555 Timer Oscillator

A voltage-controlled oscillator (VCO) using the timer 555 is shown in figure.

555-timer-voltage-controlled-oscillator

The circuit is sometimes called a voltage-to-frequency converter because the output frequency can be changed by changing the input voltage.

As discussed in previous blog posts, pin 5 terminal is voltage control terminal and its function is  to control the threshold and trigger levels. Normally, the control voltage is ++2/3V_CC because of the internal voltage divider. However, an external voltage can be applied to this terminal directly or through a pot, as illustrated in figure, and by adjusting the pot, control voltage can be varied. Voltage across the timing capacitor is depicted in figure, which varies between +V_control and ½ V_control. If control voltage is increased, the capacitor takes a longer to charge and discharge; the frequency, therefore, decreases. Thus the fre­quency can be changed by changing the control volt­age. Incidentally, the control voltage may be made available through a pot, or it may be output of a transistor circuit, op-amp, or some other device.

Mobile incoming call indicator

Description

This circuit can be used to escape from the nuisance of mobile phone rings when you are at home. This circuit will give a visual indication if placed near a mobile phone even if the ringer is deactivated.

When a call is coming to the mobile phone, the transmitter inside it becomes activated. The  frequency of the transmitter is around 900MHz.The  coil L1 picks up these oscillations by induction and feds it to the base of Q1. This makes the transistor Q1 activated.Since the Collector of Q1 is connected to the pin 2 of IC1 (NE555) , the IC1 is triggered to make the LED connected at  its output pin (pin 3) to blink. The blinking of the LED is the indication of incoming call.

Circuit diagram with Parts list

Notes. 

• The coil L1 can be made by making 150 turns of 36 SWG enameled copper wire on a 5mm dia plastic former.Or you can purchase a 10 uH coil from shop if available.
• The circuit can be powered from a 6V battery.
• Assemble the circuit on a good quality PCB.
• C1 & C3 are to be polyester  capacitors.
• The electrolytic capacitor C2 must be rated 10V.

9 V regulator using 7809

Description.

Here is the circuit diagram of 9 V regulator using popular 7809 IC.The 7809 is a 9 V voltage regulator IC with features such as internal current limit,safe area protection,thermal protection etc.A 16 V transformer brings down the 230V mains  , 1A bridge rectifier rectifies it and capacitor C1 filters it and 7809 regulates it to produce a steady9V DC  output.


Circuit diagram with Parts list. 

Notes. 

• If a current of 300 mA or above is required ,fit a proper heat sink to the IC 7809.
• If 1A bridge is not available,make one using four 1N 4007 diodes.

Street light circuit

Description.

The circuit diagram present here is that of a street light that automatically switches ON when the night falls and turns OFF when the sun rises.In fact you can this circuit for implementing any type of automatic night light.

The circuit uses an LDR to sense the light .When there is light the resistance of LDR will be low.So the voltage drop across POT R2 will be high.This keeps the transistor Q1 ON.The collector of Q1(BC107) is coupled to base of Q2(SL100).So Q2 will be OFF and so do the relay.The bulb will remain OFF.

When night falls the resistance of LDR increases to make the voltage across the POT R2 to decrease below 0.6V.This makes transistor Q1 OFF which in turn makes Q2 ON. The relay will be energized and the bulb will glow.

Circuit diagram with Parts list.

Notes.

• POT R2 can be used to adjust the sensitivity of the circuit.
• You can use bulb of any wattage ,provided that relay should have the sufficient rating.
• The circuit can be powered from a regulated 9V DC power supply.
• Click Here! to get the power supply circuit for this project.
• The relay K1 can be a 9V SPDT relay.

555 Timer as an Astable Multivibrator

An astable multivibrator, often called a free-running multivibrator, is a rectan­gular-wave generating cir­cuit. Unlike the monostable multivibrator, this circuit does not require any ex­ternal trigger to change the state of the output, hence the name free-running. Before going to make the circuit, make sure your 555 IC is working. For that go through the article: How to test a 555 IC for working An astable multivibrator can be produced by adding resistors and a capacitor to the basic timer IC, as illustrated in figure. The timing during which the output is either high or low is determined by the externally connected two resistors and a capacitor. The details of the astable multivibrator circuit are given below.

Take a look @ 555 Ic Pin configuration and 555 block diagram before reading further.

Pin 1 is grounded; pins 4 and 8 are shorted and then tied to supply +Vcc, output (V_OUT is taken form pin 3; pin 2 and 6 are shorted and the connected to ground through capacitor C, pin 7 is connected to supply + V_CC through a resistor R_A; and between pin 6 and 7 a resistor R_B is connected. At pin 5 either a bypass capacitor of 0.01  F is connected or modulation input is applied.

555 Tester circuit

Description.

NE555 is an IC which is widely used in timers and control circuits. A circuit for independent testing this IC is given here.

Here the NE555 is wired as an astable multivibrator. When the push button switch S1 is pressed the LEDs D1 & D2 will flash alternatively. That is when output is high D2 will glow & when output is low D3 will glow. The rate of flashing will depend on components R1,R2 & C1.

When push button S1 is pressed,C1 will start charging through R1&R2.When the voltage across C1 rises above 2 of 3 is the supply voltage the internal Flip Flop toggles . The pin 7 becomes low & C1 starts discharging. When the voltage across C1 goes below 1of 3 of supply voltage the internal Flip Flop resets & pin7 goes high. The C1 again starts charging.All this will take place if the IC is healthy.

According to the frequency of this charging & discharging D1&D2 will flash. From these observations we can conclude that IC NE555 is faulty or not .

Circuit diagram with Parts list.

Notes.

• Assemble the circuit on a good quality PCB or common board.
• Power the circuit from a 9V radio battery.
• If D1 and D2 flashes on the pressing of S1,we can assume that the IC is working.

555 Timer as Monostable Multivibrator

A monostable multivibrator (MMV) often called a one-shot multivibrator, is a pulse generator circuit in which the duration of the pulse is determined by the R-C network,connected externally to the 555 timer. In such a vibrator, one state of output is stable while the other is quasi-stable (unstable). For auto-triggering of output from quasi-stable state to stable state energy is stored by an externally connected capaci­tor C to a reference level. The time taken in storage determines the pulse width. The transition of output from stable state to quasi-stable state is accom­plished by external triggering. The schematic of a 555 timer in monostable mode of operation is shown in figure.

555 Timer – A Complete Basic Guide

A complete basic tutorial of 555 Timer IC.

This article covers every basic aspect of 555 Timer IC. You may already know that SE/NE 555 is a Timer IC introduced by Signetics corporation in 1970′s. In this article we cover the following information about 555 Timer IC.

1. Introduction to 555 Timer IC

2. 555 Timer IC Pin Configuration

3. Basics of 555 Timer

4. Block Diagram

5. Working Principle

1. Introduction

One of the most versatile linear ICs is the 555 timer which was first introduced in early 1970 by Signetic Corporation giving the name as SE/NE 555 timer. This IC is a  monolithic timing circuit that can produce accurate and highly stable time delays or oscillation. Like other commonly used op-amps, this IC is also very much reliable, easy to use and cheaper in cost. It has a variety of applications including monostable and astable multivibrators, dc-dc converters, digital logic probes, waveform generators, analog frequency meters and tachometers, temperature measurement and control devices, voltage regulators etc. The timer basically operates in one of the two modes either as a monostable (one-shot) multivibrator or as an astable (free-running) multivibrator.The SE 555 is designed for the operating temperature range from – 55°C to 125° while the NE 555 operates over a temperature range of 0° to 70°C.

The important features of the 555 timer are :

• It operates from a wide range of power supplies ranging from + 5 Volts to + 18 Volts supply voltage.
• Sinking or sourcing 200 mA of load current.
• The external components should be selected properly so that the timing intervals can be made into several minutes Proper selection of only a few external components allows timing intervals of several minutes along with the frequencies exceeding several hundred kilo hertz.
• It has a high current output; the output can drive TTL.
• It has a temperature stability of 50 parts per million (ppm) per degree Celsius change in temperature, or equivalently 0.005 %/ °C.
• The duty cycle of the timer is adjustable with the maximum power dissipation per package is 600 mW and its trigger and reset inputs are logic compatible.

Voltage doubler circuit using NE555

Description:

The circuit diagram of a very simple voltage doubler using NE555 timer is shown here. Here IC NE555 is wired as an astable mutivibrator operating at around 9KHz. The base of the two transistors (Q1 and Q2) is shorted and output of the astable multivibrator (pin 3) is connected to it. When the output of astable multivibrator is low, Q1 will be OFF and Q2 will be ON. The negative terminal of the capacitor C3 will be shorted to ground through T2 and it will be charged to the input supply voltage. When the output of the astable multi vibrator is high, transistor Q1 will be ON and transistor Q2 will be OFF. The capacitor C4 will be charged to the voltage across capacitor C3 plus the input supply voltage (that is double the input voltage). This is how the circuit works.

This voltage doubler circuit can deliver only up to 50mA output current and above that current limit the output voltage will be dramatically reduced. The actual output voltage will be around 19V for a 12V DC input and also the output voltage will be a bit unstable. Anyway, for low current applications this circuit is well enough.

Notes:

The circuit can be assembled on a vero board.

The output current should not be allowed to exceed 70mA.

IC1 must be mounted on a holder.

Remote Control Circuit Through RF Without Microcontroller

Description

This is a simple type remote control by using RF communication without microcontroller. In this project a remote has been designed for various home appliances like television, fan, lights, etc. It gives lot of comfort to the user since we can operate it by staying at one place. We can control any of the appliances by using this remote within the range of 400 foots. In this project consist of two sections, transmitter (remote) and receiver section. Whenever we are pressing any key in the remote it generates the corresponding RF signals, and these signals are received by the receiver unit. ASK transmitter and receiver is used as transmitter and receiver. HT12E, HT12D encoders and decoders are used in this electronic circuit. The block digram of the whole circuit is given below.

USB Lamp Circuit

Description.

Here is a simple USB powered lamp that can be used to light your desktop during power failures. The circuit operates from the 5 Volt available from the USB port.The 5V from the USB port is passed through current limiting resistor R2 and transistor Q1. The base of transistor Q1 is grounded via R1 which provides a constant bias voltage for Q1 together with D2.The diode D1 prevents the reverse flow of current from battery.C1 is used as a noise filter.Two white LED’s are used here for the lamp, you can also use a 2 V torch bulb instead of LED’s. LED D3  indicates connection with USB port.

Line Follwer Robot-Using 2051 MC

This Robot uses two motors control rear wheels and the single front wheel is free. It has 4-infrared sensors on the bottom for detect black tracking tape, when the sensors detected black color, output of comparator, LM324 is low logic and the other the output is high.



Microcontrollor AT89C2051 and H-Bridge driver L293D were used to control direction and speed of motor

Circuit diagram of Robot.

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HR JOB Interview Questions and Answers-12

What are your career options right now?

Prepare for this question by thinking of how you can position yourself as a desired commodity. If you are still working, describe the possibilities at your present firm and why, though you’re greatly appreciated there, you’re looking for something more (challenge, money, responsibility, etc.). Also mention that you’re seriously exploring opportunities with one or two other firms.

If you’re not working, you can talk about other employment possibilities you’re actually exploring. But do this with a light touch, speaking only in general terms. You don’t want to seem manipulative or coy.

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Why do you want to work at our company?


This question is your opportunity to hit the ball out of the park, thanks to the in-depth research you should do before any interview.

Best sources for researching your target company: annual reports, the corporate newsletter, contacts you know at the company or its suppliers, advertisements, articles about the company in the trade press.

HR JOB Interview Questions and Answers-10

Describe your ideal company, location and job?



The only right answer is to describe what this company is offering, being sure to make your answer believable with specific reasons, stated with sincerity, why each quality represented by this opportunity is attractive to you.

Remember that if you’re coming from a company that’s the leader in its field or from a glamorous or much admired company, industry, city or position, your interviewer and his company may well have an “Avis” complex. That is, they may feel a bit defensive about being “second best” to the place you’re coming from, worried that you may consider them bush league.

This anxiety could well be there even though you’ve done nothing to inspire it. You must go out of your way to assuage such anxiety, even if it’s not expressed, by putting their virtues high on the list of exactly what you’re looking for, providing credible reason for wanting these qualities.

If you do not express genuine enthusiasm for the firm, its culture, location, industry, etc., you may fail to answer this “Avis” complex objection and, as a result, leave the interviewer suspecting that a hot shot like you, coming from a Fortune 500 company in New York, just wouldn’t be happy at an unknown manufacturer based in Topeka, Kansas.

HR JOB Interview Questions and Answers-9

Where do you see yourself five years from now?



Reassure your interviewer that you’re looking to make a long-term commitment…that this position entails exactly what you’re looking to do and what you do extremely well. As for your future, you believe that if you perform each job at hand with excellence, future opportunities will take care of themselves.

Example: “I am definitely interested in making a long-term commitment to my next position. Judging by what you’ve told me about this position, it’s exactly what I’m looking for and what I am very well qualified to do. In terms of my future career path, I’m confident that if I do my work with excellence, opportunities will inevitable open up for me. It’s always been that way in my career, and I’m confident I’ll have similar opportunities here.”

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Aren’t you overqualified for this position?

As with any objection, don’t view this as a sign of imminent defeat. It’s an invitation to teach the interviewer a new way to think about this situation, seeing advantages instead of drawbacks.

Example: “I recognize the job market for what it is – a marketplace. Like any marketplace, it’s subject to the laws of supply and demand. So ‘overqualified’ can be a relative term, depending on how tight the job market is. And right now, it’s very tight. I understand and accept that.”

“I also believe that there could be very positive benefits for both of us in this match.”

“Because of my unusually strong experience in ________________ , I could start to contribute right away, perhaps much faster than someone who’d have to be brought along more slowly.”

“There’s also the value of all the training and years of experience that other companies have invested tens of thousands of dollars to give me. You’d be getting all the value of that without having to pay an extra dime for it. With someone who has yet to acquire that experience, he’d have to gain it on your nickel.”
“I could also help you in many things they don’t teach at the Harvard Business School. For example…(how to hire, train, motivate, etc.) When it comes to knowing how to work well with people and getting the most out of them, there’s just no substitute for what you learn over many years of front-line experience. You company would gain all this, too.”

“From my side, there are strong benefits, as well. Right now, I am unemployed. I want to work, very much, and the position you have here is exactly what I love to do and am best at. I’ll be happy doing this work and that’s what matters most to me, a lot more that money or title.”

“Most important, I’m looking to make a long term commitment in my career now. I’ve had enough of job-hunting and want a permanent spot at this point in my career. I also know that if I perform this job with excellence, other opportunities cannot help but open up for me right here. In time, I’ll find many other ways to help this company and in so doing, help myself. I really am looking to make a long-term commitment.”

NOTE: The main concern behind the “overqualified” question is that you will leave your new employer as soon as something better comes your way. Anything you can say to demonstrate the sincerity of your commitment to the employer and reassure him that you’re looking to stay for the long-term will help you overcome this objection.

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HR Job Interview Questions And Answers -7

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HR Job Interview Questions And Answers -6

The "Silent Treatment"

Like a primitive tribal mask, the Silent Treatment loses all it power to frighten you once you refuse to be intimidated. If your interviewer pulls it, keep quiet yourself for a while and then ask, with sincere politeness and not a trace of sarcasm, “Is there anything else I can fill in on that point?” That’s all there is to it.

Whatever you do, don’t let the Silent Treatment intimidate you into talking a blue streak, because you could easily talk yourself out of the position.

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HR Job Interview Questions And Answers -5

Why are you leaving (or did you leave) this position ?
(If you have a job presently)

If you’re not yet 100% committed to leaving your present post, don’t be afraid to say so. Since you have a job, you are in a stronger position than someone who does not. But don’t be coy either. State honestly what you’d be hoping to find in a new spot. Of course, as stated often before, you answer will all the stronger if you have already uncovered what this position is all about and you match your desires to it.

(If you do not presently have a job.)

Never lie about having been fired. It’s unethical – and too easily checked. But do try to deflect the reason from you personally. If your firing was the result of a takeover, merger, division wide layoff, etc., so much the better.
But you should also do something totally unnatural that will demonstrate consummate professionalism. Even if it hurts , describe your own firing – candidly, succinctly and without a trace of bitterness – from the company’s point-of-view, indicating that you could understand why it happened and you might have made the same decision yourself.

Your stature will rise immensely and, most important of all, you will show you are healed from the wounds inflicted by the firing. You will enhance your image as first-class management material and stand head and shoulders above the legions of firing victims who, at the slightest provocation, zip open their shirts to expose their battle scars and decry the unfairness of it all.


For all prior positions:

Make sure you’ve prepared a brief reason for leaving. Best reasons: more money, opportunity, responsibility or growth.

HR Job Interview Questions And Answers -4

Tell me about something you did – or failed to do – that you now feel a little ashamed of ?
As with faults and weaknesses, never confess a regret. But don’t seem as if you’re stonewalling either.

Best strategy: Say you harbor no regrets, then add a principle or habit you practice regularly for healthy human relations.

Example: Pause for reflection, as if the question never occurred to you. Then say, “You know, I really can’t think of anything.” (Pause again, then add): “I would add that as a general management principle, I’ve found that the best way to avoid regrets is to avoid causing them in the first place. I practice one habit that helps me a great deal in this regard. At the end of each day, I mentally review the day’s events and conversations to take a second look at the people and developments I’m involved with and do a double check of what they’re likely to be feeling. Sometimes I’ll see things that do need more follow-up, whether a pat on the back, or maybe a five minute chat in someone’s office to make sure we’re clear on things…whatever.”

“I also like to make each person feel like a member of an elite team, like the Boston Celtics or LA Lakers in their prime. I’ve found that if you let each team member know you expect excellence in their performance…if you work hard to set an example yourself…and if you let people know you appreciate and respect their feelings, you wind up with a highly motivated group, a team that’s having fun at work because they’re striving for excellence rather than brooding over slights or regrets.”

HR Job Interview Questions And Answers-3

What are your greatest weaknesses ?
Disguise a strength as a weakness.

Example: “I sometimes push my people too hard. I like to work with a sense of urgency and everyone is not always on the same wavelength.”

Drawback: This strategy is better than admitting a flaw, but it's so widely used, it is transparent to any experienced interviewer.

BEST ANSWER: (and another reason it's so important to get a thorough description of your interviewer's needs before you answer questions): Assure the interviewer that you can think of nothing that would stand in the way of your performing in this position with excellence. Then, quickly review you strongest qualifications.

Example: “Nobody's perfect, but based on what you've told me about this position, I believe I' d make an outstanding match. I know that when I hire people, I look for two things most of all. Do they have the qualifications to do the job well, and the motivation to do it well? Everything in my background shows I have both the qualifications and a strong desire to achieve excellence in whatever I take on. So I can say in all honesty that I see nothing that would cause you even a small concern about my ability or my strong desire to perform this job with excellence.”

Alternate strategy (if you don't yet know enough about the position to talk about such a perfect fit):

Instead of confessing a weakness, describe what you like most and like least, making sure that what you like most matches up with the most important qualification for success in the position, and what you like least is not essential.

Example: Let's say you're applying for a teaching position. “If given a choice, I like to spend as much time as possible in front of my prospects selling, as opposed to shuffling paperwork back at the office. Of course, I long ago learned the importance of filing paperwork properly, and I do it conscientiously. But what I really love to do is sell (if your interviewer were a sales manager, this should be music to his ears.)

HR Job Interview Questions And Answers-2

What are your greatest strengths ?
You know that your key strategy is to first uncover your interviewer's greatest wants and needs before you answer questions. And from Question 1, you know how to do this.

Prior to any interview, you should have a list mentally prepared of your greatest strengths. You should also have, a specific example or two, which illustrates each strength, an example chosen from your most recent and most impressive achievements.

You should, have this list of your greatest strengths and corresponding examples from your achievements so well committed to memory that you can recite them cold after being shaken awake at 2:30AM.

Then, once you uncover your interviewer's greatest wants and needs, you can choose those achievements from your list that best match up.

As a general guideline, the 10 most desirable traits that all employers love to see in their employees are:

A proven track record as an achiever...especially if your achievements match up with the employer's greatest wants and needs.

Intelligence...management "savvy".
Honesty...integrity...a decent human being.

Good fit with corporate culture...someone to feel comfortable with...a team player who meshes well with interviewer's team.

Likeability...positive attitude...sense of humor.

Good communication skills.

Dedication...willingness to walk the extra mile to achieve excellence.

Definiteness of purpose...clear goals.

Enthusiasm...high level of motivation.

Confident...healthy...a leader.

HR Job Interview Questions And Answers -1

Tell me about yourself ?

Start with the present and tell why you are well qualified for the position. Remember that the key to all successful interviewing is to match your qualifications to what the interviewer is looking for. In other words you must sell what the buyer is buying. This is the single most important strategy in job hunting.
So, before you answer this or any question it's imperative that you try to uncover your interviewer's greatest need, want, problem or goal.
To do so, make you take these two steps:

Do all the homework you can before the interview to uncover this person's wants and needs (not the generalized needs of the industry or company)

As early as you can in the interview, ask for a more complete description of what the position entails. You might say: “I have a number of accomplishments I'd like to tell you about, but I want to make the best use of our time together and talk directly to your needs. To help me do, that, could you tell me more about the most important priorities of this position? All I know is what I (heard from the recruiter, read in the classified ad, etc.)”

Then, ALWAYS follow-up with a second and possibly, third question, to draw out his needs even more. Surprisingly, it's usually this second or third question that unearths what the interviewer is most looking for.

You might ask simply, "And in addition to that?..." or, "Is there anything else you see as essential to success in this position?:

This process will not feel easy or natural at first, because it is easier simply to answer questions, but only if you uncover the employer's wants and needs will your answers make the most sense. Practice asking these key questions before giving your answers, the process will feel more natural and you will be light years ahead of the other job candidates you're competing with.

After uncovering what the employer is looking for, describe why the needs of this job bear striking parallels to tasks you've succeeded at before. Be sure to illustrate with specific examples of your responsibilities and especially your achievements, all of which are geared to present yourself as a perfect match for the needs he has just described.