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Saturday, 8 May 2021

FM Receiver Block Diagram with Explanation

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Block Diagram of FM Receiver with Explanation

Standard broadcast for FM is 88-108 MHz. The maximum permissible deviation is 200 KHz. In FM the intermediate frequency is 10.7 MHz. In FM the operating frequencies are much higher than that in AM. It additionally contain a de-emphasis and limiter circuit. The method of demodulation is totally different for the methods used in AM detection. A superheterodyne FM receiver is shown in figure.


The first section is the RF section, which is a tunable circuit connected to the antenna terminals. It is used to select only the desired RF signal out off a number of frequencies to the receiver. The RF amplifier is a tuned voltage amplifier and it contains a parallel LC tunes circuit. This tuned circuit selects the desired RF signal from a number of frequencies to the receiver.


In the mixer the incoming signal frequency is mixed with the frequency generated by a local oscillator to convert it into a lower fixed frequency called intermediate frequency. It is 10.7 MHz in FM receivers. The local oscillator will be a high frequency oscillator. The RF amplifiers and the local oscillator are tunes together, so that difference frequency at the output of the mixer will be equal to the intermediate frequency. The local oscillator frequency always kept above the signal frequency by an amount equal to IF.


The output of the mixer is applied to the IF amplifier stages. The intermediate frequency and the bandwidth required in FM are higher than that in AM receivers. Typical bandwidth for a receiver operating in 88-108 MHz and IF of 10.7 MHz is 200 KHz. Two IF amplifier stages are often provided.


FM demodulation is totally different from AM demodulation. Balanced slope detector, Foster-Seeley discriminator and Ratio detectors are common types of demodulators used for FM detection. De-emphasis circuit is used to attenuate the high frequencies in order to compensate the boosting at the transmitter.


The amplitude of the FM signal remains constant. But by traveling from the transmitter to the receiver antenna, external sources produce unwanted variations in the signal amplitudes. These variations are easy to detect because the amplitude of the original FM signal remains constant. The limiter is a form of clipping device that does not produce an output, when the positive or negative amplitude of the FM signal exceeds a pre-determined level. So FM receivers can be integarated with amplitude limiters to take away the amplitude variation caused by noise. Hence FM reception is more immune to noise than AM reception.


There are different methods of obtain AGC in an FM receiver. The limiter user has leak type bias; this bias voltage changes proportional to the input voltage and is thus used for Automatic Gain Control. Occasionally a further Automatic Gain Control detector is used which takes positive output of the final IF amplifier and it rectifies and filters in the common manner.

Wednesday, 5 May 2021

Superheterodyne Receiver Block Diagram

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Superheterodyne receiver is the most popular type of radio receiver. In superheterodyne receiver, the selected RF signal is converted to a lower fixed frequency called intermediate frequency (IF) by the process of heterodyning (mixing) of two frequencies. This intermediate frequency is 455 KHz in AM receivers. The IF signal conveys the same information as the selected RF signal. The block diagram of a superheterodyne AM receiver is shown in the figure.

RF amplifier

The first section of a radio receiver is always a RF section, which is a tunable circuit connected to the antenna terminals. It is used to select only the desired RF signal out off a number of frequencies to the receiver. The RF amplifier is a tuned voltage amplifier and it contains a parallel LC tunes circuit. This tuned circuit selects the desired RF signal from a number of frequencies to the receiver.

The second purpose of the amplifier is the pre-amplification of the RF signal before mixing. When the RF signal reaches the antenna, a very weak voltage is induced in it. It is necessary first to amplify the RF signal to a suitable level for further processing. Usually only one RF amplifier stage is used in superheterodyne receivers.


The amplified RF signal is fed to the mixer stage where the RF signal is mixed with a high frequency generated by a local oscillator. It contains a LC tuned circuit. Usually the local oscillator and RF amplifier are tuned together with the help of a gang capacitor. In standard broadcast receivers, the local oscillator frequency is always made higher than the RF signal frequency. The Mixing of the selected RF signal (fs) and the local oscillator frequency (fo) produce two additional frequencies — ( fs + fo) and ( fs — fo ). The difference in frequency (fs — fo) is always adjusted to be 455 KHz which is known as intermediate frequency, IF.  In the mixer stage, with the help of gang capacitor, the local oscillator frequency is always adjusted to be above the RF signal frequency by an amount equal to the intermediate frequency, 455 KHz.

That is, IF = Local oscillator frequency — Selected RF frequency

In standard broadcast receivers, the local oscillator frequency fo is made higher than the incoming signal frequency fs by an amount equal to the intermediate frequency fi.

i.e, fo = fs + fi  or  fs = fo – fi

Now a frequency fsi manages to reach the mixer, such that

fsi = fo + fi = fs + 2fi

This frequency will also produce an intermediate frequency fi when mixed with the local oscillator frequency fo. This has the effect of two stations have receiving simultaneously and is naturally undesirable. The frequency fsi is called the image frequency. The image frequency rejection of a radio receiver depends on the selectivity of the RF amplifiers and must be achieved before the IF stage. Once the spurious frequency enters the first amplifier, it becomes impossible to remove it from the wanted signal.

IF amplifier stage

The signal with frequency 455 KHz from the output of the mixer stage is applied to the IF amplifier stage IF amplifiers are fixed tuned amplifiers which are tuned to the intermediate frequency. These amplifiers give very high amplification to IF signal. To improve the gain and bandwidth, two or three IF amplifier stages are used. Each stage uses a pair of mutually coupled tuned circuit which is tuned to the required IF. They are called intermediate frequency transformer, IFT. The factors influencing the selection of intermediate frequency are

1. If IF is too high, selectivity and adjacent channel rejection become poorer and tracking become difficult.

2. If IF is low, image frequency rejection become poorer. It becomes worse if signal frequency is raised.

3. If IF is too low, selectivity becomes too sharp and resulting in cutoff of sidebands. Also high frequency stable local oscillator is also needed.

The value of IF for

• AM — KHz

• FM — 10.7 MHz

TV — 36 & 46 MHz

µ-wave & radar — 30, 60, 70 MHz

IF will influenced by high and low values. Hence a compromise is needed. So there will be two IF stages — the first one with a high IF value and the second one with a low IF value. The high IF pushes the image frequency farther away from the signal frequency and therefore permits much better attenuation of it. The second lower IF has all the properties of low fixed operating frequency, particularly sharp selectivity and hence good adjacent channel rejection.


The output of the IF amplifier is applied to the envelope detector where the audio signal is extracted from the AM signal. Diode is commonly used for AM demodulation. RF signal is suppressed by the filter circuit.

Automatic gain control (AGC) or Automatic volume control (AVC)

While we are tuning a radio receiver, the signal strength of different stations will be different. So the volume control has to be readjusted each time the receiver is tuned from one station to another. So the automatic gain control (AGC) or Automatic Volume Control (AVC) is employed in all modem receivers. AGC is a system in which the overall gain of radio receiver is changed automatically with change in strength of receiving signal in order to keep the output constant. The negative DC voltage obtained at the output of the AGC filter (in the envelope detector) is proportional to the receiving signal strength. This negative DC voltage is used for obtaining automatic gain control in simple AGC system. The negative DC voltage applied to a selected number of RF and IF stages. Negative bias voltage reduces the gain of the stages to which AGC is applied. Since the AGC voltage is proportional to the signal strength, when the signal strength is high, the AGC voltage produced will also be high and the reduction in gain will be high. When the signal strength is low the AGC voltage will also be low and there is less reduction in gain. Thus the overall gain of the radio receiver remains substantially constant.

Advantages of super heterodyne receiver

1. Better selectivity and better adjacent channel rejection.

2. Improved sensitivity

3. Gain is stable and no bandwidth variations over the tuning range.

Generation of the intermediate frequency in the mixer stage is an important characteristic of superheterodyne receiver. At this frequency, higher amplification and better gain stability can be obtained. In a superheterodyne receiver most of the selectivity and amplification is produced by the IF amplifiers. The most important factor regarding the sensitivity of a radio receiver is the gain of the intermediate frequency amplifiers. The IF amplifier provides most of the gain and therefore the sensitivity of the receiver. Since IF amplifiers use double tuned circuit there is no bandwidth variations over the tuning range. Since the characteristics of the IF amplifiers are independent of the frequency to which the receiver is tuned, the selectivity and the sensitivity of the superheterodyne receiver is made throughout its tuning range.

Tuesday, 4 May 2021

Tuned Radio Frequency (TRF) Receiver Block Diagram

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The TRF receiver is the simplest type of AM radio receiver. The block diagram of a Tuned Radio Frequency (TRF) receiver is shown in the figure. Infinite number of transmitters installed throughout the world radiates radio waves in space. In general, these transmitters radiate different frequencies. Electromagnetic waves surrounding an antenna will induce currents of their frequency in the antenna. A provision should be there in the receiver to select only the desired RF signal out of a number of frequencies to the receiver. This function of selecting the desired RF signal and rejecting the rest is achieved by the tuned voltage amplifiers in the RF amplifier stage. Tuned RF amplifiers contain a parallel LC tuned circuit. The desired RF signal is selected by the tuned circuit.

When the RF signal reaches the receiving antenna, a very weak voltage is induced in it. It is not possible to extract the audio signal from this voltage. It is necessary first to amplify the RF signal to a required level. This is achieved in a radio receiver with the help of tuned RF amplifier. Thus RF amplifier serves two purposes.

1. Selection of desired RF signal

2. Amplification of the selected RF signal to a suitable value. Usually two or three tuned RF amplifier stages are used.

The amplified RF signal is applied to the detector or demodulator stage where the audio signal is extracted from the audio signal. Diode detectors are the most common detector used for AM detection.

The demodulated signal amplitude will be very small in amplitude. In order to drive a loudspeaker, it must be first amplified. The audio amplifier stage includes the audio voltage and power amplifier. The audio voltage amplifier will be a class A amplifier and the power amplifier will be a class B push-pull amplifier. The voltage and power level of the audio signal from the output of the detector is raised in this stage. The signal gets sufficient energy to drive the loudspeaker. The output of the audio amplifier stage is applied to the loudspeaker. It will reproduce the original sound by converting the electrical audio frequency waves into sound waves.

Advantages of a TRF receiver

1. It is simple to design.

2. Its alignment is very easy.

Disadvantages of a TRF receiver

1. Poor selectivity and hence insufficient adjacent channel rejection.

2. Poor sensitivity

3. Instability of gain and bandwidth variation over the tuning range.

TRF receiver is suffered from the variation of the bandwidth over the tuning range. So the receiver will pickup adjacent stations as well as the one to which it is tuned. i.e., the selectivity of the TRF receiver varies with frequency. In TRF receiver the amplification of the signal also varies with the frequency. So the TRF receiver suffers from the instability of gain. These entire problems can be solved using superheterodyne receivers.

Significance of tuned amplifiers in radio receivers

Infinite number of transmitters installed throughout the world radiates radio waves in space. In general, these transmitters radiate different frequencies. Electromagnetic waves surrounding an antenna will induce currents of their frequency in the antenna. A provision should be there in the receiver to select only the desired RF signal out of a number of frequencies to the receiver. This function of selecting the desired RF signal and rejecting the rest is achieved by the tuned voltage amplifiers in the RF amplifier stage. Tuned RF amplifiers contain a parallel LC tuned circuit. The tuned RF amplifier contains a parallel tuned LC circuit. The RF amplifier also amplifies the selected RF signal to a suitable level. Also four frequencies are present at the output of the mixer.

1. Local oscillator frequency

2. The selected RF frequency

3. Local oscillator frequency + RF signal frequency

4. Local oscillator frequency – RF signal frequency

From these four signals, we have to select the difference frequency which is equal to 455 KHz. The fixed tuned amplifiers in the IF section are tuned to 455 KHz to select only this frequency and provides a high gain. Thus tuned amplifiers play a very significant role in radio reception.

Sunday, 2 May 2021

Main function of Radio Receiver

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Main functions of a radio receiver are,

1. Selection of RF signals from a number of different frequencies surrounding the antenna.

2. The amplification of selected RF signal.

3. Demodulation of audio signal from the modulated wave.

4. Amplification of the audio signal after detection to drive the loudspeaker.

Performance of a Radio receiver

The performance of a radio receiver depends on the following factors.

Sensitivity: Sensitivity of a radio receiver is its ability to amplify weak signals. It is defined as the minimum amount of radio frequency input voltage required to produce a desired amount of audio output. It is expressed in microvolt or in decibel. Sensitivity varies over the tuning band. In superheterodyne receivers, the factors determining the sensitivity are gain of IF and RF amplifiers and noise figure.

Selectivity: Selectivity of a radio receiver is called as its capability to select the signal of desired frequency and to reject the rest of the unwanted signal. It is selectivity, which determines the adjacent channel rejection of a receiver. Adjacent channel is a range of frequencies that just above or below the required channel. It is the characteristic that determines the extent to which the receiver is capable of distinguishing between the desired signal and signals of other frequencies. It varies with receiving frequency and become worst when the receiving frequency is raised. In superheterodyne receivers, selectivity mainly depend on the response of the IF section. RF section and mixers play a small part.

Fidelity: The ability of a radio receiver to reproduce the original sound exactly is called fidelity.

Tuesday, 20 April 2021

Logic Devices for Interfacing

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A microcomputer system consists of four components namely microprocessor, memory, input devices and output devices. In order to design a microprocessor based system for a particular application, the designer has to select suitable memories and I/O devices, and interface them to the microprocessor. But these memories and I/O devices must be compatible with the microprocessor, both in speed and timing characteristics. If a particular device is not compatible, additional electronic circuit has to be designed, through which the device may be connected to the CPU. Before discussing interfacing circuits for connecting memory and I/O devices to the microprocessor, let us have a review of logic devices used for interfacing.

1. Tristate devices

Normally a logic circuit has only two states: Logic 1 and Logic 0. Tristate logic device has three states: Logic 1, Logic 0 and high impedance (high Z state). The term "Tristate" is the trademark of National Semiconductor Company and is used to represent the three logic states. A tristate logic device has a third input called enable input.

Here the enable input is active low input i.e., inverter is active only if a low is given to the enable input. If the enable input is disabled (logic high), the inverter will enter a high impedance state. That is, the inverter will not respond for the input.

2. Buffer

The buffer is a logic circuit that amplifies the current or power. It has one input and one output line. The logic level of output is the same as that of the input i.e., logic 1 input provides logic 1 output. The symbol for buffer is shown in Figure.

The buffer is commonly used to increase the driving capability of a logic circuit. It is also known as driver.

3. Decoder

A decoder is a logic circuit used for detecting the presence of a specified combination of bits on its inputs and to indicate that code by a specified output level. Generally a decoder has n inputs and 2n outputs. Figure shows a 2:4 decoder with active low output lines.

For example, if the input is 01, the output line 1 will be low and all other output lines are high. Here, the decoder will function only if a low is given to the enable input (enable input is active low). Decoders are commonly used in interfacing I/O devices and memory to the microprocessor.

4. Semiconductor Memory

A memory unit is an integral part of a microcomputer system. It is used to store programs, data and result. A microprocessor based system uses a number of memory devices of different technologies such as magnetic memory, semiconductor memory and optical memory. The speed of the memory must match with the operating speed of the CPU. If the memory is slow, the CPU has to wait for data and instructions. Memory devices are broadly classified into two groups.

(i) Primary memory

(ii) Storage memory

Primary memories are fast semiconductor memories. While storage memory refers to the storage medium comprising slow devices such as magnetic tapes, hard disks, floppy disks, compact disks (CD) etc. These devices are used to hold large data files and huge programs such as compilers, application programs etc. The primary features of these devices are high storage capacity, low cost and slow access. The access time for these devices is of the order of millisecond.

Primary memory

It refers to the storage area which can be directly accessed by the processor. All programs and data must be stored in primary memory prior to execution. In primary memories the access time must be compatible with the read/write time of the processor. Access time is the time to access any particular memory location. Therefore semiconductor memories are used as primary memories. (The access time for semiconductor memory is only 50 ns. Also, CPU is a semiconductor device.

Semiconductor memories are broadly classified into two.

(1) RAM (Random Access Memory)

(2) ROM (Read Only Memory)


In a random access memory, any memory location can be accessed in a random way. That is, the access time is same for each and every memory location. RAM is also called read/write memory (R/WM), since the processor can write into or read from this memory. RAM is also a volatile memory. That is, it stores information as long as the power is supplied to it. Its contents are lost when power supply is switched off.

RAM is again classified into two.

(a) Static RAM (SRAM)

(b) Dynamic RAM (DRAM)

Static RAM retains the stored information as long as power supply is ON. But DRAM loses its stored information in a few milliseconds even though its power supply is ON. A DRAM stores information in the form of charge on a capacitor; which leaks away in very short time. Therefore its content must be periodically refreshed for restoring the capacitor charge (usually every 2ms). Thus DRAM requires a refreshing and control circuitry which will increase the cost of the system.

A DRAM requires only one transistor and a capacitor. That is, DRAM requires only one transistor per memory cell. (Memory cell is an electronic circuitry which stores a binary bit 0 or 1). But SRAM uses six transistors in a memory cell. Therefore, packing density is more for DRAM compared to SRAM. Also, DRAM consumes less power.


ROM is a non volatile memory. That is, it retains the stored information even if the power is OFF. This memory is used for storing programs and data permanently (i.e., need not be altered later). It is cheaper than RAM. Different types of ROM available in market are

Masked ROM

In masked ROM, the information is stored permanently by the manufacturer at the time of manufacturing.

Example: Audio CD of a movie.

PROM (Programmable ROM):

This memory can be programmed by the user with a special 'PROM Programmer'; which selectively burns the fuses (within the PROM) according to the bit pattern to be stored.

EPROM (Electrically Programmable ROM):

The content of an EPROM can be erased and can be reprogrammed more than once. To erase its content, it is exposed to ultraviolet radiation for about 20 minutes. To facilitate the exposure of ultraviolet radiations, the EPROM chips are packed in a case which has transparent window.

Limitations of EPROM chips are

(a) It must be taken out of the circuit to erase it.

(b) The entire chip must be erased.

(c) The erasing process takes 15 to 20 minutes.

EEPROM or EEPROM (Electrically Erasable Programmable ROM):

They are also called Electrically Alterable ROM (EAROM). They need not be removed from the circuit board for erasure. Also, EEPROM is byte erasable. That is, selective erasure of its content is possible. Its content can be erased and programmed on the system board itself very easily on a byte by byte basis (need not be taken out of the circuit). Its disadvantage is that different voltage levels are required for erasing, writing and reading the stored information.

Flash Memory

It is also electrically erasable and reprogrammable. The major difference between Flash memory and EEPROM is in the erasure procedure. In Flash memory, the entire content is erased in one operation. That is, it is not byte by byte erasable like EEPROM. Unlike EEPROM, flash memory uses one transistor memory cell resulting in high packing density, lower cost and higher reliability.

In a microprocessor based product, programs are generally written in ROM and data that are likely to vary are stored in RAM.

For example, in a microprocessor controlled microwave oven, the program that 'runs' the oven is permanently stored in ROM; and the data such as starting time, baking period and temperature are entered in RAM through key pad.

Saturday, 17 April 2021

Basic Operations of Microprocessor

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A microprocessor is a programmable electronic device that has computing and decision making capability similar to that of a central processing unit (CPU) of a computer. Today, the applications of the microprocessor are increasing at a faster rate. Microprocessor can be embedded in a large system or it can be a stand alone unit capable of controlling different processes. It can also function as CPU of a computer. At a very elementary level, we can draw an analogy between microprocessor operations and functions of a human brain. The brain gets inputs from eyes, ears etc (input devices) and sends processed information to "output devices" such as face in the form of expressions and emotions. Generally a microprocessor is a programmable device, which accepts binary data from an input device, process the data according to the instructions stored in the memory, and provides the result to an output device. Prior to going into the details of a microprocessor, we must have a basic knowledge of computers.

Basic elements of a computer

All computer systems consist of three basic functional blocks as shown in figure.

(1) Central Processing Unit (CPU)

(2) Memory

(3) Input and Output devices

A system designed with a microprocessor as its central processing unit is called a microcomputer. A microprocessor based system includes a microprocessor as CPU, semiconductor memories, input and output devices, interfacing devices and so on. The organization of a microcomputer (microprocessor based system) is shown in Figure. These functional blocks are linked together with three internal buses. Bus is a communication path between the CPU and peripherals (devices) with a group of wires to carry bits.

The three buses are the data bus, the address bus and the control bus. The input and output devices are connected to the input and output ports respectively. A port is a physical interface on a computer through which data are passed to and from the peripherals. An instruction is a command given to the computer to perform a given task. A group of instructions designed to solve a specific problem is called a program. These instructions and data are stored in specific locations in the memory. Each location has a unique address associated with it.


Instructions are obtained by the CPU by placing the address (of the memory location where instruction is stored) in the address bus. Now the instructions are transferred to the CPU through the data bus. The CPU executes these instructions sequentially to get the final result. The processed data (result) is stored back in the memory or sent to peripheral devices like monitor, connected to the computer. All these processes are controlled and coordinated by the signals on the control bus generated by the CPU.


As stated earlier, microprocessor can function as CPU of a computer. It includes all logic circuitry necessary for performing various operations specific to that processor. For the sake of clarity, the microprocessor can be divided into three segments.

(a) Arithmetic and logic unit (ALU)

(b) Registers

(c) Control Unit.


This is the area of the microprocessor where various computing functions are performed. The ALU performs arithmetic operations like addition and subtraction, and logical operations like AND, OR and NOT. We can consider ALU as a section of CPU which contains all the logic circuits needed for performing different operations specific to that processor. A particular instruction (i.e., machine code of a particular instruction) will activate the appropriate logic circuit in the ALU so that a particular task is performed. This is called microprogramming which is done in the design stage of the microprocessor. We can compare the operation of microprocessor with the operation of our brain. In early childhood, we learn a word "sit" and the physical motion needed for the action "sit" are embedded in our brain. Later, when we hear the word "sit", our brain activates a series of actions for our muscles and bones, so that we perform the action "sit". In this analogy, the word "sit" is like an instruction to the microprocessor and action initiated by the brain are like microprogram.

The bit pattern (machine code of instruction) required to initiate these microprograms are given to the programmer in the form of instruction set of the microprocessor. The programmer selects the appropriate bit pattern (instruction) from the instruction set, for a given task and enters them sequentially to the memory through an input device. When CPU reads these bit patterns (instruction) one at a time, it initiates the appropriate microprogram through the control unit and performs the task specified in the instruction.


We can consider registers as temporary memory locations seen inside the processor. These registers are identified by the letters A, B, C, D, E, H, and L.

Control Unit

The control unit provides the necessary control signals for all the operations in the processor. It controls the flow of data between the microprocessor, the memory and the peripheral devices like keyboard and monitor.

Advantages of Microprocessor based systems

(i) Processing speed is high.

(ii) Automation of industrial processes and office administration.

(iii) Since the device is programmable, there is flexibility to alter the system by changing the software alone.

(iv) Compact and low cost.

(v) It is more reliable.

(vi) Operations and maintenance are easier.


Applications of Microprocessor based systems

Microprocessors are widely used in control applications.

(i) Microprocessor based systems are widely used in frequency meters, frequency synthesizers, spectrum analyzers etc.

(ii) In industry, they are widely used for controlling various parameters like speed, temperature and pressure.

(iii) In telephone industry they are widely used in digital telephone sets, telephone exchange and modems.

(iv) They are used in automobiles for monitoring various quantities like air-fuel mixture, temperature, speed etc.

(v) 32-bit microprocessors are widely used in CAD machines.

(vi) The car, maruti wagonR also uses a 32 bit processor for controlling the MPFI unit.

Tuesday, 13 April 2021

Microprocessor Programming Languages

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Taming the microprocessor, for a particular application is done by giving instructions to the microprocessor. Instruction is a command given to the microprocessor to carry out a particular task. An instruction activates the particular logic circuit, so that a specific task will be performed. The instruction set is the set of all instructions that a specific microprocessor is intended to execute. That is a microprocessor understands only an instruction present in the instruction set of that particular microprocessor.


To communicate with the microprocessor, the programmer must give the instructions in the binary language because the microprocessor understands only the binary language (1s and 0s). These binary code instructions are called machine language.


It is tedious and error prone for people to recognize and write instructions in binary language; so these instructions are written in hexadecimal code and entered in a computer by using Hex keys.


For example, the binary instruction 0011 1100 is equivalent to 3C in hexadecimal. This instruction can be entered in a computer with a Hex keyboard by pressing two keys; 3 and C. The monitor program of the system translates these keys into their equivalent binary pattern.


Assembly language


It is not easy to recognize a program written in hexadecimal numbers. Therefore, every maker of a microprocessor has set up a symbolic code for every instruction called mnemonics. The mnemonic of a particular instruction consists of letters that suggest the operation to be performed by that instruction.


Example: The binary code 0011 1100 (3CH in hexadecimal) is represented by the mnemonic INR A. (Hexadecimal numbers are usually followed by the letter H)


Here INR stands for increment and A represent accumulator. This instruction suggests the operation of incrementing the accumulator content by one.


The complete set of 8085 mnemonics is called assembly language and a program written in these mnemonics are called assembly language program. Writing a program in assembly language is much easier and faster than writing a program in machine language. Also assembly language is specific to each microprocessor. That is, the assembly language for 8085 microprocessor is entirely different from the assembly language for Motorola 68000. A microprocessor specific language is called a low level language. Thus machine language and assembly language are microprocessor specific and are both considered as low level languages. The mnemonics are convened to machine Ianguage (binary pattern) by using a program called assembler.

High level languages


Programming languages that are intended to be machine independent are called high level languages. BASIC, PASCAL, C, C++, JAVA etc are examples for high level languages. Instructions written in these languages are called statements rather than mnemonics. A program written in BASIC for a computer with Intel 8085 microprocessor can generally be run on another computer with a different microprocessor (Motorola). A program written in its high level language is termed as source code.


The instructions written in high level language is converted to machine language by using a program called a complier or an interpreter. The compiler or Interpreter translates the source code into the machine language compatible with the microprocessor being used in the system. The machine language equivalent of the source code is also called object code.

The primary difference between compiler and interpreter lies in the process of generating machine.


Machine Language


• The program developed using 1’s and 0’s is called machine language program. The machine can understand only machine language programs.

• The program developed using mnemonics is called assembly language program. Assembler is a conversion software, which can convert assembly language programs to machine language programs.

• The machine language and assembly language programs are machine (processor) dependent.

• The language which can be used to develop software independent of the hardware (processor) are called High Level Languages.

• The compiler or interpreter is a software which can convert high level language programs to machine language programs.

Applications of Microcontrollers

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Microcontrollers are also called embedded controllers or single chip microcomputers. Microcontroller is simply a computer on a chip. Microcontrollers find applications in environment where personal computers (PC) cannot be used. Following are some of its applications.

Important applications of in microcontrollers are

1. Used to measure and control the temperature of a furnace and ovens, speed of an electric motor, pressure of boilers etc.

2. Used in automobiles for automatic control of fuel and air mixture, ignition system, to test various conditions of engine, brakes etc.

3. Used in military equipments, RADAR, missiles etc.

4. Used in medical instrumentations like patient monitoring in ICU, pathological analysis, measurement of physiological parameters etc.

5. Used in home appliances like washing machines, microwave ovens etc where some physical parameters are monitored and controlled.

6. Used in electronic toys making them more entertaining and easy to use.         

7. They are widely used in controlling pumps, alarms, and other power applications. It is also used in communication equipment.

8. The Microcontroller output is binary values, but application equipments display, motor, speakers etc. work in analog signal.

9. There are many applications where you have to display numbers. The most popular display device used for displaying number is seven segment LED displays.

10. Microcontroller keeps the speed of the motor as constant. It adjusts the speed of the motor by changing the duty cycle of the signal applied to it. Hence constant speed can be maintained.

11. The electro mechanical relays have been used for many years in industry to control high dc or ac voltages and currents. Relays also provide isolation between the controller and the circuit under control.

12. It helps in Keyboard interfacing. When a key is pressed, the microcontroller identifies the pressed key by using either a software based or hardware based technique and then performs the assigned operation.

13. It helps in Stepper Motor interfacing. In order for getting accurate position control of rotating shafts, the Microcontroller 8051 is connected to it for constant speed.

Monday, 12 April 2021

Communication System Block Diagram Explanation

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Communications Systems


The process of transmission of information or message from one end to another is known as communication. When electromagnetic or radio waves are utilized for communication purpose, then it is called as radio communication. Electronic communication is started with wire telegraphy in the first half of nineteenth century. After a decade of years, telephony was developed, In the beginning of the twentieth century, radios come into existence. Radio communication made possible by the invention of the triode tubes. 


The modern communication system involves the process of sorting, processing and storing of information before conveying the message. During transmission, the filtering of noise takes place. Finally there includes the processing steps like decoding, storage and interpretation. Some types of communication include radar, telecommunications, mobile, computer, radio telemetry etc. The essential requirements of any communication system are fundamentally same.


Communication System Block Diagram with Explanation


The general block diagram of a general communication system is shown in figure. Any communication system is consist of an information source, transmitter, receiver, channel and noise.




The purpose of communication system is to communicate a message. This message comes from an information source. The message from an information source may be a speech from an individual or a numerical data from a computer. The total number of messages consists of individual messages which can be distinguished from one another. The amount of information contained in any given message is measured in bits depending upon the method of communication.




The message comes from an information source may not be an electrical signal. Unless the message that comes from the information source is electrical in nature, it will be unsuitable for sending. So the physical quantity must be converted into an electrical signal before it is applied to the transmitter. This is done with a transducer. The transducer will convert the physical quantity (in which the information is presented) into a corresponding electrical signal. For example, a carbon microphone will convert sound into electrical signal. The output from the transducer is known as signal. The signals are of two types — analogue type or digital type. According to the type of signals used, communication systems are also classified into either analogue or digital systems. In modem communication systems, the analogue signals are converted into digital signals, and thereafter transmitted through a digital system.


Even though the message that comes from the information source is electrical in nature, it is unsuitable for immediate sending. A lot of process must be done on the message to make it suitable for transmission. The transmitter is required to process the incoming information. The main process to be done is known as modulation. Modulation is a process in which some characteristics of a high frequency sine wave (carrier) is varied in accordance with the instantaneous values of the message signals. In a transmitter, the information modulates a carrier. That is, the information is impressed on a high frequency sine wave. The method of modulation may be analog or digital, high level or low level. The system may be amplitude modulator, frequency modulator, phase modulator, or pulse code modulator or combination of these.




Channel is the medium through which the information is transmitted from the transmitter to the receiver. The channel may be free space, air, wire, or fiber optic channel. In radio communication, the medium is free space where as in line communication it is a cable or a wire. In radio communication, information is transmitted as electromagnetic waves into the free space. In line communication it is transmitted as electric signals through cable. The acoustic channel is not used for long distance communication.


Noise source


The reason for noise is


1. Some distortion in the system

2. Because of introduction of noise, which is present in a transmission system.


Noise is defined as any unwanted form of energy tending to interfere with the proper and easy reception and reproduction of wanted signals. Noise can interfere with the signal at any point in a communication system. There are many ways of classifying noise, It is most convenient here to divide noise into two broad groups — internal noise and external noise.


External noise is the noise whose sources are external to the receiver. For example, atmospheric noise and industrial noise. Internal noise is the noise created within the receiver itself. For example, thermal agitation noise.




The transmitted signal finally reaches at the receiver. The main function of a receiver is to demodulate the modulated incoming signal so as to retrieve the original message. The signal from the channel is amplified and the information is extracted in the desired form with the help of a transducer.

Friday, 9 April 2021

Modulation and Need for Modulation

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Modulation and Need of Modulation

Modulation may be defined as a process by which any characteristics of a wave is varied as a function of the instantaneous value of another wave. The first wave, which is normally a high frequency sine wave, is known as carrier wave. The second wave is known as the modulating wave and the resultant wave is known as the modulated wave. The rate at which the variation takes place is equal to the modulating wave frequency. Modulating signal is an electrical signal having sound, picture or any other type of information.

Audio frequencies ranges from 20 Hz to 20 KHz. Sound waves propagated in air directly beyond a few hundred meters. Radio frequency means anything above 20 KHz. Radio waves are electromagnetic in nature, are capable of being propagated upto infinite distance in space. Sound waves can be able to propagated upto infinite distance in space. Sound waves can be able to propagated upto infinite distance in space by superimposing them on radio waves. This is what is done by the modulation process.

A carrier sine wave can be represented by the equation, e = Esin(ωt+φ), where ‘e’ is the instantaneous value of carrier sine wave, E is the maximum amplitude, ω is the angular frequency and φ is the phase. An unmodulated carrier has constant amplitude, a constant frequency and a constant phase relationship with respect to some reference. In modulation process one of these three parameters of the carrier may be varied by the modulating wave or signal. Hence at any moment its variation from the unmodulated value is proportional to the instantaneous value of modulating voltage. Depending on which characteristics of the carrier is varied by the modulating signal, there are three types of modulation – amplitude, frequency or phase modulation. The need for modulation is explained below.

1. The height of the antenna required for transmission and reception of a signal must be equal to ¼ th of the wavelength of the signal used for communication. We know, f = C/λ, where f is the frequency used, C is the velocity of the electromagnetic wave and λ is the wavelength. If frequency is small, λ is high and hence height of the antenna required must be comparatively large. If frequency is large, λ is small and hence height of the antenna required must be comparatively small. For example, a 15 KHz electromagnetic wave has a wavelength of λ = 3 x 108/15 x 103 = 20,000 m. Therefore the height of the antenna is λ/4 = 20,000/4 = 5000 m or 5 Km. Therefore the 15 KHz signal requires an antenna of 5 Km height. A vertical antenna of this size is unthinkable. Since the frequency is inversely proportional to the antenna height, a higher frequency must be used to reduce the antenna height.

2. At low frequencies, the transmitting power must be very large. The construction of a transmitter having such a huge power handling capacity is a difficult task. A radio frequency signal will travel a greater distance than the same amount of energy transmitted as sound signal.

3. All sound signals are within the range of 20 Hz to 20 KHz. If we transmit these sound waves directly, all waves from different stations and sources would be inseparably mixed up. In order to separate the various signals from different stations, it is necessary to transmit them at different portions of electromagnetic spectrum. This will also overcome the poor radiations at low frequencies. A tuned circuit is used in the receiver to select a desired transmission within a predetermined range and to reject all the other unwanted signals.

Thursday, 8 April 2021

Fundamentals of Electromagnetic Waves

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Electromagnetic waves are oscillations that transmit through free space with the velocity as that of light. Free space is the space that does not interfere with the normal radiation and propagation of the radio waves. Free space has no magnetic or gravitational field, no solid bodies and no ionized particles. Free space is unlikely exist anywhere. However the concept of free space is used because it simplifies the approach to wave propagation. Radio waves are electromagnetic in nature, has an electric field and magnetic field. Electromagnetic are transverse wave, that the oscillations are perpendicular to the direction of propagation. Also the direction of electric field, magnetic field and the direction of propagation are mutually perpendicular to each other.

Polarization: Polarization is refers to the physical orientation of the radiated wave in space. A wave is said to be vertically polarized, when all its electric intensity vectors are vertical. A wave is said to be horizontally polarized when all its electric intensity vectors are horizontal. A vertical antenna will radiate vertically polarized wave and a horizontal antenna radiates horizontally polarized waves.

Reflection: Electromagnetic waves will be reflected by a conducting medium. They will be reflected by ground, mountains and buildings. This is much similar to the reflection of light by a mirror.

Refraction: Refraction takes place when electromagnetic waves pass from one propagating medium to another medium having a different density. They will get refracted as they pass through the layers of the atmosphere having different degrees of ionization.

Diffraction: Diffraction of electromagnetic waves occurs due to the presence of small slits in a conducting plane or sharp edges of obstacles. The electromagnetic waves may be diffracted around the tall massive objects.

Attenuation and absorption: The power density of the wave diminishes rapidly with distance from the source of electromagnetic waves. The attenuation is proportional to the square of displacement. In free space, absorption of radio waves does not occur because there is nothing to absorb them. However atmosphere is tend to absorb radio waves because some of the energy from the wave is transferred to the atoms and molecules of the atmosphere. Thus the energy of the waves may be absorbed quite significantly.

Ground Wave Propagation:

Frequency below high frequency range { very low frequency (3 KHz to 30 KHz), low frequency (30 KHz to 300 KHz) and medium frequency (300 KHz to 3 Mhz)} will travel along the curvature of the earth. So these waves are called the ground waves or surface waves. Ground waves are propagated by means of a type of waveguide effect, which uses the earth surface and the lowest ionized layer of the atmosphere as the two waveguide walls. Ground wave propagation is one of the two means of the beyond the horizon propagation. Ground waves must be vertically polarised to prevent the short circuit of the electric field components.

A ground wave is attenuated in two ways.

1. A wave induces currents in the ground over which it passes and they loses some of energy by absorption.

2. Because of the diffraction the wave front gradually tilts over as the wave propagate over the earth, its tilts increases more and more and increasing the tilt causes greater short circuiting of the electric field component of the wave and hence the field strength reduction. Eventually at some distance from the antenna the waves lies down and dies.

Use: Medium wave radio communication

Sky wave propagation

The ionosphere is the upper portion of the atmosphere which absorbs a large quantities of the energy from the sun, it becoming get heated and ionized due to the heat. There were several degrees of ionization at different height. The various layers of ionosphere have specific effects on the propagation of radio waves particularly at high frequency. Under certain conditions, waves in the high frequency range (3 MHz to 30 MHz) are return to the earth by the ionized layers of atmosphere so they are called sky waves. The mechanism involved in this process is refraction. The ionization density increases for a wave approaching the given layer (ionosphere) at an angle, so the refractive index of the layer is reduced. Hence the incident wave gradually bends further and further away from the normal. At a particular layer it will bend downward and finally emerging from the ionized layer at an angle equal to the angle of incidence as shown in figure. This is the second method for the beyond the horizon propagation.

Skip distance

It is the distance upto which sky waves of given frequency cannot be received or minimum distance from transmitting antenna to the point at which sky wave of a given frequency is returned to earth by ionosphere. It depends on frequency of transmission, critical frequency, and height of layer and increases as ionization in the layer reduces. It is the shortest distance measured along the surface of the earth at which a sky wave of fixed frequency will be returned to the earth.

Use: Short wave communication.

Frequency above high frequency range generally travels through the troposphere, the portion of the atmosphere closest to ground. So space waves are sometimes called troposphere waves. Space wave propagation depends on line of sight (LOS) conditions. So the space waves are limited in this propagation by the curvature of earth. When earth curvature can be neglected, space wave propagation take place in the manner illustrated is shown in the figure.

Here energy reaches the receiver in two ways

1. By a ray travelling directly between transmitting and receiving antennas (Direct wave).

2. By a ray that reaches the receiver after reflection from the surface of the ground (Ground reflected wave) or Satellite reflected wave.

The field strength at the receiving antenna is the vector sum of the fields represented by the two rays.

Tuesday, 6 April 2021

Cable meaning in Electronics

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What is Cable in Electronics?


It is an insulated bundle of metal wires or threadlike fibres that carry electric current. They are widely used to distribute electric power and to transmit communication signals. They are also used to connect parts of computers and other electronic devices. Fiber optic cables have also been developed which transmit communications signals in the form of pulses of light. Most communications cables consist of conductors and insulation. Simple cables are made up of a single pair of insulated wires twisted together. Multiconductor cables such as telephone lines contain, hundreds or even thousands of conductors bound together. Submarie cables serve as a communication link between continents. In 1844 American painter and inventor Samuel F.B. Morse completed the first long distance telegraph cable in America.

Coaxial Cables

They are made up of special conductors called coaxials. A coaxial is a copper tube with a copper wire running through its centre. Insulation holds the wire in place. The tube and the wire have the same axis and are therefore called coaxials. A typical coaxial has about the same diameter as a pencil. Many telephone calls, especially long distance calls travel over coaxial cables. When used for telephone conversations coaxial work in pairs. One coaxial carries signals in one direction and the other carries signals in the other direction. Cable television systems use coaxial cables to transmit TV programmes.

Cable Television

Television programmes transmitted to viewers via wires from the broadcasting station constitute a cable television system. Since their initial introduction in the 1970’s cable systems have become common in areas well enough populated to be financially feasible. By 1988, 50% of the US households subscribed to cable television. In recent years, there has been some use of fiber cables instead of conventional copper or aluminium cables. Channel selectors allow for reserving certain channels to subscribers who have paid extra for access.

Cable Railway or Cable Car

Railways running on aerial cables were invented in the later half of 17th century and early half od 18th century to move coal from coal mines to the harbours by crossing the hills and mountains. Now the cable railways are mostly used for ski resorts and other tourist attractions. The ccapacity of passenger units varies from chairs to cabins that can hold more than hundred passengers. The first street railway to run on underground cables was developed by Andrew Hallidie in the San Francisco (USA) in the year 1873. The complex cable systems were subject to breakdowns and need much energy. It was in the beginning of 19th century, electric street cars began to replace cable railways.

Thursday, 1 April 2021

Abacus and Calculator meaning in Electronics

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Abacus and Calculator meaning in Electronics


Abacus is a calculating device which consists of balls strung on wires or rods set in a frame. It is almost certainly of Babylonian origin but its use decreased in Europe with the beginning of Arabic numerals in about the 10th century AD. Until recently it was still use in the Middle East and Japan. Ancient types of abacus have also been found in China, thought that same to have taken there by Arabic traders. The first known use of them in China was during the twelfth century where the device was called the ‘Suan-Pan’. It can be used to do mathematical functions such as addition, subtraction, multiplication and division and to calculate square roots and cube roots.



It is a device that adds, subtracts, multiplies and divides with accuracy and speed. A mechanical calculator was built by the German mathematician Wilhelm Schickard in 1623 using a set of metal wheels. Around 1642 the French Mathematician Blaise Pascal made a similar machine that could handle up to nine digit numbers. In 1673, the German Mathematician Gottfried Lelbniz made a device similar to Pascal’s. Beginning in the 1960’s electronic calculators and digital computers became very popular. Besides adding, subtracting, multiplying and dividing many electronic calculators perform more complicated functions such as extracting square roots and cube roots. Many models also contain a memory in which numbers and instructions for solving problems can be stored for future use.

Friday, 26 March 2021

Branches of Medical Treatment

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Here are a list of branches of medical treatment are as follows,


In 1847 and 1848, a Scottish doctor named Sir James Y Simpson used chloroform to relieve the pain of childbirth. Queen Victoria was one among the first to be anesthetized during childbirth. Without anesthesia, doctor can’t do complicated surgical operations. As the anesthetic makes the patient to not suffer from pain, it deeply lessens the physical shock and emotional stress during the operation. General anesthesia involves the loss of feeling in the whole body while local anesthesia is the loss of pain sensation in any of the part of the body.


Cardiology is the branch of medicine that deals with diagnosis and treatment of heart disorders. Doctors who specialize in cardiology are called cardiologists. Cardiologists interview and examine patients for possible heart disease. First, the cardiologist asks if the patients has experienced symptoms that suggest heart disease such as chest pain, shortness of breath, and ankle swelling. The cardiologist then examines the patient by checking the blood pressure, by feeling the beat of the heart and checking the pulse.


It is the branch of medicine that deals with the prevention, diagnosis and treatment of skin diseases. Doctors who specialize in this field are called dermatologists. Skin ailments treated by dermatologists include inflammations, infections, burns and tumours. Dermatologists also treat many children and teen-agers who have acne or certain allergies. Dermatologists are trained to recognize changes in the skin that indicate a disease in other parts of the body.

Forensic Science

Forensic science generally is interpreted as the application of science to legal matters, most often to criminal cases. Forensic medical science dates back to the Greeks. In the U.S it began in 1812 in New York City at the college of physicians and surgeons. Later in the 19th century, Alphonse Bertillon (France) established a system based on measurements of the human body. In 1869 the value of fingerprints was established by Sir William Herschel (England).


The history of Neurology started in 1760's with the publication of work of Swiss physiologist Albrecht von Haller's book on the topic, human physiology. In this book he discarded popular notions about nerves in favor of data he gained experimentally. He proved, for instance, that stimulus to a nerve produced a sharp muscle contraction and thereby demonstrated that nervous stimulation controlled muscle movement. He also showed that nerves channel and carry impulses that produce sensation in tissues.


Ophthalmology is the field of medicine involving the diagnosis and treatment of eye diseases. An ophthalmologist, sometimes called an oculist, must have a medical degree and three to five years of specialized training in a hospital. Ophthalmologists limit their medical practice to the eye. They examine the eye with special equipment and determine the degree of refraction in the lens of the eye. Refraction is a measurement of the eye's ability to see. If the examination shows that the patient needs glasses, the ophthalmologist gives the patient a prescription for them. Glasses are made by an optician. An ophthalmologist who discovers that an eye condition requires corrective surgery is qualified to perform the necessary operation. Albrecht Von Graefe (Germany) is known as the founder of modern ophthalmology because of his contribution during the mid 1800's.


Optometry is a profession devoted to the care of vision. Optometrists give eye health and vision examinations. They diagnose vision problems that affect a persons ability to see near and distant objects clearly and to judge distance. They also test the ability of the eyes to work together ana to change focus easily Optometrists prescribe eye glasses and contact lenses to correct faulty vision. They also may recommend vision therapy to help a person overcome certain vision problems. If an optometrist diagnoses symptoms that indicate disease in the eye or any other part of the body, the person is referred to a doctor.


Orthodontics is the branch of dentistry in medicine that deals with the prevention and correction of irregular positions of the teeth. In addition to causing poor personal appearance, irregularly positioned teeth are difficult to clean. Thus, they are more likely to decay and promote gum diseases. They also can cause chewing and speech problems. Irregularities in the position of teeth are called malocclusions. Malocclusions usually arise during childhood as the teeth grow. They most commonly occur when the teeth are too large for the available law space. Under such conditions, the teeth become crowded and turned out of position. In some cases, one of the jaw bones is larger than the other, creating a condition of overbite or under bite. Malocclusions can sometimes be prevented by the early removal of certain deciduous teeth.


Orthopaedics is a branch of medicine that deals with treatment of disorders of bones and muscles and their related tissues. Doctors who practice orthopaedics are called orthopaedic surgeons. They treat a wide range of disorders including fractures and injuries to ligaments, tendons and so on. They also treat the deformities of the limbs and spine. Some orthopaedic disorders are present at birth. Others occur during childhood due to problems of growth or in later life as a result of aging. Still others result from injury or illness. People injured in car accidents and athletic or recreational activities account for a large number of the patients treated by orthopaedic specialists.


Osteology is the science related with the structure and function of bones. Osteologists study the bones of human beings and animals. They can determine the sizes and living habits of prehistoric animals from bones. They also can tell the age, sex, height and weight of the person or animal from which the bones came. Osteology also includes the study of bone disorders and diseases.


Pathology is the study of disease or any condition that limits the power, length or enjoyment of life Comparative pathology compares human diseases with those of various animals. Human pathology is a branch of medicine. Pathologists use modern instruments and methods, such as electron microscopy, to help them recognize the changes caused by disease in the tissues and organs of the body. They try to explain why a diseased body acts differently from a normal body Pathologists use their knowledge of diseased tissues and body fluids to aid treatment. Pathological tests help doctors diagnose a disease and to establish the extent of its attack. These tests may include examination of the blood, urine and tissues. The use of laboratory tests to diagnose disease is called clinical pathology.

Plastic Surgery

Plastic surgery is a branch of medicine that deals with the repair or reshapes the defects of body. It includes repairing the muscles, bones, nerves and blood vessels. The origin of word plastic comes from a Greek word that means shape or mould. Plastic surgeon moulds the body tissues. They rearrange, take away or replace tissue to reinstate normal function to deformed or injured body parts. Plastic surgeons also attempt to recover the look of aging tissue.

Sports Medicine

Sports medicine is a field that provides health care for physically active people. Its main purpose is to minimize the risk of injury and to treat effectively injuries that do occur. Sports medicine draws on the knowledge of many specialists, including doctors, athletic trainers, physiologists and physical educators. These professionals’ help in shaping the kind of training required to help athletes carry out their top abilities without injury. They also evaluate coaching methods, the enforcement of regulations to prevent injuries and the design and use of athletic equipment and facilities.


Surgery is the branch of medicine that deals with the treatment of disease, deformities or injuries by operations. The doctor who performs the operation is called a surgeon. Every doctor has some training in surgery and is qualified to perform simple operations. But surgeons are specially trained so that they have the judgment and skill to perform complicated operations. Four to seven years of training after medical school are necessary for doctors to qualify as surgical specialists.

Veterinary Medicine

Veterinary medicine is the branch of medicine that deals with the study of diseases of animals. Animal doctors are called veterinary surgeons or vets. Their work is especially valuable because many animal diseases can be transmitted to human beings. Such diseases are called Zoonoses. They include rabies, brucellosis, tuberculosis, psittacosis.

Wednesday, 24 March 2021

List of Biomedical Devices

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Here are a list of biomedical equipment used in Hospitals,

Electrocardiograph (ECG)

Electrocardiograph (ECG) is an instrument used to diagnose heart disorders. For each time the heart beats, ECG produces the electrical currents. Through these currents, we can examine the rate and pattern of contraction of the heart. An electrocardiograph picks up these currents and records them on paper. The electrocardiograph may be connected to a printer, which prints the record. This record is called an electrocardiogram, often abbreviated to ECG. The electrocardiograph may also be connected to an oscilloscope, an instrument that displays the currents on a TV-type screen. An electrocardiograph contains amplifying and recording equipment. Wires run from the machine to electrodes-strips of metal that conduct electricity. In 1903 Dutch physiologist Willem Einthoven invented the first crude electrocardiograph in the form of a string galvanometer. He was awarded the 1924 Nobel Prize in medicine and physiology for this work.

Electroencephalograph (EEG)

Electroencephalograph is an instrument used to measure and record the electrical voltages produced by neurons in the brain. A recording of this electrical activity is called an Electroencephalograph. Doctors and neuroscientists use the electroencephalograph to study normal brain activity, as well as abnormal brain states that caused by injury, tumour, infection or even death. To record an electroencephalogram, medical personnel attach electrodes from the electroencephalograph to the patient's scalp. Hans Berger, a German psychiatrist invented the first electroencephalograph in 1929 to measure the rhythmical electrical activity of the human brain


Thermometer is a biomedical device that measures the temperature of solid, liquid and gases. The action of a thermometer is based on the fact that certain measurable physical characteristics of substances change when the temperature changes. These characteristics include the volume of a liquid and the length of a solid. Another is the resistance - that is, the opposition to the flow of electricity - in an electrical conductor. There are three principal types of thermometres: (1) liquid-in-glass, (2) deformation type and (3) electrical. Many types of thermometers are made as both digital thermometres and disposable thermometers.


Syringe is a pump-like device. It is a tube, tapered at one end, with a plunger or a soft, hollow bulb at the other. The plunger or bulb either creates suction or forces fluid from the syringe. Syringes are used to spray or inject liquids or to remove them by suction.


Spirometer is an instrument that measures the amount of air a person breathes. Doctors use spirometers mainly to diagnose the certain respiratory disorders and to evaluate treatment. A common type of spirometer consists of two cylinders, one filled with air and the other with water. Both cylinders are open at one end. The air-filled cylinder, which is attached to weights, floats open-end down in the water-filled cylinder. The patient breathes through the mouth into a tube extending from the air cylinder. When the person exhales, the amount of air in this cylinder increases and the cylinder rises in the water. As the patient inhales, air leaves the cylinder and it falls. The movement of the air cylinder provides a measure of the volume of air breathed and is recorded on a strip of paper called a spirogram.


The first catheter was made in 1929 by a German physician named, Werner Theodor Otto Forssmann. He made it with a thin rubber tube.  It was intended to examine the diseased hearts. In 1936, other physicians of United States named Dickinson W Richards and Andre F Cournand make developments on Forssmann's catheter and experimented on animals. But the first successful human cardiac catheterization was happened in 1941 under the control of physicians named, Richards and Cournand. The catheter can measure the rate of flow of blood, oxygen and also the blood pressure.


Humidifier is a biomedical device which increases the amount of moisture in indoor air or a stream at air. The working principle of Humidifier is by letting water to evaporate from a pan or from a wet surface or by circulating moisture in air. Humidifiers are used in industry to create an atmosphere suitable for testing or processing certain materials. In homes, humidifiers help reduce static electricity and prevent wood structures and furniture from becoming brittle.


Ophthalmoscope is an optical instrument used for examining the interior part of the eye. Ophthalmologists and optometrists can diagnose many eye conditions by using the ophthalmoscope to examine abnormalities in the eye. There are two main types of ophthalmoscopes. They are the direct ophthalmoscope and the indirect ophthalmoscope. The direct ophthalmoscope contains a light, a prism and a mirror and lenses. These parts are mounted in the head of the instrument, which is attached to a handle containing a battery. The prism and mirror project the light on the back of the eye. The lenses enable the examiner to focus the light to provide a clear, magnified view of the eye's interior. The indirect ophthalmoscope consists of a light worn on the examiner's head and a lens held in front of the patient's eye. This instrument enables the examiner to see a larger area than the direct ophthalmoscope does, but with lower magnification. The ophthalmoscope was invented in 1851 by German physician and physicist Hermann Ludwig Von Helmholtz for the purpose of examining the interior of an eye through its pupil.

Pace Maker

Clarence Walton Lillehei, an American physician built the first pacemaker in 1957. Lillehei’s pacemaker was an electric unit that could be inserted in the patients chest where it would give off an electrical jolt in order to regulate the pace of the heart beat.


In 1863 French physiologist Etienne Jules Marey invented the first sphygmograph for the purpose of recording blood pressure. An external sphygmomanometer that allowed the measurement of blood pressure in clinical settings was developed in 1896 by Scipione Riva-Rocci (Italy).


The sphygmometer was invented in 1835 by French physician Julius Herisson. It transmitted impulses from the pulse beat to a mercury column and made each beat visible to the observer. Herisson 's sphygmometer was the first tool to visually show and numerically measure the pulse beat without the need to puncture an artery.


To aid his research on the mechanics of the cochlea, Hungarian-born physicist Georg Von Bekesy (U.S) developed an “audiometer” during the 1960s. Designed to test the hearing function, it was able to distinguish between deafness caused by functional loss in the cochlea and that caused by a problem with the auditory nerve.


Centrifuge is an instrument used to separate two liquids mixed together, or solid particles that are mixed with water or any liquid. The centrifuge causes the heavier liquid or the solid particles to move to the bottom of the container, leaving the lighter substances on the top. It usually consists of a large wheel connected to an electric motor. The mixtures to be separated are balanced in containers on each side of the wheel. When the motor is turned on, the wheel rotates rapidly and the containers swing out from the centre. A smaller centrifuge consists of a small rotating top in which test tubes of material can be placed at an angle. The centrifuges turn from 800-6000 times per minute. The ultra centrifuge is a newer kind of centrifuge with tremendous speed. It can spin at around 80,000 turns per minute. The rotating part of an ultra centrifuge touches nothing solid. It is balanced on a cushion of air. The ultra centrifuge whirls by means of jets of compressed air that touch the outer surface. Ultra centrifuges are used to study viruses.


Endoscope is a medical instrument used to determine the interior part of a hollow organ or a cavity of body. Unlike other devices, endoscopes are put directly into the organ or cavity that is to be examined. There are several types of endoscopes. Most endoscopes consist of a flexible or rigid hollow tube with a lens at one end. Arnaud designed the first endoscopic lamp used to illuminate the interior of orifices in humans around 1819. He built his instrument with a biconvex lens.


Incubator is an apparatus that maintains a favorable environment for growth and development. Some types of incubators are used by hatcheries to hatch chicks from eggs. Others are used in hospitals to maintain the lives of newborn or prematurely born babies. Some are used in laboratories for research. All these incubators differ in design, but their chief function-to provide a controlled environment - is the same. In 1884 an incubator warmed by Kerosene lamps appeared in Paris at La Maternite. American physician Julius H. Hess designed an electric incubator for premature infants and filed for a patent in 1933.


Microscope is an instrument that magnifies extremely small objects so they can be seen easily. It is one of the most important tools for diagnostic purposes. For instance, Doctors and biologists, use microscopes to determine bacteria and blood cells.



In 1854, a music teacher named Manuel Patricio Rodriguez Garcia from England developed the first laryngoscope that permitted a clear view of glottis at work. Garcia found that the vocal cords are the reason for the voice and its tones. With this laryngoscope, it became possible to see any obstacles occurring in the larynx.


An instrument doctors use to hear the sounds produced by certain organs of the body, such as the heart, lungs, intestines, veins and arteries. The stethoscope picks up the sounds made by these organs and excludes other sounds. Listening in this way, known as auscultation, is an aid to diagnosis. It alerts the doctor to characteristic changes of sound caused by different types of diseases. The stethoscope consists of a body contact piece, which is placed against the body of the patient and ear pieces, which are placed in the ears of the doctor. Hollow rubber tubing connects the body contact piece to the ear pieces. Doctors use either a bell, diaphragm or combination bell-diaphragm body contact piece. The bell type of contact piece picks up low-pitched sounds. The diaphragm type picks up high-pitched sounds. Rene Laennec a French physician, made the first stethoscope in 1816.


In 1626 Italian physician Santorio Santorio, also known as Sanctorius, adapted the thermometer invented by Galileo Galilei (Italy) in 1593 for the purpose of measuring human temperature in a clinical setting. Santorio's device was called a “thermoscope".


Ventillator is a machine that helps a person breathe. A ventillator may be used if illness or an accident causes breathing to become difficult or to stop. It also can be used to administer oxygen or to treat a patient with a mist containing medications. Ventillators are often called respirators or resuscitators. There are two basic types - positive pressure and negative pressure ventillators. A positive pressure ventillator forces air into the lungs under pressure. After the lungs are filled, the machine cuts off the pressure and the natural elasticity of the lungs expels the air. Such machines operate as either assist ventillators or automatic ventillators. Assist ventillators are triggered by the patient's breathing. They help extremely weak people inhale. Automatic ventillators control respiration completely and aid people whose breathing muscles are paralysed.