INTRODUCTION

This project is used to measure the various parameters like Temperature, humidity and Light and display them on a LCD. Temperature and light is sensed by respective sensors and sensor output is amplified and given to ADC. Microcontroller controls these parameters and keeps them at some predefined levels using relay interface. These relays can be connected to Fan/Heater.

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BLOCK DIAGRAM

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BLOCK DIGRAM

Fig1: Block diagram of Multichannel Monitoring System

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DESCRIPTION OF BLOCK DIAGRAM

It mainly consist of following blocks

1. Sensors: we are going to use temperature sensor and light sensor to sense temperature and light respectively. These sensors sense the parameters and gives corresponding voltage output

2. Amplifier: As the voltage output from the sensors is in miliVolts, it has to be increased to 0 to 5 volts range. We are going to use linear amplifier for this purpose.

3. ADC: The main part of our project is microcontroller which reads only digital input (0V & 5V) but the output of Amplifier is in analog form, so it has to be converted into digital format, for this purpose we are going to use ADC to convert analog output from amplifier into the digital output to be given to microcontroller

4. Microcontroller: This is the CPU (central processing unit) of our project. We are going to use microcontroller of 8051 family. The various functions of microcontroller are like I. Reading the digital input from ADC which is derived from Temperature and Light sensor. II. Sending this data to LCD so that the person operating this project should read the values of temperature and light. III. Controlling the parameters like Temperature, light are turning On/Off the respective relays. IV. Sending the values of temperature and light to the computer using serial port

5. Relay: We have used 2 relays in our project. First one will be turned on when the temperature falls below the desired value. And the second relay will be turned on when temperature reaches above the desired value. (e.g. if the desired value is 20 degree C, then Relay 1 will be turned on when temperature is 19 or below and Relay 2 will be turned on when temperature are 21 or above)

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CIRCUIT DIAGRAM

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CIRCUIT DIAGRAM

Fig2: Circuit diagram of Multichannel Monitoring System

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LIGHT CONTROLLER

Fig3: Circuit diagram of Light Controller

Principle and Working:

The circuit above shows a simple application of light operated switch. This circuit senses the ambience light and depending on the presence/absence of sufficient ambience light, it turns the bulb On/Off automatically. The bulb gets on when there is insufficient ambience light (e.g. evening or night time) and switches off automatically when enough ambiences light are present. (e.g. In day time, when the sun light is present additional light may not be needed.) This bulb can also be your street lamp that needs to be switched on every evening, and switched off every morning. The circuit does this job automatically without any manual interference.

Let’s See how this works: - During day time when sunlight falls on LDR, the resistance of LDR decreases. The decrement of resistance causes more potential across VR1 and very less potential across LDR. The potential across LDR is directly fed to the base of transistor TR1 (shown in circuit). Because of the low potential difference across TR1's base and emitter, the transistor TR1 goes into cutoff, and restricts any flow of current from collector to emitter. This non availability of sufficient current causes the relay to get de-magnetized and switches off any device attached to it (bulb in this case). Similarly when sunlight is not present (i.e. at night), the resistance of LDR increases and hence the potential across LDR also increases. The increased potential causes transistor to move from cutoff to saturation, allowing maximum current to pass from collector to emitter. The increased current turns the relay ON and also the bulb attached to it.

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HUMIDITY SENSOR

Fig4: Circuit diagram of Humidity Sensor

Dew (condensed moisture) adversely affects the normal performance of sensitive electronic devices. A low-cost circuit described here can be used to switch off any gadget automatically in case of excessive humidity. At the heart of the circuit is an inexpensive (resistor type) dew sensor element. Although dew sensor elements are widely used in video cassette players and recorders, these may not be easily available in local market. However, the same can be procured from authorized service centers of reputed companies. The author used the dew sensor for FUNAI VCP model No. V.I.P. 3000A (Part No: 6808-08-04, reference no. 336) in his prototype. In practice, it is observed that all dew sensors available for video application possess the same electrical characteristics irrespective of their physical shape/size, and hence are interchangeable and can be used in this project. The circuit is basically a switching type circuit made with the help of a popular dual op-amp IC LM358N which is configured here as a comparator. (Note that only one half of the IC is used here.) Under normal conditions, resistance of the dew sensor is low (1 kilo-ohm or so) and thus the voltage at its non-inverting terminal (pin 3) is low compared to that at its inverting input (pin 2) terminal. The corresponding output of the comparator (at pin 1) is accordingly low and thus nothing happens in the circuit. When humidity exceeds 80 per cent, the sensor resistance increases rapidly. As a result, the non-inverting pin becomes more positive than the inverting pin. This pushes up the output of IC1 to a high level. As a consequence, the LED inside the opto-coupler is energized. At the

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same time LED1 provides a visual indication. The opto-coupler can be suitably interfaced to any electronic device for switching purpose. Circuit comprising diode D2, resistors R5 and R6 and capacitor C1 forms a low-voltage, low-current power supply unit. This simple arrangement obviates the requirement for a bulky and expensive step-down transformer.

A humidity sensor also called a hygrometer, measures and regularly reports the relative humidity in the air. They may be used in homes for people with illnesses affected by humidity; as part of home heating, ventilating, and air conditioning (HVAC) systems; and in humidors or wine cellars. Humidity sensors can also be used in cars, office and industrial HVAC systems, and in meteorology stations to report and predict weather.

A humidity sensor senses relative humidity. This means that it measures both air temperature and moisture. Relative humidity, expressed as a percent, is the ratio of actual moisture in the air to the highest amount of moisture air at that temperature can hold. The warmer the air is, the more moisture it can hold, so relative humidity changes with fluctuations in temperature.

The most common type of humidity sensor uses what is called “capacitive measurement.” This system relies on electrical capacitance, or the ability of two nearby electrical conductors to create an electrical field between them. The sensor itself is composed of two metal plates with a non-conductive polymer film between them. The film collects moisture from the air, and the moisture causes minute changes in the voltage between the two plates. The changes in voltage are converted into digital readings showing the amount of moisture in the air.

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TEMPERATURE SENSOR

Fig5: The LM35 - An Integrated Circuit Temperature Sensor

1. Why Use LM35s to Measure Temperature?

You can measure temperature more accurately than a using a thermistor.The sensor circuitry is sealed and not subject to oxidation, etc.The LM35 generates a higher output voltage than thermocouples and may not require that the output voltage be amplified.

2. What Does an LM35 Do? How does it work?

It has an output voltage that is proportional to the Celsius temperature.The scale factor is .01V/oCThe LM35 does not require any external calibration or trimming and maintains an accuracy of +/-0.4 oC at room temperature and +/- 0.8 oC over a range of 0 oC to +100 oC.Another important characteristic of the LM35DZ is that it draws only 60 micro amps from its supply and possesses a low self-heating capability. The sensor self-heating causes less than 0.1OC temperature rise in still air.

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3. How Do You Use An LM35? (Electrical Connections)

Here is a commonly used circuit. For connections refer to the picture above.In this circuit, parameter values commonly used are:Vc = 4 to 30v5v or 12 v are typical values used.Ra = Vc /10-6Actually, it can range from 80 KW to 600 KW , but most just use 80 KW.

Fig6: Temperature Sensor LM35

4. What Can You Expect When You Use An LM35?

You will need to use a voltmeter to sense Vout.The output voltage is converted to temperature by a simple conversion factor.The sensor has a sensitivity of 10mV / oC.Use a conversion factor that is the reciprocal that is 100 oC/V.The general equation used to convert output voltage to temperature is:Temperature ( oC) = Vout * (100 oC/V)So if Vout is 1V, then, Temperature = 100 oCThe output voltage varies linearly with temperature.

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COMPONENTS

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COMPONENT USED

1. PIC 16f72/89c52 controller

2. LM 7805 voltage regulator

3. LDR LIGHT SENSOR

4. LM 35 TEMPERATURE SENSOR

5. DS154 HUMIDITY SENSOR

6. 12 VOLT 1AMP STEPDOWN TRANSFORMER

7. 1N 4007 DIODE

8. CRYSTAL OSCILLATOR

9. RELAY 12 VOLT SPST

10. CAPACITOR

11. RESISTER

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MICRO CONTROLLER

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PIC 16 F 72

Fig7: Pin diagram of PIC16F72

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PIC 16F72

FEATURES:

1. High-Performance RISC CPU - Only 35 single word instructions to learn - All instructions are 1µs (@4MHz) except for program branches - Operating speed: DC - 20MHz clock input

2. Peripheral Features - Two 8-bit timer/counter(TMR0, TMR2) with 8-bit programmable prescalar - One 16-bit timer/counter - High source/sink current: 25mA - 12.5 ns resolution - Capture/Compare PWM (CCP) Module

3. Special Microcontroller Features - Power-On Reset - Power-up Timer (PWRT) and Oscillator Start-Up Timer (OST) - Power saving SLEEp mode

4. CMOS Technology - Fully static design - Low power, high speed CMOS FLASH technology - Wide operating voltage range: 2.0V to 5.5V - < 0.6 mA typical @ 3V, 4MHz

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ADVANTAGES OF MICROCONTROLLER

1. If a system is developed with a microprocessor, the designer has to go for external memory such as RAM, ROM or EPROM and peripherals and hence the size of the PCB will be large enough to hold all the required peripherals.

2. But the microcontroller has got all these peripheral facilities on a single chip so development a similar system with a microcontroller reduces PCB size and cost of the design.

3. One of the major difference between a microcontroller and a microprocessor is that a controller often deals with bits, not bytes as in the real world application, for example switch contacts can only be open or close, indicators should be lit or dark and motors can be either turned on or off and so forth.

4. The Microcontroller has two 8-bit timers/ counters built within it, which makes it more suitable to this application since we need to produce some accurate timer delays. It is even more advantageous that the timers also act as interrupt.

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LM 35 TEMPERATURE SENSOR

Fig8:LM35 Temperature Sensor

The measurement of negative temperatures (below 0°C) requires a negative voltage source. However, this project does not use any negative voltage source, and therefore will demonstrate the use of sensor for measuring temperatures above 0°C (up to 100°C).

The output voltage from the sensor is converted to a 10-bit digital number using the internal ADC of the PIC16F688. Since the voltage to be measured by the ADC ranges from 0 to 1.0V (that corresponds to maximum temperature range, 100 °C), the ADC requires a lower reference voltage (instead of the supply voltage Vdd = 5V) for A/D conversion in order to get better accuracy. The lower reference voltage can be provided using a Zener diode, a resistor network, or sometime just simple diodes. You can derive an approximate 1.2V reference voltage by connecting two diodes and a resistor in series across the supply voltage, as shown below. As a demonstration, I am going to use this circuit in this project. I measured the output voltage across the two diodes as 1.196 V. The resistor R I used is of 3.6K, but you can use 1K too. The important thing is to measure the voltage across the two diodes as accurate as possible.

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LIGHT DEPENDENT RESISTOR

Fig9: Light Dependent Resistor

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WHAT IS LDR? BASICS OF LIGHT DEPENDENT RESISTOR:

An LDR (Light dependent resistor), as its name suggests, offers resistance in response to the ambient light. The resistance decreases as the intensity of incident light increases, and vice versa. In the absence of light, LDR exhibits a resistance of the order of mega-ohms which decreases to few hundred ohms in the presence of light. It can act as a sensor, since a varying voltage drop can be obtained in accordance with the varying light. It is made up of cadmium sulphide (CdS).

An LDR has a zigzag cadmium sulphide track. It is a bilateral device, i.e., conducts in both directions in same fashion.

Light Dependent Resistor – it is a passive light transducer. It is also called as photo-conductive cell because its conductivity changes due to change in light intensity.

Basic Principle – when light falls on it its resistance decreases and when it is dark its resistance is maximum. The change in resistance is directly proportional to intensity of light falling on it.

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Construction – it is made up of photo sensitive material like cadmium sulphide (CdS), Selenium (Se), Cadmium Selenide (CdSe) or Lead Sulphide (PbS). It is deposited on insulating surface like ceramic substrate in the form of zigzag wire as shown in following figure. It is enclosed in round metallic or plastic case and two electrodes are taken out for external connections. The structure is covered with glass sheet to protect it from moisture and dust and allows only light to fall on it.

Fig10: Construction of Light Dependent Resistor

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APPLICATIONS OF L D R:

It is used in burglar alarm to give alarming sound when a burglar invades sensitive premises.

It is used in street light control to switch on the lights during dusk (evening) and switch off during dawn (morning) automatically.

It is used in Lux meter to measure intensity of light in Lux. It is used in photo sensitive relay circuit.

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VOLTAGE REGULATOR

LM78M05 3-TERMINAL POSITIVE VOLTAGE REGULATORS:

Fig11: Voltage Regulator IC 7805

FEATURES OF VOLTAGE REGULATOR:

Output current in excess of 0.5A No external components Internal thermal overload protection Internal short circuit current-limiting Output transistor safe-area compensation Available in TO-220, TO-39, and TO-252 D-PAK packages Output voltages of 5V, 12V, and 15V

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DESCRIPTION:

The LM341 and LM78MXX series of three-terminal positive voltage regulators employ built-in current limiting, thermal shutdown, and safe-operating area protection which make them virtually immune to damage from output overloads.

With adequate heat sinking, they can deliver in excess of 0.5A output current. Typical applications would include local (on-card) regulators which can eliminate the noise

and degraded performance associated with single-point regulation.

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CAPACITORS

Capacitors are common components of electronic circuits, used almost as frequently as resistors. Basic difference between the two is the fact that capacitor resistance (called reactance) depends on voltage frequency, not only on capacitors' features. Common mark for reactance is Xc and it can be calculated using the following formula:

f representing the frequency in Hz and C representing the capacity in Farads.

For example, 5nF capacitor's reactance at f = 125 kHz equals:

While, at f = 1.25MHz, it equals:

Capacitor has infinitely high reactance for direct current, because f =0.

Capacitors are used in circuits for filtering signals of specified frequency. They are common components of electrical filters, oscillator circuits, etc.

Basic characteristic of capacitor is its capacity - higher the capacity is, higher is the amount of electricity capacitor can accumulate. Capacity is measured in Farads (F). As one Farad represents fairly high capacity value, microfarad (µF), nanoFarad (nF) and picoFarad (pF) are commonly used. As a reminder, relations between units are (1F= 106µF = 109nF = 1012pF) that is 1µF=1000nF and 1nF=1000pF. It is essential to remember this notation, as same values may be marked differently in different electrical schemes. For example, 1500pF may be used interchangeably with 1.5nF; 100nF may replace 0.1µF, etc. Bear in mind that simpler notation system is used, as with resistors. If the mark by the capacitor in the scheme reads 120 (or 120E) capacity equals 120pF, 1n2 stands for 1.2nF, n22 stands for 0.22nF, while .1µ (or .1u) stands for 0.1µF capacity and so forth.

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Capacitors come in various shapes and sizes, depending on their capacity, working voltage, insulator type, temperature coefficient and other factors. All capacitors can divide in two groups: those with changeable capacity values and those with fixed capacity values.

1. The Block-Capacitors:

Commonly, capacitors are marked by a number representing the capacity value printed on the capacitor. Beside this value, number representing the maximal capacitor working voltage is mandatory, and sometimes tolerance, temperature coefficient and some other values are printed too. If, for example, capacitor mark in the scheme reads 5nF/40V, it means that capacitor with 5nF capacity value is used and that its maximal working voltage is 40v. Any other 5nF capacitor with higher maximal working voltage can be used instead, but they are as a rule larger and more expensive.

Sometimes, especially with capacitors of low capacity values, capacity may be represented with colors, similar to four-ring system used for resistors . The first two colors (A and B) represent the first two digits, third color (C) is the multiplier, fourth color (D) is the tolerance, and the fifth color (E) is the working voltage.

With disk-ceramic capacitors and tubular capacitors working voltage is not specified, because these are used in circuits with low or no DC voltage. If tubular capacitor does have five color rings on it, then the first color represents the temperature coefficient, while the other four specify its capacity value in the previously described way.

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Fig12-Capacitors

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2. ELECTROLYTIC CAPICTORS:

Electrolytic capacitors represent the special type of capacitors with fixed capacity value. Thanks to the special construction, they can have exceptionally high capacity, ranging from one to several thousand µF. They are most frequently used in transformers for leveling the voltage, in various filters, etc.

Electrolytic capacitors are polarized components, meaning that they have positive and negative connector, which is of outmost importance when connecting the capacitor into a circuit. Positive connector has to be connected to the node with a high voltage than the node for connecting the negative connector. If done otherwise, electrolytic capacitor could be permanently damaged due to electrolysis and eventually destroyed.

Explosion may also occur if capacitor is connected to voltage that exceeds its working voltage. In order to prevent such instances, one of the capacitor's connectors is very clearly marked with a + or -, while working voltage is printed on capacitor body.

Several models of electrolytic capacitors, as well as their symbols, are shown on the picture below.

Fig13: Electrolyte Capacitor

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3. CERAMIC CAPACITORS:

These capacitors are widely used for instrumentation work as transducers. They are manufactured the same way as the polystyrenes capacitors. Capacitors with different ceramic dielectrics which is usually titanium dioxide are used for a varied type instrumentation applications. The type of capacitors to be used for a particular application depends on the dielectric material used and the response at various frequencies.

One type, with dielectric constants between 6 to 16, had low dielectric loss even at frequencies as high as 100GHz. Another type, with dielectric constant of nearly 90, can be made with a wide range of temperature co-efficient which varies from +200 to 800.

Fig14: Ceramic Capacitor

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4. VARIABLE CAPACITOR:

Variable capacitors are mostly used in radio tuning circuits and they are sometimes called 'tuning capacitors'. They have very small capacitance values, typically between 100pF and 500pF (100pF = 0.0001µF). The type illustrated usually has trimmers built in (for making small adjustments - see below) as well as the main variable capacitor.

Fig15: Symbol of Variable Capacitor

Many variable capacitors have very short spindles which are not suitable for the standard knobs used for variable resistors and rotary switches. It would be wise to check that a suitable knob is available before ordering a variable capacitor.

Fig16: Variable Capacitor

Variable capacitors are not normally used in timing circuits because their capacitance is too small to be practical and the range of values available is very limited. Instead timing circuits use a fixed capacitor and a variable resistor if it is necessary to vary the time period.

CRYSTAL OSCILLATOR

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A crystal oscillator is an electronic circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency. This frequency is commonly used to keep track of time (as in quartz wristwatches), to provide a stable clock signal for digital integrated circuits, and to stabilize frequencies for radio transmitters and receivers. The most common type of piezoelectric resonator used is the quartz crystal, so oscillator circuits designed around them were called "crystal oscillators".

OPERATION:

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A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions.

Almost any object made of an elastic material could be used like a crystal, with appropriate transducers, since all objects have natural resonant frequencies of vibration. For example, steel is very elastic and has a high speed of sound. It was often used in mechanical filters before quartz. The resonant frequency depends on size, shape, elasticity, and the speed of sound in the material. High-frequency crystals are typically cut in the shape of a simple, rectangular plate. Low-frequency crystals, such as those used in digital watches, are typically cut in the shape of a tuning fork. For applications not needing very precise timing, a low-cost ceramic resonator is often used in place of a quartz crystal.

When a crystal of quartz is properly cut and mounted, it can be made to distort in an electric field by applying a voltage to an electrode near or on the crystal. This property is known as piezoelectricity. When the field is removed, the quartz will generate an electric field as it returns to its previous shape, and this can generate a voltage. The result is that a quartz crystal behaves like a circuit composed of an inductor, capacitor and resistor, with a precise resonant frequency. (see RLC circuit).

Quartz has the further advantage that its elastic constants and its size change in such a way that the frequency dependence on temperature can be very low. The specific characteristics will depend on the mode of vibration and the angle at which the quartz is cut (relative to its crystallographic axes).[5] Therefore, the resonant frequency of the plate, which depends on its size, will not change much, either. This means that a quartz clock, filter or oscillator will remain accurate. For critical applications the quartz oscillator is mounted in a temperature-controlled container, called a crystal oven, and can also be mounted on shock absorbers to prevent perturbation by external mechanical vibrations.Quartz timing crystals are manufactured for frequencies from a few tens of kilohertz to tens of megahertz. More than two billion (2×109) crystals are manufactured annually. Most are small devices for consumer devices such as wristwatches, clocks, radios, computers, and cell phones. Quartz crystals are also found inside test and measurement equipment, such as counters, signal generators, and oscilloscopes.

RELAY

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A relay is an electrical switch that opens and closes under the control of another electrical circuit. In the original form, the switch is operated by an electromagnet to open or close one or many sets of contacts. It was invented by Joseph Henry in 1835. Because a relay is able to control an output circuit of higher power than the input circuit, it can be considered to be, in a broad sense, a form of an electrical amplifier.

Fig17: Relay

Relay – Operation:

When a current flows through the coil, the resulting magnetic field attracts an armature that is mechanically linked to a moving contact. The movement either makes or breaks a connection with a fixed contact. When the current is switched off, the armature is usually returned by a spring to its resting position. Latching relays exist that require operation of a second coil to reset the contact position.

By analogy with the functions of the original electromagnetic device, a solid-state relay operates a thyristor or other solid-state switching device with a transformer or light-emitting diode to trigger it.

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SA simple electromagnetic relay, such as the one taken from a car in the first picture, is an adaptation of an electromagnet. It consists of a coil of wire surrounding a soft iron core, an iron yoke, which provides a low reluctance path for magnetic flux, a moveable iron armature, and a set, or sets, of contacts; two in the relay pictured. The armature is hinged to the yoke and mechanically linked to a moving contact or contacts. It is held in place by a spring so that when the relay is de-energized there is an air gap in the magnetic circuit. In this condition, one of the two sets of contacts in the relay pictured is closed, and the other set is open. Other relays may have more or fewer sets of contacts depending on their function. The relay in the picture also has a wire connecting the armature to the yoke. This ensures continuity of the circuit between the moving contacts on the armature, and the circuit track on the Printed Circuit Board (PCB) via the yoke, which is soldered to the PCB.

When an electric current is passed through the coil, the resulting magnetic field attracts the armature and the consequent movement of the movable contact or contacts either makes or breaks a connection with a fixed contact. If the set of contacts was closed when the relay was de-energized, then the movement opens the contacts and breaks the connection, and vice versa if the contacts were open. When the current to the coil is switched off, the armature is returned by a force, approximately half as strong as the magnetic force, to its relaxed position. Usually this force is provided by a spring, but gravity is also used commonly in industrial motor starters. Most relays are manufactured to operate quickly. In a low voltage application, this is to reduce noise. In a high voltage or high current application, this is to reduce arcing.

If the coil is energized with DC, a diode is frequently installed across the coil, to dissipate the energy from the collapsing magnetic field at deactivation, which would otherwise generate a voltage spike dangerous to circuit components. Some automotive relays already include that diode inside the relay case. Alternatively a contact protection network, consisting of a capacitor and resistor in series, may absorb the surge. If the coil is designed to be energized with AC, a small copper ring can be crimped to the end of the solenoid. This "shading ring" creates a small out-of-phase current, which increases the minimum pull on the armature during the AC cycle.

By analogy with the functions of the original electromagnetic device, a solid-state relay is made with a thyristor or other solid-state switching device. To achieve electrical isolation an opt coupler can be used which is a light-emitting diode (LED) coupled with a photo transistor.

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RESISTORS

Resistor is one of the most common and simple parts used in electronics. So, what is a resistor? Why are they so useful? A resistor is anything that resists the flow of electricity. Now that is pretty broad isn't it? Pretty much everything resists the flow of electricity, except for super conductors, however "resistor" generally applies to a component that looks something like this.]

Fig18: Resistors

OHM:

What is an ohm? Just like voltage or amperage, ohm is a unit. Ohm is used to measure how much a resistor resists the flow of electricity. The higher the rating the more it resists. Just like the hose, the more bends, or the tighter the bend, the more it resists the water. In this tutorial I use a LED as an example for the resistor. Exactly what an LED is will be covered in a later tutorial, for now all you need to know it that it is a type of light bulb. They are found in all sorts of electronics. They are commonly used to show that something is on, and are normally green or red.

OHM’S LAW:

You may have heard about this before in school, the famous equation V=IR. This is very important when working with resistors. Using this formula you can find out how much current (amperage) will flow though a resistor at a set voltage. For this you want to use a variation of the formula (solve for I, I stands for current) I=V/R.

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So why would I ever need this? Here is a very common example, you have a nice LED (Light Emitting Diode) and you want to use 5V to power it. If you decided to connect 5V directly to the LED then your LED might last for a second or two, it would then turn a black color and stop working, they also smell horrible, of course I have never done this :).

So how can you stop this? Well the title of this tutorial gives it away, a resistor! The average LED takes around 35mA of current and a red LED has a forward voltage of around 1.7V, the voltage it takes to make it light up. That means that it uses 1.7V*0.035A=~0.06W. Now we need to know how many amps we need at 5V to equal 0.06W. First we divide 0.06W by 5V = ~0.012A. Well what this means is that if we can power the LED with 5V and 12mA then it won't burn out. To limit the amount of current down to 12mA we need a resistor, but how many ohms? We use another variation of Ohm's Law R=V/I, R=5V/0.012A. We need a resistor with the value of around 417ohms for this LED.

Now I commonly use 220ohm resistors with LED and most can take it. I have yet to burn one out with a 220ohm resistor at 5V. Just to be sure let’s find out how much current will flow though a 220ohm resistor at 5V. In this example we know R and V so we solve for I, I=5V/220ohm. approximately 23mA, but wait that is not through the resistor. When something (the LED) uses more power than provided (providing 23mA when 35mA are needed) the voltage will drop and the current will increase. That is why we need to calculate the wattage, W=VI. 5V*0.023A=0.115W, now how much current will flow if the voltage is 1.7V? W/V=I 0.115W/1.7V=~0.07A or 70mA.

I know what you are thinking, "OK, do you really do all this for a LED?" honestly, no, but that is because 220ohms is usually safe, but for things like high power LED or LED in series/parallel, I do.

What's the value?

Resistors are measured in ohms as you probably figured out by now, but how do we know how many ohms the resistor is? As you can see in the picture below resistors have colored bands on them. Those colors tell you what the value of the resistor is and the tolerance. Here is close up of a 220ohm resistor.

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Each color represents a number.

The first two bands are the 1st and 2nd digits. In this case the two red bands on the right. So that makes red or 22. The next band is the multiplier. You add that many 0s to the end of your original number. On this one it is brown, 1. That means our resistor is 220ohm. If it were a black stripe it would be 22ohm or if it were another red strip it would be 2200ohm or 2.2K ohm.

Wait! What is that other band for? This band tells you the tolerance. Gold is +-5%, silver is +-10%, and if it is missing it is +-20%. In our case it is gold so the value of the resistor is 220ohm+-5% or 209-231ohm.

COLOR DIGIT MULTIPLIER TOLERANCE VOLTAGE

Black 0 x 1 pF ±20% Brown 1 x 10 pF ±1% Red 2 x 100 pF ±2% 250V Orange 3 x 1 nF ±2.5% Yellow 4 x 10 nF 400V Green 5 x 100 nF ±5% Blue 6 x 1 µF Violet 7 x 10 µF Grey 8 x 100 µF White 9 x 1000 µF ±10%

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VOLTAGE DIVIDER

Another fantastic use of resistor, a voltage divider does just that, it divides voltage. A common voltage divider looks like this.

Fig19: Circuit diagram of Voltage Divider

The output is equal to Vo=V*[R2/(R1+R2)]. If R1=R2 and VDD=5V then:5*[x/(x+x)]5*[x/2x]5*1/2VO=2.5VThe voltage divider is useful for reading a voltage with a microcontroller that is over the maximum voltage it can read. I have used a voltage divider to read 0-400V with a microcontroller running at 5V (meaning it can't read anything over 5V with out damage).

The problem with voltage dividers is if you draw any current from the output then the voltage will drop. If you are using a microcontroller to read the voltage then the amount of current it draws from it is so little that the drop is not noticeable. The higher value you use for the resistors the more it is affected by current draw. For example if you used the ratio described above a 1ohm to 1ohm divider would be a lot less effected by current draw then a 1M ohm to 1M ohm (1M ohm = 1,000,000ohms). However the voltage divider draws power and that is calculated with Ohm's Law, I=V/(R1+R2). So using 1ohm for R1 and R2 with VDD=5V you would draw 2.5A! However with 1M ohm for each you would draw only 0.0000025A! For most cases I use 10K ohm to 100K ohm for a nice balance.

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THERMISTOR

A thermistor is a type of resistor whose resistance varies with temperature. The word is a portmanteau of thermal and resistor. Thermistor are widely used as inrush current limiters, temperature sensors, self-resetting over current protectors, and self-regulating heating elements.

Thermistor differ from resistance temperature detectors (RTD) in that the material used in a thermistor is generally a ceramic or polymer, while RTDs use pure metals. The temperature response is also different; RTDs are useful over larger temperature ranges, while thermistor typically achieve a higher precision within a limited temperature range.

Fig20: Thermister

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BASIC OPERATION:

Assuming, as a first-order approximation, that the relationship between resistance and temperature is linear, then:ΔR = kΔT

Where

ΔR = change in resistanceΔT = change in temperaturek = first-order temperature coefficient of resistance

Thermistor can be classified into two types depending on the sign of k. If k is positive, the resistance increases with increasing temperature, and the device is called a positive temperature coefficient (PTC) thermistor, or posistor. If k is negative, the resistance decreases with increasing temperature, and the device is called a negative temperature coefficient (NTC) thermistor. Resistors that are not thermistor are designed to have a k as close to zero as possible, so that their resistance remains nearly constant over a wide temperature range.The current is measured using an ammeter. Over large changes in temperature, calibration is necessary. Over small changes in temperature, if the right semiconductor is used, the resistance of the material is linearly proportional to the temperature. There are many different semiconducting thermistor with a range from about 0.01 Kelvin to 2,000 Kelvin (-273.14°C to 1,700°C).

Most PTC thermistor are of the "switching" type, which means that their resistance rises suddenly at a certain critical temperature. The devices are made of a doped polycrystalline ceramic containing barium titanate (BaTiO3) and other compounds. The dielectric constant of this ferroelectric material varies with temperature. Below the Curie point temperature, the high dielectric constant prevents the formation of potential barriers between the crystal grains, leading to a low resistance. In this region the device has a small negative temperature coefficient. At the Curie point temperature, the dielectric constant drops sufficiently to allow the formation of potential barriers at the grain boundaries, and the resistance increases sharply. At even higher temperatures, the material reverts to NTC behavior. The equations used for modeling this behavior were derived by W. Heywang and G. H. Jonker in the 1960s.

Another type of PTC thermistor is the polymer PTC, which is sold under brand names such as "Polyswitch" "Semi fuse", and "Multifuse". This consists of a slice of plastic with carbon grains embedded in it. When the plastic is cool, the carbon grains are all in contact with each other, forming a conductive path through the device. When the

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plastic heats up, it expands, forcing the carbon grains apart, and causing the resistance of the device to rise rapidly. Like the BaTiO3 thermistor, this device has a highly nonlinear resistance/temperature response and is used for switching, not for proportional temperature measurement.

Yet another type of thermistor is a Sinister, a thermally sensitive silicon resistor. Sinister are similarly constructed and operate on the same principles as other thermistor, but employ silicon as the semi conductive component material.

APPLICATIONS OF THERMISTORS:

NTC thermistor is used as resistance thermometers in low-temperature measurements of the order of 10 K.NTC thermistor can be used as inrush-current limiting devices in power supply circuits. They present a higher resistance initially which prevents large currents from flowing at turn-on, and then heat up and become much lower resistance to allow higher current flow during normal operation. This thermistor is usually much larger than measuring type thermistor, and is purposely designed for this application.NTC thermistor is regularly used in automotive applications. For example, they monitor things like coolant temperature and/or oil temperature inside the engine and provide data to the ECU and, indirectly, to the dashboard.Thermistor is also commonly used in modern digital thermostats and to monitor the temperature of battery packs while charging.

VARIABLE RESISTORS:

Construction:Variable resistors consist of a resistance track with connections at both ends and a wiper which moves along the track as you turn the spindle. The track may be made from carbon, cermets (ceramic and metal mixture) or a coil of wire (for low resistances). The track is usually rotary but straight track versions, usually called sliders, are also available.

Variable resistors may be used as a rheostat with two connections (the wiper and just one end of the track) or as a potentiometer with all three connections in use. Miniature versions called presets are made for setting up circuits which will not require further adjustment.

Variable resistors are often called potentiometers in books and catalogues. They are specified by their maximum resistance, linear or logarithmic track, and their physical size. The standard spindle diameter is 6mm.

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The resistance and type of track are marked on the body: 4K7 LIN means 4.7 k linear track. 1M LOG means 1 M logarithmic track.

Some variable resistors are designed to be mounted directly on the circuit board, but most are for mounting through a hole drilled in the case containing the circuit with stranded wire connecting their terminals to the circuit board.Linear (LIN) and Logarithmic (LOG) tracksLinear (LIN) track means that the resistance changes at a constant rate as you move the wiper. This is the standard arrangement and you should assume this type is required if a project does not specify the type of track. Presets always have linear tracks.

Logarithmic (LOG) track means that the resistance changes slowly at one end of the track and rapidly at the other end, so halfway along the track is not half the total resistance! This arrangement is used for volume (loudness) controls because the human ear has a logarithmic response to loudness so fine control (slow change) is required at low volumes and coarser control (rapid change) at high volumes. It is important to connect the ends of the track the correct way round, if you find that turning the spindle increases the volume rapidly followed by little further change you should swap the connections to the ends of the track.

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Rheostat

This is the simplest way of using a variable resistor. Two terminals are used: one connected to an end of the track, the other to the moveable wiper. Turning the spindle changes the resistance between the two terminals from zero up to the maximum resistance.

Rheostats are often used to vary current, for example to control the brightness of a lamp or the rate at which a capacitor charges.

If the rheostat is mounted on a printed circuit board you may find that all three terminals are connected! However, one of them will be linked to the wiper terminal. This improves the mechanical strength of the mounting but it serves no function electrically.

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.

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.

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Fig21:Variable Resistors

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LICUID CRYSTAL DISPLAY

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LIQUID CRYSTEL DISPLAY

LCD:

The LCD is a dot matrix liquid crystal display that displays alphanumeric kana (Japanese) character and symbol. The built-in controller & driver LSIs provide convenient connectivity between a dot matrix LCD and most 4 or 8 bit microprocessor or microcontroller. Here we have used 16*2 LCD. Several commands are used to operate this LCD which enables when RS (register select) is enabled.In recent years the LCD is finding wide spread use to replace LEDs .this is due to the following reasons:1. The declining prices of LCDs.2. The ability to display numbers, characters and graphics.3. Easy of programming for characters and graphics.4. Incorporation of a refreshing controller into the LCD, thereby relieving the CPU of the task of refreshing the LCD.

Fig22: 2A general purpose alphanumeric LCD, with two lines of 16 characters.

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Fig23: Reflective twisted pneumatic liquid crystal display

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WORKING: A liquid crystal display (LCD) is a thin, flat electronic visual display that uses the light modulating properties of liquid crystals (LCs). LCs does not emit light directly. They are used in a wide range of applications including: computer monitors, television, instrument panels, aircraft cockpit displays, signage, etc. They are common in consumer devices such as video players, gaming devices, clocks, watches, calculators, and telephones. LCDs have displaced cathode ray tube (CRT) displays in most applications. They are usually more compact, lightweight, portable, less expensive, more reliable, and easier on the eyes. They are available in a wider range of screen sizes than CRT and plasma displays, and since they do not use phosphors, they cannot suffer image burn-in.

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Fig24: Working of LCD

They are used in a wide range of applications, including computer monitors, television, instrument panels, aircraft cockpit displays, signage, etc. They are common in consumer devices such as video players, gaming devices, clocks, watches, calculators, and telephones. LCDs have displaced cathode ray tube (CRT) displays in most applications. They are usually more compact, lightweight, portable, less expensive, more reliable, and easier on the eyes. They are available in a wider range of screen sizes than CRT and plasma displays, and since they do not use phosphors, they cannot suffer image burn-in.

LCDs are more energy efficient and offer safer disposal than CRTs. Its low electrical power consumption enables it to be used in battery-powered electronic equipment. It is an electronically-modulated optical device made up of any number of pixels filled with liquid crystals and arrayed in front of a light source (backlight) or reflector to produce images in color or monochrome. The earliest discovery leading to the development of LCD technology, the discovery of liquid crystals, dates from 1888. By 2008, worldwide sales of televisions with LCD screens had surpassed the sale of CRT units. LCDs with a small number of segments, such as those used in digital watches and pocket calculators, have individual electrical contacts for each segment. An external dedicated circuit supplies an electric charge to control each segment. This display structure is unwieldy for more than a few display elements.

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Small monochrome displays such as those found in personal organizers, electronic weighing scales, older laptop screens, and the original Nintendo Game Boy have a passive-matrix structure employing super-twisted nematic (STN) or double-layer STN (DSTN) technology (the latter of which addresses a color-shifting problem with the former), and color-STN (CSTN) in which color is added by using an internal filter. Each row or column of the display has a single electrical circuit. The pixels are addressed one at a time by row and column addresses. This type of display is called passive-matrix addressed because the pixel must retain its state between refreshes without the benefit of a steady electrical charge. As the number of pixels (and, correspondingly, columns and rows) increases, this type of display becomes less feasible. Very slow response times and poor contrast are typical of passive-matrix addressed LCDs.

LCD pin description:

PIN SYMBOL I/O DESCRIPTION1 Vss - Ground2 Vcc - +5v power supply 3 VEE - Power supply to control contrast4 RS I RS=0 to select command resistor.

RS =1 to select data resistor5 R/W I R/W=0 for write ,R/W=1 for read6 E I/O Enable7 DB0 I/O The 8 bit data bus8 DB1 I/O The 8 bit data bus9 DB2 I/O The 8 bit data bus10 DB3 I/O The 8 bit data bus11 DB4 I/O The 8 bit data bus

12 DB5 I/O The 8 bit data bus13 DB6 I/O The 8 bit data bus14 DB7 I/O The 8 bit data bus

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PINOUT:

Vss (Ground)VCC (5V)Contrast (use a potentiometer for variable contrast, or just connect to GND)Register Select (RS), 0 = command write, 1 = data writeRead/Write (R/W), 0 = write to display, 1 = read from displayEnable (EN) - used to clock in dataDB0 (not used in 4-bit mode) - LSbDB1 (not used in 4-bit mode)DB2 (not used in 4-bit mode)DB3 (not used in 4-bit mode)DB4 - LSb in 4-bit modeDB5DB6DB7 - MSbBacklight + (5V)Backlight - (GND)

4-bit and 8-bit modes:

An HD44780 LCD can be operated in two different modes: 4-bit mode and 8-bit mode. In 8-bit mode, pins 7-14 of the LCD are connected to eight I/O pins on the microcontroller; while in 4-bit mode, pins 11-14 on the LCD are connected to four I/O pins on the microcontroller. The advantage to operating in 8-bit mode is that the programming is a bit simpler and data can be updated more quickly. The obvious reason to operate in 4-bit mode is to save four I/O pins on the PIC microcontroller.

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MICRO CODE

// LCD module connections

sbit LCD_RS at RB4_bit;sbit LCD_EN at RB5_bit;sbit LCD_D4 at RB0_bit;sbit LCD_D5 at RB1_bit;sbit LCD_D6 at RB2_bit;sbit LCD_D7 at RB3_bit;

sbit LCD_RS_Direction at TRISB4_bit;sbit LCD_EN_Direction at TRISB5_bit;sbit LCD_D4_Direction at TRISB0_bit;sbit LCD_D5_Direction at TRISB1_bit;sbit LCD_D6_Direction at TRISB2_bit;sbit LCD_D7_Direction at TRISB3_bit;// End LCD module connections

void main() {

int i=0; char text[]="16x2 LCD Disply";

ADCON1=0x06; // Configure all input and output in to digital Lcd_init(); // Initialize LCD Lcd_Cmd(_LCD_CLEAR); // Clear display Lcd_Cmd(_LCD_CURSOR_OFF); // Cursor off

do { Lcd_Out(1,1," Electronic "); //Write text on raw 1 Lcd_Out(2,1," Work Space "); //Write text on raw 1 Delay_ms(1000); Lcd_Cmd(_LCD_CLEAR); // Clear display for(i=0;i<16;i++){

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Lcd_Chr(1,i+1,text[i]); //Display character by character Delay_ms(500); } } while (1);}

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POWER SUPPLIES

Types of Power Supply:

There are many types of power supply. Most are designed to convert high voltage AC mains electricity to a suitable low voltage supply for electronics circuits and other devices. A power supply can by broken down into a series of blocks, each of which performs a particular function.

For example a 5V regulated supply:

Each of the blocks is described in more detail below:

Transformer - steps down high voltage AC mains to low voltage AC. Rectifier - converts AC to DC, but the DC output is varying. Smoothing - smooths the DC from varying greatly to a small ripple. Regulator - eliminates ripple by setting DC output to a fixed voltage.

Dual Supplies:

Some electronic circuits require a power supply with positive and negative outputs as well as zero volts (0V). This is called a 'dual supply' because it is like two ordinary supplies connected together as shown in the diagram.

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Dual supplies have three outputs, for example a ±9V supply has +9V, 0V and -9V outputs.

Transformer only:

The low voltage AC output is suitable for lamps, heaters and special AC motors. It is not suitable for electronic circuits unless they include a rectifier and a smoothing capacitor.

Transformer + Rectifier:

Fig25:-Circuit of Bridge Rectifier

The varying DC output is suitable for lamps, heaters and standard motors. It is not suitable for electronic circuits unless they include a smoothing capacitor.

Transformer + Rectifier + Smoothing:

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The smooth DC output has a small ripple. It is suitable for most electronic circuits.

Transformer + Rectifier + Smoothing + Regulator:

The regulated DC output is very smooth with no ripple. It is suitable for all electronic circuits.

TRANSFORMER

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.

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Transformercircuit symbol

Fig26:-Transformer

Step-up transformers increase voltage, step-down transformers reduce voltage. Most power supplies use a step-down transformer to reduce the dangerously high mains voltage (230V in UK) to a safer low voltage.

The input coil is called the primary and the output coil is called the secondary. There is no electrical connection between the two coils; instead they are linked by an alternating magnetic field created in the soft-iron core of the transformer. The two lines in the middle of the circuit symbol represent the core.

Transformers waste very little power so the power out is (almost) equal to the power in. Note that as voltage is stepped down current is stepped up.

The ratio of the number of turns on each coil, called the turns ratio, determines the ratio of the voltages. A step-down transformer has a large number of turns on its primary (input) coil which is connected to the high voltage mains supply, and a small number of turns on its secondary (output) coil to give a low output voltage. s

turns ratio =Vp

=sNp

andpower out = power in

Vs Ns Vs × Is = Vp × Ip

Vp = primary (input) voltageNp = number of turns on primary coilIp  = primary (input) current

   Vs = secondary (output) voltageNs = number of turns on secondary coilIs  = secondary (output) current

RECTIFIER

There are several ways of connecting diodes to make a rectifier to convert AC to DC. The bridge   rectifier is the most important and it produces full-wave varying DC. A full-wave rectifier can also be made from just two diodes if a centre-tap transformer is used, but this method is rarely used now that diodes are cheaper. A single   diode can be used as a rectifier but it only uses the positive (+) parts of the AC wave to produce half-wave varying DC.

Bridge rectifier:

A bridge rectifier can be made using four individual diodes, but it is also available in special packages containing the four diodes required. It is called a full-wave rectifier

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because it uses all the AC wave (both positive and negative sections). 1.4V is used up in the bridge rectifier because each diode uses 0.7V when conducting and there are always two diodes conducting, as shown in the diagram below. Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages). Please see the Diodes page for more details, including pictures of bridge rectifiers.

Bridge rectifierAlternate pairs of diodes conduct, changing

overthe connections so the alternating directions ofAC are converted to the one direction of DC.

Output: full-wave varying DC(using all the ACs wave)

Single diode rectifier:

A single diode can be used as a rectifier but this produces half-wave varying DC which has gaps when the AC is negative. It is hard to smooth this sufficiently well to supply electronic circuits unless they require a very small current so the smoothing capacitor does not significantly discharge during the gaps. Please see the Diodes page for some examples of rectifier diodes.

Single diode rectifierOutput: half-wave varying DC(using only half the AC wave)

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Smoothing:

Smoothing 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 diagram shows the unsmoothed varying DC (dotted line) and the smoothed DC (solid line). The capacitor charges quickly near the peak of the varying DC, and then discharges as it supplies current to the output.

Note that smoothing significantly increases the average DC voltage to almost the peak value (1.4 × RMS value). For example 6V RMS AC is rectified to full wave DC of about 4.6V RMS (1.4V is lost in the bridge rectifier), with smoothing this increases to almost the peak value giving 1.4 × 4.6 = 6.4V smooth DC.

Smoothing is not perfect due to the capacitor voltage falling a little as it discharges, giving a small ripple voltage. For many circuits a ripple which is 10% of the supply voltage is satisfactory and the equation below gives the required value for the smoothing capacitor. A larger capacitor will give fewer ripples. The capacitor value must be doubled when smoothing half-wave DC.

C = smoothing capacitance in farads (F)Io  = output current from the supply in amps (A)Vs = supply voltage in volts (V), this is the peak value of the unsmoothed DCf    = frequency of the AC supply in hertz (Hz), 50Hz in the UK

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Regulator

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

Many of the fixed voltage regulator ICs have 3 leads and look like power transistors, such as the 7805 +5V 1A regulator shown on the right. They include a hole for attaching a heatsink if necessary.

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DIODES

Circuit symbol:  

Example:

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Function:

Diodes allow electricity to flow in only one direction. The arrow of the circuit symbol shows the direction in which the current can flow. Diodes are the electrical version of a valve and early diodes were actually called valves.

Forward Voltage Drop:

Electricity uses up a little energy pushing its way through the diode, rather like a person pushing through a door with a spring. This means that there is a small voltage across a conducting diode, it is called the forward voltage drop and is about 0.7V for all normal diodes which are made from silicon. The forward voltage drop of a diode is almost constant whatever the current passing through the diode so they have a very steep characteristic (current-voltage graph).

Reverse Voltage:

When a reverse voltage is applied a perfect diode does not conduct, but all real diodes leak a very tiny current of a few µA or less. This can be ignored in most circuits because it will be very much smaller than the current flowing in the forward direction. However, all diodes have a maximum reverse voltage (usually 50V or more) and if this is exceeded the diode will fail and pass a Large current in the reverse direction, This is called breakdown.

Ordinary diodes can be split into two types: Signal diodes which pass small

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current of 100mA or less and Rectifier diodes which can pass large currents.

In addition there are LEDs (which have their own page) and Zener diodes (at the bottom of this page).

Zener diodes:

Example:

Circuit symbol:

a = anode, k = cathode

Zener diodes are used to maintain a fixed voltage. They are designed to 'breakdown' in a reliable and non-destructive way so that they can be used in reverse to maintain a fixed voltage across their terminals. The diagram shows how they are connected, with a resistor in series to limit the current.

Zener diodes can be distinguished from ordinary diodes by their code and breakdown voltage which are printed on them. Zener diode codes begin BZX... or BZY... Their breakdown voltage is printed with V in place of a decimal point, so 4V7 means 4.7V for example.

Zener diodes are rated by their breakdown voltage and maximum power:

The minimum voltage available is 2.7V. Power ratings of 400mW and 1.3W are common.

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PCB DESIGNING

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PROCEDURE OF PCB MAKING

Cut the board

Printing the mask patternEtchingApply the fluxMake the holeApply the solder-resist (option)Soldering

CUTTING:

The PCB must be cut according to the size of the circuit to make. Also, it is mainly related with the size of the equipment to incorporate the PCB into.

When cutting the positive exposure printed board, the attention is necessary. The sensitizer which reacts to the ultraviolet rays is painted to the positive exposure printed board. Because it is, it is necessary to cut in the place which isn't exposed to the ultraviolet rays when cutting the board.

I cover the paper to the thing except the cut part, and it stops with the cellophane tape and cut it. When cutting, I make the sensitizer surface the upward. This is to prevent from being hurt in the sensitizer surface. It is necessary to be careful of the scraps which is included among the paper, too. This time, I used the aluminum packing of the printed board as the cover.

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FIXATION OF THE MASK PATTERN:

Make the sensitizer surface of the positive exposure printed board the upward and pile the film of the mask pattern on it.Adjust the position of the mask pattern carefully and fix it with the glass of the clamp equipment while careful so as not for the mask to shift.

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PRINT OF THE MASK PATTERN:

Print the mask pattern using the fluorescence light.Set the clamp equipment which set the printed board, the mask under the fluorescence light.The ultraviolet rays in the sun are very strong and in the case in the daytime, the exposure completes as much as the 2 minutes.The ultraviolet rays of the fluorescence light are weak. About 20 minutes are necessary to expose.When the exposiong time is short, the long development time is necessary.

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DEVELOPMENT OF THE SENSITIZER:

Put the board that the print of the mask pattern was ended in the developer of the sensitizer and it removes the unnecessary sensitizer.The part which the ultraviolet rays lashed dissolves in the developer and the copper foil appears.The part which the ultraviolet rays didn't lash doesn't dissolve in the developer and is left as the mask pattern.This mask pattern doesn't dissolve in the etchant.

This time, in the development time, it was to be in the about 3 minutes.In the development time, it changes with the size of the printed board, the area which dissolves the sensitizer.

Check the mask pattern carefully at this point.When the mask pattern is broken, repair in resist pen.When the pattern contacts next, shave with the cutter knife.

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ETCHING:

Put the etchant in the etching equipment and set the temperature.As for the etchant, 40-43 degC are the suitable temperature.Don't raise more than 45 degC.

Measure the temperature with the stick thermometer.

Send the air to the liquid tank and stir the etchant.

To hang the printed board in the etchant, make a 1-mm hole in the one of the corners of the printed board.Pass the titanium wire through the hole and hang it from the top of the liquid tank.

The small hole is open to the lid of the liquid tank, too.Adjust in the length of the titanium wire to become the middle of the liquid tank.

Hang the printed board into the etchant.Because the etching time depends on the size of the printed board, the quantity of the copper to dissolve, draw up the printed board sometimes and confirm it.The area of the copper to dissolve becomes long in the time when wide.

This time, it was to be in the about 8 minutes.

Because the copper in the part of the mask has melted when doing the long time etching, it is necessary to confirm briskly.

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Be careful so as not for there to be an etchant in the others when drawing up the printed board to confirm the etching condition.

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REMOVAL OF THE MASK:

You can make the hole before the mask removal, too. When making the such procedure, in the hole making, you don't wait for the flux dryness.The printed board that the etching was ended has the sensitizer for the mask.

If there is necessity, it makes the size of the printed board the size of the last before removing the mask.

The following way is simple to remove the sensitizer.Irradiate the ultraviolet rays again to the printed board that the etching ended and that it washed in the water.(A little long time)Then, put the printed board in the developer again and dissolve the sensitizer.

In this way, you can remove the sensitizer even if you don't scour off.As the other way, it is possible to remove using the resist solvent, too.Remove the part which was corrected with the resist pen and so on in this way.There is a way of wiping up after spraying the absolute alcohol, too.You do until the copper foil in all wiring parts becomes beautiful.

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APPLICATION OF THE FLUX:

The copper foil of the printed wiring which removed the mask becomes the condition that it is easy for the surface to oxidize.When leaving just as it is, the oxidation discolors blackly of the surface of the copper foil and soldering becomes difficult.To prevent from the oxidation of the copper foil, the flux must be applied.

The flux is the liquid which has the stickiness little.It is the knack that, when painting, it paints quickly. The stickiness of the flux becomes strong when painting slowly and it isn't possible to paint it beautifully.

After painting the flux, it makes dry up sufficiently.By applying the flux, soldering, too, becomes easy.

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MAKE THE HOLES:

Make the holes which pass the lead line of the parts through the printed board.In case of the electronic parts of the resistors, the capacitors and so on, it uses the drill bit of the 0.6-mm.For the lead line of the case of the high frequency transformer, it uses the 1-mm drill bit.It is easily opened when using the electric mini drill to make a hole of 0.6 mm, 1.0 mm.

As for the hole to fasten the printed board to the case and so on, it uses the 3.2-mm drill bit.Make the hole with the appropriate size in the size of each part, the screw kind.

The hole to have opened with the drill becomes the condition that the perimeter is sharp(the burr). Use the bit of the a little big drill to remove this.In case of 0.6 mm, it is 2.5 mm.In case of 1.0 mm, it is 2.5 mm.In case of 3.2 mm, it is 6.0 mm.It is possible to remove if having the bit of the drill with the hand and doing it the 1-twice lightly.

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SOLDERING

Fig27:- Soldring

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Mount the parts and assemble the circuit into the complete PCB.Solder the parts to the PCB, while seeing parts mounting drawing.

To be careful at this time is to install from the part with the height which is as short as possible. When having put the parts with the tall earlier, it becomes difficult to install the part with the short.

I think that the following order is proper.

Jumpers Resistors Diode- Ceramic capacitors - ICs - Crystal oscillator (Xtal) -Transistor - Electrolytic capacitors -Transformers for the use of high frequency relays.

STEP OF SOLDERING:

Rub the PCB with a steel wool and the PCB is ready

Start with the smallest components working up to the taller components, soldering any interconnecting wires last.

Place the component into the board, making sure it goes in the right way around and the part sits flush against the board.

Bend the leads slightly to secure the part.

Make sure the soldering iron has warmed up and if necessary use the damp sponge to clean the tip.

sPlace the soldering iron on the pad.

Using your free hand feed the end of the solder onto the pad (top picture).

Remove the solder, then the soldering iron.

Leave the join to cool for a few seconds.

Using a pair of cutters trim the excess component lead (middle picture). 

If you make a mistake heat up the join with the soldering iron, whilst the solder is molten, place the tip of your solder extractor by the solder and push the button (bottom picture).

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SOFTWARE

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SOFTWARE

The firmware for this project is developed with Micro Pro for PIC compiler. The link to download the compiled HEX code is provided at the bottom of this section. The configuration bits for PIC16F688 are

Oscillator -> Internal RC No Clock Watchdog Timer -> Off Power Up Timer -> On Master Clear Enable -> Enabled Code Protect -> Off Data EE Read Protect -> Off Brown Out Detect -> BOD Enabled, SBOREN Disabled Internal External Switch over Mode -> Enabled Monitor Clock Fail-Safe -> Enabled

/* Digital Thermometer using PIC16F72 and LM35 Internal Oscillator @ 4MHz, MCLR Enabled, PWRT Enabled, WDT OFF Copyright @ Rajendra Bhatt November 8, 2010 */

// LCD module connectionssbit LCD_RS at RC4_bit;sbit LCD_EN at RC5_bit;sbit LCD_D4 at RC0_bit;sbit LCD_D5 at RC1_bit;sbit LCD_D6 at RC2_bit;sbit LCD_D7 at RC3_bit;sbit LCD_RS_Direction at TRISC4_bit;sbit LCD_EN_Direction at TRISC5_bit;sbit LCD_D4_Direction at TRISC0_bit;sbit LCD_D5_Direction at TRISC1_bit;sbit LCD_D6_Direction at TRISC2_bit;sbit LCD_D7_Direction at TRISC3_bit;// End LCD module connections// Define Messageschar message0[] = "LCD Initialized";char message1[] = "Room Temperature";// String array to store temperature value to display

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char *tempC = "000.0";char *tempF = "000.0";// Variables to store temperature valuesunsigned int tempinF, tempinC;unsigned long temp_value;void Display_Temperature() { // convert Temp to characters if (tempinC/10000) // 48 is the decimal character code value for displaying 0 on LCD tempC[0] = tempinC/10000 + 48; else tempC[0] = ' '; tempC[1] = (tempinC/1000)%10 + 48; // Extract tens digit tempC[2] = (tempinC/100)%10 + 48; // Extract ones digit // convert temp_fraction to characters tempC[4] = (tempinC/10)%10 + 48; // Extract tens digit // print temperature on LCD Lcd_Out(2, 1, tempC); if (tempinF/10000) tempF[0] = tempinF/10000 + 48; else tempF[0] = ' '; tempF[1] = (tempinF/1000)%10 + 48; // Extract tens digit tempF[2] = (tempinF/100)%10 + 48; tempF[4] = (tempinF/10)%10 + 48; // print temperature on LCD Lcd_Out(2, 10, tempF);}void main() { ANSEL = 0b00000100; // RA2/AN2 is analog input ADCON0 = 0b01001000; // Connect AN2 to S/H, select Vref=1.19V CMCON0 = 0x07 ; // Disbale comparators TRISC = 0b00000000; // PORTC All Outputs TRISA = 0b00001110; // PORTA All Outputs, Except RA3 and RA2 Lcd_Init(); // Initialize LCD Lcd_Cmd(_LCD_CLEAR); // CLEAR display Lcd_Cmd(_LCD_CURSOR_OFF); // Cursor off Lcd_Out(1,1,message0); Delay_ms(1000); Lcd_Out(1,1,message1); // Write message1 in 1st row // Print degree character Lcd_Chr(2,6,223); Lcd_Chr(2,15,223); // Different LCD displays have different char code for degree symbol // if you see greek alpha letter try typing 178 instead of 223 Lcd_Chr(2,7,'C');

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Lcd_Chr(2,16,'F'); do { temp_value = ADC_Read(2); temp_value = temp_value*1168; tempinC = temp_value/1000; tempinC = tempinC*10; tempinF = 9*tempinC/5 + 3200; Display_Temperature(); Delay_ms(1000); // Temperature sampling at 1 sec interval } while(1);}

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PROGRAM A PIC MICROCONTROLLER:

There are lots of cool hardware projects on the web. Many require you to program a microcontroller. Programming, or burning, happens when we copy software from a computer into the flash memory of a microchip. This is just like copying something to a USB flash drive, but it requires a special connection. Without the ability to burn firmware you can't build that awesome open source project -- and you can't develop your own.

Today we'll burn a PIC microcontroller from Microchip - in this case Microchip is a proper noun referring to this company. "PICs" are the brains in tons of projects -- this USB color changing light, or these analog gauges, for example.

Check out the video to see different ways to program a PIC, and read on to build your own simple JDM2 style programmer.

Basic connections:

Before we delve into the details of programming, let’s take a look at the basic connections needed to get a PIC up and running.

Vdd/Vss (power and ground):

Vdd and Vss are the labels Microchip uses to designate the positive supply and ground. Vdd is generally a 5 volt positive supply. Other names for Vdd include: Vcc, power, supply, "+", the bumpy side of the battery, and the red wire. Vss is "ground", almost always 0 volts. You'll also see ground referred to as: negative, ground, "-", gnd, the flat side of the battery, and the black wire. Most circuit boards use a ground

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plane; this means that all ground pins connect to the copper areas that remain after other wires have been routed. Ground planes are economical and environmentally friendly - copper must be chemically etched from any unfilled areas on a circuit board, this uses more acid etchants and creates a larger copper waste stream. Check out the RGB color changer circuit board to the right, the large blue area is a ground plane.

Don't forget to connect any pins marked Avdd and Avss. These pins allow you to provide a clean supply to the analog portions of the chip. Read more about routing these connections [pdf!] if you design a device that does super-duper delicate measurements with the analog to digital converter.

Each pair of Vdd/Vss or Avdd/Avss pins gets a 0.1uf capacitor (C1 in the diagram below). These are called "decoupling" capacitors because they isolate (decouple) the chip from noise in the power supply. This noise will cause wild oscillations in the circuit if left unchecked. 0.1uf capacitors should be dirt cheap, buy 100+ online to save a bundle. In practice, a capacitor should be put on every supply (Vdd) pin. If the supply and ground pins aren't next to each other, an annoying thing that happens all too often, connect one side of the capacitor as close to the supply pin as possible and the other to a common ground plane.

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VPP/MCLR/master clear and reset:

Spikes in the power supply can freeze up a PIC or cause erratic behavior. Most PICs have an MCLR function that causes a full reset when this happens. To use this function, put a 10K resistor (R1) between the power supply and the MCLR pin.

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Minimum connection example:

This gallery shows how to make the bare minimum connections for several different PIC microcontrollers.

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Programming connections:

A PIC in a bare circuit is great, but we need to get some software into it before it's useful. I always add a simple 5 pin connection to the circuit board so that the chip can be programmed without removing it from the circuit. This saves a ton of time with socketed chips, but is absolutely required for surface mount chips that can't be removed from the circuit board. This method of programming is called In-Circuit-Serial-Programming (ICSP). Even if you plan to use a socket programmer, read on to understand what connections the programmer makes to the PIC when you put it in the socket.

Vdd/Vss:

We took care of these connections earlier. The programmer MUST share a ground connection to the circuit board, and a connection to the supply voltage is generally used as well.

MCLR/VPP:

The MCLR reset pin is also used to put the PIC in programming mode. When a programmer applies the "programming voltage" (Vpp) to this pin, the chip readies itself for new firmware to be copied. Vpp varies among PIC models, but can be as high as 13 volts. If we route this pin to a header and connect a programmer, the programming voltage will go through the MCLR resistor (R1) and enter the rest of the circuit. Everything on the circuit board could be ruined by 13 volts -- a one-way valve is needed to keep the high Vpp voltage where it belongs. A small signal diode (D1) does exactly that. I usually use the common 1n4148 for this purpose.

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PROGRAMMERS

A programmer is the key to getting software into a PIC. This device physically connects your PC to a microcontroller. They vary greatly in price and complexity.

Pin wigglers:

Pin wigglers are the simplest programmers - they do little more than help delicate PC outputs switch the VPP, data, and clock voltages. These simple circuits usually "buffer" the serial or parallel port pins. PC software wiggles pins to program the PIC. This is a pretty versatile concept - software controls everything. Port wigglers are cheap, use few parts, and are easy to make.

Some examples of pin wigglers are the NOPPP and the famous JDM2. Several applications support these programmers. I like WinPIC800 because it's updated for the latest 18F PIC chips. You can also check out the older WinPIC and ICPROG.

Intelligent programmers:

Intelligent programmers are more expensive than pin wigglers. These programmers have their own microcontroller that actually programs the target chip. Microchips own USB programmers (or the Olimex clones) are an example of this type of programmer. Microcontroller experiment kits from electronics stores often come with this type of programmer - kit programmer usually only program a very narrow range of PICs.

These programmers are designed to work with specific programming software, and aren't usually supported by generic programs like WINPIC800. The programmers mentioned earlier work with the free MPLAB development application. MikroElektronika makes custom programmers that work with their own C, Pascal, and Basic compilers.

Debuggers:

Debuggers program, but they also add play and pause functions to the program code. This helps software authors hunt down annoying problems during firmware development. Like intelligent programmers, debuggers work with specific applications. Microchip's ICD2 and the exact copy at Olimex work with Microchip's MPLAB development environment and compilers. There are a few USB and serial ICD2-alikes that you can build yourself. These aren't clones because they lack some functionality of the originals, such as adjustable voltage levels.

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Building the JDM2:

In this project we'll make a programmer based on the well-worn JDM2 pin wiggler design. It uses a not so simple circuit to generate a 13 v programming voltage from a PC serial port. The original design is by Jens Dyekjaer Madsen.

Download the circuit board, and other files for this project, here. The circuit board was designed using Cadsoft Eagle. You can download a free version.

Limitations:

The JDM2 design has a few limitations:It uses a negative ground voltage to get the full +13 volts separation between ground and VPP. Make sure you disconnect any power source from the circuit before programming with a JDM2.It won't work with most laptops because the serial port voltage is too low.It probably won't work with a USB to serial adapter for the same reason.The PIC 16F line requires 13 volts on Vpp, newer 18F PICs use 12.5 volts, and the newest PICs (24F/32F) use 6 volts or less. If you want to program a newer 18F PIC with a JDM2, you should use a diode (D1) as shown in the diagram. This diode will reduce the programming voltage by about .6 volts, leaving a nearly perfect 12.4 volts.

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JDM2 STYLE PIC PROGRAMMER

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APPLICATION

1. Ideal for aquaculture applications- fish farming, grow-out operations and live fish transportation.

2. Multiple channel functionality-Up to 8 measurements simultaneously

Monitored and displayed. Up to 8 digital inputs monitored

3. Easy to read - all measurements clearly displayed on a large LCD in bold 9 mm characters.

4. Easy to use - the operator sets high and low limits for each channel as well as common alarm. One alarm light per channel and common alarm with built-in buzzer notifies operator of out-of-range conditions.

5. Adaptable for different inputs - will accept direct inputs from oxygen and temperature sensors as well as any 4-20mA input for other measurements such as pH or salinity.

6. Automatic calibration for oxygen probes- no need for look-up tables; calibrate with a few simple key strokes.

7. Data logging & PC connectivity - store data with built-in logger and download to a PC to capture and view data directly.

8. Relay output option - control solenoid valves, blowers etc. or activate external alarm. Features a 4-20 mA analog output.

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ADVANTAGES

1. This project can be used in Mechanical companies to measure various parameters of operating machines like temperature and light.

2. Can be used in green houses to control the temperature, humidity and light for the proper growth of plants. 3. Temperature monitoring and controlling action can be used in home or various halls like conference room, seminar hall to control the temperature of room.

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FUTURE DEVELOPMENT

1. We can monitor more parameters like Humidity, PH of soil, pressure, and water level and at the same time control them.

2. We can send this data to a remote location using mobile or internet. 3. We can draw graphs of variations in these parameters using computer.

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CONCLUSION

As we gone through this project we came across to many of its advanced application and use in many of the field areas like medical, farming, fishing etc.This project basically describes the basic nature of the circuit (internal).this project is very useful and being implemented in many of the companies and country so that they can make their circuit more efficient and effective. Technology always keeps on improving day by day so as the efficiency and size improves the usage of this circuit also increases. We have to ensure that we use the right technology at right time and place.

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BIBLIOGRAPHY

Besides the values and useful advice of our H.O.D. Mr.N.K. Sharma and project incharge Mrs.Parul Gupta. We referred different types of books, magazines and websites it import information in preparing the project as well as the unit.

ELECTRONIC DEVICE AND CIRCUIT THEORY BY ROBERT L. BOYLSTEAD AND LOUIS NASHELSKY

OP-AMP AND LINEAR INTEGRATED CIRCUIT BY RAMAKANT A GAYAKWAD

BASIC ELECTRONICS BY V.K. MEHTA

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REFERENCES

1. www.google.com2. www.wikipedia.com 3. www.electronicslab.com

4. www.electronics4u.com 5. www.pearsoned.co.in./muhammadalimazidi 6. David A Bell” Electronics device and circuit” oxford university press, New Delhi. 7. Jacob Milliman and Chiritos C Halkias- ”Electronics device and circuits” MC Graw Hill. 8. Robert Boylested- “Electronics device and circuits” Pearson education. 9. Dr.Bhim Rao- “Introduction to power electronics” Anamaya Publisher, New Delhi. 10.www.imagineeringezine.com

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