## Saturday, 2 December 2017

### Kirchhoffs Circuit Law

Kirchhoffs Law
In 1845, a German physicist, Gustav Kirchhoff developed a pair or set of rules or laws which deal with the conservation of current and energy within electrical circuits. These two rules are commonly known as:

Kirchhoffs Current Law, (KCL)

Kirchhoffs Voltage Law, (KVL)

Kirchhoffs Current Law, (KCL)
Kirchhoffs Current Law or KCL, states that the “total current or charge entering a junction or node is exactly equal to the charge leaving the node as it has no other place to go except to leave, as no charge is lost within the node“.
In other words the algebraic sum of ALL the currents entering and leaving a node must be equal to zero,

I(exiting) + I(entering) = 0

I2 + I4 + I5 + I6 + I3 + I1 = 0

Kirchhoffs Voltage Law, (KVL)
Kirchhoffs Voltage Law or KVL, states that “in any closed loop network, the total voltage around the loop is equal to the sum of all the voltage drops within the same loop” which is also equal to zero.
In other words the algebraic sum of all voltages within the loop must be equal to zero.

VAB+VBC+VCD+VDA=0

Sign Convention in Kirchhoff’s Rules:

1.    Move through EMF device in assumed direction of polarity (– to +):
e > 0

2.    Move through EMF device in opposite direction of polarity (+ to –):
e < 0
3.    Move through resistor in assumed direction of current (with current
arrow):
DV = –IR
4.    Move through resistor in opposite direction of current (against current
arrow):
DV = +IR
5.    Move through capacitor from + plate to – plate (with E-field):
DV = –q/C

6.    Move through capacitor from – plate to + plate (against E-field):
DV = +q/C

### Important Question 2

1. What is engineering?
The application of science to the needs of humanity and a profession in which a knowledge of the mathematical and natural sciences gained by study, experience, and practice is applied with judgment to develop ways to use economically the materials and forces of nature for the benefit of mankind.
2. What is the difference between Electronics and Electrical?
Electronics work on DC and with a voltage range of -48vDC to +48vDC. If the electronic device is plugged into a standard wall outlet, there will be a transformer inside which will convert the AC voltage you are supplying to the required DC voltage needed by the device. Examples: Computer, radio, T.V, etc...
Electric devices use line voltage (120vAC, 240vAC, etc...). Electric devices can also be designed to operate on DC sources, but will be at DC voltages above 48v. Examples: are incandescent lights, heaters, fridge, stove, etc...
3. What is Electronics?
The study and use of electrical devices that operate by controlling the flow of electrons or other electrically charged particles.
4. What is Communication?
Communication means transferring a signal from the transmitter which passes through a medium then the output is obtained at the receiver. (or)communication says as transferring of message from one place to another place called communication.

5. Define the terms?

1.Resistor: A resistor is an electrical component that limits or regulates the flow of electrical current in an electronic circuit.
2.Capacitor : A capacitor is a passive electronic component that stores energy in the form of an electrostatic field.
3.Diode: A diode is a semiconductor device with two terminals, typically allowing the flow of current in one direction only.
4.Transistor: A transistor is a semiconductor device that regulates current or voltage flow and acts as a switch or gate for electronic signals.

6. What is microprocessor?
Microprocessor is a program controlled semi conductor device (IC), which fetches, decodes and execute instructions.
7. Why is NAND gate preferred over NOR gate for fabrication?
NAND is a better gate for design than NOR because at the transistor level the mobility of electrons is normally three times that of holes compared to NOR and thus the NAND is a faster gate.

8. What are the basic units of microprocessor?
The basic units or blocks of microprocessor are ALU, an array of registers and control unit.
9. What is a bus?
Bus is a group of conducting lines that carries data, address and control signals.
10. What is a signal?
Signal is an electric current or electromagnetic field used to convey data from one place to another.
11. What is sampling?
The process of obtaining a set of samples from a continuous function of time x(t) is referred to as sampling.
12. State sampling theorem.
It states that, while taking the samples of a continuous signal, it has to be taken care that the sampling rate is equal to or greater than twice the cut off frequency and the minimum sampling rate is known as the Nyquist rate.
13. What is cut-off frequency?
The frequency at which the response is -3dB with respect to the maximum response.
14. What is pass band?
Passband is the range of frequencies or wavelengths that can pass through a filter without being attenuated.
15. What is the principle of microwave?
Microwave essentially means very short wave. The microwave frequency spectrum is usually
taken to extend from 1GHZ to 30GHZ. The main reason why we have to go in for microwave frequency for communication is that lower frequency band are congested and demand for point to point communication continue to increase. The propagation of the microwave takes place in spacewave in v

Q. What is latch up?
Latch-up pertains to a failure mechanism wherein a parasitic thyristor (such as a parasitic silicon controlled rectifier, or SCR) is inadvertently created within a circuit, causing a high amount of current to continuously flow through it once it is accidentally triggered or turned on. Depending on the circuits involved, the amount of current flow produced by this mechanism can be large enough to result in permanent destruction of the device due to electrical overstress (EOS) .
Q. What is microcontroller?
A microcontroller is a single chip that contains the processor (the CPU), non-volatile memory for the program (ROM or flash), volatile memory for input and output (RAM), a clock and an I/O control unit.
. What is the principle of microwave?
Microwave essentially means very short wave. The microwave frequency spectrum is usually taken to extend from 1GHZ to 30GHZ. The main reason why we have to go in for microwave frequency for communication is that lower frequency band are congested and demand for point to point communication continue to increase. The propagation of the microwave takes place in spacewave in view of high gain and directivity in the form of a bean and is similar to that of light.

## Monday, 20 November 2017

### Important Question 1

1. What is Electronic?
The study and use of electrical devices that operate by controlling the flow of electrons or other electrically charged particles.

2. What is communication?
Communication means transferring a signal from the transmitter which passes through a medium then the output is obtained at the receiver. (or)communication says as transferring of message from one place to another place called communication.

3. Different types of communications? Explain.
Analog and digital communication.
As a technology, analog is the process of taking an audio or video signal (the human voice) and translating it into electronic pulses. Digital on the other hand is breaking the signal into a binary format where the audio or video data is represented by a series of "1"s and "0"s.
Digital signals are immune to noise, quality of transmission and reception is good, components used in digital communication can be produced with high precision and power consumption is also very less when compared with analog signals.

4. What is sampling?
The process of obtaining a set of samples from a continuous function of time x(t) is referred to as sampling.

5. State sampling theorem.
It states that, while taking the samples of a continuous signal, it has to be taken care that the sampling rate is equal to or greater than twice the cut off frequency and the minimum sampling rate is known as the Nyquist rate.

6. What is cut-off frequency?
The frequency at which the response is -3dB with respect to the maximum response.

7. What is pass band?
Passband is the range of frequencies or wavelengths that can pass through a filter without being attenuated.

8. What is stop band?
A stopband is a band of frequencies, between specified limits, in which a circuit, such as a filter or telephone circuit, does not let signals through, or the attenuation is above the required stopband attenuation level.

9. Explain RF?
Radio frequency (RF) is a frequency or rate of oscillation within the range of about 3 Hz to 300 GHz. This range corresponds to frequency of alternating current electrical signals used to produce and detect radio waves. Since most of this range is beyond the vibration rate that most mechanical systems can respond to, RF usually refers to oscillations in electrical circuits or electromagnetic radiation.

10. What is modulation? And where it is utilized?
Modulation is the process of varying some characteristic of a periodic wave with an external signals.
Radio communication superimposes this information bearing signal onto a carrier signal.
These high frequency carrier signals can be transmitted over the air easily and are capable of travelling long distances.
The characteristics (amplitude, frequency, or phase) of the carrier signal are varied in accordance with the information bearing signal.
Modulation is utilized to send an information bearing signal over long distances.

11. What is demodulation?
Demodulation is the act of removing the modulation from an analog signal to get the original baseband signal back. Demodulating is necessary because the receiver system receives a modulated signal with specific characteristics and it needs to turn it to base-band.

12. Name the modulation techniques.
For Analog modulation--AM, SSB, FM, PM and SM
Digital modulation--OOK, FSK, ASK, Psk, QAM, MSK, CPM, PPM, TCM, OFDM

13. Explain AM and FM.
AM-Amplitude modulation is a type of modulation where the amplitude of the carrier signal is varied in accordance with the information bearing signal.
FM-Frequency modulation is a type of modulation where the frequency of the carrier signal is varied in accordance with the information bearing signal.

14. Where do we use AM and FM?
AM is used for video signals for example TV. Ranges from 535 to 1705 kHz.
FM is used for audio signals for example Radio. Ranges from 88 to 108 MHz.

15. What is a base station?
Base station is a radio receiver/transmitter that serves as the hub of the local wireless network, and may also be the gateway between a wired network and the wireless network.
16. How many satellites are required to cover the earth?
3 satellites are required to cover the entire earth, which is placed at 120 degree to each other. The life span of the satellite is about 15 years.

17. What is a repeater?
A repeater is an electronic device that receives a signal and retransmits it at a higher level and/or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances without degradation.
18. What is an Amplifier?
An electronic device or electrical circuit that is used to boost (amplify) the power, voltage or current of an applied signal.

19. Example for negative feedback and positive feedback?
Example for –ve feedback is ---Amplifiers And for +ve feedback is – Oscillators

20. What is Oscillator?
An oscillator is a circuit that creates a waveform output from a direct current input. The two main types of oscillator are harmonic and relaxation. The harmonic oscillators have smooth curved waveforms, while relaxation oscillators have waveforms with sharp changes.

21. What is an Integrated Circuit?
An integrated circuit (IC), also called a microchip, is an electronic circuit etched onto a silicon chip. Their main advantages are low cost, low power, high performance, and very small size.

22. What is crosstalk?
Crosstalk is a form of interference caused by signals in nearby conductors. The most common example is hearing an unwanted conversation on the telephone. Crosstalk can also occur in radios, televisions, networking equipment, and even electric guitars.

23. What is resistor?
A resistor is a two-terminal electronic component that opposes an electric current by producing a voltage drop between its terminals in proportion to the current, that is, in accordance with Ohm's law:
V = IR.

25. What is inductor?
An inductor is a passive electrical device employed in electrical circuits for its property of inductance. An inductor can take many forms.

26. What is conductor?
A substance, body, or device that readily conducts heat, electricity, sound, etc. Copper is a good conductor of electricity.

27. What is a semi conductor?
A semiconductor is a solid material that has electrical conductivity in between that of a conductor and that of an insulator(An Insulator is a material that resists the flow of electric current. It is an object intended to support or separate electrical conductors without passing current through itself); it can vary over that wide range either permanently or dynamically.

28. What is diode?
In electronics, a diode is a two-terminal device. Diodes have two active electrodes between which the signal of interest may flow, and most are used for their unidirectional current property.

29. What is transistor?
In electronics, a transistor is a semiconductor device commonly used to amplify or switch electronic signals. The transistor is the fundamental building block of computers, and all other modern electronic devices. Some transistors are packaged individually but most are found in integrated circuits

30. What is op-amp?
An operational amplifier, often called an op-amp , is a DC-coupled high-gain electronic voltage amplifier with differential inputs[1] and, usually, a single output. Typically the output of the op-amp is controlled either by negative feedback, which largely determines the magnitude of its output voltage gain, or by positive feedback, which facilitates regenerative gain and oscillation.

31. What is a feedback?
Feedback is a process whereby some proportion of the output signal of a system is passed (fed back) to the input. This is often used to control the dynamic behaviour of the system.

32. Advantages of negative feedback over positive feedback.
Much attention has been given by researchers to negative feedback processes, because negative feedback processes lead systems towards equilibrium states. Positive feedback reinforces a given tendency of a system and can lead a system away from equilibrium states, possibly causing quite unexpected results.

33. What is Barkhausen criteria?
Barkhausen criteria, without which you will not know which conditions, are to be satisfied for oscillations.
“Oscillations will not be sustained if, at the oscillator frequency, the magnitude of the product of the
transfer gain of the amplifier and the magnitude of the feedback factor of the feedback network ( the magnitude of the loop gain ) are less than unity”.
The condition of unity loop gain -A? = 1 is called the Barkhausen criterion. This condition implies that
A?= 1and that the phase of - A? is zero.

34. What is CDMA, TDMA, FDMA?
Code division multiple access (CDMA) is a channel access method utilized by various radio communication technologies. CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code) to allow multiple users to be multiplexed over the same physical channel. By contrast, time division multiple access (TDMA) divides access by time, while frequency-division multiple access (FDMA) divides it by frequency.
An analogy to the problem of multiple access is a room (channel) in which people wish to communicate with each other. To avoid confusion, people could take turns speaking (time division), speak at different pitches (frequency division), or speak in different directions (spatial division). In CDMA, they would speak different languages. People speaking the same language can understand each other, but not other people. Similarly, in radio CDMA, each group of users is given a shared code. Many codes occupy the same channel, but only users associated with a particular code can understand each other.

35. explain different types of feedback
Types of feedback:
Negative feedback: This tends to reduce output (but in amplifiers, stabilizes and linearizes operation). Negative feedback feeds part of a system's output, inverted, into the system's input; generally with the result that fluctuations are attenuated.
Positive feedback: This tends to increase output. Positive feedback, sometimes referred to as "cumulative causation", is a feedback loop system in which the system responds to perturbation (A perturbation means a system, is an alteration of function, induced by external or internal mechanisms) in the same direction as the perturbation. In contrast, a system that responds to the perturbation in the opposite direction is called a negative feedback system.
Bipolar feedback: which can either increase or decrease output.

36. What are the main divisions of power system?
The generating system,transmission system,and distribution system

37. What is the need for base values?
The components of power system may operate at different voltage and power levels. It will be convenient for analysis of power system if the voltage, power, current ratings of the components of the power system is expressed with referance to a common value called base value.
38. What is meant by impedance diagram.
The equivalent circuit of all the components of the power system are drawn and they are interconnected is called impedance diagram.

39. What is the need for load flow study.
The load flow study of a power system is essential to decide the best operation existing system and for planning the future expansion of the system. It is also essential for designing the power system.

40. What is Instrumentation Amplifier (IA) and what are all the advantages?
An instrumentation amplifier is a differential op-amp circuit providing high input impedances with ease of gain adjustment by varying a single resistor.

41. Explain the concept of frequency re-use.
The whole of the geographical area is divided into hexagonal shape geometrical area called cell and each cell having its own transceiver. Each BTS (cell site) allocated different band of frequency or different channel. Each BTS antenna is designed in such a way that i cover cell area in which it is placed with frequency allotted without interfering other cell signals. The design process of selecting and allocating channel groups for all of the cellular base station within system is called frequency reuse.

42. What is CDMA?
CDMA stands for Code Division Multiple Access which uses digital format. In CDMA systems several transmissions via the radio interface take place simultaneously on the same frequency bandwidth. User data is combined at the transmitter’s side with a code, then transmitted. On air, all transmission get mixed. At the receiver's side the same code is used as in the transmitter’s side. The code helps the receiver to filter the user information of the transmitter from incoming mixture of all transmissions on the same frequency band and same time.

43. Explain Bluetooth.
Bluetooth is designed to be a personal area network, where participating entities are mobile and require sporadic communication with others. It is omni directional i.e. it does not have line of sight limitation like infra-red does. Ericsson started the work on Bluetooth and named it after the Danish king Harold Bluetooth. Bluetooth operates in the 2.4 GHz area of spectrum and provides a range of 10 metres. It offers transfer speeds of around 720 Kbps.

44.  What are different categories of antenna and give an example of each?

Different categories of antenna are as follows:

1. Wire Antennas - Short Dipole Antenna
2. Microstrip Antennas - Rectangular Microstrip (Patch) Antennas
3. Reflector Antennas - Corner Reflector
4. Travelling Wave Antennas - Helical Antennas
5. Aperture Antennas - Slot Antenna
6. Other Antennas - NFC Antennas

45. What is handover and what are its types?
Handover in mobile communication refers to the process of transferring a call from one network cell to another without breaking the call.
There are two types of handover which are as follows:

Hard Handoff: hard handoff is the process in which the cell connection is disconnected from the previous cell before it is made with the new one.

Soft Handoff: It is the process in which a new connection is established first before disconnecting the old one. It is thus more efficient and smart.

46.What is ionospheric bending?
When a radio wave travels into the ionospheric layer it experiences refraction due to difference in density. The density of ionospheric layer is rarer than the layer below which causes the radio wave to be bent away from the normal. Also the radio wave experiences a force from the ions in the ionospheric layer. If incident at the correct angle the radio wave is completely reflected back to the inner atmosphere due to total internal reflection. This phenomenon is called ionospheric reflection and is used in mobile communication for radio wave propagation also known as ionospheric bending of radio waves.

47. What are GPRS services?

## GPRS services are defined to fall in one of the two categories :

- PTP ( Point to point)
- PTM ( Point to Multipoint)
Some of the GPRS services are not likely to be provided by network operators during early deployment of GPRS due in part to the phased development of standard. Market demand is another factor affecting the decision of operators regarding which services to offer first.

## Advantages of CDMa are as follows :

1. Frequency diversity : Transmission is spread out over a large bandwidth due to that less affected by noise. If bandwidth is increased S/N ratio increases, which means noise will be reduced.
2. Multiplication Resistance : Chipping codes used for CDMA not only exhibit low correlation but also low autocorrelation. Hence a version of the signal that is delayed by more than one chip interval does not interfere with dominant signal as in other multipath environments.
3. Privacy : Due to spread spectrum is obtained by the use of noise like signals, where each user has a unique code, so privacy is inherent.
4. Graceful Degradation. In CDMA, more users access the system simultaneously as compared to FDMa, TDMA.

## 49. What are the advantages of spread spectrum?

SPread spectrum has the following advantages :

1. No crosstalk interference.
2. Better voice quality/data integrity and less static noise.
3. Lowered susceptibility to multipath fading.
4. Inherent security.
5. Co-existence.
6. Longer operating distances.
7. Hard to detect.
8. Hard to intercept or demodulate.
9. Harder to jam than narrow bands.
10. Use of ranging and radar

## 50. Explain the steps involved in demodulating a signal.

Once the signal is coded, modulated and then sent, the receiver must demodulate the signal. This is usually done in two steps :
1. Spectrum spreading (e.g., direct sequence or frequency hopping) modulation is removed.
2. The remaining information bearing signal is demodulated by multiplying with a local reference identical in structure and synchronised with received signal.

## 51. How can a Pseudo Random Noise COde be usable?

To be usable for direct sequence spreading, a PN code must meet the following conditions :

1. Sequence must be built from 2 levelled numbers.
2. The codes must have sharp autocorrelation peak to enable code synchronization.
3. Codes must have a low cross-correlation value, the lower it is, more are the number of users which can be allowed in the system.
4. The codes should be “balanced” i.e. the difference between ones and zeros in code may only be 1.

## Thursday, 5 October 2017

### Temperature Controlled DC Fan using Microcontroller

A Temperature Controlled DC Fan is a system which automatically turns on a DC Fan when the ambient temperature increases above a certain limit.
Generally, electronic devices produce more heat. So this heat should be reduced in order to protect the device. There are many ways to reduce this heat. One way is to switch on the fan spontaneously.
This article describes two such circuits that automatically, switches the fan when it detects the temperature inside the device greater than its threshold value.

### Circuit 1 Temperature Controlled DC Fan using 8051

#### Principle

The project works on the principle of Analog to Digital Conversion. The Analog data from the LM35 temperature sensor is given to the analog to digital converter ADC0804.
The analog output of the temperature sensor will vary at 10mV per degree Celsius.
ADC0804 is an 8-bit ADC. For a reference voltage of 5V, we’ll get a resolution of 5V/28 = 20mV. Which means, this is the minimum change in the analog value from the sensor which is recognisable by the ADC IC.
As per the changes in the temperature, the output of the ADC is generated. The digital output of the ADC is given to Microcontroller to calculate the temperature and control the fan accordingly.

#### Components

Microcontroller Section
• AT89C51 Microcontroller
• AT89C51 Programmer Board
• 11.0592 MHz Quartz Crystal
• 33pF Ceramic Capacitor
• 2 x 10KΩ Resistor
• 10µF Electrolytic Capacitor
• Push Button
• 16 X 2 LCD Display
• 10KΩ POT
Temperature Sensor Section
• LM35
• 10KΩ Resistor
• 150pF Ceramic Capacitor
• 1KΩ x 8 Resistor Pack
• 2N2222 NPN Transistor
• 1N4007 Diode
• 12V Relay
• 1KΩ Resistor
• Fan

#### Configuring ADC0804 for this Project

The configuration of the ADC0804 is explained here. First, we need to connect the 5V regulated power supply to the Vcc pin (Pin 20). Then, connect the analog and digital ground pins (Pins 8 and 10) to the GND.
In order to use the internal clock, we need to connect a 10KΩ resistor between CLK IN (Pin 4 and CLK R (Pin 19) and then, connect a 150pF cap between pins 4 and GND to complete the oscillator circuit.
The CS pin (Pin 1) is connected to GND to enable the ADC.
In order to read the data from the ADC continuously by the microcontroller, we need to connect the RD pin (Pin 2) to the GND.
For the ADC to continuously read the analog data from the sensor, we need to short the Write pin (Pin 3) with the Interrupt pin (Pin 5).
The analog output of the sensor (LM35) is connected to the Vin+ (Pin 6) of the ADC. The negative analog input pin i.e. Vin- of the ADC is connected to the GND.
The converted digital data which is an 8-bit data will be available at DB0 to DB7 (Pins 18 to 11).

#### Circuit Design

The main components of the project are 8051 Microcontroller, 16×2 LCD Display, LM35 Temperature Sensor, ADC0804, Relay and Fan.
The basic connections with respect to microcontroller include clock, reset and EA. Clock consists of an 11.0592 MHz crystal and two 33pF capacitors. The reset circuit consists of a 10µF capacitor, 10KΩ resistor and a push button. The EA pin is pulled high with a 10KΩ resistor.
Now we’ll see the connections with respect to other components.
For the LCD display, a 10KΩ pot is connected to contrast adjust pin. The three control pins of the LCD are connected to the pins P3.6, GND and P3.7.
The 8 data pins of the LCD are connected to PORT1 of the microcontroller.
The basic connections with respect to ADC are explained in its configuration. The 8 digital outputs of the ADC must be connected to PORT 2 of the microcontroller.
The next component we are going to connect is LM35. Connect the data pin of the LM35 to the analog input pin i.e. Pin 6 of ADC.
Finally, we need to connect the Relay circuit consisting of resistor, transistor and relay to the PORT0 of the microcontroller with PORT 0 pulled-up externally.
Connect the input of relay i.e. base of the transistor to P0.0 pin of the microcontroller.

#### Working

The aim of this project is to design a temperature controlled fan using 8051 microcontroller, in which the fan is automatically turned ON or OFF according to the temperature. The working of the project is explained here.
In this circuit, the LM35 temperature sensor will give continuous analog output corresponding to the temperature sensed by it. This analog signal is given to the ADC, which converts the analog values to digital values.
The digital output of the ADC is equivalent to sensed analog voltage.
In order to get the temperature from the sensed analog voltage, we need to perform some calculations in the programming for the microcontroller.
Once the calculations are done by the microcontroller according to the logic, the temperature is displayed on the LCD. Like this, the microcontroller will continuously monitor the temperature.
If the temperature exceeds more than 50 deg Celsius (as per the code), the microcontroller will turn on the relay to start the fan. If the temperature drops below 40 deg Celsius (as per the

### Water Level Indicator Mini Project

The Water Level Indicator employs a simple mechanism to detect and indicate the water level in an overhead tank or any other water container.
The sensing is done by using a set of nine probes which are placed at nine different levels on the tank walls (with probe 9 to probe 1 placed in increasing order of height, common probe (i.e. a supply carrying probe) is placed at the base of the tank). The level 8 represents the “tank full” condition while level 0 represents the “tank empty” condition.
When the water-level is below the minimum detectable level (MDL), the seven segment display is arranged to show the digit 0, indicating that the tank is empty, when the water reaches level1 (but is below level2) the connection between the probes gets completed (through the conducting medium – water) and the base voltage of transistor increases.
This causes the base-emitter junction of transistor to get forward biased, this switches transistor from cut-off to conduction mode thus PIN (B7) of microcontroller is pulled to ground hence, the corresponding digit displayed by the seven segment display is 1.
The similar mechanism applies to the detection of all the other levels. When the tank is full, all input pins of microcontroller become low. This causes the display to show 8 and also in this case a buzzer sound is given, thereby indicating a “tank full” condition.
Most water level indicators are equipped to indicate and detect only a single level. The Water Level Indicator implemented here can indicate up to nine such levels and the microcontroller displays the level number on a seven segment display.
So, the circuit not only capable of cautioning a person that the water tank has been filled up to certain level, but also indicates that the water level has fallen below the minimum detectable level. This circuit is important in appliances such as the water cooler where there is a danger of motor-burnout when there is no water in the radiator used up also it can be used in fuel level indication.
In this project we show the water level indicator using eight transistors which conducts as level rises, a buzzer is also added which will automatically start as the water level becomes full, auto buzzer start with the help of microcontroller. With the help of this project we not only show the level of water on seven segment display but also indicate the water full condition using a buzzer.

### Water Level Indicator Project Circuit Features:

1. Easy installation.
2. Low maintenance.
3. Compact elegant design.
4. The Automatic water level controller ensures no overflows or dry running of pump there by saves electricity and water.
5. Avoid seepage of roofs and walls due to overflowing tanks.
6. Fully automatic, saves man power.
7. Consume very little energy, ideal for continuous operation.
8. Automatic water level controller provides you the flexibility to decide for yourself the water levels for operations of pump set.
9. Shows clear indication of water levels in the overhead tank.

### How to Design Water Level Indicator Project using AVR Microcontroller?

• A constant 5v power supply is given to the microcontroller and rest of the circuit from a battery.
• The tank has 9 conductive type sensors (other types of sensors have been mentioned earlier but in our project only conductive type are used) embedded into it and 8 wires of sensors out of 9 are connected to transistors and the 9th is connected to 5v+ supply.
• The use of transistor is it acts as inverter (i.e. in on state gives low voltage at output and in non conducting state gives high voltage at its output), all transistors outputs are connected to PORTB of microcontroller.
• Seven segment display is connected to PORTD. It is connected in common cathode fashion.
The Output for the 7th level is not only shown on seven segment display but also indicated with a discontinuous buzzer sound.
• Output for the 8th level (i.e. tank full condition) is not only shown in seven segment display but also indicated with a continuous buzzer sound.

### How Water Level Indicator Project Circuit Works?

The operation of this project is very simple and can be understood easily. In our project “water level indicator” there are 3 main conditions:
1. There is no water available in the source tank.
2. Intermediate level i.e. either of 3rd to 7th level.
3. There is ample amount of water available in the source tank.
So let us discuss more about these 3 conditions

#### CONDITION 1: Water not available

When the tank is empty there is no conductive path between any of the 8 indicating probes and the common probe (which is connected to 5v+ supply) so the transistor base emitter region will not have sufficient biasing voltage hence it remains in cut off region and the output across its collector will be Vc approximately 4.2v.
As in this case the microcontroller is used in the active low region (which means it considers 0-2 volts for HIGH and 3-5 volts for LOW) now the output of transistor which is 4.2v approximately will be considered as LOW by the microcontroller and hence the default value given by microcontroller to the seven segment display is 0 which indicates as the tank is empty.

#### CONDITION 2: Intermediate levels

Now as the water starts filling in the tank a conductive path is established between the sensing probes and the common probe and the corresponding transistors get sufficient biasing at their base, they starts conducting and now the outputs will be Vce (i.e. 1.2v-1.8v) approximately which is given to microcontroller.
Here the microcontroller is programmed as a priority encoder which detects the highest priority input and displays corresponding water level in the seven segment display.
In this project while the water level reaches the 7th level i.e. last but one level along with display in seven segment a discontinuous buzzer is activated which warns user that tank is going to be full soon.

#### CONDITION 3: Water full

When the tank becomes full, the top level probe gets the conductive path through water and the corresponding transistor gets into conduction whose output given to microcontroller with this input microcontroller not only displays the level in seven segment display but also activates the continuous buzzer by which user can understand that tank is full and can switch off the motor and save water.

#### Water Level Indicator Project Working Flow Chart:

Flow chart gives the clear and easy understanding of the project. The process goes on as follows:
The microcontroller checks for tank full condition, if the condition is satisfied it indicates the same on display unit and also sounds a buzzer if the condition fails it checks again and this process continues and the corresponding level is indicated in the display unit.

#### Water Level Indicator Project Applications:

• Automatic Water level Controller can be used in Hotels, Factories, Homes Apartments, Commercial Complexes, Drainage, etc., It can be fixed for single phase motor, Single Phase Submersibles, Three Phase motors. (For 3Æ and Single Phase Submersible Starter is necessary) and open well, Bore well and Sump. We can control two motor and two sumps and two overhead tanks by single unit.
• Automatic water level controller will automatically START the pump set as soon as the water level falls below the predetermined level (usually 1/2 tank) and shall SWITCH OFF the pump set as soon as tank is full.
• Fuel level indicator in vehicles.
• Liquid level indicator in the huge containers in the companies.
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