Temperature_Control

INTRODUCTION Now a days whole industrial operation are controlled through the control system, as the control system will take care of the I/O results. The control system can be applied for controlling the output using different inputs. Therefore the control system application extends for vast areas. Temperature control system is one of them. The present temperature control system is a microcontroller based one. The advantage of using the microcontroller in control system is that it will take care of much input and many outputs at a time. The other thing is that the microcontroller is intelligent one by the program inside. It will take care of every thing and so the parameters can be varied. The control system is divided into two categories like a) Open loop b) Close loop. Open loop control system is that which doesn’t automatically correct for variations in its output, is called an open-loop system. Close loop control system is that which will take the output data to control it’s input so that output will vary to attain the required output. The present temperature control system is a closed loop application. Therefore it will take the data from its output and will process the data to control the output to attain the constant temperature. The microcontroller used is PIC16F873. Temperature set here is in centigrade. The present project has various applications in the field of temperature related applications such as chemical processing unit, cold storage units, other research laboratories etc. FEATURES :-  MICROCONTROLLER BASED APPLICATION  TEMPERAURE CAN BE SET BY THE USER  TEXT LCD IS USED FOR DISPLAY THE SET TEMPERATURE.  CLOSED LOOP CONTROL SYSTEM USED.  TEMPERATURE (CELSIUS) UP TO TWO DIGIT CAN BE CONTROLLED. BLOCK DIAGRAM :- Sensor section uses a centigrade sensor for the sensing temperature and send signal after amplifying it to the microcontroller section. Microcontroller section uses 8-bit microcontroller convert incoming analog signal into digital signal by A/D converter. And compare with setting temperature. So that incoming temperature is rise above the setting one so that it will send a signal to trip the relay. Switch is for setting temperature. Display is seven-segment display for showing the setting temperature. Tripping device is for switching the load for necessary action. PRINCIPLE : - The Thermal relay is the control system based on the microcontroller design. To implement the system, a temperature sensor, a A/D converter and a CPU is required. The temperature sensor senses the temperature of the equipment and outputs an analog voltage, which has a linear relationship with the temperature. This analog voltage is converted to digital form by the A/D converter, which is on-chip to the microcontroller. At what temperature the relay will be tripped is initially stored in the on-chip EEPROM memory. The processor always compares the stored value with the digital value provided by the A/D converter. When it matches, the controller gives a trip signal to a electro-mechanical switch. TEMPERATURE SENSING :- The three terminal IC LM35, used for temperature sensing, gives voltage output which is directly proportional to absolute temperature variations, over a temperature range of –50C to 150C. The output of the LM35 varies at the rate of 10mV/C and is inherently linear, thus requiring no external linearizing circuit. Please note that zero deg. Centigrade is equal to 0V. The IC is pre-calibrated to give an output of 250mV at 25C, but external calibration can also be performed. This temperature sensor works over a wide range of voltages, starting from +4V to +40V , which adds to the versatility of its application in various temperature sensing circuits. The temperature transducer can be used for temperature monitoring at far off places without at drop in the signal level. For digital temperature display, the voltage output of the sensor is fed to the analog input of the microcontroller. The middle element here is an operational amplifier which is connected in between the sensor and the microcontroller. The op-amp acts as a voltage follower. The output of the temperature sensor is connected to the input of the op-amp which provides a very high input impedance to the sensor. This method is used to reduce the loading on the sensor and to keep the self heating of the sensor to a minimum. CIRCUIT DIAGRAM :- CIRCUIT DESCRIPTION -: The output voltage of the temperature sensor that varies at 10mV/C is fed to the analog input of the microcontroller. There is an integral 10-bit A/D convertor on-chip to the microcontroller PIC16F873. The output of the on-chip A/D convertor is incremented by one at the input signal rise of 4.88mV. For example, at 20C, the sensor output voltage is 200mV, so the A/D converter output will be 200mV/4.88mV = 40.98 in decimal or 29 in hex. In software, the hexadecimal value for each temperature setting is stored permanently in the microcontroller. Each time the microcontroller compares the A/D converter output to the stored value for that setting. When the A/D converter output value exceeds the stored value, a relay connected to the output port is tripped. In this project, we have a provision for different temperature settings at a resolution of 10C. A text LCD is provided to see the setting temperature & current room temperature. Power supply :- Power supply is important part for operation of the microcontroller. Microcontroller operate at +5 volt and also for other digital IC and for displays. A 220V AC to 9-0- 9 v transformer is used and for rectification two diodes 1N4007 are connected for rectification of the step down AC supply. Filter capacitor of 1000F is used. Then it is regulated to +5V using a regulator 7805. 0.1 F capacitor is used for filtration of high frequency noise . LED is given for power on indication. Brief discussion about microcontroller:- The past three decades have seen the introduction of a technology that has radically changed the way in which we analyze the control the world around us. Born of parallel developments in computer architecture and integrated circuit fabrication, the microprocessor or “ computer on a chip” first became a commercial reality in 1971 with introduction of 4-bit 4004 by Intel corp. A byproduct of microprocessor development was the microcontroller. The same fabrication techniques and programming concept that make possible the general-purpose microprocessor also yielded the microcontroller. Microcontroller are not as well as known to the general public, or to many in the technical community, as are he more glamorous microprocessor . The public is however very aware that “ something “ is responsible for all of the smart VCRs, clock radios, washers and dryers, video games, telephones, microwaves ,TVs, automobiles, toys vending machines, copiers, elevators, irons and myriads of other articles that are intelligent and programmable. Companies are also aware that being competitive in this age of microchip requires their products, or the machinery they use to make those products, to have some “smart”. The design incorporates all of the features found in a microprocessor CPU; ALU, PC, SP, register. It also has added the other features needed to make a complete computer: ROM, RAM, parallel I/O, serial I/O, counters, and a clock circuit. Like the microprocessor , a microcontroller is a general purpose device, but one that is meant to read data, perform limited calculations on that data, and control its environment based on those calculation. The prime use of a microcontroller is to control the operation of a machine using a fixed program that is stored in ROM and that does not change over the lifetime of the system. The design approach of the microcontroller mirrors that of the microprocessor : make a single design that can be used in as many applications as possible in order to sell, hopefully, as many as possible. The microprocessor accomplishes the goal by having a very flexible and extensive repertoire of multi-byte instructions. These instruction work in a hardware configuration that enables large amounts of memory and I/O to be connected address and data bus pins on integrated circuit package. Much of the activity in the microprocessor has to do with moving code and data to and from external memory to the CPU. The architecture feature s working registers that can be programmed to take part in the memory access process, and instruction set is aimed at expediting this activity in order to improve throughput. The pins connected to the microprocessor to external memory are unique, each having a single function. Data is handled in byte, or larger , sizes. The microcontroller design uses a much more limited set of single and double byte instructions that are used to move code and data from internal memory to ALU. Many instructions are coupled with pins on integrated circuit package, the pins are “programmable” – that is capable of having several different functions depending on the wishes of the programmer. The microcontroller is concerned with getting data from and to its own pins ; the architecture and instruction set are optimised to handle data in bit and byte size. The contrast between a microcontroller and a microprocessor is best exemplified by the fact that most microprocessor s have many operational codes(opcodes) for moving data from external memory to the CPU; microcontrollers may have one or two. Microprocessor may have one or two types of bit handling instructions; microcontrollers have many. Two summarize , the microprocessor is concerned with rapid movement of code and data from external addresses to the chip, the microcontroller is concerned with rapid movement of bits within the chip. The microcontroller can function as a computer with the addition of no external digital parts, the microprocessor must have many additional parts to be operational. PIC16F873(8 bit Flash MCU):- Microcontroller features:- • High performance RISC CPU • Only 35 instructions to learn • All single cycle instruction except for program branches which are two cycle • Operating speed DC- 20MHz clock input DC – 200 ns instruction cycle • 4Kx 14 word of flash program memory Up to 192x 8 bytes of data memory(RAM) Up to128x8 bytes of EEPROM data memory • Interrupt capability • Eight level deep hardware stack • Direct indirect, and relative addressing modes • power on reset(POR) • power up timer (PWT) and oscillator stand up timer (OST) • watchdog timer (WDT) with its own on chip RC oscillator oscillator for reliable operation • programmable code protection • power saving sleep mode • selectable oscillator option • Low power , high speed CMOS system • Fully static design • In-circuit serial programming • Processor read/write access to program memory • Wide operating voltage range 2.0 V to 5.5 V Peripheral features:- • Timer 0: 8-bit timer/counter with 8-bit prescaler • Timer1: 16-bit timer/counter with prescaler, can be incremented during sleep via external crystal/clock • Timer 2: 8-bit timer / counter with 8-bit period register prescaler and post scaler • Two capture , compare PWM modules • Capture is 16- bit max, resolution is 12.5ns , • Compare is 16-bit max resolution is 200ns. Fig.. PINOUT DIAGRAM OF PIC 16F873 FIG.. INTERNAL ARCHITECTURE OF PIC16F873 MEMORY ORGANIZATION There are three memory blocks in each of these PIC-MICROS. THE Program Memory and Data Memory have separate buses so that concurrent access can occur and is detailed in this section. Program Memory Organization The PIC16F87X PICmicros have a 13-bit program counter capable of addressing an 8k x 14 program memory space. The PIC 16F877/876 devices have 8K PIC16F873/874 devices have 4K x 14. Accessing a location above the physically implemented address will causes a wraparound. The reset vector is at 000h and the interrupt vector is at 0004h. Data Memory Organization There data memory is partitioned into multiple banks which contain the General Purpose Registers and the Special Function Registers. Bits RP1 and RPO are the bank select bits. (STATUS) = 00 Bank0 =01 Bank1 =10 Bank2 =11 Bank3 Each bank extends up to 7Fh (128 bytes). The lower locations of each bank are reserved for the Special Function Registers. Above the Special Function Registers are General Purpose Registers, implemented as static RAM. All implemented banks contain special function registers. Some “high use” special function registers from one bank may be mirrored in another bank for coded reduction and quicker access. GENERAL PURPOSE REGISTER FILE The register file can be accessed either directly, or indirectly thought the Files Select Register FSR. STATUS REGISTER The STATUS register, shown in Figure , contains the arithmetic status of the ALU, the RESET status and the bank select bits for data memory. The STATUS register can be the destination for any instruction, as with any other register. If the STATUS register is the destination for an instruction that affects the Z,DC or C bits, then the write to these three bits is disabled, these bits are set or cleared according to the device logic. Furthermore, the TO and PD bits are not writable. Therefore, the result of an instruction with the STATUS register as destination may be different than intended. For example, CLRF STATUS will clear the upper-three bits and set the Zbit. This leaves the STATUS register as 000u uluu (Where u = unchanged). I/O PORTS Some pins for these I/O ports are multiplexed with an alternate function for the peripheral features on the device. In general, when a peripheral is enabled, that pin may not be used as a general purpose I/O pin. PORTA and the TRISA Register PORTA is a 6-bit wide bi-directional port. The corresponding data direction register is TRISA. Setting a TRISA bit (=1) will make the corresponding PORTA pin an input, i.e., put the corresponding output driver in a hi-impedance mode. Clearing a TRISA bit (=0) will make the corresponding PORTA pin an output, i.e., put the contents of the output latch on the selected pin. Reading the PORTA register reads the status of the pins whereas writing to it will write to the port latch. All entire operations are read-modify-write operations. Therefore a write to a port implies that the port pins are read, this value is modified, and then written to the port data latch. Pin RA4 is multiplexed with the Timer0 module clock input to become the RA4/T0CKI pin. The RA4/T0CKI pin is a Schmitt Trigger input and an open drain output. All other RA port pins have TTL input levels and full CMOS output drivers. Other PORTA pins are multiplexed with analog inputs and analog VREF input. The operation of each pin is selected by clearing/setting the control bits in the ADCON1 register (A/D Control Register1). The TRISA register controls the direction of the RA pins, even when they are being used as analog inputs. The user must ensure the bits in the TRISA register are maintained set when using them as analog inputs. SPECIAL FEATURES OF THE CPU These PICmicros have a host of features intended to maximize system reliability, minimize cost through elimination of external components, provide power saving cooperating modes and offer code protection. these are: • OSC Selection • Reset - Power-on Reset (POR) - Power-up Timer (PWRT) - OSCILLATOR Start-up Timer (OST) - Brown-out Reset (BOR) • Interrupts • Watchdog Timer (WDT) • SLEEP • Code protection • Id locations • In-circuit serial programming • low voltage Programming • In-Circuit Debugger These devices have a Watchdog Timer which can be shut off only through configuration bits. It runs off its own RC oscillator for added reliability. There are two timers that offer necessary delays on power-up. One is the Oscillator Start-up Timer (OST), intended to keep the chip in reset until the crystal oscillator is stable. The other is the Power-up Timer (PWRT), which provides a fixed delay of 72 ms (nominal) on power-up only designed to keep the part in reset while the power super designed to keep the part in reset while the power supply stabilizes. With these two timers on-chip, most applications need to external reset circuitry. SLEEP mode is designed to offer a very low current power-down mode. The user can wake-up from SLEEP through external reset, Watchdog Timer Wake-up, or through an interrupt, Several oscillator options are also made available to allow the part of fit the application. The RC oscillator option saves system cost while the LP crystal option saves power. A set of configuration bits are used to select various options. Configuration Bits The configuration bits can be programmed (read as ‘0’) or left unprogrammed (read as ‘1”) to select various device configurations. These bits are mapped in program memory location 2007h. The user will note that address 2007h is beyond the user program memory space. In fact, it belongs to the special test/configuration memory space(2000h – 3FFFh). Which can be accessed only during programming Oscillator Configurations The PIC16F87X can be operated in four different oscillator modes. The user can program two configuration bits (FOSC1 and FOSC0) to select one of these four modes: • LP Low Power Crystal • XT Crystal/Resonator • HS High Speed Crystal/Resonator • RC Resistor/Capacitor 10-BIT A/D CONVERTER The analog-to-digital (A/D) converter module can have up to eight analog inputs for a device. The analog input charges a sample and hold capacitor. The output of the sample and hold capacitor is the input into the converter. The converter then generates a digital result of this analog level via successive approximation. This A/D conversion, of the analog input signal, results in a corresponding 10-bit digital number. The analog reference voltages (positive and negative supply) are software selectable to either the device’s supply voltages (AVDD, AVss) or the voltage level on the AN3/VREF+ and AN2/VREF-pins. The A/D converter has a unique feature of being able to operate while the device is in SLEEP mode. The A/D module has four registers. These registers are: • A/D Result High Register (ADRESH) • A/D Result Low Register (ADRESL) • A/D Control Register0 (ADCON0) • A/D Control Register1 (ADCON1) Operation The ADRESH:ADRESL registers contains the 10-bit result of the A/D conversion. When the A/D conversion is complete, the result is loaded into this A/D result register pair, the GO/DONE bit (ADCON0) is cleared, and A/D interrupt flag bit, ADIF, is set. After the A/D module has been configured as desired, the selected channel must be acquired before the conversion is started. The analog input channels must have their corresponding TRIS bits selected as inputs. After this acquisition time has elapsed the A/D conversion can be started. The following steps should be followed for doing an A/D conversion: 1. Configure the A/D module: • Configure analog pins / voltage reference/ and digital I/O (ADCON1) • Select A/D input channel (ADCON0) • Select A/D conversion clock (ADCON0) • Turn on A/D module (ADCON0) 2. Configure A/D interrupt (if desired): • Clear the ADIF bit • Set the ADIE bit • Set the GIE bit 3. Wait the required acquisition time. 4. Start conversion: • Set the GO/DONE bit (ADCON0) 5. Wait for A/D conversion to complete, by either: • Polling for the GO/DONE bit to be cleared or ADIF bit to be set OR • Waiting for the A/D interrupt 6. Read A/D Result register pair (ADRESH:ADRESL), clear the ADIF bit, if required. 7. For next conversion, go to step 1 or step 2 as required. Acquisition time is the time that the A/D module’s holding capacitor is connected to the external voltage level. Then there is the conversion time of 12 TAD, which is started when the GO bit is set. The sum of these two times is the sampling time. There is a minimum acquisition time to ensure that the holding capacitor is charged to a level that will give the desired accuracy for the A/D conversion. A/D Conversion Initialization BSF STATUS, RP0 ; Select Bank1 CLRF ADCON1 ; Configure A/D inputs, ; result is left justified BSF PIE1, ADIE ; Enable A/D interrupts BCF STATUS, RP0 ; Select Bank0 MOVLW 0xC1 ; RC Clock, A/D is on, Channel 0 is selected MOVWF ADCON0 ; BCF PIR1, ADIF ; Clear A/D interrupt flag bit BSF INTCON, PEIE ; Enable peripheral interrupts BSF INTCON, GIE ; Enable all interrupts ; ; Ensure that the required sampling time for the selected input ; channel has elapsed. Then the conversion may be started. ; BSF ADCON0, GO ; Start A/D Conversion : ; The ADIF bit will be set and the GO/DONE : ; bit is cleared upon completion of the : ; A/D Conversion. WATCH DOG TIMER :- The watch dog timer is a free running on-chip RC oscillator which does not require any external components . This RC oscillator is separate from the RC oscillator of the OSC1/CLKIN pin. That means that the WDT will run, even if the clock on the OSC1/CLKIN and OSC2/CLKOUT pins of the device has been stopped, for example , by execution of a SLEEP instruction. During normal operation, a WDT time out generates a device reset(watchdog timer reset). If the device is in sleep mode, a WDT time out causes the device to wake up and continue with normal operation( watchdog timer wake-up). The TO bit in the status register will be declared upon a watchdog timer time out. The WDT can be permanently disabled by clearing the configuration bit WDTE. INSTRUCTION SET :- As it is a RISC processor therefore it has only 35 instructions. LM35 TEMPERATURE SENSOR The LM35 is a temperature sensor which provides an output voltage that is directly proportional to the temperature being measured in degree Celsius. This means that if the temperature is 0C, the output voltage is 0 V. the output voltage increases by 10mV for every degree Celsius, i.e. at 19.8C, the output voltage is 0.198V. This is an important advantage over other temperature sensors that are calibrated in Kelvin. Using such sensors to measure in degree Celsius requires a very stable reference voltage that must be deducted from the reading. Another advantage of the LM35 is its very low current consumption of less than 60A. this means a long battery life and small internal power dissipation, so errors caused by internal heat are minimal The accuracy of the LM35 is typically 0.4C at 25C 7805 THREE TERMINAL +5v VOLTAGE REGULATOR :- The regulator 7805 positive regulator offer shelf contained , fixed-voltage capability up to 1 ampere of load current and input voltages up to 35 volts. This unit provides a unique on chip trimming system to set the output voltages to within +/- 1.5% of nominal on the 7805. It provide a line as well as load regulation. All protective feature like thermal shutdown current limiting , and safe area control have been design into these units and since these regulator requires only a small output capacitor for satisfactory performance ease of application is assured. Although the voltage fixed the output voltage can be increased by voltage divider method. The low quiescent current of the device ensures good regulation when this method is used. FIG….. PINOUT OF 7805 Liquid crystal display LCD :- Electronic displays can be classified into three generations. While the first-generation displays comprised the bulky cathode ray tube (CRT) displays, the second-generation was marked by the eye-catching LED and fluorescent displays which consumed a lot of power. This necessitated the search for a power-efficient alternative, leading to the development of liquid crystal display (LCD). As LCD weighs very little and consumes negligible power, it is being widely used in gadgets, ranging from consumer to sophisticated industrial products. Although an LCD's performance cannot be compared to its counterparts, rapid advancements have narrowed the performance gap. Functioning of LCD LCD consists of two substrates that form a 'flat bottle' containing the liquid crystal mixture. The inside surfaces of the bottle or cell are coated with a polymer that is buffed (surface is finished with lines) to align the molecules of liquid crystal. The liquid crystal molecules align on the surfaces in the direction of the buffing. For twisted nematic devices, the two surfaces are buffed orthogonal to one another, forming a 90-degree twist from one surface to the other (see Fig. 1). The helical structure has the ability to control light. A polariser (it is a material which allows the light wave only in one particular direction) is AC SOURCE FOR DRIVING I placed in front and an analyser/ reflector is placed at the back of the cell. When randomly polarised light passes through the front polariser, it becomes linearly polarised. It then passes through the front glass and is rotated by the liquid crystal molecules and passes through the rear glass. If the analyser is rotated 90 degrees to the polariser, the light will pass through the analyser. This light will be reflected back through the cell. The observer will see the background of the display, which in this case is the silver grey of the reflector. When an appropriate drive signal is applied to the cell electrodes an electric field is set up across the cell. The liquid crystal molecules will rotate in the direction of the electric field. The incoming linearly polarised light passes through the cell unaffected and is absorbed by the rear analyser. The observer sees a black character on a silver grey background (see Fig. 2).When the electric field is turned off, the molecules relax back to their 90-degree twist structure. This is referred to as a positive image, reflective viewing mode. The liquid crystal Liquid crystals are long chains of organic molecules that exhibit the properties of a liquid, still have the long range ordering of a solid. The liquid crystalline state constitutes an intermediate phase or mesophase between solids and liquids. There are several types of liquid crystals and the ones used for displays are called thermotropic liquid crystals. As the name implies, thermotropic liquid crystals are affected by heat. If heat is added to the crystalline phase of the liquid crystal, it will transition into the smectic phase (melting point). As more heat is added, the liquid crystal will go through the nematic phase (used for display applications), and finally into the isotropic phase (clearing point),Fig. 3. Twisted nematic (TN),super twisted nematic (STN), and active matrix (AM LCD) displays use the nematic phase for their operations. This phase is selected for its physical properties and the widest temperature range it can operate. It should be noted that the fluids used for display purposes are mixtures of several different liquid crystals. By mixing, a eutectic mixture will result with the melting point depressed well below room temperature. Construction A liquid crystal display (LCD) is a parallel plate capacitor, with a dielectric between the plates. The selected glass is coated with a transparent metal coating. for the electrodes of the display. The glass is usually a soda lime type, but in some instances it can be a more expensive borosilicate type. The transparent metal coating can be any thin layer of conductive material, such as gold, silver, or tin. In order to keep the cost down and have a reasonable process window with a highly transparent coating, the industry has been using indium tin oxide as the preferred electrode material. Photoresist is then put on top of the transparent metal coating and a photolithography process is used to image patterns in the photoresist. These patterns can be segments of numeric digits or they can be icons/patterns that represent various functions. The exposed patterns are then developed and the glass is sent through an acid bath where the excess metal coating is removed. The remaining photoresist is stripped off and the patterned segment and common plane electrodes are generated. After the electrodes have been made, an insulating layer is put on top of them. This is a silicon dioxide layer that is used to seal the electrode surface, act as an electrical barrier, and index match the electrodes and the glass. The next layer to be applied is the liquid crystal alignment layer. This is usually a polyamide type material and has been chosen for its environmental stability in high moisture and heat conditions. More importantly, due to its ability to cause the molecules of liquid crystal to align their long axis in the direction in which the polymer has been buffed. Buffing is a process where surface is finished with thin lines and the direction of the thin lines can be controlled by the control of buffing wheel. Two halves of the displays are buffed at right angles to one another. Since the liquid crystal molecules tend to arrange themselves parallel to one another, it causes a helical structure to be formed between the two electrode faces. This helical structure is a 90-degree rotation of the liquid crystal molecules from one side of the display to the other. After the polymer is buffed, a glue ring or seal is printed on the glass. This is a thermoset epoxy type material, with a very high glass transition temperature. Pins are attached to the display to allow the user to either mount the display in a socket or solder it directly into a circuit board. From an end user standpoint, pins are the easiest to use since there is no requirement for a compression bezel or expensive heat seal bonding equipment. The pins are attached to the glass with a structural epoxy on the back. On the top, we apply an electrically conductive epoxy, with an RTV over coating. Pins are the most reliable connection method. Heat seals are similar to flexible circuit boards, with the difference being that the interface tabs are made of a conductive hot-melt adhesive. Generally, particles such as carbon, gold, or silver are added to the adhesive to make it conductive. The pads of the heat seal are aligned with the pads of the display, a hot bar is brought down under pressure, and the conductive adhesive is melted and bonded to the display. The adhesive is allowed to cool and an electrical bond is made with the display. Elastomers are silicon strips of alternating conductors and insulators. These materials are generally soft and compliant, and can be easily compressed between the display and circuit board. Elastomers require a bezel to squeeze the display and circuit board together. There are two common types of LCDs which use this material. They are : 1. TN (twisted nematic) – The twisted nematic field effect mode arranges the liquid crystal molecules by controlling their movement with electric voltage so as to twist them by 90° in the direction of their thickness. It controls the light passing through the polariser placed on the two plates of the LCD by controlling the movement of the liquid crystal molecules.Almost all the medium and small type segment LCD are of these type. Hence this type is most common type used. 2. STN (super twisted nematic) While the TN mode arranges the liqud crystal molecules by twisting them by 90°the STN effect mode arranges them by giving a still larger twist and provides a display by refringence effect of the liquid crystal. The LCD structure in STN mode is same as that in TN mode. But as it has a different arrangement of liquid crystal, and by birefringence effect f liquid crystal. The LCD structure in STN mode is same as that in TN mode but as it has a different arrangement of liquid crystal and birefringence effect, there is a colour in the display and also a background colour. In STN mode , a wide viewing angle is obtained. The STN mode also offers a high contrast display compare to the TN mode. This mode is widely used in large size full dotmatrix LCD modules. For colours it has multiple modes depending on the combination of the polariser and retardation film. Energy consumption – LCD normally require very little energy to operate- typically 5A to 25A at five volts(per square inch) for a display. In addition, auxiliary lighting will require supplementary energy. All LCD require a pure ac drive voltage. Inadvertent DC voltage , such as DC component in an AC signal, can significantly reduce the life of LCDs and must be limited to 50mV DC. LCD PIN This section deals with driving a liquid crystal display (LCD) using the Hitachi HD 44780 or a comparable IC as the LCD controller. LCD device characteristics: - LCDs are available in a variety of models having one to four rows of 8 to 20 characters each. A display with two rows of 16 characters is used for this example project. Almost all aspects of the design can be used with other models of LCD, since the internal structures of the various LCD models are almost the same, differing only in the number of driver chips used. The display module is powered from a 5-v supply. Connecting an LCD to a microcontroller is very simple, requiring either a 4-bit or an 8 bit bus. A 4-bit interface saves I/O pins but requires that the commands and data be split into 4-bit pieces which are sent one after the other. Thus the saving in I/O lines comes at the price of more complicated software. To simplify understanding of the software the example uses a 8-bit interface. Three control lines are required in addition to the data lines. The connections of the LCD are defined in table below. Pin Designation Description 1 Vss Ground 2 Vdd Power ( +5v) 3. V0 Contrast 4. RS Register select 5. R/W Read/write 6. E Enable 7. 14. DBO DB7 Data line 0 Data line 7 The voltage at the V0 pin adjusts the contrast of the display. Normally this voltage is provided by an adjustable voltage divider. The three control lines direct the data transfers to and from the display modules as described below. The control line E ( enable) enable or disables the display. When the display is enabled it monitors the values of the other two control lines and interprets the data lines accordingly. When the display is disabled it ignores the status of the other two control lines and places its data lines drivers in a high impedance state ( tri-state). The data bus can then be used for other purpose. The control line R/W ( read/Write) determines whether data is read from or written to the LCD. Finally, the RS ( register select) line distinguishes between commands and display characters. ELECTROMECHANICAL RELAY :- The tripping device is electromechanical switch. The relay will trip whenever it will receive a 12v. The inside construction is a simple. There is a magnetic coil on plastic & magnetic material. Copper wire is wound on it. The wire used is very thin having a resistance 200. It is hinged on a iron frame at one side. An iron plate is coated and copper contact is set. The contact point is always set between two contact points A & B. The one side of the plastic is always attached by a spring S with iron frame, that its contact point remain contact with upper contact point with A. There is a plastic plate set on the iron frame to hold contacts. There are two contacts. There are two contacts for two coil sides. The contact pin for A, B contact point and there is another point which is connected to load contact(movable). The moving contact helps in changing taps in auto-transformer. As takes load current it is made thicker. Electromagnetic force is produced by the magnetic flux, which is produced by the operating quantity. The electromagnetic force exerted on the moving element, is proportional to the square of the flux in the air gap or the square of the current. Fig.. internal structure of the tripping device. CONSTRUCTION :- The circuit board is divided into three parts like power supply, microcontroller, temperature sensing section & display sections. So there are four PCBs used for the application. Before mounting the components on PCB, PCB is to be thoroughly checked using eye glass as there is no cracks on the board. All the components are to be mounted on the PCB by soldering it. Therefore during soldering the soldering technique is to be followed. IC’s to be mounted on the IC bases for better servicing facility. Temperature sensor is to be mounted on the PCB. Power supply unit is to be regulated using voltage regulator IC 7805. Microconrtroller is to programmed using the programmer and is to be placed on the IC base. Ac cord is to be connected to the transformer to supply 220 v A.C. Transformer used here is 9V-0-9V , center tapped one. 9v is regulated to get output of 5V after regulator. OPERATION GUIDELINES :- A user can easily operate the control system. There is a seven-segment display for display of set temperature. There is a key for setting the temperature of the control system. For clear operation follow the operation given below  Mains supply of 220V is given to the circuit using the AC cord  It will show project name, project designed by ( group name) & commands to operate.  The display will show the setting value on the LCD.  If the temperature above the setting one, then A LED will glow and relay will switch.  Then again to set another trip point user have to press reset switch. APPLICATIONS :- Control system is now a days control system is used widely to get better machinery result & to reduce the manpower for using . Control systems will automatically monitors and control system automatically at high accuracy. Specially the microcontroller is particularly has various advantage over traditional control systems. As it can control many unit at a time. The system using the microcontroller is very compact therefore can be installed site easily. Now a days the temperature controller system has many application areas like in research areas, cold storage, and chemical processing units, food processing units, and highly inflammable applications. The control system is closed loop one so the application will control temperature by switching on/off the coolers in application. Whenever the temperature rises above it will on the cooler so that it will cool down the atmosphere automatically till the atmosphere cools down to the set temperature. The present application will not allow the temperature of the atmosphere to rise above certain point. Application areas :-  Cold storage ( stores different vegetables)  Industrial applications  Cinema halls  Food processing unit where process occurs at particula temperature.  Chemical processing units etc….. SOFTWARE list p=pic16f877 #include ********************************************************************** R01 EQU 21h R02 EQU 22h ; ORG 0000 MAIN CLRF PORTA CLRF PORTB CLRF PORTC CLRF R01 CLRF R02 MOVLW H'FF' MOVWF TRISC CLRF TRISB MOVLW B'00011111' MOVWF TRISA MOVLW H'04' ;H'8E' MOVWF ADCON1 ; SW_CHEK BTFSC PORTC, 0 B $+2 B L0 BTFSC PORTC, 1 B $+2 B L1 BTFSC PORTC, 2 B $+2 B L2 BTFSC PORTC, 3 B $+2 B L3 BTFSC PORTC, 4 B $+2 B L4 BTFSC PORTC, 5 B $+2 B L5 BTFSC PORTC, 6 B $+2 B L6 BTFSC PORTC, 7 B SW_CHEK B L7 ; L0 MOVLW H'20' MOVWF PORTB CALL AD_CON MOVFW R01 SUBLW H'2E' BC $-4 BSF PORTA, 5 CALL AD_CON MOVFW R01 SUBLW H'2E' BC $-4 BCF PORTA, 5 B L0 ; L1 MOVLW H'30' MOVWF PORTB CALL AD_CON MOVFW R01 SUBLW H'42' BC $-4 BSF PORTA, 5 CALL AD_CON MOVFW R01 SUBLW H'42' BC $-4 BCF PORTA, 5 B L1 ; L2 MOVLW H'40' MOVWF PORTB CALL AD_CON MOVFW R01 SUBLW H'57' BC $-4 BSF PORTA, 5 CALL AD_CON MOVFW R01 SUBLW H'57' BC $-4 BCF PORTA, 5 B L2 ; L3 MOVLW H'50' MOVWF PORTB CALL AD_CON MOVFW R01 SUBLW H'6C' BC $-4 BSF PORTA, 5 CALL AD_CON MOVFW R01 SUBLW H'6C' BC $-4 BCF PORTA, 5 B L3 ; L4 MOVLW H'60' MOVWF PORTB CALL AD_CON MOVFW R01 SUBLW H'80' BC $-4 BSF PORTA, 5 CALL AD_CON MOVFW R01 SUBLW H'80' BC $-4 BCF PORTA, 5 B L4 ; L5 MOVLW H'70' MOVWF PORTB CALL AD_CON MOVFW R01 SUBLW H'94' BC $-4 BSF PORTA, 5 CALL AD_CON MOVFW R01 SUBLW H'94' BC $-4 BCF PORTA, 5 B L5 ; L6 MOVLW H'80' MOVWF PORTB CALL AD_CON MOVFW R01 SUBLW H'A9' BC $-4 BSF PORTA, 5 CALL AD_CON MOVFW R01 SUBLW H'A9' BC $-4 BCF PORTA, 5 B L6 ; L7 MOVLW H'90' MOVWF PORTB CALL AD_CON MOVFW R01 SUBLW H'BD' BC $-4 BSF PORTA, 5 CALL AD_CON MOVFW R01 SUBLW H'BD' BC $-4 BCF PORTA, 5 B L7 ; AD_CON MOVLW H'41' MOVWF ADCON0 BSF ADCON0, GO BTFSC ADCON0, GO B $-1 MOVFW ADRESH MOVWF R01 RETURN END CONCLUSION :- The control system is feasible one therefor it has tremendous application facilities. As the system is programmable one therefore it will control the temperature automatically at setting temperature and doesn’t allows the atmosphere temperature to rise above setting temperature. The particular facility of setting temperature by a user is important one. In addition to this the application is based on a microcontroller therefore it has greater advantages over all other microprocessor-based application in compactness, cost, features etc. SYNOPSIS Generally we find problem due to rise of temperature in industrial applications, food processing units. The present project has solution to meet the challenge. This project has application in the field of temperature related applications such as chemical processing unit, cold storage units, other research laboratories etc. A control system will take care of the I/O results. The control system can be applied for controlling the output using different inputs. Therefore the control system applications extends for a vast areas. Temperature control system is one of them. The present temperature control system is a microcontroller based one. The advantage of using the microcontroller in control system is that it will take care of many inputs and many outputs at a time. The other thing is that the microcontroller is intelligent one by the program inside. It will take care of every thing and so the parameters can be varied. The control system is divided into two categories like Open loop control system is that which doesn’t automatically correct for variations in it’s output, is called an open-loop system. Close loop control system is that which will take the output data to control it’s input so that output will vary to attain the required output. The present temperature control system is a closed loop application. Therefore it will take the data from its output and will process the data to control the output to attain the constant temperature. The microcontroller used is PIC16F873. Temperature set here is in centigrade & can be set from 1 to 99 C.