Density Based Traffic Light Control System

Table of Contents

1.Introduction 2. Literature survey 3.Formation of the Problem 4.System specification 5.Design of solution 6.Implementation 7.Results and Discussions 8.System testing 9.Conclusion and future scope 10.References

List of Figures

Figure 2.1 A typical embedded system block block diagram Figure 2.2 The structure of a GSM network  Figure 4.1: AT89C51 Pin Diagram Figure 4.2 Oscill Osc illator ator and timing circuit Figure 4.3 SMOD Register  Figure 4.4 TCON Register  Figure 4.5 TMOD Register  Figure 4.6 IE Register  Figure 4.7 IP Register  Figure 4.8 PSW Register  Figure 4.9 PORT3 Alternate Use Figure 4.10 Data framing Figure 4.11 Data transfer  Figure 4.12 SCON Register  Figure 4.13 UART modes Figure 4.14Voltage levels for RS232 and TTL

ABSTRACT

TITLE:

DENSITY BASED TRAFFIC LIGHT CONTROL SYSTEM

AIM:

The main objective of this project is to control the traffic lights based on the density of the vehicles. DESCRIPTION:

In this system IR sensors are used to measure the density of the vehicles which are fixed within a fixed distance. All the sensors are interfaced with the microcontroller which in turn controls the traffic signal system according to density detected by the sensors.

If the traffic density is high on particular side more priority is given for that side. The sensors continuously keep sensing density on all sides and the green signal is given to the side on priority basis, where the sensors detect high density. The side with next priority level follows the first priority level.

By using this system traffic can be cleared without irregularities and time delays even though there is no traffic on the other side can be avoided.

SOFTWARE:

Embedded C. TOOLS USED:

KEIL uvision2 IDE HARDWARE:

1.

PCB

for micro controllers

2. 8051 controller, 3. DB9 Connectors 4. IR sensor pairs 5. Red, green LED·s 6. 11.0592 MHz quartz crystal, 7. Resistors, Capacitors

BLOCK DIAGRAM

IR - E

LCD

-

Traffic signal lights

89C51

Key board

-

Step

Bridge

Filter

down

Rectifier

Circuit

Power supply to all sections Regulator

CHAPTER 1

Introduction

1.1 Overview

The overview of this project is to implement Density based traffic controlling system using IR  technology and 89S52 controller. 89S52 is very efficient architecture which can be used for low end security systems and IR is widely adapted technology for communication. 1.2Purpose

Purpose of the current work is to study and analyse the counting and controlling system by using 8051 controller. 1.3 Scope

Current work focuses on how to use effectively IR and 8051 controllers for digital security systems.

CHAPTER 2 Literature survey

2.1 Embedded Systems An embedded system is a special-purpose computer system designed to perform one or a few dedicated functions, often with real-time computing constraints. It is usually embedded  as part of a complete device including hardware and mechanical parts. In contrast, a general-purpose computer, computer, such as a s a personal computer, can do many different tasks depending on programming. Embedded systems control many of  the common devices in use today. Since the embedded system is dedicated to specific tasks, design engineers can optimize it, reducing the size and cost of the product, pr oduct, or increasing the reliability and performance. Some embedded systems are mass-produced, mass-produced, benefiting b enefiting from economics of scale. Physically, embedded systems range from portable devices such as digital watches and mp4 players, to large stationary installations like traffic lights, factory controllers, or the systems controlling nuclear power stations. Complexity varies from low, with a single microcontroller chip, to very high with multiple units, peripherals and networks mounted inside a large chassis or enclosure. In general, "embedded system" is not an exactly defined term, as many systems have some element of   programmability.  programmability. For F or example, handheld computers share some elements with embedded systems ² such as the operating systems and microprocessors which power them ² but are not truly embedded systems,  because they allow different applications to be loaded and periphe p eripherals rals to be b e connected 2.2 Characteristics 1. Embedded systems are designed to do some specific task, rather than be a general-purpose general-purpose computer for multiple tasks. Some also have r eal-time performance constraints that must be met, for reasons such as safety and usability; others may have low or no performance requirements, allowing the system hardware to be simplified to reduce r educe costs. 2. Embedded systems are not always standalone devices. Many embedded systems consist of small, computerized parts within a larger device that serves a more general purpose. For example, the features an embedded system for tuning the strings, but the overall purpose of the Robot Guitar is, of course, to play music. Similarly, an embedded system in automobile a utomobiless provides a specific function as a subsystem of the car itself. 3. The program instructions instructions written for embedded systems are referred to as firmware, and are stored in read-only memory or flash memory chips. They run with limited computer hardware har dware resources: little memory, small s mall or non-existent keyboard and/or screen.

Figure 2.1 A typical typical embedded system block diagram 2.3 Micro Controllers

The micro controller, nowadays, is an indispensable device for electrical/electronic engineers and also for technicians in the area, because of its versatility and its enormous application. .Born of parallel developments in computer architecture and integrated circuit fabrication ,the microprocessor or computer on chip first becomes a commercial reality in 1971.with the introduction of the 4 bit 4004 by a small, unknown company by the name of Intel corporation. Other, well established, semiconductor firms soon followed Intel¶s pioneering technology so that  by the late 1970¶s we could choose from a half dozen or so micro processor typThe 1970s also saw the growth of the number of personal computer users from a Handful of hobbyists and hackers to millions of business, industrial, governmental, defense, and educational and private users now enjoying the advantages of inexpensive computing. A bye product of microprocessor development was the micro controller. The same fabrication techniques and programming concepts that make possible general-purpose microprocessor also yielded the micro controller. Among the applications of a micro controller we can mention industrial automation, mobile telephones, radios, microwave ovens and VCRs. Besides, the present trend in digital electronics is toward restricting to micro controllers and chips that concentrate a great quantity of 

logical circuits, like PLDs (Programmable Logic Devices) and GALs (Gate Array Logic). In dedicated systems, the micro controller is the best solution, because it is cheap and easy to manage. 2.6 Communication:

Communication refers to the sending, receiving and processing of information by electric means. As such, it started with wire telegraphy in the early 80s, developing with telephony and radio some decades later. Radio communication became the most widely used and refined through the invention of and use of transistor, integrated circuit, and other semi-conductor devices. Most recently, the use of satellites and fiber optics has made communication even more wide spread, with an increasing emphasis on computer and other data communications.

A modern communications system is first concerned with the sorting, processing and storing of  information before its transmission. The actual transmission then follows, with further processing and the filtering of noise. Finally we have reception, which may include processing steps such as decoding, storage and interpretation. In this context, forms of communications include radio, telephony and telegraphy, broadcast, point to point and mobile communications (commercial and military), computer communications, radar, radio telemetry and radio aids to navigation. It is also important to consider the human factors influencing a particular system, since they can always affect its design, planning and use.

Wireless communication has become an important feature for commercial products and a popular research topic within the last ten years. There are now more mobile phone subscriptions than wired-line subscriptions. Lately, one area of commercial interest has been low-cost, low-power, and short-distance wireless communication used for personal wireless networks." Technology advancements are providing smaller and more cost effective devices for integrating computational processing, wireless communication, and a host of other functionalities. These embedded communications devices will be integrated into applications ranging from homeland security to industry automation and monitoring. They will also enable custom tailored engineering solutions, creating a revolutionary way of  disseminating and processing information. With new technologies and devices come new business

activities, and the need for employees in these technological areas. Engineers who have knowledge of  embedded systems and wireless communications will be in high demand. Unfortunately, there are few adorable environments available for development and classroom use, so students often do not learn about these technologies during hands-on lab exercises. The communication mediums were twisted pair, optical fiber, infrared, and generally wireless radio.

2.7

IR Remote Theory

The cheapest way to remotely control a device within a visible range is via Infra-Red light. Almost all audio and video equipment can be controlled this way nowadays. Due to this wide spread use the required components are quite cheap, thus making it ideal for us hobbyists to use IR control for our own projects. IR sensor is the combination of IR LED with PHOTO DIODE. DIODE. After this combination we are connecting the DARLINGTON PAIR TRANSISTOR. End of the IR sensor we have to connect a NOT gate for the inverting purpose means low input have corresponding corresponding low output. At last this entire connector is connected to any one external interrupt to generating the interruption of the main program.

Infra-Red actually is normal normal light light with with a particular colour. We We humans humans can't see this colour because its wave length length of 950nm is below below the visible spectrum. That's one of the reasons why IR is chosen for remote control purposes, we want to use it but we're not interested in seeing it. Another reason is because IR LEDs are quite easy to make, and therefore can be very cheap. IR LED wave length range 1.6m to 2.4m. Materials used for IR LED are InSB, Ge,Si, GaAs, CdSe . These IR s are not visible range for observation purpose we have to connect LED s are not.

CHAPTER 3

Problem formulation

The problem with the traffic system is that for every minute the vehicles at the 4-way road will  be heavy and the traffic lights shall be changed to each side for some fixed time. Even though there are no vehicles at particular side, the traffic signals will glow for given fixed time.Due to that there is time waste process. Due to this other side vehicles have to wait for the time to complete the process. So to reduce the wastage of time, we can implement the system that controls the traffic based on the heavy flow of vehicles at any particular side. With this system, we shall count the number of vehicles at each side at the junction and give th path to the  particular side which has heavy flow of vehicles and keep remaining stop position. So that for  this to count the number of vehicles at side of the junction, we shall use IR technology.

CHAPTER 4

System Specification 4.1 89S52 Micro Controller Features: 

Compatible with MCS-51® Products



8K Bytes of In-System Programmable (ISP) Flash Memory

 ± Endurance: 1000 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

Description

The AT89S52 is a low-power, high-performance CMOS 8-bit microcontroller with 8K bytes of insystem programmable Flash memory. The device is manufactured using Atmels high-density nonvolatile memory technology and is compatible with the industry- standard 80C51 instruction set and pin out. The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory programmer. By combining a versatile 8-bit CPU with in-system programmable Flash on a monolithic chip, the Atmel AT89S52 is a powerful microcontroller which provides a highlyflexible 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.

Pin Description VCC:

Pin 40 provides supply voltage to the chip. The voltage source is + 5V.

GND:

Pin 20 provides ground.

Port 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 b ytes during Flash programming and outputs the code bytes during program verification. External pull ups are required during program verification. 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), respectively, as shown in the f ollowing table. Port 1 also a lso receives the low-order address bytes during Flash programming and verification.

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 pullups 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 uses 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 uses 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 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 pullups 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 AT89S52, as shown in the following table. Port 3 also receives some control signals for Flash programming and verification.

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 96 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/PR OG: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. 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. 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.

Special Function Registers A map of the on-chip memory area called the Special Function Register (SFR) space is shown in Table 1. Note that not all of the addresses are occupied, and unoccupied addresses may not be implemented on the chip. Read accesses to these addresses will in general return random data, and write accesses will have an indeterminate effect. User software should not write 1s to these unlisted locations, since they may be used in future products to invoke new features. In that case, the reset or inactive values of the new bits will always be 0.

Timer 2 Registers: Control and status bits are contained in registers T2CON (shown in Table 2) and T2MOD (shown in Table 3) for Timer 2. The register pair (RCAP2H, RCAP2L) is the Capture/Reload registers for Timer 2 in 16-bit capture mode or 16-bit auto-reload mode.

Interrupt Registers: The individual interrupt enable bits are in the IE register. Two priorities can be set for each of the six interrupt sources in the IP register.

Dual Data Pointer Registers: To facilitate accessing both internal and external data memory, two banks of 16-bit Data Pointer Registers are provided: DP0 at SFR address locations 82H-83H and DP1 at 84H85H. Bit DPS = 0 in SFR AUXR1 selects DP0 and DPS = 1 selects DP1. The user should always initialize the DPS bit to the appropriate value before accessing the respective Data Pointer Register.

Power Off Flag: The Power Off Flag (POF) is located at bit 4 (PCON.4) in the PCON SFR. P OF is set to 1 during power up. It can be set and rest under software control and is not affected by reset.

Memory Organization MCS-51 devices have a separate address space for Program and Data Memory. Up to 64K bytes each of external Program and Data Memory can be addressed.

Program Memory If the EA pin is connected to GND, all program fetches are directed to external memory. On the AT89S52, if EA is connected to VCC, program fetches to addresses 0000H through 1FFFH are directed to internal memory and fetches to addresses 2000H through FFFFH are to external memory.

Data Memory The AT89S52 implements 256 bytes of on-chip RAM. The upper 128 bytes occupy a parallel address space to the Special Function Registers. This means that the upper 128 bytes have the same addresses as the SFR space but are physically separate from SFR space. When an instruction accesses an internal location above address 7FH, the address mode used in the instruction specifies whether the CPU accesses the upper 128 bytes of RAM or the SFR space. Instructions which use direct addressing access of the SFR space. For example, the following direct addressing instruction accesses the SFR at location 0A0H (which is P2).

MOV 0A0H, #data Instructions that use indirect addressing access the upper 128 bytes of RAM. For example, the following indirect addressing instruction, where R0 contains 0A0H, accesses the data byte at address 0A0H, rather than P2 (whose address is 0A0H). MOV @R0, #data Note that stack operations are examples of indirect addressing, so the upper 128 bytes of data RAM are available as stack space.

Watchdog Timer (One-time Enabled with Reset-out) The WDT is intended as a recovery method in situations where the CPU may be subjected to software upsets. The WDT consists of a 13-bit counter and the Watchdog Timer Reset (WDTRST) SFR. The WDT is defaulted to disable from exiting reset. To enable the WDT, a user must write 01EH and 0E1H in sequence to the WDTRST register (SFR location 0A6H). When the WDT is enabled, it will increment every machine cycle while the oscillator is running. The WDT timeout period is dependent on the external clock frequency. There is no way to disable the WDT except through reset (either hardware reset or WDT overflow (reset). When WDT overflows, it will drive an output RESET HIGH pulse at the RST pin.

Using the WDT To enable the WDT, a user must write 01EH and 0E1H in sequence to the WDTRST register (SFR location 0A6H). When the WDT is enabled, the user needs to service it by writing 01EH and 0E1H to WDTRST to avoid a WDT overflow. The 13-bit counter overflows when it reaches 8191 (1FFFH), and this will reset the device. When the WDT is enabled, it will increment every machine cycle while the oscillator is running. This means the user must reset the WDT at least every 8191 machine cycles. To reset the WDT the user must write 01EH and 0E1H to WDTRST. DTRST is a write-only register. The WDT counter cannot be read or written. When WDT overflows, it will generate an output RESET pulse at the RST pin. The RESET pulse duration is 96xTOSC, where TOSC=1/FOSC. To make the best use of the WDT, it should be serviced in those sections of code that will periodically be executed within the time required to prevent a WDT reset.

WDT during Power-down and Idle

In Power-down mode the oscillator stops, which means the WDT also stops. While in Powerdown mode, the user does not need to service the WDT. There are two methods of exiting Power-down mode: by a hardware reset or via a level-activated external interrupt which is enabled prior to entering Power-down mode. When Power-down is exited with hardware reset, servicing the WDT should occur as it normally does whenever the AT89S52 is reset. Exiting Power-down with an interrupt is significantly different. The interrupt is held low long enough for the oscillator to stabilize. When the interrupt is brought high, the interrupt is serviced. To prevent the WDT from resetting the device while the interrupt pin is held low, the WDT is not started until the interrupt is pulled high. It is suggested that the WDT be reset during the interrupt service for the interrupt used to exit Power-down mode. To ensure that the WDT does not overflow within a few states of exiting Power-down, it is best to reset the WDT just before entering Power-down mode. Before going into the IDLE mode, the WDIDLE bit in SFR AUXR is used to determine whether the WDT continues to count if enabled. The WDT keeps counting during IDLE WDIDLE bit = 0) as the default state. To prevent the WDT from resetting the AT89S52 while in IDLE mode, the user should always set up a timer that will periodically exit IDLE, service the WDT, and reenter IDLE mode. With WDIDLE bit enabled, the WDT will stop to count in IDLE mode and resumes the count upon exit from IDLE.

UART Serial data communication uses two methods, asynchronous and synchronous. The synchronous method transfers a block of data (characters ) at a time, while the asynchronous method transfers a single byte at a time. It is possible to write software to use either of these methods, but programs can be tedious and long. For this reason, there are special IC chips made by the manufacturers for the serial data communications. These chips are commonly referred to as UART ( universal asynchronous receivertransmitter) and USART ( universal synchronous receiver-transmitter). The 8052 has built-in UART.

Timer 0 The 16-bit register of timer 0 is accessed as low byte and high byte. The low byte register is called TL0 ( Timer 0 low byte) and the high byte register is referred to as TH0 ( Timer 0 high byte). These registers can be accessed like any other registers , such as A,B,R0,R1,R2 etc. for example the instruction MOV TL0,#4FH moves the value 4FH into TL0, the low byte of Timer 0. These registers can also be read like any other register. For example, MOV R5,TH0 saves TH0 ( high byte of Timer 0) in R5.

Timer1 Timer 1 is also 16 bits and its 16-bit register is split into two bytes, referred to as TL1 (Timer 1 low byte ) and TH1 ( Timer 1 high byte). These registers are accessible in the same way as the registers of Timer 0.

Timer 2 Timer 2 is a 16-bit Timer/Counter that can operate as either a timer or an event counter. The type of operation is selected by bit C/T2 in the SFR T2CON (shown in Table 2). Timer 2 has three operating modes: capture, auto-reload (up or down counting), and baud rate generator. The modes are selected by bits in T2CON, as shown in Table 3. Timer 2 consists of two 8-bit registers, TH2 and TL2. In the Timer function, the TL2 register is incremented every machine cycle. Since a machine cycle consists of 12 oscillator periods, the count rate is 1/ 12 of the oscil lator frequency.

In the Counter function, the register is incremented in esponse to a 1-to-0 transition at its corresponding external input pin, T2. In this function, the external input is sampled during S5P2 of every machine cycle. When the samples show a high in one cycle and a low in the next cycle, the count is incremented. The new count value appears in the register during S3P1 of the cycle following the one in which the transition was detected. Since two machine cycles (24 oscillator periods) are required to recognize a 1to-0 transition, the maximum count rate is 1/24 of the oscillator frequency. To ensure that a given level is sampled at least once before it changes, the level should be held for at least o ne full machine cycle.

Capture Mode In the capture mode, two options are selected by bit EXEN2 in T2CON. If EXEN2 = 0, Timer 2 is a 16-bit timer or counter which upon overflow sets bit TF2 in T2CON. This bit can then then be used to generate an interrupt. interrupt. If EXEN2 = 1, Timer 2 performs performs the same operation, but a 1- to-0 transition at external input T2EX also causes the current value in TH2 and TL2 to be captured into RCAP2H and RCAP2L, respectively. In addition, the transition at T2EX causes bit EXF2 in T2CON to be set. The EXF2 bit, like TF2, can generate an interrupt. The capture mode is illustrated in Figure 5.

Auto-reload (Up or Down Counter) Timer 2 can be programmed to count up or down when configured in its 16-bit auto-reload mode. This feature is invoked by the DCEN (Down Counter Enable) bit located in the SFR T2MOD (see Table 4). Upon reset, the DCEN bit is set to 0 so that timer 2 will default to count up. When DCEN is set, Timer 2 can count up or down, depending on the value of the T2EX pin.

options are selected by bit EXEN2 in T2CON. If EXEN2 = 0, Timer 2 counts up to 0FFFFH and then sets the TF2 bit upon overflow. The overflow also causes the timer registers to be reloaded with the 16-bit value in RCAP2H and RCAP2L. The values in Timer in Capture ModeRCAP2H and RCAP2L are preset by software. If EXEN2 = 1, a 16- bit reload can be Figure 6 shows Timer 2 automatically counting up when DCEN=0. In this mode, two trigger ed either by an overflow or by a 1-t o-0 transition at external input T2EX. This transition also sets the EXF2 bit. Both the TF 2 and EXF2 bits can generate an interrupt if  enabled.

Setting the DCEN bit enables Timer 2 to count up or down, as shown in Figure 6. In this mode, the T2EX pin controls the direction of the count. A logic 1 at T2EX makes Timer 2 count up. The timer will overflow at 0FFFFH and set the TF2 bit. This overflow also causes the 16-bit value in RCAP2H and RCAP2L to be reloaded into the timer registers, TH2 and and TL2, respectively. A logic 0 at T2EX T2EX makes Timer 2 count down. The timer underflows when TH2 and TL2 equal the values stored in RCAP2H and RCAP2L. The underflow sets the TF2 bit and causes 0FFFFH to be reloaded into the timer registers .The EXF2 bit toggles whenever Timer 2 overflows or underflows and can be used as a 17th bit of resolution. In this operating mode, EXF2 does not flag an interrupt.

Timer 2 is selected as the baud rate generator by setting TCLK and/or RCLK in T2CON (Table 2). Note that the baud rates for transmit and receive can be different if Timer 2 is used for the receiver or transmitter and Timer 1 is used for the other function. Setting RCLK and/or TCLK puts Timer 2 into its baud rate generator mode, as shown in Figure 8. The baud rate generator mode is similar to the autoreload mode, in that a rollover in TH2 causes the Timer 2 registers to be reloaded with the 16-bit value in registers RCAP2H and RCAP2L, which are preset by software. The baud rates in Modes 1 and 3 are determined by Timer 2s overflow rate according to the following equation.

The Timer can be configured for either timer or counter operation. In most applications, it is configured for timer operation (CP/T2 = 0). The timer operation is different for Timer 2 when it is used as a baud rate generator. Normally, as a timer, it increments every machine cycle (at 1/12 the oscillator frequency). As a baud rate generator, however, it increments every state time (at 1/2 the oscillator frequency). The baud rate formula is given below.

Where (RCAP2H, RCAP2L) is the content of RCAP2H and RCAP2L taken as a 16-bit unsigned integer. Timer 2 as a baud rate generator is shown in Figure 8. This figure is valid only if RCLK or TCLK = 1 in T2CON. Note that a rollover in TH2 does not set TF2 and will not generate an interrupt. Note too, that if EXEN2 is set, a 1-to-0 transition in T2EX will set EXF2 but will not cause a reload from (RCAP2H, RCAP2L) to (TH2, TL2). Thus, when Timer 2 is in use as a baud rate generator, T2EX can be used as an extra external interrupt. Note that when Timer 2 is running (TR2 = 1) as a timer in the baud rate generator mode, TH2 or TL2 should not be read from or written to. Under these conditions, the Timer is incremented every state time, and the results of a read or write may not be accurate. The RCAP2 registers may be read but should not be written to; because a write might overlap a reload and cause write and/or reload errors. The timer should be turned off (clear TR2) before accessing the Timer 2 or RCAP2 registers.

Interrupts The AT89S52 has a total of six interrupt vectors: two external interrupts (INT0 and INT1), three timer interrupts (Timers 0, 1, and 2), and the serial port interrupt. These interrupts are all shown in Figure 10. Each of these interrupt sources can be individually enabled or disabled by setting or clearing a bit in Special Function Register IE. IE also contains a global disable bit, EA, which disables all interrupts at once. Note that Table 5 shows that bit position IE.6 is unimplemented. In the AT89S52, bit position IE.5 is also unimplemented. User software should not write 1s to these bit positions, since they may be used in future AT89 products. Timer 2 interrupt is generated by the logical OR of bits TF2 and EXF2 in register T2CON. Neither of these flags is cleared by hardware when the service routine is vectored to. In fact, the service routine may have to determine whether it was TF2 or EXF2 that generated the interrupt, and that bit will have to be cleared in software. The Timer 0 and Timer 1 flags, TF0 and TF1, are set at S5P2 of the cycle in which the timers overflow. The values are then polled by the circuitry in the next cycle. However, the Timer 2 flag, TF2, is set at S2P2 and is polled in the same cycle in which the timer overflows.

Oscillator Characteristics XTAL1 and XTAL2 are the input and output, respectively, of an inverting amplifier that can be configured for use as an on-chip oscillator, as shown in Figure 11. 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 12. 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 hig h and low time specifications must be

observed. Oscillator connections

Note: C1, C2 = 30 pF ± 10 pF for Crystals = 40 pF ± 10 pF for Ceramic Resonators

Idle Mode In 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. Note that when idle mode is terminated term inated by a hardware reset, the device normally resumes program e xecution 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 mode is terminated by a reset, the instruction i nstruction following the one that invokes idle mode should not write to a port pin or to external memory.

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. Exit from Power-down mode can be initiated either by a hardware reset or by an enabled external interrupt. Reset redefines the SFRs but does not change the on-chip RAM. The reset should not be ac tivated before VCC is restored r estored to its normal operating level and must be held active long enough to allow the oscillator to restart and stabilize. Status of External Pins during Idle and Power-down Modes

4. LIQUID CRYSTAL DISPLAY:

LCD stands for  Liquid Crystal Display. LCD is finding wide spread use replacing LEDs (seven segment LEDs or other multi segment LEDs) because of the following reasons: 1. The declining prices of LCDs. 2. The ability to display numbers, characters and graphics. This is in contrast to LEDs, which are limited limited to numbers and a few characters. 3. Incorporation of a refreshing controller into the LCD, thereby relieving the CPU of the task of refreshing the LCD. In contrast, the LED must be refreshed by the CPU to keep displaying the data. 4. Ease of programming for characters and graphics.

These components are ³specialized´ for being used with the microcontrollers, which means that they cannot be activated by standard IC circuits. They are used for writing different messages on a miniature LCD.

A model described here is for its low price and great possibilities most frequently used in practice. It is based on the HD44780 microcontroller ( Hitachi) and can display messages in two lines with 16 characters each . It displays all the alphabets, Greek letters, punctuation marks, mathematical symbols etc. In addition, it is possible to display symbols that user makes up on its own. Automatic shifting message on display (shift left and right), appearance of the  pointer, backlight etc. are considered as useful characteristics. Pins Functions

There are pins along one side of the small printed board used for connection to the microcontroller. There are total of 14 pins marked with numbers (16 in case the background light is built in). Their function is described in the table below: Function

Pin Number

Name

Logic State

Description

Ground

1

Vss

-

0V

Power supply

2

Vdd

-

+5V

Contrast

3

Vee

-

0 - Vdd

4

Control of 

5

RS

R/W

operating

0 1

Data / commands

E

7

D0

commands D0 ± D7 are interpreted as data

0

Write data (from controller to LCD)

1

Read data (from LCD to controller)

0

6

D0 ± D7 are interpreted as

Access to LCD disabled

 Normal operating 1 Data/commands are transferred to From 1 to 0 LCD 0/1

Bit 0 LSB

8

D1

0/1

Bit 1

9

D2

0/1

Bit 2

10

D3

0/1

Bit 3

11

D4

0/1

Bit 4

12

D5

0/1

Bit 5

13

D6

0/1

Bit 6

14

D7

0/1

Bit 7 MSB

LCD screen: LCD screen consists of two lines with 16 characters each. Each character consists of 5x7 dot matrix. Contrast on display depends on the power supply voltage and whether  messages are displayed in one or two lines. For that reason, variable voltage 0-Vdd is applied on  pin marked as Vee. Trimmer potentiometer is usually used for that purpose. Some versions of  displays have built in backlight (blue or green diodes). When used during operating, a resistor for  current limitation should be used (like with any LE diode).

LCD Basic Commands

All data transferred to LCD through outputs D0-D7 will be interpreted as commands or as data, which depends on logic state on pin RS: RS = 1 - Bits D0 - D7 are addresses of characters that should be displayed. Built in processor  addresses built in ³map of characters´ and displays corresponding symbols. Displaying position is determined by DDRAM address. This address is either previously defined or the address of   previously transferred character is automatically incremented. RS = 0 - Bits D0 - D7 are commands which determine display mode. List of commands which LCD recognizes are given in the table below: Command

RS RW D7 D6 D5 D4 D3 D2 D1 D0 Execution Time

Clear display

0

0

0

0

0

0

0

0

0

1

1.64mS

Cursor home

0

0

0

0

0

0

0

0

1

x

1.64mS

Entry mode set

0

0

0

0

0

0

0

1 I/D S

40uS

Display on/off control

0

0

0

0

0

0

1

D

U B

40uS

Cursor/Display Shift

0

0

0

0

0

1 D/C R/L

x

x

40uS

Function set

0

0

0

0

1 DL N

x

x

40uS

Set CGRAM address

0

0

0

1

Set DDRAM address

0

0

1

DDRAM address

40uS

Read BUSY flag (BF)

0

1 BF

DDRAM address

-

Write to CGRAM or DDRAM

1

0 D7 D6 D5 D4 D3

D2 D1 D0

40uS

Read from CGRAM or DDRAM

1

1 D7 D6 D5 D4 D3

D2 D1 D0

40uS

F

CGRAM address

40uS

I/D 1 = Increment (by 1) 0 = Decrement (by 1)

R/L 1 = Shift right 0 = Shift left

S 1 = Display shift on

DL 1 = 8-bit interface

0 = Display shift off

0 = 4-bit interface

D 1 = Display on 0 = Display off

N 1 = Display in two lines 0 = Display in one line

U 1 = Cursor on

F 1 = Character format 5x10 dots

0 = Cursor off

0 = Character format 5x7 dots

B 1 = Cursor blink blink on 0 = Cursor blink off

D/C 1 = Display shift 0 = Cursor shift

LCD Connection

Depending on how many lines are used for connection to the microcontroller, there are 8 bit and 4-bit LCD modes. The appropriate mode is determined at the beginning of the process in a phase called ³initialization´. In the first case, the data are transferred through outputs D0-D7 as it has been already explained. In case of 4-bit LED mode, for the sake of saving valuable I/O  pins of the microcontroller, there are only 4 higher bits (D4-D7) used for communication, while other may be left unconnected. Consequently, each data is sent to LCD in two steps: four higher bits are sent first (that normally would be sent through lines D4-D7), four lower bits are sent afterwards. With the help of initialization, LCD will correctly connect and interpret each data received. Besides, with regards to the fact that data are rarely read from LCD (data mainly are transferred from

microcontroller to LCD) one more I/O pin may be saved by simple connecting R/W pin to the Ground. Such saving has its price. Even though message displaying will be normally performed, it will not be possible to read from busy flag since it is not possible to read from display. LCD Initialization

Once the power supply is turned on, LCD is automatically cleared. This process lasts for  approximately 15mS. After that, display is ready to operate. The mode of operating is set by default. This means that: 1. Display is cleared 2. Mode DL = 1 Communication through 8-bit interface  N = 0 Messages are displayed in one line F = 0 Character font 5 x 8 dots 3. Display/Cursor on/off  D = 0 Display off  U = 0 Cursor off  B = 0 Cursor blink off  4. Character entry ID = 1 Addresses on display are automatically incremented by 1 S = 0 Display shift off  Automatic reset is mainly performed without any problems. Mainly but not always! If for  any reason power supply voltage does not reach full value in the course of 10mS, display will

start perform completely unpredictably. If voltage supply unit can not meet this condition or if it is needed to provide completely safe operating, the process of initialization by which a new reset enabling display to operate normally must be applied. Algorithm according to the initialization is being performed depends on whether  connection to the microcontroller is through 4- or 8-bit interface. All left over to be done after  that is to give basic commands and of course- to display messages.

Fig: Procedure on 8-bit initialization. initialization. CONTRAST CONTR OL:

To have a clear view of the characters on the LCD, contrast should be adjusted. To adjust the contrast, the voltage should be varied. For this, a preset is used which can behave like a variable

voltage device. As the voltage of this preset is varied, the contrast of the LCD can be adjusted. Potentiometer

Variable resistors used as potentiometers have all three terminals connected. This arrangement is normally used to vary voltage, for example to set the switching point of a circuit with a sensor, or control the volume (loudness) in an amplifier circuit. If the terminals at the ends of the track are connected across the power supply, then the wiper terminal will provide a voltage which can be varied from zero up to the maximum of the supply.

Potentiometer Symbol

Presets

These are miniature versions of the standard variable resistor. They are designed to be mounted directly onto the circuit board and adjusted only when the circuit is built. For example to set the frequency of an alarm tone or the sensitivity of a light-sensitive circuit. A small screwdriver or  similar tool is required to adjust presets. Presets are much cheaper than standard variable resistors so they are sometimes used in projects where a standard variable resistor would normally be used. Multiturn presets

are used where very precise adjustments must be made. The screw must be

turned many times (10+) to move the slider from one end of the track to the other, giving very fine control.

Preset Symbol

LCD INTERFACING WITH THE MICR OCONTR OLLER:

Vcc P2.0

4 (RS)

1

P2.1

5 (R/W)

2

P2.2

6(EN)

3

Gnd

PRESET (CONTRAST CONTROL)

LCD

Vcc

FOR BACKLIGHT

Gnd

PURPOSE

Infrared LED (IR LED) IR sensor is the combination of IR LED with PHOTO DIODE. After this this combination we are connecting the DARLINGTON PAIR PAIR TRANSISTOR. End of the IR sensor we have to connect a NOT gate for the inverting purpose means low input have corresponding low outputInfra-Red actually is normal light light with with a particular colour. We humans can't

see this

colour because its wave length length of 950nm is below below the visible spectrum. That's one of the reasons why IR is chosen for remote control purposes, we want to use it but we're not interested in seeing it. Another reason is because IR LEDs are quite easy to make, and therefore can be very cheap. Although we humans can't see the Infra-Red light emitted from a remote control doesn't mean we can't make it visible. A video camera or digital photo camera can "see" the Infra-Red light as you can see in this picture. If you own a web cam, point your remote to it, press any button and you'll see the LED flicker.

They

do dozens of different jobs and are found in all kinds of 

devices. Among other things, they form the numbers on digital clocks, transmit information from remote controls, light up watches and tell you w hen your appliances are turned on. Collected together, they can form images on a jumbo television screen or illuminate a traffic lig ht.

FIG.3.1 IR LED USED I N REMOTE CONTR OL

DARLINGTON PAIR: An emitter follower offers high impedance of 500Kohms. For applications requiring still higher input impedance, we may use what is calle d Darlington in place of conventional transistor. This Darlington pair basically consists of two transistors cascaded in cc configuration. In the figure shown below the input impedance of the second transistor Constitutes the load impedance of the first.

We thus conclude that in comparison with a conventional single transistor emitter follower has in higher current gain, higher input impedance and almost the same voltage gain lower out put impedances.

Fig:

Darlington Pair

Modulation

Modulation is the answer to make our signal stand out above the noise. With modulation we make the IR light source blink in a particular frequency. The IR receiver will be tuned to that frequency, so it can ignore everything else.

ou can think of this blinking as attracting the receiver's attention. We humans also notice the  blinking of yellow lights at construction sites instantly, even in bright daylight. Y

In the picture above you can see a modulated signal driving the IR LED of the transmitter on the left side. The detected signal is coming out of the receiver at the other side. In serial communication we usually speak of 'marks' and 'spaces'. The 'space' is the default signal, which is the off state in the transmitter case. No light is emitted during the 'space' state. During the 'mark' state of the signal the IR light is pulsed on and off at a particular frequency. Frequencies between 30kHz and 60kHz are commonly used in consumer electronics. At the receiver side a 'space' is represented by a high level of the receiver's output. A 'mark' is then automatically represented by a low level. Please note that the 'marks' and 'spaces' are not the 1-s and 0-s we want to transmit. The real relationship between the 'marks' and 'spaces' and the 1-s and 0-s depends on the protocol that's  being used. More information about that can be found on the pages that describe the protocols.

TRANSMITTER:

In the picture below we can see a modulated signal driving the IR LED of the transmitter  on the left side. The detected signal is coming out of the receiver at the other side.

: FIG.3.2 IR TRANSMITTER 

The transmitter usually is a battery powered handset. It should consume as little power as  possible, and the IR signal should also be as strong as possible to achieve an acceptable control distance. Preferably it should be shock proof as well.

Many chips are designed to be used as IR transmitters. The older chips were dedicated to only one of the many protocols that were invented. Nowadays very low power microcontrollers are used in IR transmitters for the simple reason that they are more flexible in their use. When no   button is pressed they are in a very low power sleep mode, in which hardly any current is consumed. The processor when wakes up to transmit the appropriate IR command only a key is  pressed

FIG.3.3 TRANSISTOR CIRCUIT USED TO DRIVE IR LED

Quartz crystals are seldom used in such handsets. They are very fragile and tend to break  easily when the handset is dropped. Ceramic resonators are much more suitable here, because they can withstand larger physical shocks. The fact that they are a little less accurate is not important. The current through the LED (or LEDs) can vary from 100mA to well over 1A! In order  to get an acceptable control distance the LED currents have to be as high as possible. A trade-off  should be made between LED parameters, battery lifetime and maximum control distance. LED currents can be that high because the pulses driving the LEDs are very short. Average power  dissipation of the LED should not exceed the maximum value though. You should also see to it that the maximum peek current for the LED is not exceeded. All these parameters can be found in the LED's data sheet.

A simple transistor circuit can be used to drive the LED. A transistor with a suitable h fe and switching speed should be selected for for this purpose. The The resistor values can simply be calculated using Ohm's law. Remember that the nominal voltage drop over an IR LED is approximately 1.1V. The normal driver, described above, has one disadvantage. As the battery voltage drops, the current through the LED will decrease as well. This will result in a shorter  control distance that can be covered. An emitter follower circuit can avoid this. The 2 diodes in series will limit the pulses on the base of the transistor to 1.2V. The base-emitter voltage of the transistor subtracts 0.6V from that, resulting in constant amplitude of 0.6V at the emitter. This constant amplitude across a constant resistor results in current pulses of a constant magnitude. Calculating the current through the LED is simply applying ohm¶ law. PHOTODIODES: Unfortunately for us there are many more sources of Infrared light. The sun is the brightest source of all, but there are many others, like: light bulbs, candles, central heating system, and even our body radiates Infrared light. In fact everything that radiates heat, also radiates Infrared light. Therefore we have to take some precautions to guarantee that our IR message gets across to the receiver with out errors.

Photodiodes are used for the detection of optical power (UV, Visible, and IR) and for t he conversion of optical power to electrical power. The photodiode spectral response can be measured in X-

ray, UV, visible, or IR. X-ray photodiodes are optimized for X-ray, X-ray, gamma ray, and beta radiation detection.

UV enhanced photodiodes are optimized for the UV and blue spectral regions, Photodiodes are a twoelectrode, radiation-sensitive junction formed formed in a semiconductor semiconductor material in which the reverse current varies with illumination. Photodiodes are used for the detection of optical power and for the conversion of optical power to electrical power. Photodiodes can be PN, PIN, or avalanche. avalanche. PN photodiodes feature a two-electrode, radiation-sensitive PN junction formed in a semiconductor material in which the

reverse current varies with illumination. PIN photodiodes photodiodes are diodes with a large intrinsic region sandwiched between P-doped and N-doped N-doped semiconducting regions. Photons absorbed in this region create electron-hole pairs that are then separated by an electric field, thus generating an electric current in a load circuit

REGULATED POWER SUPPLY:

The power supplies are designed to convert high voltage AC mains electricity to a suitable low voltage supply for electronic circuits and other devices. A RPS (Regulated Power Supply) is the Power Supply with Rectification, Filtering and Regulation being done on the AC mains to get a Regulated power supply for Microcontroller and for the other devices being interfaced to it. A power supply can by broken down into a series of blocks, each of which performs a particular function. A d.c power supply which maintains the output voltage constant irrespective of a.c mains fluctuations or load variations is known as Regulated D.C Power Supply

For example a 5V regulated power supply system as shown below:

Transformer: A transformer is an electrical device which is used to convert electrical power from one Electrical circuit to another without change in frequency.

Transformers convert AC electricity from one voltage to another with little loss of   power. Transformers work only with AC and this is one of the reasons why mains electricity is AC. Step-up transformers increase in output voltage, step-down transformers transformers decrease in output voltage. Most power supplies use a step-down transformer to reduce the dangerously high mains voltage to a safer safer low voltage. The input coil is called the primary and the output coil coil is called 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 circuit symbol represent the core. Transformers waste very little little power so the   power out is (almost) equal to the power in. Note that as voltage is stepped down current is stepped up. The ratio ratio of the number of turns on each coil, called the turn¶s ratio, 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.

An Electrical Transformer

Turns ratio = Vp/ VS = Np/NS Power Out= Power In VS X IS=VP X IP Vp = primary (input) voltage Np = number of turns on primary coil Ip = primary (input) current

RECTIFIER:

A circuit which is used to convert ac to dc is known as RECTIFIER. The process of conversion ac to dc is called rectification

TYPES OF RECTIFIERS:

y

Half wave Rectifier

y

Full wave Rectifier 1. Centre tap full wave rectifier. 2. Bridge type full bridge rectifier.

Comparison of rectifier circuits:

Type of Rectifier Parameter

Number of diodes

PIV of diodes

D.C output voltage

Vdc at no-load

Ripple factor

Ripple frequency

Rectification efficiency

Half wave

Full wave

Bridge

1

2

4

Vm

2Vm

Vm

Vm/z

2Vm/

2Vm/

0.318Vm

0.636Vm

0.636Vm

1.21

0.482

0.482

f 

2f 

2f 

0.406

0.812

0.812

0.287

0.693

0.812

Vm/2

Vm/2

Vm/2

Transformer Utilization Factor(TUF)

RMS voltage Vrms

Full-wave Rectifier: From the above comparison we came to know that full wave bridge rectifier as more advantages than the other two rectifiers. So, in our project we are using full wave bridge rectifier circuit.

Bridge Rectifier:

A bridge rectifier makes use of four diodes in a bridge arrangement to achieve fullwave rectification. This is a widely used configuration, both with individual diodes wired as shown and with single component bridges where the diode bridge is wired internally.

A bridge rectifier makes use of four diodes in a bridge arrangement as shown in fig (a) to achieve full-wave rectification. This is a widely used configuration, both with individual diodes wired as shown and with single component bridges where the diode bridge is wired internally.

Fig (A)

Operation: During positive half cycle of secondary, the diodes D2 and D3 are in forward biased w hile D1 and D4 are in reverse biased as shown in the fig(b). The current flow direction is shown in the fig (b) with dotted arrows.

Fig (B) During negative half cycle of secondary voltage, the diodes D1 and D4 are in forward biased while D2 and D3 are in reverse rever se biased as shown in the fig(c). The current flow dire ction is shown in the fig (c) with dotted arrows.

Fig(C)

Filter: A Filter is a device which removes the ac component of rectifier output but allows the dc component to reach the load.

Capacitor Filter: We have seen that the ripple content in the rectified output of half wave rectifier is 121% or that of full-wave or bridge rectifier or bridge rectifier is 48% such high percentages of ripples is not acceptable for most of the applications. Ripples can be removed by one of the following methods of  filtering.

(a) A capacitor, in parallel to the load, provides an easier by pass for the ripples voltage though it due to low impedance. At ripple frequency and leave the D.C. to appear at the load.

(b) An inductor, in series with the load, prevents the passage of the ripple current (due to high impedance at ripple frequency) while allowing the dc (due to low resistance to dc).

(c) Various combinations of capacitor and inductor, such as L-section filter

section filter, multiple

section filter etc. which make use of both the properties mentioned in (a) and (b) above. Two cases of  capacitor filter, one applied on half wave rectifier and another with full wave rectifier. Filtering is performed by a large value electrolytic capacitor connected across the DC supply to act as a reservoir, supplying current to the output when the varying DC voltage from the rectifier is falling. The capacitor charges quickly near the peak of the varying DC, and then discharges as it supplies current to the output. Filtering significantly increases the average DC voltage to almost the peak value (1.4 × RMS value).

To calculate the value of capacitor(C), C = ¼*¥3*f*r*Rl Where, f = supply frequency, r = ripple factor, Rl = load resistance : In our circuit we are using 1000µF hence large value of capacitor is placed to

Note

reduce ripples and to improve the DC component.

Regulator: Voltage regulator ICs is available with fixed (typically 5, 12 and 15V) or variable output voltages. The maximum current they can pass also rates them. Negative voltage regulators are available, mainly for use in dual supplies. Most regulators include some automatic protection from excessive current ('overload protection') and and overheating ('thermal protection').

Many of the fixed voltage

regulators ICs have 3 leads and look like power transistors, such as the 7805 +5V 1A regulator shown on the right. The LM7805 is simple to use. You simply connect the positive lead of your unregulated DC power supply (anything from 9VDC to 24VDC) to the Input pin, connect the negative lead to the Common pin and then when you turn on the power, y ou get a 5 volt supply from the output pin.

Fig 6.1.6 A Three Terminal Voltage Regulator

78XX: The Bay Linear LM78XX is integrated linear positive regulator with three terminals. The LM78XX offer several fixed output voltages making them useful in wide range of applications. When used as a zener diode/resistor combination replacement, the LM78XX usually results in an effective output impedance improvement of two orders of magnitude, lower quiescent current. The LM78XX is available in the TO-252, TO-220 & TO-263packages,

Features:  Output Current of 1.5A  Output Voltage Tolerance of 5%  Internal thermal overload protection

 Internal Short-Circuit Limited  Output Voltage 5.0V, 6V, 8V, 9V, 10V, 12V, 15V, 18V, 24V.

CHAPTER 5

System Design

Designing of this system is possible when you select the specific controller to suite.For this we selected 89S52 controller.With the help help of 89S52 controller traffic control system can be be implemented successfully with the help IR technology.To the controller we connected IR  transmitter and receiver circuit.Instead of IR transmitter and receiver we can go with photo diode and photo transmitters also.Here we are using four IR pairs for each side. Whenever vehicles reach the junction junction on each side, then IR detects the vehicle vehicle by sending signal to controller and the controller will counts the count of vehicles. And calculate the mximum count from them and give the path to side which has maximum count by glowing green LED and other three sides red LED shall be glow.

5.1 Hardware Design: 5.1.1 Schematic

J3 LCD

    0     1    2    3    4    5    6    7     D   .   .   .   .   .   .   .   .     C     S     N    0     0    0    0    0    0    0    0    C    N         3     WE R     P    P    P    P    P    P    P    P    V    G

        d       c       n       c       g

VCC

VCC

VCC

    0    1    2    3    4    5    6         1 2 3 4 5 6 7 8 9 1    1    1    1    1    1    1

R6 C5

CAP C7

POT

U3

C4

2

V+

6

C1+ C1-

VC2+ C2-

P2 CAP

5 9

14

4 8

13

3

7

7 2

8

T1I N R1OUT

T1OUT R1I N

T2I N

T2OUT R2I N

R2OUT

1 3

CAP C6

U1

J3

4 5 11

CAP

12 10

TXD

9

RXD

SW1

C1 C

1 2

1 2

3

3

4 5

4 5

6

6

7 8

7 8

6 1 MAX232

CON8

CONNECTOR DB9

9

P1. 0

VCC

P1. 1 P1. 2 P1. 3 P1. 4

P0. 0/AD0 P0. 1/AD1 P0. 2/AD2

P1. 5

P0. 3/AD3

P1. 6 P1. 7

P0. 4/AD4 P0. 5/AD5 P0. 6/AD6 P0. 7/AD7

J7

    1 2

C3

1 U6

EA/VPP

J4

CON2

2

1

RXD

10

2 3

TXD

11 12

4 5

13 14

6

15

7 8

16 17

CON8

1

2

3

4

18

J2

39

1

38 37

2 3

36

4

35 34

5 6

33 32

7 8

RST

R4 R

40

P3. 0/RXD

ALE/PROG PSEN

31

CON8

30 29 J2

P3. 1/TXD P3. 2/ I NT0 P3. 3/ I NT1

P2. 7/A15

P3. 4/T0 P3. 5/T1

P2. 6/A14 P2. 5/A13

P3. 6/WR

P2. 4/A12

P3. 7/RD

P2. 3/A11 P2. 2/A10

XTAL2

P2. 1/A9 P2. 0/A8

28 27

1 2

26

3

25 24 23

4 5 6

22 21

7 8

CAP

t / f  4pin

Y1

3

CON8

CR Y STAL C2

4

19 20

CAP

D1

D2

D4

D6

DI ODE

D I ODE

D I ODE

D I ODE

C9

XTAL1 GND

U5 +5V 1

LM7805/TO

VI N

    DVOUT     N     G     3

2

AT89S52

C8 104

R5 R

= 1000UF/25V Title

C