another type of D-sub is the MD, or Micro DB connector. This connector is slimmer than a standard D-sub, with pins even smaller than the ones used on HD connectors. The MD is also commonly called a half-pitch DB connector. These are often used in SCSI applications, and the most popular types are the MD50 and MD68 connections. MD-connectors can use latch clips or thumbscrews as anchoring mechanisms.

D-sub connectors are usually described by the total number of pins that they can hold. In some cases, a DB25 connector may only have 4 or 5 pins loaded into it; however, it is still called a DB25 connector and not a DB4 or DB5. Another example is the HD15 connector used by monitorsmost monitor cables only are loaded with 14 pins, but it is still called an HD15 connector.

Interfacing Between Microcontroller and Db9 Connector

4.9 ULN2003RELAY DRIVER:

ULN2003 is a high voltage and high current Darlington transistor array.

DESCRIPTION:

The ULN2003 is a monolithic high voltage and high current Darlington transistor arrays. It consists of seven NPN Darlington pairs that feature high-voltage outputs with common-cathode Clamp diode for switching inductive loads. The collector-current rating of a single Darlington pair is 500mA. The Darlington pairs may be paralleled for higher current capability. Applications include relay drivers, hammer drivers, lamp drivers, display drivers (LED gas discharge), line drivers, and logic buffers.

The ULN2003 has a 2.7kW series base resistor for each Darlington pair for operation directly with TTL or 5V CMOS devices.

Fig : ULN 2003FEATURES Pin no.:16 Temperature, Operating Range:-20C to +85C Transistor Polarity: NPN Transistors, No. of:7 Case Style:DIP-16 Temp, Op. Min:-20C Temp, Op. Max:85C Base Number:2003 Channels, No. of:7 Current, Output Max:500mA Device Marking:ULN2003A IC Generic Number:2003 Input Type: TTL, CMOS 5V Logic Function Number:2003 Output Type: Open Collector Transistor Type: Power Darlington Voltage, Input Max:5V Voltage, Output Max:50VPIN Diagram:

The ULN2001A, ULN2002A, ULN2003 and ULN2004Aare high Voltage, highcurrent Darlington arrays each containing seven open collector Darlington pairs withcommon emitters. Each channel rated at 500mAand can withstand peak currents of600mA.Suppressiondiodesare included for inductive load driving and the inputs arepinned opposite the outputs to simplify board layout.These versatile devices are useful for driving a wide range of loadsincluding solenoids, relays DC motors; LED displays filament lamps, thermal print headsand high power buffers. The ULN2001A/2002A/2003A and 2004A are supplied in 16 pinplastic DIP packages with a copper lead frame to reduce thermal resistance. They areavailable also in small outline package (SO-16) as ULN2001D/2002D/2003D/2004D.

Fig: Schematics of Darlingtons pair

Fig: Darlington pair

Darlington pairs are back to back connection of two transistors with some source resistors and when they are arranged as shown in the circuit they are used to amplify weak signals. The amount by which the weak signal is amplified is called the GAIN. .

FEATURES OF DRIVER: Seven Darlingtons per package Output currents500mA per driver(600mA peak) Integrated suppression diodes for inductive loads Outputs can be paralleled for high currents TTL/CMOS/PMOS/DTL compatible inputs. Inputs pinned opposite to outputs Simplified layout

Figure shows the Darlington pair connection of transistor. The circuit above is a Darlington Pair driver. The first transistors emitter feeds into the second transistors base and as a result the input signal is amplified by the time it reaches the output. The important point to remember is that the Darlington Pair is made up of two transistors

FEATURES* 500mA rated collector current (Single output).* High-voltage outputs: 50V.* Inputs compatible with various types of logic.* Relay driver application.

4.10 RELAYA relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. 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.

A relay is an electrically operated switch. Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts. The coil current can be on or off so relays have two switch positions and most have double throw (changeover) switch contacts as shown in the diagram. Fig 4.8 Relay showing coil and switch contacts

Relays allow one circuit to switch a second circuit which can be completely separate from the first. For example a low voltage battery circuit can use a relay to switch a 230V AC mains circuit. There is no electrical connection inside the relay between the two circuits; the link is magnetic and mechanical.

The coil of a relay passes a relatively large current, typically 30mA for a 12V relay, but it can be as much as 100mA for relays designed to operate from lower voltages. Most ICs (chips) cannot provide this current and a transistor is usually used to amplify the small IC current to the larger value required for the relay coil. The maximum output current for the popular 555 timer IC is 200mA so these devices can supply relay coils directly without amplification.

Relays are usually SPDT or DPDT but they can have many more sets of switch contacts, for example relays with 4 sets of changeover contacts are readily available. For further information about switch contacts and the terms used to describe them please see the page on switches.

Most relays are designed for PCB mounting but you can solder wires directly to the pins providing you take care to avoid melting the plastic case of the relay.

The supplier's catalogue should show you the relay's connections. The coil will be obvious and it may be connected either way round. Relay coils produce brief high voltage 'spikes' when they are switched off and this can destroy transistors and ICs in the circuit. To prevent damage you must connect a protection diode across the relay coil.

The figure shows a relay with its coil and switch contacts. You can see a lever on the left being attracted by magnetism when the coil is switched on. This lever moves the switch contacts.

There is one set of contacts (SPDT) in the foreground and another behind them, making the relay DPDT. The relay's switch connections are usually labelled COM, NC and NO: COM = Common, always connect to this; it is the moving part of the switch. NC = Normally Closed, COM is connected to this when the relay coil is off. NO = Normally Open, COM is connected to this when the relay coil is on.

Applications of relays

Relays are used to and for:

Control a high-voltage circuit with a low-voltage signal, as in some types of modems or audio amplifiers. Control a high-current circuit with a low-current signal, as in the starter solenoid of an automobile. Detect and isolate faults on transmission and distribution lines by opening and closing circuit breakers. Time delay functions. Relays can be modified to delay opening or delay closing a set of contacts. A very short (a fraction of a second) delay would use a copper disk between the armature and moving blade assembly. Current flowing in the disk maintains magnetic field for a short time, lengthening release time. For a slightly longer (up to a minute) delay, a dashpot is used. A dashpot is a piston filled with fluid that is allowed to escape slowly. The time period can be varied by increasing or decreasing the flow rate. For longer time periods, a mechanical clockwork timer is installed.

4.11 TEMPERATURE SENSOR(LM35)

Features n Calibrated directly in Celsius (Centigrade) n Linear + 10.0 mV/C scale factor n 0.5C accuracy guarantee able (at +25C) n Rated for full 55 to +150C range n Suitable for remote applications n Low cost due to wafer-level trimming n Operates from 4 to 30 volts n Less than 60 A current drain n Low self-heating, 0.08C in still air n Nonlinearity only 14C typical n Low impedance output, 0.1 for 1 mA load

The LM35 series are precision integrated-circuit temperature sensors, whose output voltage is linearly proportional to the Celsius (Centigrade) temperature. The LM35 thus has an advantage over linear temperature sensors calibrated in Kelvin, as the user is not required to subtract a large constant voltage from its output to obtain convenient Centigrade scaling. The LM35 does not require any external calibration or trimming to provide typical accuracies of 14C at room temperature and 34C over a full 55 to +150C temperature range. Low cost is assured by trimming and calibration at the wafer level. The LM35s low output impedance, linear output, and precise inherent calibration make interfacing to readout or control circuitry especially easy. It can be used with single power supplies, or with plus and minus supplies. As it draws only 60 A from its supply, it has very low self-heating, less than 0.1C in still air. The LM35 is rated to operate over a 55 to +150C temperature range, while the LM35C is rated for a 40 to +110C range (10 with improved accuracy). The LM35 series is available packaged in hermetic TO-46 transistor packages, while the LM35C, LM35CA, and LM35D are also available in the plastic TO-92 transistor package. The LM35D is also avail- able in an 8-lead surface mount small outline package and a plastic TO-220 package. Fig 4.10: Basic Centigrade Temperature Sensor (+2C to +150C)

Applications: The LM35 can be applied easily in the same way as other integrated circuit temperature sensors. It can be glued or cemented to a surface and its temperature will be within about 0.01C of the surface temperature. This presumes that the ambient air temperature is almost the same as the surface temperature; if the air temperature were much higher or lower than the surface temperature, the actual temperature of the LM35 die would be at an intermediate temperature between the surface temperature and the air temperature. This is especially true for the TO-92 plastic package, where the copper leads are the principal thermal path to carry heat into the device, so its temperature might be closer to the air temperature than to the surface temperature. To minimize this problem, be sure that the wiring to the LM35, as it leaves the device, is held at the same temperature as the surface of interest. The easiest way to do this is to cover up these wires with a bead of epoxy which will insure that the leads and wires are all at the same temperature as the surface, and that the LM35 dies temperature will not be affected by the air temperature.

4.12 LED

A light-emitting diode (LED) is a semiconductor light source. LEDs are used as indicator lamps in many devices, and are increasingly used for lighting. When a light-emitting diode is forward biased (switched on), electrons are able to recombine with holes within the device, releasing energy in the form of photons. This effect is called electroluminescence and the color of the light (corresponding to the energy of the photon) is determined by the energy gap of the semiconductor. An LED is often small in area (less than 1mm2), and integrated optical components may be used to shape its radiation pattern. LEDs present many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved robustness, smaller size, faster switching, and greater durability and reliability. Types of LEDS Fig 4.12(a): Types of LED

Light-emitting diodes are used in applications as diverse as replacements for aviation lighting, automotive lighting as well as in traffic signals. The compact size, the possibility of narrow bandwidth, switching speed, and extreme reliability of LEDs has allowed new text and video displays and sensors to be developed, while their high switching rates are also useful in advanced communications technology.

Electronic Symbol:

Fig 4.12(b): symbol of LED

Colors and materials of LEDSConventional LEDs are made from a variety of inorganic semiconductor materials, the following table shows the available colors with wavelength range, voltage drop and material.

White LEDSLight Emitting Diodes (LED) have recently become available that are both white and bright, so bright that they seriously compete with incandescent lamps in lighting applications. They are still pretty expensive as compared to a GOW lamp but draw much less current and project a fairly well focused beam.When run within their ratings, they are more reliable than lamps as well. Red LEDs are now being used in automotive and truck tail lights and in red traffic signal lights. You will be able to detect them because they look like an array of point sources and they go on and off instantly as compared to conventional incandescent lamps.

Fig 4.12(c): White LED spectrum

LEDs are monochromatic (one color) devices. The color is determined by the band gap of the semiconductor used to make them. Red, green, yellow and blue LEDs are fairly common. White light contains all colors and cannot be directly created by a single LED. The most common form of "white" LED really isn't white. It is a Gallium Nitride blue LED coated with a phosphor that, when excited by the blue LED light, emits a broad range spectrum that in addition to the blue emission, makes a fairly white light.There is a claim that these white LED's have a limited life. After 1000 hours or so of operation, they tend to yellow and dim to some extent. Running the LEDs at more than their rated current will certainly accelerate this process.There are two primary ways of producing high intensity white-light using LEDs. One is to use individual LEDs that emit three primary coloursred, green, and blueand then mix all the colours to form white light. The other is to use a phosphor material to convert monochromatic light from a blue or UV LED to broad-spectrum white light, much in the same way a fluorescent light bulb works. Due to metamerism, it is possible to have quite different spectra that appear white.

4.13 IN4007

Diodes are used to convert AC into DC these are used as half wave rectifier or full wave rectifier. Three points must he kept in mind while using any type of diode. 1. Maximum forward current capacity 2. Maximum reverse voltage capacity 3. Maximum forward voltage capacity

Fig: IN4007 diodesThe number and voltage capacity of some of the important diodes available in the market are as follows: Diodes of number IN4001, IN4002, IN4003, IN4004, IN4005, IN4006 and IN4007 have maximum reverse bias voltage capacity of 50V and maximum forward current capacity of 1 Amp. Diode of same capacities can be used in place of one another. Besides this diode of more capacity can be used in place of diode of low capacity but diode of low capacity cannot be used in place of diode of high capacity. For example, in place of IN4002; IN4001 or IN4007 can be used but IN4001 or IN4002 cannot be used in place of IN4007.The diode BY125made by company BEL is equivalent of diode from IN4001 to IN4003. BY 126 is equivalent to diodes IN4004 to 4006 and BY 127 is equivalent to diode IN4007.

Fig:PN Junction diode

PN JUNCTION OPERATION Now that you are familiar with P- and N-type materials, how these materials are joined together to form a diode, and the function of the diode, let us continue our discussion with the operation of the PN junction. But before we can understand how the PN junction works, we must first consider current flow in the materials that make up the junction and what happens initially within the junction when these two materials are joined together. Current Flow in the N-Type Material Conduction in the N-type semiconductor, or crystal, is similar to conduction in a copper wire. That is, with voltage applied across the material, electrons will move through the crystal just as current would flow in a copper wire. This is shown in figure 1-15. The positive potential of the battery will attract the free electrons in the crystal. These electrons will leave the crystal and flow into the positive terminal of the battery. As an electron leaves the crystal, an electron from the negative terminal of the battery will enter the crystal, thus completing the current path. Therefore, the majority current carriers in the N-type material (electrons) are repelled by the negative side of the battery and move through the crystal toward the positive side of the battery. Current Flow in the P-Type Material Current flow through the P-type material is illustrated. Conduction in the P material is by positive holes, instead of negative electrons. A hole moves from the positive terminal of the P material to the negative terminal. Electrons from the external circuit enter the negative terminal of the material and fill holes in the vicinity of this terminal. At the positive terminal, electrons are removed from the covalent bonds, thus creating new holes. This process continues as the steady stream of holes (hole current) moves toward the negative terminal.

4.14 RESISTORS

A resistor is a two-terminal electronic component designed to oppose an electric current by producing a voltage drop between its terminals in proportion to the current, that is, in accordance with Ohm's law: V = IR Resistors are used as part of electrical networks and electronic circuits. They are extremely commonplace in most electronic equipment. Practical resistors can be made of various compounds and films, as well as resistance wire (wire made of a high-resistivity alloy, such as nickel/chrome).The primary characteristics of resistors are their resistance and the power they can dissipate. Other characteristics include temperature coefficient, noise, and inductance. Less well-known is critical resistance, the value below which power dissipation limits the maximum permitted current flow, and above which the limit is applied voltage. Critical resistance depends upon the materials constituting the resistor as well as its physical dimensions; it's determined by design.Resistors can be integrated into hybrid and printed circuits, as well as integrated circuits. Size, and position of leads (or terminals) are relevant to equipment designers; resistors must be physically large enough not to overheat when dissipating their power.

A resistor is a two-terminal passive electronic component which implements electrical resistance as a circuit element. When a voltage V is applied across the terminals of a resistor, a current I will flow through the resistor in direct proportion to that voltage. The reciprocal of the constant of proportionality is known as the resistance R, since, with a given voltage V, a larger value of R further "resists" the flow of current I as given by Ohm's law:

Resistors are common elements of electrical networks and electronic circuits and are ubiquitous in most electronic equipment. Practical resistors can be made of various compounds and films, as well as resistance wire (wire made of a high-resistivity alloy, such as nickel-chrome). Resistors are also implemented within integrated circuits, particularly analog devices, and can also be integrated into hybrid and printed circuits.The electrical functionality of a resistor is specified by its resistance: common commercial resistors are manufactured over a range of more than 9 orders of magnitude. When specifying that resistance in an electronic design, the required precision of the resistance may require attention to the manufacturing tolerance of the chosen resistor, according to its specific application. The temperature coefficient of the resistance may also be of concern in some precision applications. Practical resistors are also specified as having a maximum power rating which must exceed the anticipated power dissipation of that resistor in a particular circuit: this is mainly of concern in power electronics applications. Resistors with higher power ratings are physically larger and may require heat sinking. In a high voltage circuit, attention must sometimes be paid to the rated maximum working voltage of the resistor.The series inductance of a practical resistor causes its behavior to depart from ohms law; this specification can be important in some high-frequency applications for smaller values of resistance. In a low-noise amplifier or pre-amp the noise characteristics of a resistor may be an issue. The unwanted inductance, excess noise, and temperature coefficient are mainly dependent on the technology used in manufacturing the resistor. They are not normally specified individually for a particular family of resistors manufactured using a particular technology. A family of discrete resistors is also characterized according to its form factor, that is, the size of the device and position of its leads (or terminals) which is relevant in the practical manufacturing of circuits using them.UnitsThe ohm (symbol: ) is the SI unit of electrical resistance, named after Georg Simon Ohm. An ohm is equivalent to a volt per ampere. Since resistors are specified and manufactured over a very large range of values, the derived units of milliohm (1 m = 103 ), kilohm (1 k = 103 ), and megohm (1 M = 106 ) are also in common usage.The reciprocal of resistance R is called conductance G = 1/R and is measured in Siemens (SI unit), sometimes referred to as a mho. Thus a Siemens is the reciprocal of an ohm: S = 1. Although the concept of conductance is often used in circuit analysis, practical resistors are always specified in terms of their resistance (ohms) rather than conductance.VARIABLE RESISTORSAdjustable resistorsA resistor may have one or more fixed tapping points so that the resistance can be changed by moving the connecting wires to different terminals. Some wire wound power resistors have a tapping point that can slide along the resistance element, allowing a larger or smaller part of the resistance to be used.Where continuous adjustment of the resistance value during operation of equipment is required, the sliding resistance tap can be connected to a knob accessible to an operator. Such a device is called a rheostat and has two terminals.

Potentiometer A potentiometer is a manually adjustable resistor. The way this device works is relatively simple. One terminal of the potentiometer is connected to a power source. Another is hooked up to ground (a point with no voltage or resistance and which serves as a neutral reference point), while the third terminal runs across a strip of resistive material. This resistive strip generally has a low resistance at one end; its resistance gradually increases to a maximum resistance at the other end. The third terminal serves as the connection between the power source and ground, and is usually interfaced to the user by means of a knob or lever. The user can adjust the position of the third terminal along the resistive strip in order to manually increase or decrease resistance. By controlling resistance, a potentiometer can determine how much current flow through a circuit. When used to regulate current, the potentiometer is limited by the maximum resistivity of the strip.

The power of this simple device is not to be underestimated. In most analog devices, a potentiometer is what establishes the levels of output. In a loud speaker, for example, a potentiometer directly adjusts volume; in a television monitor, it controls brightness. A potentiometer can also be used to control the potential difference, or voltage, across a circuit. The setup involved in utilizing a potentiometer for this purpose is a little bit more complicated. It involves two circuits: the first circuit consists of a cell and a resistor. At one end, the cell is connected in series to the second circuit, and at the other end it is connected to a potentiometer in parallel with the second circuit. The potentiometer in this arrangement drops the voltage by an amount equal to the ratio between the resistance allowed by the position of the third terminal and the highest possible resistivity of the strip. In other words, if the knob controlling the resistance is positioned at the exact halfway point on the resistive strip, then the output voltage will drop by exactly fifty percent, no matter how high the potentiometer's input voltage. Unlike with current regulation, voltage regulation is not limited by the maximum resistivity of the strip

4.15 CAPACITORS

A capacitor or condenser is a passive electronic component consisting of a pair of conductors separated by a dielectric. When a voltage potential difference exists between the conductors, an electric field is present in the dielectric. This field stores energy and produces a mechanical force between the plates. The effect is greatest between wide, flat, parallel, narrowly separated conductors.An ideal capacitor is characterized by a single constant value, capacitance, which is measured in farads. This is the ratio of the electric charge on each conductor to the potential difference between them. In practice, the dielectric between the plates passes a small amount of leakage current. The conductors and leads introduce an equivalent series resistance and the dielectric has an electric field strength limit resulting in a breakdown voltage.The properties of capacitors in a circuit may determine the resonant frequency and quality factor of a resonant circuit, power dissipation and operating frequency in a digital logic circuit, energy capacity in a high-power system, and many other important aspects.

A capacitor (formerly known as condenser) is a device for storing electric charge. The forms of practical capacitors vary widely, but all contain at least two conductors separated by a non-conductor. Capacitors used as parts of electrical systems, for example, consist of metal foils separated by a layer of insulating film.Capacitors are widely used in electronic circuits for blocking direct current while allowing alternating current to pass, in filter networks, for smoothing the output of power supplies, in the resonant circuits that tune radios to particular frequencies and for many other purposes.A capacitor is a passive electronic component consisting of a pair of conductors separated by a dielectric (insulator). When there is a potential difference (voltage) across the conductors, a static electric field develops in the dielectric that stores energy and produces a mechanical force between the conductors. An ideal capacitor is characterized by a single constant value, capacitance, measured in farads. This is the ratio of the electric charge on each conductor to the potential difference between them.The capacitance is greatest when there is a narrow separation between large areas of conductor, hence capacitor conductors are often called "plates", referring to an early means of construction. In practice the dielectric between the plates passes a small amount of leakage current and also has an electric field strength limit, resulting in a breakdown voltage, while the conductors and leads introduce an undesired inductance and resistance.

Theory of operationCapacitance

Charge separation in a parallel-plate capacitor causes an internal electric field. A dielectric (orange) reduces the field and increases the capacitance.

A simple demonstration of a parallel-plate capacitorA capacitor consists of two conductors separated by a non-conductive region. The non-conductive region is called the dielectric or sometimes the dielectric medium. In simpler terms, the dielectric is just an electrical insulator. Examples of dielectric mediums are glass, air, paper, vacuum, and even a semiconductor depletion region chemically identical to the conductors. A capacitor is assumed to be self-contained and isolated, with no net electric charge and no influence from any external electric field. The conductors thus hold equal and opposite charges on their facing surfaces, and the dielectric develops an electric field. In SI units, a capacitance of one farad means that one coulomb of charge on each conductor causes a voltage of one volt across the device. The capacitor is a reasonably general model for electric fields within electric circuits. An ideal capacitor is wholly characterized by a constant capacitance C, defined as the ratio of charge Q on each conductor to the voltage V between them:

Sometimes charge build-up affects the capacitor mechanically, causing its capacitance to vary. In this case, capacitance is defined in terms of incremental changes:

Energy storageWork must be done by an external influence to "move" charge between the conductors in a capacitor. When the external influence is removed the charge separation persists in the electric field and energy is stored to be released when the charge is allowed to return to its equilibrium position. The work done in establishing the electric field, and hence the amount of energy stored, is given by:

Current-voltage relationThe current i(t) through any component in an electric circuit is defined as the rate of flow of a charge q(t) passing through it, but actual charges, electrons, cannot pass through the dielectric layer of a capacitor, rather an electron accumulates on the negative plate for each one that leaves the positive plate, resulting in an electron depletion and consequent positive charge on one electrode that is equal and opposite to the accumulated negative charge on the other. Thus the charge on the electrodes is equal to the integral of the current as well as proportional to the voltage as discussed above. As with any ant derivative, a constant of integration is added to represent the initial voltage v (t0). This is the integral form of the capacitor equation, .Taking the derivative of this, and multiplying by C, yields the derivative form, .The dual of the capacitor is the inductor, which stores energy in the magnetic field rather than the electric field. Its current-voltage relation is obtained by exchanging current and voltage in the capacitor equations and replacing C with the inductance L.DC circuitsRC circuit

A simple resistor-capacitor circuit demonstrates charging of a capacitor.A series circuit containing only a resistor, a capacitor, a switch and a constant DC source of voltage V0 is known as a charging circuit. If the capacitor is initially uncharged while the switch is open, and the switch is closed at t = 0, it follows from Kirchhoff's voltage law that

Taking the derivative and multiplying by C, gives a first-order differential equation,

At t = 0, the voltage across the capacitor is zero and the voltage across the resistor is V0. The initial current is then i (0) =V0 /R. With this assumption, the differential equation yields

where 0 = RC is the time constant of the system.As the capacitor reaches equilibrium with the source voltage, the voltage across the resistor and the current through the entire circuit decay exponentially. The case of discharging a charged capacitor likewise demonstrates exponential decay, but with the initial capacitor voltage replacing V0 and the final voltage being zero.AC circuitsSee also: reactance (electronics)and electrical impedance deriving the device specific impedancesImpedance, the vector sum of reactance and resistance, describes the phase difference and the ratio of amplitudes between sinusoidally varying voltage and sinusoidally varying current at a given frequency. Fourier analysis allows any signal to be constructed from a spectrum of frequencies, whence the circuit's reaction to the various frequencies may be found. The reactance and impedance of a capacitor are respectively

where j is the imaginary unit and is the angular velocity of the sinusoidal signal. The - j phase indicates that the AC voltage V = Z I lags the AC current by 90: the positive current phase corresponds to increasing voltage as the capacitor charges; zero current corresponds to instantaneous constant voltage, etc.Note that impedance decreases with increasing capacitance and increasing frequency. This implies that a higher-frequency signal or a larger capacitor results in a lower voltage amplitude per current amplitudean AC "short circuit" or AC coupling. Conversely, for very low frequencies, the reactance will be high, so that a capacitor is nearly an open circuit in AC analysisthose frequencies have been "filtered out".Capacitors are different from resistors and inductors in that the impedance is inversely proportional to the defining characteristic, i.e. capacitance.Parallel plate model

Dielectric is placed between two conducting plates, each of area A and with a separation of d.The simplest capacitor consists of two parallel conductive plates separated by a dielectric with permittivity (such as air). The model may also be used to make qualitative predictions for other device geometries. The plates are considered to extend uniformly over an area A and a charge density = Q/A exists on their surface. Assuming that the width of the plates is much greater than their separation d, the electric field near the centre of the device will be uniform with the magnitude E = /. The voltage is defined as the line integral of the electric field between the plates

Solving this for C = Q/V reveals that capacitance increases with area and decreases with separation.The capacitance is therefore greatest in devices made from materials with a high permittivity.

Several capacitors in parallel.NetworksSee also: Series and parallel circuitsFor capacitors in parallelCapacitors in a parallel configuration each have the same applied voltage. Their capacitances add up. Charge is apportioned among them by size. Using the schematic diagram to visualize parallel plates, it is apparent that each capacitor contributes to the total surface area.

For capacitors in series

Several capacitors in series.Connected in series, the schematic diagram reveals that the separation distance, not the plate area, adds up. The capacitors each store instantaneous charge build-up equal to that of every other capacitor in the series. The total voltage difference from end to end is apportioned to each capacitor according to the inverse of its capacitance. The entire series acts as a capacitor smaller than any of its components.

Capacitors are combined in series to achieve a higher working voltage, for example for smoothing a high voltage power supply. The voltage ratings, which are based on plate separation, add up. In such an application, several series connections may in turn be connected in parallel, forming a matrix. The goal is to maximize the energy storage utility of each capacitor without overloading it.Series connection is also used to adapt electrolytic capacitors for AC use.Non-ideal behaviourCapacitors deviate from the ideal capacitor equation in a number of ways. Some of these, such as leakage current and parasitic effects are linear, or can be assumed to be linear, and can be dealt with by adding virtual components to the equivalent circuit of the capacitor. The usual methods of network analysis can then be applied. In other cases, such as with breakdown voltage, the effect is non-linear and normal (i.e., linear) network analysis cannot be used, the effect must be dealt with separately. There is yet another group, which may be linear but invalidate the assumption in the analysis that capacitance is a constant. Such an example is temperature dependence.Breakdown voltageMain article: Breakdown voltageAbove a particular electric field, known as the dielectric strength Eds, the dielectric in a capacitor becomes conductive. The voltage at which this occurs is called the breakdown voltage of the device, and is given by the product of the dielectric strength and the separation between the conductors, Vbd = EdsdThe maximum energy that can be stored safely in a capacitor is limited by the breakdown voltage. Due to the scaling of capacitance and breakdown voltage with dielectric thickness, all capacitors made with a particular dielectric have approximately equal maximum energy density, to the extent that the dielectric dominates their volume. For air dielectric capacitors the breakdown field strength is of the order 2 to 5 MV/m; for mica the breakdown is 100 to 300 MV/m, for oil 15 to 25 MV/m, and can be much less when other materials are used for the dielectric. The dielectric is used in very thin layers and so absolute breakdown voltage of capacitors is limited. Typical ratings for capacitors used for general electronics applications range from a few volts to 100V or so. As the voltage increases, the dielectric must be thicker, making high-voltage capacitors larger than those rated for lower voltages. The breakdown voltage is critically affected by factors such as the geometry of the capacitor conductive parts; sharp edges or points increase the electric field strength at that point and can lead to a local breakdown. Once this starts to happen, the breakdown will quickly "track" through the dielectric till it reaches the opposite plate and cause a short circuit. The usual breakdown route is that the field strength becomes large enough to pull electrons in the dielectric from their atoms thus causing conduction. Other scenarios are possible, such as impurities in the dielectric, and, if the dielectric is of a crystalline nature, imperfections in the crystal structure can result in an avalanche breakdown as seen in semi-conductor devices. Breakdown voltage is also affected by pressure, humidity and temperature. Equivalent circuit

Two different circuit models of a real capacitorAn ideal capacitor only stores and releases electrical energy, without dissipating any. In reality, all capacitors have imperfections within the capacitor's material that create resistance. This is specified as the equivalent series resistance or ESR of a component. This adds a real component to the impedance:

As frequency approaches infinity, the capacitive impedance (or reactance) approaches zero and the ESR becomes significant. As the reactance becomes negligible, power dissipation approaches PRMS = VRMS /RESR.Similarly to ESR, the capacitor's leads add equivalent series inductance or ESL to the component. This is usually significant only at relatively high frequencies. As inductive reactance is positive and increases with frequency, above a certain frequency capacitance will be canceled by inductance. High-frequency engineering involves accounting for the inductance of all connections and components.If the conductors are separated by a material with a small conductivity rather than a perfect dielectric, then a small leakage current flows directly between them. The capacitor therefore has a finite parallel resistance, and slowly discharges over time (time may vary greatly depending on the capacitor material and quality).

5. SOFTWARE REQUIREMENTS

5.1 INTRODUCTION TO KEIL MICRO VISION (IDE) Keil an ARM Company makes C compilers, macro assemblers, real-time kernels, debuggers, simulators, integrated environments, evaluation boards, and emulators for ARM7/ARM9/Cortex-M3, XC16x/C16x/ST10, 251, and 8051 MCU families. Keil development tools for the 8051 Microcontroller Architecture support every level of software developer from the professional applications engineer to the student just learning about embedded software development. When starting a new project, simply select the microcontroller you use from the Device Database and the Vision IDE sets all compiler, assembler, linker, and memory options for you.Keil is a cross compiler. So first we have to understand the concept of compilers and cross compilers. After then we shall learn how to work with keil.

5.2 CONCEPT OF COMPILERCompilers are programs used to convert a High Level Language to object code. Desktop compilers produce an output object code for the underlying microprocessor, but not for other microprocessors. I.E the programs written in one of the HLL like Cwill compile the code to run on the system for a particular processor like x86 (underlying microprocessor in the computer). For example compilers for Dos platform is different from the Compilers for Unix platformSo if one wants to define a compiler then compiler is a program that translates source code into object code. The compiler derives its name from the way it works, looking at the entire piece of source code and collecting and reorganizing the instruction. See there is a bit little difference between compiler and an interpreter. Interpreter just interprets whole program at a time while compiler analyses and execute each line of source code in succession, without looking at the entire program.The advantage of interpreters is that they can execute a program immediately. Secondly programs produced by compilers run much faster than the same programs executed by an interpreter. However compilers require some time before an executable program emerges. Now as compilers translate source code into object code, which is unique for each type of computer, many compilers are available for the same language.5.3 CONCEPT OF CROSS COMPILERA cross compiler is similar to the compilers but we write a program for the target processor (like 8051 and its derivatives) on the host processors (like computer of x86). It means being in one environment you are writing a code for another environment is called cross development. And the compiler used for cross development is called cross compiler.So the definition of cross compiler is a compiler that runs on one computer but produces object code for a different type of computer.

5.4 KEIL C CROSS COMPILERKeil is a German based Software development company.It provides several development tools like IDE (Integrated Development environment) Project Manager Simulator Debugger C Cross Compiler, Cross Assembler, Locator/Linker

The Keil ARM tool kit includes three main tools, assembler, compiler and linker. An assembler is used to assemble the ARM assembly program. A compiler is used to compile the C source code into an object file. A linker is used to create an absolute object module suitable for our in-circuit emulator.5.5 Building an Application in Vision2To build (compile, assemble, and link) an application in Vision2, you must:1. Select Project -(forexample,166\EXAMPLES\HELLO\HELLO.UV2).1. Select Project - Rebuild all target files or Build target.Vision2 compiles, assembles, and links the files in your project.

5.6 Creating Your Own Application in Vision2 To create a new project in Vision2, you must:1. Select Project - New Project.1. Select a directory and enter the name of the project file.1. Select Project - Select Device and select an 8051, 251, or C16x/ST10 device from the Device Database.1. Create source files to add to the project.1. Select Project - Targets, Groups, Files. Add/Files, select Source Group1, and add the source files to the project.1. Select Project - Options and set the tool options. Note when you select the target device from the Device Database all special options are set automatically. You typically only need to configure the memory map of your target hardware. Default memory model settings are optimal for most applications.1. Select Project - Rebuild all target files or Build target.

5.7 Debugging an Application in Vision2To debug an application created using Vision2, you must:1. Select Debug - Start/Stop Debug Session.1. Use the Step toolbar buttons to single-step through your program. You may enter G, main in the Output Window to execute to the main C function.1. Open the Serial Window using the Serial #1 button on the toolbar.Debug your program using standard options like Step, Go, Break, and so on.

5.8 Starting Vision2 and Creating a ProjectVision2 is a standard Windows application and started by clicking on the program icon. To create a new project file select from the Vision2 menu Project New Project. This opens a standard Windows dialog that asks you for the new project file name. We suggest that you use a separate folder for each project. You can simply use the icon Create New Folder in this dialog to get a new empty folder. Then select this folder and enter the file name for the new project, i.e. Project1. Vision2 creates a new project file with the name PROJECT1.UV2 which contains a default target and file group name. You can see these names in the Project.

5.9 Window Files.Now use from the menu Project Select Device for Target and select a CPU for your project. The Select Device dialog box shows the Vision2 device data base. Just select the microcontroller you use. We are using for our examples the Philips 80C51RD+ CPU. This selection sets necessary tool Options for the 80C51RD+ device and simplifies in this way the tool Configuration.

5.10 Building Projects and Creating a HEX FilesTypical, the tool settings under Options Target are all you need to start a new application. You may translate all source files and line the application with a click on the Build Target toolbar icon. When you build an application with syntax errors, Vision2 will display errors and warning messages in the Output Window Build page. A double click on a message line opens the source file on the correct location in a Vision2 editor window. Once you have successfully generated your application you can start debugging.

After you have tested your application, it is required to create an Intel HEX file to download the software into an EPROM programmer or simulator. Vision2 creates HEX files with each build process when Create HEX files under Options for Target Output is enabled. You may start your PROM programming utility after the make process when you specify the program under the option Run User Program #1.

5.11 CPU SimulationVision2 simulates up to 16 Mbytes of memory from which areas can be mapped for read, write, or code execution access. The Vision2 simulator trapsand reports illegal memory accesses. In addition to memory mapping, the simulator also provides support for the integrated peripherals of the various 8051 derivatives. The on-chip peripherals of the CPU you have selected are configured from the Device. 5.12 Database selectionYou have made when you create your project target. Refer to page 58 for more Information about selecting a device. You may select and display the on-chip peripheral components using the Debug menu. You can also change the aspects of each peripheral using the controls in the dialog boxes.

5.13 Start DebuggingYou start the debug mode of Vision2 with the Debug Start/Stop DebugSession Command. Depending on the Options for Target Debug Configuration, Vision2 will load the application program and run the startup code Vision2 saves the editor screen layout and restores the screen layout of the last debug session. If the program execution stops, Vision2 opens an editor window with the source text or shows CPU instructions in the disassembly window. The next executable statement is marked with a yellow arrow. During debugging, most editor features are still available. For example, you can use the find command or correct program errors. Program source text of your application is shown in the same windows. The Vision2 debug mode differs from the edit mode in the following aspects:_ The Debug Menu and Debug Commands described on page 28 are available. The additional debug windows are discussed in the following._ The project structure or tool parameters cannot be modified. All build commands are disabled.

5.14 Disassembly WindowThe Disassembly window shows your target program as mixed source and assembly program or just assembly code. A trace history of previously executed instructions may be displayed with Debug View Trace Records. To enable the trace history, set Debug Enable/Disable Trace Recording. If you select the Disassembly Window as the active window all program step commands work on CPU instruction level rather than program source lines. You can select a text line and set or modify code breakpoints using toolbar buttons or the context menu commands.You may use the dialog Debug Inline Assembly to modify the CPU instructions. That allows you to correct mistakes or to make temporary changes to the target program you are debugging. Numerous example programs are included to help you get started with the most popular embedded 8051 devices.The Keil Vision Debugger accurately simulates on-chip peripherals (IC, CAN, UART, SPI, Interrupts, I/O Ports, A/D Converter, D/A Converter, and PWM Modules) of your 8051 device. Simulation helps you understand hardware configurations and avoids time wasted on setup problems. Additionally, with simulation, you can write and test applications before target hardware is available.

5.15 EMBEDDED C Use of embedded processors in passenger cars, mobile phones, medical equipment, aerospace systems and defense systems is widespread, and even everyday domestic appliances such as dish washers, televisions, washing machines and video recorders now include at least one such device. Because most embedded projects have severe cost constraints, they tend to use low-cost processors like the 8051 family of devices considered in this book. These popular chips have very limited resources available most such devices have around 256 bytes (not megabytes!) of RAM, and the available processor power is around 1000 times less than that of a desktop processor. As a result, developing embedded software presents significant new challenges, even for experienced desktop programmers. If you have some programming experience - in C, C++ or Java - then this book and its accompanying CD will help make your move to the embedded world as quick and painless as possible.

6. SCHEMATIC DIAGRAM

6.1 SCHEMATIC EXPLANATIONPOWER SUPPLYThe circuit uses standard power supply comprising of a step-down transformer from 230Vto 12V and 4 diodes forming a Bridge Rectifier that delivers pulsating dc which is then filtered by an electrolytic capacitor of about 470F to 1000F. The filtered dc being unregulated, IC LM7805 is used to get 5V DC constant at its pin no 3 irrespective of input DC varying from 9V to 14V. The input dc shall be varying in the event of input ac at 230volts section varies in the ratio of V1/V2=N1/N2.The regulated 5V DC is further filtered by a small electrolytic capacitor of 10F for any noise so generated by the circuit. One LED is connected of this 5V point in series with a resistor of 330 to the ground i.e., negative voltage to indicate 5V power supply availability. The 12V point is used for other applications as on when required.

STANDARD CONNECTIONS TO MICRO CONTROLLER

ATMEL series of 8051 family of micro controllers need certain standard connections. The actual number of the Micro controller could be 89C51 , 89C52, 89S51, 89S52, as regards to 20 pin configuration a number of 89C2051. The 4 set of I/O ports are used based on the project requirement. Every micro controller requires a timing reference for its internal program execution therefore an oscillator needs to be functional with a desired frequency to obtain the timing reference as t =1/f. A crystal ranging from 2 to 20 MHz is required to be used at its pin number 18 and 19 for the oscillator. Typically 11.0592 MHz crystal is used in general for most of the circuits. Crystal provides the reference frequency only and it is not a crystal oscillator as miss understood by many but it oscillates at 11.0592MHz. Two small value ceramic capacitors of 33pF each is used as a standard connection for the crystal as shown in the circuit diagram.

RESETPin no 9 is provided with an RESET arrangement by a combination of an electrolytic capacitor and a register forming RC time constant. At the time of switch on, the capacitor gets charged, after charging it behaves as a full short circuit from the positive to the pin number 9. After the capacitor gets fully charged the current stops flowing and pin number 9 is pulled down by a 10k resistor to the ground. This arrangement of reset pin 9 going high initially and then to logic 0 i.e., low helps the program execution to start from the beginning. In absence of this the program execution could have taken place habitually anywhere from the program cycle. A pushbutton switch is connected across the capacitor so that at any given time as desired it can be pressed that discharges the capacitor and while released the capacitor starts charging again and then pin number 9 goes to high and then back to low, to enable the program execution from the beginning. This operation of high to low of the reset pin takes place in fraction of a second as decided by the time constant R and C.For example: A 10F capacitor and a 10k resistor would render a 100ms time to pin number 9 from logic high to low, there after the pin number 9 remains low.

ULN2003

ULN2003 is an IC which is used to interface relay with the microcontroller. Since the output of the micro controller is 5V and is not practicable to operate relay with that voltage. ULN2003 is nothing but a set of inverters, if logic high is given to the IC as input then its output will be logic low and vice-versa .Here in ULN2003 pin 1 to 7 are IC inputs and 10 to 16 are IC outputs.For example let us operate a load using a relay which is interfaced with microcontroller by a ULN2003 IC.Positive voltage i.e., 12V is given to 9th pin of the ULN2003 IC and also to one end of the relay coil and the GND is connected to 8th pin. When microcontroller gives logic high to the ULN2003, it gives an inverted output i.e., logic low which is connected to the other end of the relay coil. Due to this current starts flowing through the coil which makes the relay ON and also the load is switched ON.

MAX232 & RS232 MAX232 Pins 9, 10 11, & 12 are meant for interfacing to microcontroller and pin 7, 8, 13, & 14 are meant for communication to RS-232 port of PC. Since our microcontroller has got one Receiver and Transmitter pins we use pin no 11 & 12 or pin no 10 & 9. But as per standard practice, we use pin no 11 and 12 but not pin no 9 & 10 and their corresponding output pins i.e. 13 and 14 are given to DB9 or RS-232 port and that is how communication takes place.

OPERATIONConnections:The output of the power supply which is 5v is connected to the 40 pin of MC & GND is connected to its 20 pin. Port 2.0 to 2.7 of MC is connected to output pins 1 to 8 of ADC0808 i.e., Analog to Digital Converter. Port 3.0, 3.1 of MC is connected to 12 & 11 pins of Max232. Pin 13 & 14 of Max232 are connected to pin 2 and 9 of DB9 female connector. Port 3.2, 3.3, 3.4 pins of MC are connected to 10, 6, 7 pins of ADC0808. Port 3.5 pin is connected to 9th pin of ADC0808 port 3.6 pin is connected to 22 pin of ADC0808 port 1.0, 1.1, 1.2 of MC are connected to pin no 25,24,23 of ADC0808. Port pins 1.3, 1.4, 1.5, 1.6 of microcontroller are connected to pins 1, 2, 3, 4 of ULN2803. Pins 18, 17, 16, 15 of ULN2803 are connected to 4 relays input pins 26, 27, 28 and 1 of ADC0808 are given as to four temperature Sensors LM35. 12th pin of ADC0808 is given to 1K preset. 16th pin of ADC0808 is given to GND.

Working:The idea of this project is to retrieve the real time data from the high temperature furnaces on computer. Four heat Sensors i.e., LM35 are used to sense the heat and an analog to digital converter IC ADC0808 is used to convert the data into digital from because Microcontroller understands digital language. LM35 digital sensor has got 3 pins i.e., VCC, GND and output pins when LM35 is heated the voltage at output pin increases, it is connected to the analog to digital convertor IC (ADC). ADC converts this analog data to binary or digital from. This digital form of data is fed of Microcontroller. Now Microcontroller process this data and communicates with computer via RS232 communication and simultaneously switches ON & OFF the relays. Max232 IC is used for RS232 communication and ULN2003 IC is used for relay