CHAPTER THREE

ABSTRACT

Digital thermometer (Digital Thermometer) is a measuring device used in displaying Temperature values. Digital Thermometer displays temperature as discrete numerals instead of a pointer deflection on a continuous scale as in the analogue instruments. An analogue volt meter basically consists of an amplifier connected to a D Arsonval meter. In meter design for measuring DC quantities, the amplifier receives the signal under measurement, amplifies the signal to an indication using a pointer which moves along a calibrated scale. It is versatile and accurate measuring instrument that is employed in many laboratory measurements.

This project is divided into five topics, the chapter one is introduction of digital thermometer, chapter two deals with the literature review of the above work. Chapter three is the main body of the project, principles of operation and the circuit diagram. In Chapter four, implementation, testing, soldering and coupling is discussed.

Finally, chapter five deals with the recommendation and conclusion of the digital volt meter.

CHAPTER ONE

INTRODUCTION

Thermometer,instrumentusedtomeasure temperature. The most commonly used thermometer is the mercury-in-glass type, which consists of a uniform-diameter glass capillary that opens into a mercury-filled bulb at one end. The assembly is sealed to preserve a partial vacuum in the capillary. If the temperature increases, the mercury expands and rises in the capillary. The temperature may then be read on an adjacent scale. Mercury is widely used for measuring ordinary temperatures; alcohol, ether, and other liquids are also employed for this purpose.

Theinventionofthethermometer is attributed to Galileo, although the sealed thermometer did not come into existence until about 1650. The modern alcohol and mercury thermometers were invented by the German physicist Gabriel Fahrenheit, who also proposed the first widely adopted temperature scale, named after him, in which 32 F is the freezing point of water and 212 F is its boiling point at standard atmospheric pressure. Various temperature scales have been proposed since his time; in the centigrade, or Celsius, scale, devised by the Swedish astronomer Anders Celsius and used in most of the world, the freezing point is 0, the boiling point is 100.

TYPES OF THERMOMETERS

Awidevarietyofdevices are employed as thermometers. The primary requirement is that one easily measured property, such as the length of the mercury column, should change markedly and predictably with changes in temperature. The variation of that property should also remain fairly linear with variations in temperature. In other words, a unit change in temperature should lead to a unit change in the property to be measured at all points of the scale.

Theelectricalresistance of conductors and semiconductors increases with an increase in temperature. This phenomenon is the basis of the resistance thermometer in which a constant voltage, or electric potential, is applied across the thermistor, or sensing element. For a thermistor of a given composition, the measurement of a specific temperature will induce a specific resistance across the thermistor. This resistance can be measured by a galvanometer and becomes a measure of the temperature.

Variousthermistorsmade of oxides of nickel, manganese, or cobalt are used to sense temperatures between -46 and 150 C (between -50 and 300 F). Similarly, thermistors employing other metals or alloys are designed for use at higher temperatures; platinum, for example, can be used up to 930 C (1700 F). With proper circuitry, the current reading can be converted to a direct digital display of the temperature.

Veryaccuratetemperature measurements can be made with thermocouples, in which a small voltage difference (measured in millivolts) arises when two wires of dissimilar metals are joined to form a loop, and the two junctions have different temperatures. To increase the voltage signal, several thermocouples may be connected in series to form a thermopile. Since the voltage depends on the difference of the junction temperatures, one junction must be maintained at a known temperature; otherwise an electronic compensation circuit must be built into the device to measure the actual temperature of the sensor.

Thermistorsandthermocouples often have sensing units less than cm (less than s in) in length, which permits them to respond rapidly to temperature changes and also makes them ideal for many biological and engineering uses.

Outdoor Thermometer

A red-dyed alcohol thermometer measures an outside air temperature of about 6 C (about 43 F). In a thermometer, an expanding fluid such as alcohol or mercury is trapped within a closed glass rod. As the fluid expands or contracts, it is measured by marks calibrated for given temperatures. The scale may be marked for either the Celsius or Fahrenheit temperature scales or both.

Theopticalpyrometer is used to measure temperatures of solid objects at temperatures above 700 C (about 1300 F), where most other thermometers would melt. At such high temperatures, solid objects radiate sufficient energy in the visual range to permit optical measurement by exploiting the so-called glow color phenomenon. The color at which hot objects glow changes from dull red through yellow to nearly white at about 1300 C (about 2400 F). The pyrometer contains a light bulb type of filament controlled by a rheostat (dimmer switch) that is calibrated so that the colors at which the filament glows correspond to specific temperatures. The temperature of a glowing object can be measured by viewing the object through the pyrometer and adjusting the rheostat until the filament blends into the image of the object. At this point the temperatures of the filament and the object are equal and can be read from the calibrated rheostat.Anothertemperature-measuring device, used mainly in thermostats, relies on the differential thermal expansion between two strips or disks made of different metals and either joined at the ends or bonded together.

SPECIAL-PURPOSE THERMOMETERS

Thermometersmayalso be designed to register the maximum or minimum temperature attained. A mercury-in-glass clinical thermometer, for example, is a maximum-reading instrument in which a trap in the capillary tube between the bulb and the bottom of the capillary permits the mercury to expand with increasing temperature, but prevents it from flowing back unless it is forced back by vigorous shaking. Maximum temperatures reached during the operation of tools and machines may also be estimated by special paint patches that change color when certain temperatures are reached.

Table of Equivalent Temperatures

Celsius and Fahrenheit temperatures can be interconverted as follows: C = (F - 32) 100/180; F = (C 180/100) + 32. Celsius and Kelvin can be interconverted as follows:

C = (K - 273.15); K = (C + 273.15).

ACCURACY OF MEASUREMENT

Accuratemeasurementof temperature depends on the establishment of thermal equilibrium between the thermometric device and its surroundings; that is, when at equilibrium no heat is exchanged between the thermometer and the material it touches or material in its vicinity. A clinical thermometer, therefore, must be inserted long enough (more than one minute) to reach near-equilibrium with the human body to yield an accurate reading. It should also be inserted deep enough, and have sufficient contact with the body, to indicate temperature accurately. These conditions are almost impossible to achieve with an oral thermometer, which generally indicates a body temperature lower than that given by a rectal thermometer. Insertion times can be significantly reduced with small, rapidly reacting thermometers such as thermistor devices.

Anythermometerindicates only its own temperature, which may not agree with the actual temperature of the object to be measured. In measuring the air temperature outside a building, for example, if one thermometer is placed in the shade and one in the sun, only a few centimeters away, the readings on the two instruments may be quite different, although the air temperature is the same. The thermometer in the shade may lose heat by radiation to cold building walls. Its reading, therefore, will be slightly below the true air temperature. On the other hand, the thermometer placed in the sun will absorb the sun's radiant heat. As a result, the indicated temperature may be significantly above the true air temperature. To avoid such errors, accurate temperature determinations require the shielding of the thermometer from hot and cold sources to or from which heat might be transferred by radiation, conduction, or convection.

Measurement helps in the discovering of size, length or amount of particular quantities. In other words there are different measuring devices used in laboratory such as thermometer, digital voltmeter, frequency meter, capacitance meter etc

This project deals on digital thermometer. A thermometer is an electronic devices used in the measurement of temperature. A thermometer can be grouped into two namely: digital and analogue thermometer. The digital thermometer makes use of an analogue to digital converter. This converts the analogue quantity temperature to digital or converts the analogue temperature to binary form. The binary is sent to the decoder, where it is converted then displayed via a seven-segment display. There are several methods by which the readings of a digital instrument can be displayed but the two main types are the LED (light emitting diode) and LCD (liquid cryptal display). Both units consist of seven segments. The LED display devices require more current than the LCDs and so they consume more power. They are widely used in bench digital thermometers where power consumption is not a primary consideration. This project consists of developing a digital thermometer that can solve the problem of abnormalities in measurement by providing an effective output. The design specifications of the digital thermometer are expected to have namely;

-temperature regulator

-variable resistors- (ADC) converter-Microcontroller

-Decoder (BCD)

-A display

-Sensor (thermistor)

-A probes

The digital thermometer is grouped according to the type of conversion such as

Ramp type

Continuous balance

Successive-approximation

Integrating

An ADC (analogue to digital converter) is also known as a dual slope converter or integrating converter. This type of converter is generally preferred over other types because it offers accuracy simplicity in design and a relatively indifference to noise which makes it very reliable. A ramp A/D converter works very much like the counter-ramp. (Continuous balance Digital Thermometer). The difficulty with ramp-type A/D converter is the long time it takes to count up to higher temperature but the successive approximation A/D converter cuts down the conversion time. The advantages of the successive-approximation are that the digitizing process is faster.

ADVANTAGES OF THE DIGITAL THERMOMETER

The numerical display of the digital meter eliminates error due to parallax Errors associated with human reading and interpolation are reduced

Digital instruments have automatic range and polarity selection and this reduces the need for training its operators on the usage. Digital instruments provide output in digital form suitable for further processing, recording or interfacing with computer, printer etc

Finally, accuracy in digital meter is better as readings are often correct to within +0.1% and -0.1% of the true value, while the analogue type may have an error as large as +10%

Mercury and digital thermometers are the most common types of household devices for measuring body temperature. In mercury thermometers, an increase in warmth causes mercury to expand and rise in a glass tube. Digital thermometers measure temperature with electronic sensors.

CHAPTER TWO

LITERATURE REVIEW

History

Temperature measurement is important to a wide range of activities, including manufacturing, scientific research, and medical practice.The accurate measurement of temperature developed relatively recently in human history. The invention of the thermometer is generally credited to the Italian mathematician-physicist Galileo Galilei (15641642). In his instrument, built about 1592, the changing temperature of an inverted glass vessel produced an expansion or contraction of the air within it, which in turn changed the level of the liquid with which the vessel's long, openmouthed neck was partially filled. This general principle was perfected in succeeding years by experimenting with liquids such as mercury and by providing a scale to measure the expansion and contraction brought about in such liquids by rising and falling temperatures.

By the early 18th century as many as 35 different temperature scales had been devised. The German physicist Daniel Gabriel Fahrenheit in 170030 produced accurate mercury thermometers calibrated to a standard scale that ranged from 32, the melting point of ice, to 96 for body temperature. The unit of temperature (degree) on the Fahrenheit temperature scale is 1/180 of the difference between the boiling (212) and freezing points of water. The first centigrade scale (made up of 100 degrees) is attributed to the Swedish astronomer Anders Celsius, who developed it in 1742. Celsius used 0 for the boiling point of water and 100 for the melting point of snow. This was later inverted to put 0 on the cold end and 100 on the hot end, and in that form it gained widespread use. It was known simply as the centigrade scale until in 1948 the name was changed to the Celsius temperature scale. In 1848 the British physicist William Thomson (later Lord Kelvin) proposed a system that used the degree Celsius but was keyed to absolute zero (273.15 C); the unit of this scale is now known as the kelvin. The Rankin scale employs the Fahrenheit degree keyed to absolute zero (459.67 F).

Any substance that somehow changes with alterations in its temperature can be used as the basic component in a thermometer. Gas thermometers work best at very low temperatures. Liquid thermometers are the most common type in use. They are simple, inexpensive, long-lasting, and able to measure a wide temperature span. The liquid is almost always mercury, sealed in a glass tube with nitrogen gas making up the rest of the volume of the tube.

Electrical-resistance thermometers characteristically use platinum and operate on the principle that electrical resistance varies with changes in temperature. Thermocouples are among the most widely used industrial thermometers. They are composed of two wires made of different materials joined together at one end and connected to a voltage-measuring device at the other. A temperature difference between the two ends creates a voltage that can be measured and translated into a measure of the temperature of the junction end. The bimetallic strip constitutes one of the most trouble-free and durable thermometers. It is simply two strips of different metals bonded together and held at one end. When heated, the two strips expand at different rates, resulting in a bending effect that is used to measure the temperature change.

Other thermometers operate by sensing sound waves or magnetic conditions associated with temperature changes. Magnetic thermometers increase in efficiency as temperature decreases, which make them extremely useful in measuring very low temperatures with precision. Temperatures can also be mapped, using a technique called thermography that provides a graphic or visual representation of the temperature conditions on the surface of an object or land area.

Digital thermometer makes use of an analogue to digital converter. This converts the analogue temperature to binary form. The binary data is further processed, sent to a display decoder where it is converted and displayed using a seven segment display. The dual slope conversion is well suited to Digital Thermometer operation because it provides good accuracy by Paul Horowitz and Winfield hill, the art of electronics second edition 1989, Cambridge university press, USA.

According to Oxford advanced learners dictionary. Digital instrument is an instrument used for receiving and sending information as a series of the number one and zero. In this instrument, the analogue inputs is converted to a BCD code representation which is then decoded and displayed on a digital display by McKenzie smith, John Hilly and Keith Brown Electrical and Electronics technology Hughes. The first digital thermometer was invented and produced by Andrew Kay of non-linear system (and later founder of kaypro) in 1954. These digital meters have input amplifiers, a vacuum tube thermometer and also a constant input resistance of 10megaohms regardless of set measurement range. (A-D) converter consists of five basic blocks namely, an op-amp used as an integrator, a level comparator, a basic clock (for generating timing pulses),a set of decimal counters and a block of logic circuitry by B.L THERAJA and A.K THERAJA A textbook of electrical technology revised edition in two colours, S. Chand and company. Multimeter was invented in the early 1920s as radio receivers and other vacuum tube electronic devices became more common. the invention of the first multimedia is attributed to a post office engineer Donald Macadie who came dissatisfied with many separate instrument required for the maintenance of the telecommunication circuits. Macadie invented a first instrument which could measure amps, volts and ohms so the multifunctional meter was than named AVOMETER. The meter comprised a galvanometer, temperature and resistance references and a switch to select the appropriate circuit for the input under test. It was sold in 1923 by automatic coil winder and electrical equipment company (ACWEEC).

Finally, the digital thermometer is an ADC (analog-to-digital converter) which converts an analog signal into a train of pulses. The digital thermometer has limited number of discrete values. An analogue to digital converter or integrating converter is preferred over other types as it offers accuracy and simplicity in design. CHAPTER THREERESEARCH AND DESIGN METHODOLOGY

RESEARCH METHOD

The design and construction of gadgets that will be suited in real life application is not an easy thing to come by, hence the need for an efficient design. In this section, I will try to bring to light the components parts that make up the magnetically coupled 3 phase power protection, method used in the design and above all principles of operation.

COMPONENTS USED

Microcontroller (Atmel 89s52)

Transistors (C 1815)

Resistors

Ceramic Capacitors

Electrolytic capacitors

Crystal

Seven Segment Display

Silicon Diodes

Vero board and jumper wires

FUNCTIONS OF THE COMPONENTS

MICROCONTROLLER (89S52)The AT89S52 is a low-power, high-performance CMOS 8-bit microcontroller with 8K bytes of in-system programmable Flash memory. The device is manufactured using Atmels 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 highly-flexible and cost-effective solution to many embedded control applications. The AT89S52 provides the following standard features: 8K bytes of Flash, 256 bytes of RAM, 32 I/O lines, Watchdog timer, two data pointers, three 16-bit timer/counters, a six-vector two-level interrupt architecture, a full duplex serial port, on-chip oscillator, and clock circuitry. In addition, the AT89S52 is designed with static logic for operation down to zero frequency and supports two software selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial port, and interrupt system to continue functioning. The Power-down mode saves the RAM contents but freezes the oscillator, disabling all other chip functions until the next interrupt.

The microcontroller, as used here, serves as the core for the system fault calculation that is to say, it the action of the tripping circuit in the system. It runs a pre-programmed series of instructions embedded in the internal flash thus reducing the cost of working with external ROM that would have made the system bulky and non cost effective.

Below show the pin configuration of the microcontroller and the functions of each of the pins;

89s52 Microcontroller's pins

Pins 1-8: Port 1 Each of these pins can be configured as input or output.

Pin 9: RS Logical one on this pin stops microcontrollers operating and erases the contents of most registers. By applying logical zero to this pin, the program starts execution from the beginning. In other words, a positive voltage pulse on this pin resets the microcontroller.

Pins10-17: Port 3 Similar to port 1, each of these pins can serve as universal input or output. Besides, all of them have alternative functions:

Pin 10: RXD Serial asynchronous communication input or Serial synchronous communication output.

Pin 11: TXD Serial asynchronous communication output or Serial synchronous communication clock output.

Pin 12: INT0 Interrupt 0 input

Pin 13: INT1 Interrupt 1 input

Pin 14: T0 Counter 0 clock input

Pin 15: T1 Counter 1 clock input

Pin 16: WR Signal for writing to external (additional) RAM

Pin 17: RD Signal for reading from external RAM

Pin 18, 19: X2 X1 Internal oscillator input and output. A quartz crystal which determines operating frequency is usually connected to these pins. Instead of quartz crystal, the miniature ceramics resonators can be also used for frequency stabilization. Later versions of the microcontrollers operate at a frequency of 0 Hz up to over 50 Hz.

Pin 20: GND Ground

Pin 21-28: Port 2 if there is no intention to use external memory then these port pins are configured as universal inputs/outputs. In case external memory is used then the higher address byte, i.e. addresses A8-A15 will appear on this port. It is important to know that even memory with capacity of 64Kb is not used (i.e. note all bits on port are used for memory addressing) the rest of bits are not available as inputs or outputs.

Pin 29: PSEN if external ROM is used for storing program then it has a logic-0 value every time the microcontroller reads a byte from memory.

Pin 30: ALE Prior to each reading from external memory, the microcontroller will set the lower address byte (A0-A7) on P0 and immediately after that activates the output ALE. Upon receiving signal from the ALE pin, the external register (74HCT373 or 74HCT375 circuit is usually embedded) memorizes the state of P0 and uses it as an address for memory chip. In the second part of the microcontrollers machine cycle, a signal on this pin stops being emitted and P0 is used now for data transmission (Data Bus). In this way, by means of only one additional (and cheap) integrated circuit, data multiplexing from the port is performed. This port at the same time used for data and address transmission.

Pin 31: EA By applying logic zero to this pin, P2 and P3 are used for data and address transmission with no regard to whether there is internal memory or not. That means that even there is a program written to the microcontroller, it will not be executed, the program written to external ROM will be used instead. Otherwise, by applying logic one to the EA pin, the microcontroller will use both memories, first internal and afterwards external (if it exists), up to end of address space.

Pin 32-39: Port 0 Similar to port 2, if external memory is not used, these pins can be used as universal inputs or outputs. Otherwise, P0 is configured as address output (A0-A7) when the ALE pin is at high level (1) and as data output (Data Bus), when logic zero (0) is applied to the ALE pin.

Pin 40: VCC Power supply +5V

RESISTORS

There are almost as many types of resistors as there are applications. Resistors are used in amplifiers as load for active devices, in bias networks and as feedback elements. In combination with capacitors, they establish time constants and act as filters. They are used to set operating currents and gain level. Resistors are also used in power circuits to reduce voltages by dissipating power, to measure currents and signal levels. They are used in precision circuits to establish current, provide voltage ratios and to set precise gain values.

Ifabatteryisconnected across a conducting material, a certain amount of current will flow through the material. This current is dependent on the voltage of the battery, on the dimensions of the sample, and on the conductivity of the material itself. Resistors with known resistance are used for current control in electronic circuits. The resistors are made from carbon mixtures, metal films, or resistance wire and have two connecting wires attached. Variable resistors, with an adjustable sliding contact arm, are often used to control volume on radios and television sets.

The resistors found in this circuit are used for two major purposes which are

1. They are employed to set operating current of the component they are connected to.

2. They function as bias components to all transistors and microcontroller found in the circuit.

How to read Resistor Color Codes

First find the tolerance band, it will typically be gold (5%) and sometimes silver (10%). Starting from the other end, identify the first band - write down the number associated with that color; in this case Yellow is 4. Now 'read' the next color, here it is Violet so write down a '7' next to the 3rd band. (You should have '47' so far.) Now read the third or 'multiplier exponent' band and write down that as the number of zeros. In this example it is two so we get 4700. If the 'multiplier exponent' band is Black (for zero) don't write any zeros down. If the 'multiplier exponent' band is Gold move the decimal point one to the left. If the 'multiplier exponent' band is Silver move the decimal point two places to the left. If the resistor has one more band past the tolerance band it is a quality band.

BS 1852 Coding for resistor values

The letter R is used for Ohms and K for Kilo ohms M for Mega ohms and placed where the decimal point would go.

At the end is a letter that represents tolerance Where M=20%, K=10%, J=5%, G=2%, and F=1% D=.5% C=.25 B=.1%

CAPACITORSCapacitors store electric charge. They are used with resistors in timing circuits because it takes time for a capacitor to fill with charge. They are used to smooth varying DC supplies by acting as a reservoir of charge. They are also used in filter circuits because capacitors easily pass AC (changing) signals but they block DC (constant) signals. There are many types of capacitor but they can be split into two groups, polarized and unpolarised. Each group has its own circuit symbol.

Electrolytic capacitors are polarized and they must be connected the correct way round, at least one of their leads will be marked + or -. They are not damaged by heat when soldering.

There are two designs of electrolytic capacitors; axial where the leads are attached to each end (220F in picture) and radial where both leads are at the same end (10F in picture). Radial capacitors tend to be a little smaller and they stand upright on the circuit board.

It is easy to find the value of electrolytic capacitors because they are clearly printed with their capacitance and voltage rating. The voltage rating can be quite low (6V for example) and it should always be checked when selecting an electrolytic capacitor.

Small value capacitors are non-polarized and may be connected either way round. They are not damaged by heat when soldering, except for one unusual type (polystyrene). They have high voltage ratings of at least 50V, usually 250V or so. It can be difficult to find the values of these small capacitors because there are many types of them and several different labeling systems!

Many small value capacitors have their value printed but without a multiplier, so you need to use experience to work out what the multiplier should be. For example 0.1 means 0.1F

TRANSISTORS

Transistorsaremadefrom semiconductors. These are materials, such as silicon or germanium, that are doped (have minute amounts of foreign elements added) so that either an abundance or a lack of free electrons exists. In the former case, the semiconductor is called n-type, and in the latter case, p-type. By combining n-type and p-type materials, a diode can be produced. When this diode is connected to a battery so that the p-type material is positive and the n-type negative, electrons are repelled from the negative battery terminal and pass unimpeded to the p-region, which lacks electrons. With battery reversed, the electrons arriving in the p-material can pass only with difficulty to the n-material, which is already filled with free electrons, and the current is almost zero.

Thebipolartransistor was invented in 1948 as a replacement for the triode vacuum tube. It consists of three layers of doped material, forming two p-n (bipolar) junctions with configurations of p-n-p or n-p-n. One junction is connected to a battery so as to allow current flow (forward bias), and the other junction has a battery connected in the opposite direction (reverse bias). If the current in the forward-biased junction is varied by the addition of a signal, the current in the reverse-biased junction of the transistor will vary accordingly. The principle can be used to construct amplifiers in which a small signal applied to the forward-biased junction causes a large change in current in the reverse-biased junction.

Anothertypeoftransistor is the field-effect transistor (FET). Such a transistor operates on the principle of repulsion or attraction of charges due to a superimposed electric field. Amplification of current is accomplished in a manner similar to the grid control of a vacuum tube. Field-effect transistors operate more efficiently than bipolar types, because a large signal can be controlled by a very small amount of energy.

Transistors function majorly as switch or amplifiers. To function as a switch, the transistor has to be biased into saturation i.e. the base voltage exceeds 0.7v for silicon type and 0.3v for germanium type. On the other hand, the base voltage can be varied continually by an input signal for the transistor to function as an amplifier.

The transistors in this circuit are all Field Effect Transistors (FET) and they function as high speed switches.

They are used to turn the seven segment display

CIRCUIT DESCRIPTION

1.Power Supply Unit

2.Microcontroller Unit

3.Sensing Unit

4.Clock Unit

Power Supply Unit: The power supply unit is gotten from a 4.5AH 6volts DC battery.

Clock signal

Although the microcontroller has built in oscillator, it cannot operate without two external condensators and quartz crystal which stabilize its frequency (microcontrollers operating speed).

Naturally, there are some exceptions too: if this solution cannot be applied for some reason, there are always alternative ones. One of them is to bring clock signal from special source through invertors.

The oscillator in this circuit is a 10MHz crystal which produces a square wave signal that is used to synchronize all the systems function.

Microcontroller Unit

This section is the core of the system. It sees to it that all action of the traffic system is free from contention or clash. The microcontroller runs a pre written series of instruction that has been compiled and downloaded to it through a device programmer.

As all other good things, this powerful component is basically very simple and is obtained by uniting tested and high- quality "ingredients" (components) as per following receipt:

1.The simplest computers processor is used as a "brain" for the system.

2.Depending on the taste of the producer, it is added: a bit of memory, a few A/D converters, timers, input/output lines etc.

3.It is all placed in one of standard packages.

Three things have had a crucial impact on such a success of the microcontrollers:

Powerful and intelligently chosen electronics embedded in the microcontrollers can via input/output devices switches, push buttons, sensors, LCD displays, relays) control various processes and devices such as: industrial automatics, electric current, temperature, engine performance etc.

A very low price enables them to be embedded in such devices in which, until recent time it was not worth embedding anything. Thanks to that, the world is overwhelmed today with cheap automatic devices and various intelligent appliances.

Prior knowledge is hardly needed for programming. It is sufficient to have any kind of PC (software in use is not demanding at all and it is easy to learn to work on it) and one simple device (programmer) used for transferring completed programs into the microcontroller.

How microcontroller operates

Even though there is a great number of various microcontrollers and even greater number of programs designed for the microcontrollers use only, all of them have many things in common. That means that if you learn to handle one of them you will be able to handle them all. A typical scenario on whose basis it all functions is as follows:

1.Power supply is turned off and everything is so stillchip is programmed, everything is in place, and nothing indicates what is to come

2.Power supply connectors are connected to the power supply source and everything starts to happen at high speed! The control logic registers what is going on first. It enables only quartz oscillator to operate. While the first preparations are in progress and parasite capacities are being charged, the first milliseconds go by.

3.Voltage level has reached its full value and frequency of oscillator has become stable. The bits are being written to the SFRs, showing the state of all peripherals and all pins are configured as outputs. Everything occurs in harmony to the pulses rhythm and the overall electronic starts operating

4.Program Counter is reset to zero address of the program memory. Instruction from that address is sent to instruction decoder where its meaning is recognized and it is executed with immediate effect.

5.The value of the Program Counter is being incremented by 1 and the whole process is being repeated...several million times per second

CHAPTER FOUR

PRINCIPLE OF OPERATION, IMPLEMENTATION, TESTING AND RESULTS

Successful operation of the system depends on a number of factors, proper matching of the different stages, strict adherence to component tolerances and a stable power supply are essential for proper operation of the system. Therefore the implantation and testing covers the various steps taken in achieving this project. CIRCUIT DIAGRAM

The implementation of the system is done first on a breadboard. This project board is a type of board that has slots or openings where electronics components can be inserted and used to realize a system circuit without soldering the board. The above mentioned board was used in implementing the design of this project in stages to ensure viability before they were transferred to a veroboard. The implementation of the interface hardware was done in phase. These phase include testing of the design, preparation of component layout, soldering of components and packaging or casing.

TESTING OF INDIVIDUAL COMPONENTS

This stage involves the testing of the electronics components and the integrated circuits chips .this stage was carried out to ensure proper functioning of components before interconnection with others components. Values of the components were measured using a digital Multimeter. Testing for continuity in the veroboard lines were done using Multimeter also.

COUPLING AND SOLDERING

When the circuit had been tested and the component layout was ready, the components were then transferred to the veroboard and soldered. In the case of the microcontroller, the IC sockets were used to avoid bending and breaking of the IC pins and also to avoid overheating of the ICs which may lead to eventual breakdown of the components.

PRECAUTIONS

All components were kept at room temperature in a dry dust free package

After soldering, the tip of the soldering iron is run between their strips to eliminate solder hairs causing short circuits between the copper foils. A sharp pointed object is also used to scrape the area between the strips

It is necessary to prevent solder spreading to adjacent copper i.e. too much soldering was avoided on each components bridges were avoided during soldering on the veroboard

Short circuit and open circuit were avoided where necessary

Finally the component should be heated at a maximum temperature to avoid damaging the components.

CHAPTER FIVECONCLSION AND RECOMMENDATION

CONCLUSION

During the execution of this project, we observed that Digital Thermometer displays temperature as discrete numerals instead of a pointer deflection on a continuous scale as in the analogue instrument. The Digital Thermometer is an accurate measuring instrument that is employed in much laboratory measurement. It makes use of analogue to digital converter (ADC) and can drive a series of four seven segment LED display directly. The digital thermometer can be used in measuring AC or DC temperature . The components and the integrated circuit chips should be tested for continuity before soldering and couplingRECOMMENDATION

The availability of laboratory equipment remains vital and basic in the study of electrical and electronics engineering courses. This will facilitate the learning and comprehensive ability of students, since engineering courses are practical oriented, therefore student should not relent for any reasons to make use of their available laboratory equipments.Hence, good understanding on scientific and engineering knowledge will make practical exercise and involvement interesting. Therefore, student should involve themselves in practical exercise because it will improve their assimilation the theoretical aspect of engineering and scientific knowledge. Finally, the department should allocate projects at the beginning of the semester to enable the students source for fund and other materials that can help them carry out their projects.REFERENCESB.1. Theraja,A.K Theraja

A testbook of Electrical Technology (coloured edition/2003, S CHAND and company, India.

Horowitz Paul, Hill Winfield,

The Art of Electronics (second edition) 1989,

Combridge University press, USA.

Mehta V.K, Mehta Rohit

Principles of Electronics (Multi colour Edition)

2005, S CHAND and company, India.

http//en.wikipedia.org/wiki/thermometerMcKenzie Smith, John Hiley and Keith Brown.

Electrical and Electronic Technology Hughes

http//www.free-electronic-circuit.com/circuits/html.