iABSTRACTThe purpose of this project is to develop an automatic railway gate system that uses the microcontroller as a main function of design. The principle objective of this project was to design an automatic railway gate control by microcontroller. This project deals to develop a prototype of railway gate that function automatically by using microcontroller. Besides that, the interfacing program also had been developed for the integration part. The operation using microcontroller (AT89S52) that integrated with other circuits involved such as power supply, IR sensor, light and buzzer, gate motor and LCD display. All the circuits will be combining to demonstrate the operation of microcontroller (AT89S52). This system will make improvement towards the manually operation before this. Human supervision will be considered if there are problems occurred while this system was operated.CONTENTSCHAPTER TITLEPAGE

PROJECT TITLEi

REPORT STATUS VERIFICATION FORMii

STUDENTS DECLARATIONiii

SUPERVISORS DECLARATIONiv

DEDICATIONv

ACKNOWLEDGEMENTvi

ABSTRACTvii

ABSTRAKviii

CONTENTSix

LIST OF TABLESxii

LIST OF FIGURESxiii

LIST OF APPENDICESxvi

IINTRODUCTION1

1.1Project Introduction1

1.2Project Objectives2

1.3Problem Statement2

1.4Scope of Works3

1.5Methodology4

1.6Report Structure5

xIILITERATURE REVIEW6

2.1Previous System6

2.2Block Diagram Description7

2.2.1 Gate Control Unit9

2.2.2 Announcement Unit10

2.3Microcontroller10

2.3.1 AT89S5211

2.4Programming Language13

2.5Infrared Sensor14

2.5.1 IR Transmitter14

2.5.2 IR Receiver15

2.6Motor Theory16

2.7H-Bridge17

2.7.1 L293D18

2.8LCD19

2.9Proteus VSM20

2.10PIC C Compiler23

IIIMETHODOLOGY26

3.1Project Methodology26

3.2Project Flow Chart28

3.3System Flow29

3.3.1 Process Procedure30

3.4Hardware Assembly31

xiIVRESULTS AND DISCUSSION33

4.1System Explanation33

4.2The Designed Circuits36

4.2.1 Sensor Circuit36

4.2.2 Buzzer Circuit38

4.2.3 Lighting Alarm Circuit39

4.2.4 Voltage Regulator Circuit40

4.2.5 LCD Circuit41

4.2.6 Motor Circuit44

4.2.7 AT89S52 Integration Circuit46

4.3The Simulation Result47

4.3.1 Voltage Supply47

4.3.2 AT89S52 Interfacing Result48

4.4The Programming Result50

4.5Hardware Description53

4.5.1 The Constructed Circuits53

4.5.2 The Prototype57

IVCONCLUSION AND RECOMMENDATION59

5.1Conclusion59

5.2Recommendation60

REFERENCES61

xiiLIST OF TABLESNO.TITLEPAGE

4.2.5 The pin structure of LCD module43

xiiiLIST OF FIGURESNO.TITLESPAGE

2.2.1Block diagram of the system7

2.2.2The functionality between microcontrollers8

2.2.1.1The diagram of gate control unit9

2.3.1.1AT89S52 pins/terminals12

2.3.1.2AT89S52 chip12

2.5.1Infrared sensor14

2.5.1.1 IR transmitter circuit using 555 IC timer14

2.5.2.1IR receiver circuit using 555 IC timer15

2.6.1Stepper motor16

2.6.2Servo motor16

2.6.3DC motor17

2.7.1The diagram of basic H-bridge17

2.7.1.1The interfacing diagram18

2.7.1.2L293D IC chip19

2.8LCD19

2.9.1Proteus VSM20

2.9.2ISIS 7 Professional user interface21

2.9.3ARES 7 Professional user interface21

2.9.4Components selection22

2.9.5Parameter settings22

xiv2.9.6Simulation buttons23

2.10.3Create new file/project24

2.10.4Example program25

2.10.5Compile summary25

3.2Project flow chart28

3.3System flow chart29

3.3.1.1The flow of the process in the system30

3.4.1The diagram of hardware assembly done31

4.1.1The system diagram with fully explanation33

4.2.1.1The designed IR sensor circuit36

4.2.1.2Example of IR module with pins/terminals37

4.2.1.3The diagram of suggested arrangement IR module37

4.2.2.1The designed buzzer circuit38

4.2.3.1The designed lighting alarm circuit39

4.2.4.1The designed voltage regulator circuit40

4.2.5.1The designed LCD circuit interface with AT89S52 circuit41

4.2.6.1The designed motor circuit interface with AT89S52 circuit44

4.2.7.1The designed overall AT89S52 interfacing circuit46

4.3.1.1The simulation result give value of 5V47

4.3.2.1The result after AT89S52 being triggered48

4.3.2.2The result after AT89S52 triggered to back normal condition49

4.4.1The programming result52

4.5.1.1The sensor circuit53

4.5.1.2The sensor circuit on PCB53

4.5.1.3The main circuit54

4.5.1.4LCD show the notification of closing the gate55

xv4.5.1.5 The gate motor used55

4.5.1.6 The sensor located at side of the railway track56

4.5.2.1The prototype of model railway gate system57

4.5.2.2The prototype of model railway gate system58

xviLIST OF APPENDICESNO.TITLESPAGE

AGantt Chart63

BMicrochip PIC16F87XA Data Sheet65

1CHAPTER IINTRODUCTION1.1 Project Introduction In general, this project utilizes the importance of microcontroller as a main design. It used to provide improvement into manual system that exist nowadays.Microcontroller is a small unit of controller that acted following the instruction programmed. All the circuits included in this prototype were designed following the suitability of AT89S52.This automatic railway gate system was operated after signal received from the IR sensor. This signal used to trigger the AT89S52 for operating the gate motor and alarm indicators by instruction programmed.Electronic applications used to enable this system operated in automatic mode. The computer usage must be fully utilized to building up a system that encourage implementing of the technology.21.2 Project Objectives The microcontroller (AT89S52) is use to demonstrate the integration of computer method in railway gate operation.The objectives of this project are:i. To develop a prototype of railway gate that function automatically by using microcontroller. ii. To develop an interfacing program for the integration part of microcontroller operation. iii. To design an automatic railway gate control by using microcontroller. Furthermore, this project is aimed to replace the gatekeepers with an automatic system. It is develop to apply the structure of interfacing program in between to give a lot of advantages.1.3 Problem Statement Nowadays, the railway gate is operating by manual operation. It is operating in the area that there are railway line junction with the road. The railway gate management has to employ workers to be on duty for control the operation. Due to this, the worker will manually open and close the gate with under supervision.This prototype will introduce the automatic railway gate operation. This system will make improvement towards the manually operation before this. Human supervision will be considered if there are problems occurred while this system was operated.This is an idea to perform computer integration with mechanical structure to simulate what the system can do. Control system with computer applications will make the management or consumer become more effective. Therefore, this is the best example in develop railway gate management system become more efficient.31.4 Scope of Works This project covered the operation of automatic railway gate control by using microcontroller (AT89S52). The circuits involved such as power supply, IR sensor, light and buzzer, gate motor and LCD display.All of these operations will be combining to demonstrate the operation of microcontroller (AT89S52).The operations of microcontroller works follow the instruction programmed. The combining circuits were constructed on Proteus software to seen whether that circuits was right or not. After that, the hardware part was constructed after all the simulation being done.IR sensor circuit is providing signal to triggered the AT89S52. The sensed signal wills active the gate motor and LCD display. Alarm and indication light circuit was provided as additional part of this system.Additional elements can be added without affecting the remaining elements. This allows the flexibility of the developed system.41.5 Methodology This project began with the research of the proposed title. The result of that research is then discussed with the supervisor. Once the title of project was approved, the background of study for this project was explored.AT89S52 was chosen as a microcontroller. Then, the circuits simulation was performed. In the other hand, the instruction programmed also being built for the interfacing part. After all being settled, the construction of hardware part was started after the components were being chosen.In all the steps done there are troubleshooting part to resolve the problems facing. Between hardware part and instruction programmed built, there are integrated step that allows the AT89S52 to simulate all the operations of the system.After all the part is complete to built, some analysis should being made to show what the solution of the problems occurred. It involving the comparison between the research that had been done before this.51.6 Report Structure Chapter 1 introduced the project as a whole. The early and basic explanations were mentioned in this chapter. This chapter consisted of the project introduction and objectives, problem statements, scope of work, and the simplified methodology.Chapter 2 is literature review. Past projects system were taken into consideration when completing this chapter. The ways those projects and researches had been done were compared with what this project. These comparisons were done to understand what this project is all about and where it stands.Chapter 3 is methodology. It explained how this project came to be. This chapter explained the part most important of all, the flow this project. What had been researched and what needed to be done was explained in this chapter.Chapter 4 concentrated on the result and discussion of this project. What had been done was explained in diagrams and written programs. The expected results also mentioned in this chapter.Chapter 5 was the final chapter in this report. The conclusions and recommendations were placed in this chapter. In other words, the conclusion was the summary of what had been done throughout this project. After the project was done, recommendations were made and any expansions or upgrades that might be done in the future were suggested.6CHAPTER IILITERATURE REVIEW2.1 Previous System At present scenario, in the level crossing line the railway gate is operated normally by a gate keeper. This happen when the railway line is cross over the road and there are a gate that have to be controlled. The gate keeper work after receiving the information about the train arrival from the nearer station. When the train starts to leave the station, the particular station delivers the information to give the signal for gate keeper to get ready. This is the operation are followed for operating the railway gates.In addition, this automatic railway gate system can contribute a lot of benefit either to the road user or to the railway management. This type of gate can be implementing in the level crossing where the chances of accidents are higher. The computer integration will be use to provide addition in the latest technology.72.2 Block Diagram Description

Figure 2.2.1: Block diagram of the systemThis prototype of project demonstrated the Automatic Railway Gate Control by Using Microcontroller (AT89S52). The sensors are fixed at the certain distance on both sides of the gate, that is before the train arrive and after the train departure. The sensed signal is send to the microcontroller (AT89S52) and checked whether there are vehicles or people between the gate. At the same time, alarm and indication light signal are provided to the road users to warn the closing of gates.In sequences, the gate motor will move forward direction to close the gate. It will stay closed at certain time until the train has crossed the gate and reached the second sensor activate the motor in backward direction so the gate will open.8Lighting signal also provided at the certain distance as pre cautionary step for driver. Meanwhile, the nearer station also will provide an indication alarm to remind them about the crossing train. If anything happened at the gates, this alarm will alert the station. LCD display will show the arrival of the train to cross the gate as additional features of this system.

SensorLCDMotor

AT89S52MicrocontrollerBuzzerLighting

Alarm

Figure 2.2.2: The functionality between microcontrollersINTRODUCTION TO EMBEDDED SYSTEMS

2.1 EMBEDDED SYSTEM:

Embedded System is a combination of hardware and software used to achieve a single specific task. 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: 2.1.1 EMBEDDED SYSTEM DESIGN CYCLE

V Diagram

In this place we need to discuss the role of simulation software, real-time systems and data acquisition in dynamic test applications. Traditional testing is referred to as static testing where functionality of components is tested by providing known inputs and measuring outputs. Today there is more pressure to get products to market faster and reduce design cycle times. This has led to a need for dynamic testing where components are tested while in use with the entire system either real or simulated. Because of cost and safety concerns, simulating the rest of the system with real-time hardware is preferred to testing components in the actual real system.

The diagram shown on this slide is the V Diagram that is often used to describe the development cycle. Originally developed to encapsulate the design process of software applications, many different versions of this diagram can be found to describe different product design cycles. Here we have shown one example of such a diagram representing the design cycle of embedded control applications common to automotive, aerospace and defense applications.

In this diagram the general progression in time of the development stages is shown from left to right. Note however that this is often an iterative process and the actual development will not proceed linearly through these steps. The goal of rapid development is to make this cycle as efficient as possible by minimizing the iterations required for a design. If the x-axis of the diagram is thought of as time, the goal is to narrow the V as much as possible and thereby reduce development time.

The y-axis of this diagram can be thought of as the level at which the system components are considered. Early on in the development, the requirements of the overall system must be considered. As the system is divided into sub-systems and components, the process becomes very low-level down to the point of loading code onto individual processors. Afterwards components are integrated and tested together until such time that the entire system can enter final production testing. Therefore the top of the diagram represents the high-level system view and the bottom of the diagram represents a very low-level view.

Notes:

V diagram describes lots of applicationsderived from software development.

Reason for shape, every phase of design requires a complimentary test phase. High-level to low-level view of application.

This is a simplified version.

Loop Back/Iterative process, X-axis is time (sum up).

2.1.2 CHARACTERISTICS OF EMBEDDED SYSTEM An embedded system is any computer system hidden inside a product other than a computer. There will encounter a number of difficulties when writing embedded system software in addition to those we encounter when we write applications Throughput Our system may need to handle a lot of data in a short period of time.

ResponseOur system may need to react to events quickly

TestabilitySetting up equipment to test embedded software can be difficult

DebugabilityWithout a screen or a keyboard, finding out what the software is doing wrong (other than not working) is a troublesome problem

Reliability embedded systems must be able to handle any situation without human intervention

Memory space Memory is limited on embedded systems, and you must make the software and the data fit into whatever memory exists

Program installation you will need special tools to get your software into embedded systems

Power consumption Portable systems must run on battery power, and the software in these systems must conserve power

Processor hogs computing that requires large amounts of CPU time can complicate the response problem

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.

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.

2.2 APPLICATIONS

1. Military and aerospace embedded software applications2. Communication applications3. Industrial automation and process control software2.3 CLASSIFICATION

1. Real Time Systems.

2. RTS is one which has to respond to events within a specified deadline.

3. A right answer after the dead line is a wrong answer

2.3.1 RTS CLASSIFICATION1. Hard Real Time Systems2. Soft Real Time System

2.3.1.1 HARD REAL TIME SYSTEM

"Hard" real-time systems have very narrow response time.

Example: Nuclear power system, Cardiac pacemaker.POWER SUPPLY UNIT:The input to the circuit is applied from the regulated power supply. The a.c. input i.e., 230V from the mains supply is step down by the transformer to 12V and is fed to a rectifier. The output obtained from the rectifier is a pulsating d.c voltage. So in order to get a pure d.c voltage, the output voltage from the rectifier is fed to a filter to remove any a.c components present even after rectification. Now, this voltage is given to a voltage regulator to obtain a pure constant dc voltage.

Circuit Diagram

Transformer:Usually, DC voltages are required to operate various electronic equipment and these voltages are 5V, 9V or 12V. But these voltages cannot be obtained directly. Thus the a.c input available at the mains supply i.e., 230V is to be brought down to the required voltage level. This is done by a transformer. Thus, a step down transformer is employed to decrease the voltage to a required level.

Rectifier: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.

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.

Voltage regulator:As the name itself implies, it regulates the input applied to it. A voltage regulator is an electrical regulator designed to automatically maintain a constant voltage level. In this project, power supply of 5V and 12V are required. In order to obtain these voltage levels, 7805 and 7812 voltage regulators are to be used. The first number 78 represents positive supply and the numbers 05, 12 represent the required output voltage levels.

Notice in the above diagram that a relay uses an electromagnet.This is a device consisting of a coil of wire wrapped around an iron core. Whenelectricityis applied to the coil of wire it becomesmagnetic, hence the termelectromagnet.The A B and C terminals are an SPDT switch controlled by the electromagnet. When electricity is applied to V1 and V2, the electromagnet acts upon the SPDT switch so that the B and C terminals are connected. When the electricity is disconnected, then the A and C terminals are connected. It is important to note that the electromagnetismagnetically linkedto theswitchbut the two are NOT linked electrically.

CHAPTER 3

AT89S525.1 INTRODUCTION

Today, micro controllers have become an integral of all automatic and semi-automatic machines. Remote controllers, hand-held communication devices, dedicated controllers, have certainly improved the functional, operational and performance based specifications.

Microcontrollers are single chip microcomputers, more suited for control and automation of machines and process. Microcontrollers have central processing unit (CPU), memory, I/O units, timers and counters, analog to digital converters (ADC), digital to analog converters (DAC), serial ports, interrupt logic, oscillator circuitry and many more functional blocks on chip.

All these functional block on a single Integrated Circuit (IC), result into a reduced size of control board, low power consumption, more reliability and ease of integration within an application design. The usage of micro controllers not only reduces the cost of automation, but also provides more flexibility

5.2 FEATURES

Compatible with MCS-51 Products 8K Bytes of In-System Reprogrammable Flash Memory Endurance: 1,000 Write/Erase Cycles Fully Static Operation: 0 Hz to 24 MHz Three-level Program Memory Lock 256 x 8-bit Internal RAM 32 Programmable I/O Lines Two 16-bit Timer/Counters Six Interrupt Sources Programmable Serial Channel Low-power Idle and Power-down Modes

5.3 DESCRIPTION

The AT89C51 is a low-power, high-performance CMOS 8-bit microcomputer with 4K

bytes of Flash programmable and erasable read only memory (PEROM). The device is manufactured using Atmels high-density non-volatile memory technology and is compatible with the industry-standard MCS-51 instruction set and pin out.

The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional on-volatile memory programmer. By combining a versatile 8-bit CPU with Flash on a monolithic chip, the Atmel AT89S52 is a powerful microcomputer which provides highly-flexible and cost-effective solution to many embedded control applications

PIN CONFIGURATION

Fig.5.1 Pin configurationBLOCK DIAGRAM

Fig.5.2. Block diagram5.6 PIN DESCRIBTION

VCCSupply voltage.

GNDGround.

PORT 0Port 0 is an 8-bit open-drain bi-directional 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 may 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 1Port 1 is an 8-bit bi-directional 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 pulledlow will source current (IIL) because of the internal pull ups. Port 1 also receives the low-order address bytes during Flash programming and verification.

PORT 2Port 2 is an 8-bit bi-directional 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, it 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 2 also receives the high-order address bits and some control signals during Flash programming and verification.

PORT 3Port 3 is an 8-bit bi-directional 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. Port 3 also serves the functions of various special features of the AT89C51 as listed below:

PORT PINALTERNATE FUNCTIONS

P3.0RXD (serial input port)

P3.1TXD (serial output port)

P3.2INT0 (external interrupt 0)

P3.3INT1 (external interrupt 1)

P3.4T0 (timer 0 external input)

P3.5T1 (timer 1 external input)

P3.6WR (external data memory write strobe)

P3.7RD (external data memory)

Port 3 also receives some control signals for Flash programming and verification.

RSTReset input. A high on this pin for two machine cycles while the oscillator is running resets the device.

ALE/PROGAddress Latch Enable 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. If desired, ALE operation can be disabled by setting bit 0 of SFR location 8EH. With the bit set, ALE is active only during a MOVX or MOVC instruction. Otherwise, the pin is weakly pulled high. Setting the ALE-disable bit has no effect if the microcontroller is in external execution mode.

PSENProgram Store Enable is the read strobe to external program memory. When the AT89C51 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/VPPExternal 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, for parts that require 12-volt VPP.

XTAL1Input to the inverting oscillator amplifier and input to the internal clock operating circuit.

XTAL2Output from the inverting oscillator amplifier.

OSCILLATOR CHARACTERISTICSXTAL1 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 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.

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. It should be noted that when idle is terminated by a hard ware reset, the device normally resumes program execution, from where it left off, up to two machine cycles before the internal reset algorithm takes control. On-chip hardware inhibits access to internal RAM in this event, but access to the port pins is not inhibited. To eliminate the possibility of an unexpected write to a port pin when Idle is terminated by reset, the instruction following the one that invokes Idle should not be one that writes to a port pin or to external memory.

Fig.5.3. Oscillator ConnectionsNote: C1, C2 = 30 pF 10 pF for Crystals

= 40 pF 10 pF for Ceramic Resonators

Fig.5.4.External Clock Drive Configuration2X16 LCD:

Most LCD programmed in 8 bit configuration. Moreover LCD put on equipment that show the value of measurement, i.e. temperature, voltage, current, etc. There are a lot of tutorial show steps how to configure out in order to LCD on. But each LCD hasown characteristicBasic Specifications

Power requirements4.8 to 5.5Vdc @ 3Ma

User connector5-pin header; 0.025" posts on 0.10" centers

Connector pinout+5V GND SERIAL GND +5V

Serial InputRS-232 or inverted TTL, 2400/9600, N81

Operating Temperature0 to 50 C

Initializationswitches LCD power; performs soft init

Instruction prefixASCII 254 (0FE hex)

LCD typeSupertwist (STN), yellow-green

Optimum viewing direction6 o'clock

LCD Instructions by FunctionFunctionASCII Value

Clear screen1

Home cursor2

Blank display (retaining data)8

Hide cursor12

Show underline cursor14

Move cursor 1 character left16

Move cursor 1 character right20

Scroll 1 character left24

Scroll 1 character right28

Set display address (position the cursor)128 + location

Move to 1st character of 1st line128

Move tonthcharacter of 1st line128 +n

Move to 1st character of 2nd line192

Move tonthcharacter of 2nd line192 +n

Set character-generator address64 + address

RELAYS:

HistoryElectromagnetic relays were once the main ingredient in automated machinery. Factories used to control everything from conveyors to robots with huge panels filled with hundreds of relays clacking away, each in turn. This method had several drawbacks, but for years it was the only method available.

Recently, Programmable Logic Controllers (PLCs) have replaced banks of relays for automation needs. Relays are still used in small applications where a PLC would be overkill. They come in several varieties to suit a wide range of applications.

Relays have a huge number of uses, but a few very common ones constitute the vast majority. Holding circuits are used to hold power on until the connection is Broken by another signal. This is achieved by connecting one of the relay's own contacts to its coil once the relay is turned on, it stays on. . Relays are also useful for allowing one signal to switch connections at two or more different voltages since the contacts are isolated from each other. But most often, they are used to switch connections that are at different voltages than the control power.

In many cases, control power and signals generated by sensors are generated at low voltages. This is for reasons of safety and efficiency. Low voltage signals, however, are inefficient for doing high-wattage work, so a relay is used to allow the low voltage signal to switch a higher-voltage connection to do work, such as pull in a large solenoid, run a motor.

4.7.1 WHAT IS A RELAY?

A relay is an electrical switch that opens and closes under the control of another electrical circuit. Relays are one of the oldest, simplest, and yet, easiest and most useful devices. Before the advent of the mass produced transistor, computers were made from either relays or vacuum tubes, or both.

The classic electromagnetic relay is a switch which is thrown by an electromagnet. A relatively low current applied to the magnet can throw the switch, allowing a higher current to flow through that switch. The solenoid of most automobiles can be considered an electromagnetic relay.

In digital applications, it has been surpassed by the solid state relay. These relays have no moving parts, so they can switch very quickly in response to a control signal. They are built from semiconductors, and they cannot handle the current that an electromagnetic relay could but their advantage is speed. High current solid-state relays often require heat sinks to drain excess heat. 4.7.2 Relay Construction

Relays are amazingly simple devices. There are four parts in every relay:

Electromagnet

Armature that can be attracted by the electromagnet

Spring

Switching contacts

relays construction

Relay Contact Information:

Relay contacts on most of our kits and in the industrial world are labeled with

NO (Normally Open), NC (Normally Closed), and CT (Common Terminal).

A relay contact is a switch, nothing more, nothing less. It does not provide power; it simply opens and closes an electrical circuit, just like the light switch on a wall.

When the relay is de-energized or turned off there is an electrical connection between NC and Common hence normally closed. In the off state there is not a connection between NO and common, hence normally open.

When the relay is energized or turned on the NO and C makes an electrical connection and the electrical connection between NC and C is removed.

4.7.3RELAYS WORKING:

When a current flows through the coil, the resulting magnetic field attracts an armature that is mechanically linked to a moving contact. The movement either makes or breaks a connection with a fixed contact. When the current to the coil is switched off, the armature is returned by a force approximately half as strong as the magnetic force to its relaxed position. Usually this is a spring, but gravity is also used commonly in industrial motor starters. Most relays are manufactured to operate quickly. In a low voltage application, this is to reduce noise. In a high voltage or high current application, this is to reduce arcing.

If the coil is energized with DC, a diode is frequently installed across the coil, to dissipate the energy from the collapsing magnetic field at deactivation, which would otherwise generate a spike of voltage and might cause damage to circuit components. If the coil is designed to be energized with AC, a small copper ring can be crimped to the end of the solenoid. This "shading ring" creates a small out-of-phase current, which increases the minimum pull on the armature during the AC cycle.

Relay operation

4.7.4 CHOOSING OF RELAY:

1.Physical size and pin arrangement If you are choosing a relay for an existing PCB you will need to ensure that its dimensions and pin arrangement are suitable. You should find this information in the supplier's catalogue.

2.Coil voltage The relay's coil voltage rating and resistance must suit the circuit powering the relay coil. Many relays have a coil rated for a 12V supply but 5V and 24V relays are also readily available. Some relays operate perfectly well with a supply voltage which is a little lower than their rated value.

3.Coil resistance The circuit must be able to supply the current required by the relay coil. You can use Ohm'slaw to calculate the current:

Relay coil current = supply voltage

coil resistance

For example: A 12V supply relay with a coil resistance of 400 passes a current of 30mA. This is OK for a 555 timer IC (maximum output current 200mA), but it is too much for most ICs and they will require a transistor to amplify the current.

4.Switch ratings (voltage and current) The relay's switch contacts must be suitable for the circuit they are to control. You will need to check the voltage and current ratings. Note that the voltage rating is usually higher for AC, for example: "5A at 24V DC or 125V AC".

5.Switch contact arrangement (SPDT, DPDT etc) Most relays are SPDT or DPDT which are often described as "single pole changeover" (SPCO) or "double pole changeover" (DPCO). For further information please see the page on switches.

4.7.5Advantages:

1.The complete electrical isolation improves safety by ensuring that high voltages and currents cannot appear where they should not be.

2.Relays come in all shapes and sizes for different applications and they have various switch contact configurations. Double Pole Double Throw (DPDT) relays are common and even 4-pole types are available. You can therefore control several circuits with one relay or use one relay to control the direction of a motor.

3.It is easy to tell when a relay is operating - you can hear a click as the relay switches on and off and you can sometimes see the contacts moving.

4.7.6Disadvantages :

Being mechanical though, relays do have some disadvantages over other methods of electrical isolation:

1.Their parts can wear out as the switch contacts become dirty - high voltages and currents cause sparks between the contacts.

2.They cannot be switched on and off at high speeds because they have a slow response and the switch contacts will rapidly wear out due to the sparking.

3.Their coils need a fairly high current to energize, which means some micro-electronic circuits can't drive them directly without additional circuitry.

4.The back-emf created when the relay coil switches off can damage the components that are driving the coil. To avoid this, a diode can be placed across the relay coil, as will be seen in any Electronics in Meccano circuits that use relays with sensitive components.

4.7.7Applications:

Relays are used:

1.To control a high-voltage circuit with a low-voltage signal, as in some types of modems.

2.To control a high-current circuit with a low-current signal, as in the starter solenoid of an automobile.

3.To detect and isolate faults on transmission and distribution lines by opening and closing circuit breakers (protection relays).

4.To isolate the controlling circuit from the controlled circuit when the two are at different potentials, for example when controlling a mains-powered device from a low-voltage switch. The latter is often applied to control office lighting as the low voltage wires are easily installed in partitions, which may be often moved as needs change. They may also be controlled by room occupancy detectors in an effort to conserve energy.

5.To perform logic functions. For example, the Boolean AND function is realized by connecting NO relay contacts in series, the OR function by connecting NO contacts in parallel. The change-over or Form C contacts perform the XOR (exclusive or) function. Similar functions for NAND and NOR are accomplished using NC contacts. Due to the failure modes of a relay compared with a semiconductor, they are widely used in safety critical logic, such as the control panels of radioactive waste handling machinery.

6.To perform 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.

SOFTWARE REQUIRED

The Keil tool chain consists of the following executables located in the c:\c51eval\bin directory:

Vision uvw51e.exe

C Compiler c51.exe

Assembler a51.exe

Linker bL51.exe

dScopedsw51.exe

Vision IDE

Vision is a Windows based front end for the C Compiler and Assembler. It was developed in the USA as was the printed manual set. Compiler, Assembler and Linker options are set with simple mouse clicks. Vision runs on Windows 3.1, 95 and NT. The Compiler, Assembler and Linker are DOS executables. They can be accessed with your favorite batch files if you prefer. This provides maximum flexibility. This Integrated Development Environment (IDE) has been expressly designed with the user in mind. A full function editor is included. All IDE functions are intuitive via pull down menus with prompted selections. An extensive Help utility is included. External executables can be run from within Vision. This includes emulator software.

C51 C Compiler for the 8051, 8x931Hx and 8x931Ax [USB]

The C51 ANSI compiler along with the A51 assembler is designed specifically for the Intel MCS8051 microcontroller family, including the 8x931 USB. The C51 is 100% compatible with existing 8051programs. Extensions provide access to all 8051 hardware components. Sample USB/931 code is available: www.keil.com/usb. C51 supports code banking. The compiler can be run in either DOS mode or called from the Windows based front end Vision. Run from Vision which is included with every Assembler and Compiler package.Evaluation Version of the Keil Tool Set:

The evaluation version of the Keil tool set is restricted to a 2K code size and the code must be located at 0x4000. Useful object code is produced. Other than these restrictions, the tool set works exactly as the full version does. This allows you to fully evaluate the features and power of Keil products. The full version has no restrictions and is fully ANSI compliant.