Bi Stable Multi Vibrator or Set Reset Flip Flop

Bi Stable Multi Vibrator or Set Reset Flip Flop

Introduction:- Bi stable multi vibrator has two stable states that is its output can be set to 1 with set pulse or can be set to 0 with reset pulse. It is also known as set reset flip flop or SR flip flop. It is the basic unit of electronic solid state memory. It stores one bit of data that is 0 or 1.To store 8 bits data set of 8 flip flop are used. Register also uses the flip flops for storing data. Additional logic circuitry is also used to write read data.

Basically in all digital circuit supply voltage used is 5 volt dc. So in this set reset flip flop working voltage 5 volt is given to Vcc and - ve to ground. There are two input points set and reset. When a positive pulse is given to set input the output of flip flop changes to state 1. This state remains constant until a reset pulse is given to reset input. Again when we want to reset a reset pulse is given to reset input, the output reset to 0 state and remain in 0 state until set pulse is given to set input.
this property of SR flip flop make it suitable for digital bit storage. According to data bits all flip flop of eight bit storage locations are set to their corresponding bit. In simple electronics this flip flop can be used to make latching relay circuit.

Circuit Working:- When set switch is pressed positive voltage goes to the base of transistor T1 make it conducting. So the collector voltage of transistor T1 becomes 0 so biasing of transistor T2 base through R3 resistance reduce to 0 volt and T2 gets cutoff. Due to cutoff of  transistor T2 collector voltage of transistor T2 becomes 5 volt which start providing biasing to base of  transistor T1  through resistance R4 this makes T1 to remain in saturation level even after set button is depressed.
Same process is repeated when reset button is pressed. Transistor T2 start conducting so the collector voltage of T2 becomes 0 volt so biasing of T1 base trough resistance R4 reduced to 0 volt and T1 gets cutoff. Due to cutoff of transistor T1 the collector voltage of T1 becomes 5 volt which start providing biasing to base of transistor T2 trough resistance R3 this makes transistor T2 to remain in saturation level even after reset button is depressed.


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Simple Arduino program, blinking a LED for beginners

A Simple Arduino program, blinking a LED for beginners

Introduction:- Arduino  board is a complete board for learning use of micro controller.It uses micro controller IC ATMega328 16 Mega Hertz. It is 8 bit micro controller with 32 kb of program memory. It has inbuilt programmer to upload program through USB port. Input dc supply jack is provided for giving input dc supply 8-12 volt. Inbuilt voltage regulator are used to provide 5 volt and 3.3 volt regulated power supply for internal use. 13 numbers digital input / output pins are provided for external devices connection. one LED is internally connected to pin number 13. Analog I/O pins, PWM pin and serial transfer Rx Tx pins are also provided.

Micro controller is a very small computer on a single chip. It consist of inbuilt CPU, storage memory, input output ports. Arduino board has every thing required for use of micro controller. It needs to upload a program and run. In this post I am writing a very small program to explain program structure and syntax use for Arduino programming. It used open source integrated environment development software for arduino. Screen shot of arduino IDE for windows is as shown below. Software can be downloaded from net.

When you open this arduino IDE in PC you will see this screen. Open blink example from menu bar
file  examples//basic/ blink . you will see screen open with above code. now please see the code it is similar to c++ programming language. this is very first and small program for beginners. first part of program is void setup() in this function we write the code which has to executed  only once. To use any digital input/output pin we have to configure the pin as input or output with a line of code like pinMode(pin number, OUTPUT/INPUT). Here we are using function pinMode to declare LED_BUILTIN (pin 13) as a output pin.

void setup() {
  // initialize digital pin LED_BUILTIN as an output.
  pinMode(LED_BUILTIN, OUTPUT);
}

Second part of program is loop function it runs continuously till the program is not stopped.
In loop function   digitalWrite(LED_BUILTIN, HIGH);  is use to write (give) a high value to  LED_BUILTIN (pin  13). when high value is given to pin 13 led connected to this pin gets on. Function   delay(1000);   Provides a delay of 1000 mili  seconds. This keeps pin 13 high for 1000 ms. Then the function digitalWrite(LED_BUILTIN, LOW);  is use to write low on  LED_BUILTIN (pin  13). When low value is given to pin 13 led connected to this pin gets off. Again function delay(1000); is used to give 1000 ms off time for pin 13 led. this complete code is repeated continuously as it is in loop function. Code for loop function is as given below.

void loop() {
  digitalWrite(LED_BUILTIN, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(1000);                       // wait for a second
  digitalWrite(LED_BUILTIN, LOW);    // turn the LED off by making the voltage LOW
  delay(1000);                       // wait for a second
}

After writing the program code in editor window it need to compile. in editor. Below menu bar there is a tool bar. In tool bar there are tab buttons for compile and upload the program.there is tool tip on each button. so by clicking on compile button program will compile and a message of successfully compiled or some error will display in output window.if your program is written correctly it will compile successfully.after compile we have to upload the program in Arduino board. For this we have to connect our board to computer with the help of USB cable which comes with board. The USB cable serves two purpose first it gives the power supply to the board and second it upload the hex code to the board. As soon as code upload is completed a message is displayed on IDE that upload is completed. Now micro controller runs this program and you will see that led connected to pin 13 starts blinking at the rate  of 1 second off and 1 second on. To blink a led can be done by any electronic circuit. but to change on/ ff duration will required to change components. With micro controller we have to change delay time in our program and upload. you can experiment by changing time period. any other output pin can also be use to control other led. We can also use 5 volt miniature relay in place of led and control any device from relay. Maximum output current of any output pin is max 50 ma. so we should be care full to connect load to pin that current should be in safe limit. Arduino is very vast can not be cover in such a small post. so for any doubt please ask in comment or take some help from net.
This program as well as many programs are given in  examples of arduino IDE that can be used for further learning. I hope this post will help full to you. your valuable suggestion and comments are welcome for improvement.



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Functional block diagram of Television with explaination

Functional block diagram of Television with explanation

Different stages of television: - The main stages of black and white television are as follows.

Power supply stage:- Here 230 volt power supply is converted to 110 volt and 12 volt DC supply required for different sections (stages) of TV. Following type of power supply are used in TVs and many other electronics items.

1 Transformer power supply:- Consist of a step down transformer with 110 volt 12 volt and 6.3 volt secondary windings. Bridge rectifier and filter capacitor is used to produce 110 volt DC and 12 v DC. 110 volt DC is used in EHT section and 12 volt DC is used in sound section.

2 Scr based power supply:- scr (silicon controlled rectifier also known as thyristor is used to make 110 volt DC regulated supply. 110 volt DC is given to EHT section. All other supply are produced from the EHT section.

3 SMPS POWER SUPPLY :-Now a days all TVs uses smps (switch mode power supply)  power supply. More are less are electronic item uses smps power supply. Nearly 30 percent problems of TVs are due power supply and can be fixed by repairing power supply.

Tuner section :- This is the first section of TV. It has three sub section ie RF amplifier section, local oscillator section and a mixer section. It generates local oscillator frequency as per the requirement of receiving RF signal frequency. TV signal received from antenna is given to RF amplifier section with matching transformer known as balloon. The antenna output impedance is 300 ohms to be matched with tuner input impedance of 75 ohms. Balloon is used with input impedance 300 ohms and output impedance 75 ohms as impedance matching transformer between antenna and tuner. The RF signal is amplified in RF amplifier section. Then local oscillator signal and RF signal is mixed in mixer stage. The mixer stage output signal is known as video IF signal which is then sent as input signal to video IF section. AGC (Automatic gain control signal) voltage is received from VIF Section to tuner section for RF Amplifier gain control .12 V DC power supply is given to tuner for its working. In old TVs 12 channel tuner were used in which channel was changed with knob manually. Now a days all TVs are using electronic tuner in which band selection and tuning is done electronically from front panel or remote control. In electronic tuner 33 volt supply is also given as tuning voltage. In electronic tuner varactor diode is used in oscillator circuit to control the oscillator frequency by changing tuning voltage applied to varactor diode. Varactor diode capacitance is changes with reversed bais  applied voltage changes.

VIF Section:- This section has a 3 stage video IF amplifier, keyed AGC generator and demodulator built in a single IC . The video IF signal received from tuner is amplified. After amplification VIF signal is demodulated, After demodulation composite video signal is sent to video amplifier and sync separator stage. Sound IF signal is sent to sound IF section.To produce keyed AGC  VIF section receive's fly back pulses  from EHT section.

Sound IF amplifier:- In  this section sound IF signal is amplified in two stages and the signal is demodulated  to produce sound or audio signal. Audio signal a sent to audio amplifier stage through volume control.

Sound amplifier :- This section consist of four stages of  audio amplification ie first audio  amplifier, second audio amplifier, driver  stage and. Power amplification stage. All stages of audio  amplifier are built  in a single IC known as sound/audio amplifier IC. The speaker is connected to output of audio amplifier and convert amplified audio signal to sound.

Picture tube:- The function of picture tube is to produce picture. It has a cathode which is heated by filament. When cathode is heated electrons emits from cathode. With the help of control grid focusing anode, first accelerating anode and final accelerating anode an electron beam is produced and focused at the center of screen. The screen has phosphor coating in side when this electron  beam strikes on screen a light spot is produced on screen. With the help of vertical deflection coil and horizontal deflection coil this spot is deflected in sequentially way to create raster. And hence complete screen gets illuminated with a single point of light running very fast on screen . Due to persistence of vision our eyes feels continuous presence of light. The picture formation and raster details will be covered in other article.The video signal from video amplifier is given to cathode of picture tube. It is known as cathode modulation. It control the intensity of spot on screen. The movement of spot created by electron gun is synchronized with the scanning gun of camera so the position of spot and intensity of spot is exactly the same as the camera so same image is formed on the  screen. Such 25 images (50 frames) per second is produced by picture tube so that we see a movie picture on screen.

Video amplifier :- The video signal received after demodulation is amplified in video amplifier stage. The output signal is given to cathode of picture tube from the collector of video amplifier transistor. Vertical blanking pulses are also added in this stage for blanking of vertical retrace lines. In color TV video amplifier stage has a chroma IC which processes the composite video signal and produces 3 signal for red, green and blue color. These color signal are amplified in three amplifier transistors and given to red gun (red cathode), green gun and blue gun of color picture tube.

Horizontal oscillator stage:- In this stage horizontal oscillator signal of 15625 hz is generated. A sync separator circuit in side IC separates vertical sync pulses and horizontal sync pulses from composite video signal received from VIF section. A AFC circuit synchronized the horizontal oscillator with horizontal sync pulses. Vertical sync pulses are sent to vertical oscillator for synchronization.

Horizontal driver :- horizontal oscillator signal is amplified in driver stage. A driver transformer is used. The signal from secondary of driver transformer is given to base of horizontal output transistor. The collector supply to the output transistor is received from primary winding of EHT transformer. horizontal deflection Coils are connected to output of horizontal output section.

Horizontal output section:- It uses a power transistor (BU205, BU208), A EHT transformer and horizontal deflection coil placed in yoke which is mounted on picture tube neck. EHT transformer has few more winding which are used to generate 50 volt supply for vertical stage. 6.3 volt winding for picture tube(CRT) filament. Different EHT have some difference in auxiliary supply voltages.

Vertical stage:- This stage has in built vertical oscillator and vertical amplifier in a single IC. Vertical oscillator generate 50 hz saw tooth wave signal. After amplification this voltage is given to vertical deflection coil placed in yoke. The vertical oscillator uses vertical sync pulses received from sync separator to get synchronised with composite video signal. Vertical stage has two presets to adjust vertical hold of picture and vertical linearity of picture respectively.

Some common faults.
No light no sound :- problem of power supply.
Horizontal line:- problem in vertical stage.
No picture no sound but raster (light) is present :- fault is in VIF stage or in tuner stage.
Picture coming sound is not coming:- problem is in sound IF stage or audio amplifier stage.
Sound is OK but only plain light on screen :- problem in video amplifier stage.
Sound OK but no light : problem may be in horizontal oscillator or EHT section.

It is a very brief discription of black and white TV. Interested reader need to go for more details. Any question are welcome in comment. Thanks for reading.

three-phase-welding-rectifier circuit diagram with working principle

main-sections-of-lcd-tv/ LCD TV block diagram

Variable frequency variable voltage VVVF

Variable frequency variable voltage VVVF

Introduction :- The motor used in any machine need to be operate at variable speed.Earlier DC motor was used for applicatios where speed control is requred. The speed of ac motor is considered as fixed speed because the speed is depend upon number of pole and frquency of supply. But now a day with invent of VVVF drive it becomes easy to control speed of motor by producing variable voltage variable frequency supply for motor.
Working:-

In VVVF drive three phase voltage is converted in to dc voltage generally 500  v dc. Then three phase inverter circuit is used to produce 3 phase ac supply of  varable frequency and variable voltage. Voltage to frequency ratio remains constant.It uses digital control system for firing control of IGBT and inverter parameter setting. All the data of motor (such as voltage current rpm)  and operational requirements are  stored in parameters of drive.  VVVF drive has a display and key pad which are used for parameter setting. During running of motor running data load current and fault candition is also displayed on display. Drive key pad has buttons for start stop local remote forward reverse etc. In addition to this external push buttons can also be connected in control terminal block for start stop speed increase decrease etc. drive has three power terminal nuetral terminal and earth terminal for input connection. similarly three power terminal and one earth terminal for motor connection.

different makes of drive has some difference in control terminal block connection but basically all are same. With the help of instruction manual given with drive and following all instructions care fully it is easy to use VVVF drive for speed control of ac motor application. please see my blog for more articles. your comment and suggestions are welcome. 

Transistor as amplifier and switch

Use of transistor as amplifier

To use a transistor as an amplifier it is used in common emitter configuration. The operating collector current is set nearly half the max collector current with the help of collector load resistance and base biasing resistance. transistor never go in saturation or cutoff value of collector current. Some short of negative feedback is also given by providing emitter resistance and emitter by pass capacitor. This negative feed back improve the quality of signal amplified.

Use of transistor as oscillator

A transistor connected in common emitter configuration just like an amplifier circuit can be converted to a oscillator just by providing a positive feedback from output circuit to input circuit. In common emitter circuit the output wave form is always 180° out of phase with input wave form. if some part of output is fed back to input in additive phase  then it becomes oscillator. below is diagram of resistance capacitance phase shift oscillator.

Use of transistor as switch 

A transistor can be used as a switch to control small current load. Relay can  be controlled by a transistor to control heavy loads. In switch mode transistor is biased to either cutoff current (for switch off) or to saturation current (for switch on).Set reset flip flop can be used with transistor to get latching property.

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Impedance, resistance, inductive reactance and capacitive reactance

Introduction:- The current flowing in a DC circuit is basically calculated by ohm's law. The current is equal to voltage divided by resistance ie I =V/R. But in ac circuit effective resistance offered by an inductance or/and capacitance are also to be considered. The resistance to flow of ac current by an inductance is known as inductive reactance its value is given by 2πfL where f is frequency of supply and L is inductance of inductor coil. Inductive reactance is denoted by XL. Similarly the resistance offered by a capacitor is known as capacitive reactance given by 1/2πfC where f is frequency and C is capacitance of capacitor. Capacitive reactance is denoted by Xc. A circuit with two or all three components  present, the effective resistance offered by circuit is known as impedance of circuit denoted by Z. Then current I =V/Z amps. Where Z is given by formula

Resistance:- When ac supply is given to a pure resistance. The current flowing trough resistance is equal to V/R amps and it is in phase with applied voltage. The vector diagram is given below.

Pure inductance:- When ac supply is given to a pure inductance the magnitude of current is given by V/XL where XL is known as inductive reactance is equal to 2πf,L. The current is 90 degree lagging to the voltage. The vector diagram is given below.

Pure capacitance:- When ac supply is applied to a pure capacitance the current flowing through capacitor is given by V/Xc where Xc is known as capacitive reactance, given by 1/2πfC. The current is leading voltage by 90 degree. The vector diagram is given below.

Series R L circuit:- Any inductance can never be a pure inductance it has some internal resistance also. So any inductance can be considered as an inductance in series with a resistance. So for this effective resistance offered is given by Z = √R²+X_L². So the current through inductance is I = V/Z amp. Current is lagging voltage by by an angle Φ = Cos^-1 R/Z.

Series RC circuit:- When ac supply is applied to a series circuit of resistance and capacitance. In series combination of resistance and capacitance the resistance offered by circuit is given by impedance Z = √R²+ Xc². So that current through circuit is I = V/Z. The current is leading voltage by an angle Φ = Cos^-1 R/Z.

Series R L C circuit:- In series RLC circuit the current flowing through circuit is given by I = V/Z where Z is impedance of circuit given by formula

The current may be leading or lagging the voltage as per the value of capacitive / inductive reactance which ever is greater. The phase angle is given by Φ = Cos^-1 R/Z. The difference of XL and Xc taken. 

In this way the current and power factor of any series circuit can be calculated.

Effects of low power factor

Effects of low power factor

Phase angle lagging / leading:- AC (Alternating current) voltage or current is continuously varying in magnitude and direction with respect to time. Its instantenious magnitude varies according to sine function of angle from 0 to 360 degree or 0 to 2π radian. Voltage value is increases from 0 volt to maximum positive value Emax volt and then decreases back to 0 volt in positive half cycle. In negative half cycle voltage decreases from 0 volt to maximum negative value -Emax volt and then  increases to  0 volt. These are known as positive half cycle and negative half cycle. One positive half cycle and one negative half cycle makes a complete cycle. The alternating voltage cycles are repeated continuously. The number of cycles per second is known as frequency of supply. For 50 hz supply there are 50 cycles per second that means supply voltage will change its direction 50 times in a second. For one cycle it takes 1/50 second ie 20 mili second known as time period of ac cycle denoted by capital letter T. A cycle consist of one positive and one nrgative half cover 0 to 360 degree angle. 0 degree of this cycle is consider as reference point for angle measurement. For example in three phase system three alternating voltage are present whose staring point is 120 degree apart from each other. If we consider red phase as first phase then yellow phase 0 degree point is 120 degree after the red phase 0 degree starting poing. Similarly blue phase 0 degree point is 120 degree after the yellow phase 0 degree point. Again red phase will come after 120 degree of blue phase and this continue endlessly. This 120 degree is known as phase difference. As in this case yellow phase voltage come 120 degree after red phase it said like this  the yellow phase is 120 degree lagging red phase. Or red phase is leading yellow phase by 120 degree. The word leading means before and lagging means after.

Types of load :- there are mainly three types of load. Resistive load, inductive load and capacitive load.

Resistive load:-When  ac voltage is applied to a resistive load such as filament bulb the current flowing through resistance is in same page with voltage, means the 0 degree starting point of current is at the same 0 degree point of voltage. This is said as current is in phase with voltage. The power factor is cosine of angle between voltage vector and current vector (ac quantities are represented as vector)
Power factor = cos(0)
Power factor =1
So in resistive load power factor is always 1.

Inductive load:- Inductance always oppose to change of flow of current. Due to this property when ac voltage is applied to an inductive load ac current is start flowing through it but the current is some degree (say for example 30 degree) lagging the aoplied voltage. Now power factor is cosine of angle
Power factor = cos(30)
Power factor = .866
So here we say power factor is .866 lagging.

Capacitive load:- When ac supply is applied to a capacitive load the current flowing in pure capacitor is 90 degree leading with voltage. Hence the power factor is cos(90) = 0  leading.

Conclusion:- in resistive load power factor is always 1 also said unity power factor. In pure inductor power factor is 0 lagging. But inductor is always having some resistance so that power factor lies between 0 to less than 1 lagging. in case of capacitor power factor if 0 leading.

Power in ac circuit:- The power in ac circuit is product of voltage and component of current in phase with voltage. So if applied voltage is V and current flowing in circuit is I and the angle between voltage and current is phi. Then

Power = V x I x Cos(phi)
The equation show that cos(phi) is a multiplying  factor in power calculation, that,s why it is known as power factor.

Effect of power low factor:- It is clear from equation that if power factor is low then more current is required for the same load. Therefore any load which is running at low power factor will draw more current from power supply system.

Disadvantage of lower power factor

1 conductor size is line need to be of higher size as per increased demand of load current.
2 All switchgear sizes are to be of higher size.
3 Transformer will supply less power as compared to they could supply at good power factor.

Due to all these problems power supply authorities are always insists for improving power factor for industrial consumers,

Main causes of Motor burning

Introduction:- Number of motor burns  routinely and reason for motor burning is never very clearly find out. Motor can run without burning for life time of motor if all the reasons for motor burning are avoided.

Main reasons:- Motor winding burnt only because of temperature rise of winding. Reasons of high temperature of winding is heat produced in side of the motor. Heat is produced in winding of motor due to load current flowing in winding, Induced current flowing in rotor bars or winding..Heat generated in lamination due to  hysteresis loss and eddy current loss. Some heat is generated in bearings due to friction. All the sources of heat, generate heat but motor dissipate that heat efficiently as all are considered in design.If any of heat source start generating more heat, temperature of motor will increase and ultimately motor will burn.

Motor protection with overload relay- When a motor operates at a higher load than designed it gets heated. The load current increases and thermal overload relay starts working. It takes some time to trip as per current time characteristics of thermal overload relay. By tripping motor it protects motor from burning. But in this way motor gets overheat hence winding wire and stator core starts loosing their properties. After many numbers of tripping winding wire insulation is failed and motor burnt. A better practice of thermal over load setting may be use to set thermal at 90 % of motor full load current. Some person use thermal setting slightly higher then running load of motor.To avoid such failure motor must be operated within there load capacity. In machines like belt conveyor, elevators etc mechanical equipment health must be maintained to reduces unwanted frictional load. Jamming of material near moving parts to be removed to reduce load.

Motor cleaning:-Motor body, cooling fins and cooling ducts are kept clean, All heat generated in motor will dissipated and motor temperature  remains in safe limit This will improve motor cooling and hence the life of motor.

Bearings:- Bearing are maintained well lubricated so that bearings will run smoothly and their temperature lies within limit. If a motor run with dry bearing or some what jam or play in bearing, more heat will generate in bearing which will cause over heating of end shied and hence motor stator which will heat winding and ultimate motor burning takes place. Some times due to play in bearings stator core and rotor core starts rubbing each other which increases stator core temperature and hence causing winding burnt out.The load  increases because of bearing problems or core rubbing is not too much to operate overload relay that's why in these problems motor does't trips with overload before winding burnt out.

Vibration in motor:- Due to misalignment or unbalance in rotating part vibration generates in motor. Due to vibration a relative motion starts taking place between winding and stator core, between adjacent turns of coils near over hang and between soldered joint and turns of coil. This rubbing of wire results in insulation failure and causing internal short circuit.This problem is also not sense by over load relay. It can be saved by keeping operation of motor vibration free. If any vibration observed, should be rectified by alignment, balancing or some foundation defects correction.

This is what I have seen in my field experience. If some one like to give more reason please feel welcome to comment because I really like to avoid motor burning.
Thanks

Three phase induction motor reversible starter

Introduction :- Many application requires the direction reversing of induction motors.for example electric hoists, electrical overhead cranes, lifts used in industries. Electrical actuators for operating gates in pipe lines for flow control. now a days various door control mechanisms are also using reversible motors.

Basic:- direction of three phase motor is changed by inter changing the supply phase sequence by inter changing two phase connection.

Circuit diagram :- circuit diagram is given below.

 It uses two Contactor, main circuit bagrker , over load relay, and three push buttons for forward reverse and stop. Three indication lamps can be used to indicate status of running of motor. MCB is first switched on. Forward button is pressed to run in forward direction. When forward push button is pressed C1 contactor picks up and motor run in forward direction and L1 indication  lamp indicate forward running of motor. To stop motor stop button is to be pressed, it dropped out contactor and motor stops L3 indication lamp indicate the motor is stopped. Similarly to run in reverse direction reverse button is to be pressed, it picks up C2 contactor which run the motor in reverse direction by inter changing power supply two phases. This type of circuit is used in all reversing operation with minor changes. Some reversible dol starter use external ICTP in place of MCB. Some places indication lamps are not used. In this 230 volt control is used in some circuit 400 volt or 110 volt control supply is used. In case of overload of motor, thermal overload relay trips the motor and save from burning.

Three-phase-synchronous-motor
no-load vector diagram of-transformer