Photodiode Alarm

This Photodiode based Alarm can be used to give a warning alarm when someone passes through a protected area. The circuit is kept standby through a laser beam or IR beam focused on to the Photodiode. When the beam path breaks, alarm will be triggered.
Photo-Diode Alarm Circuit
Circuit Project: Photodiode Alarm circuit
The circuit uses a PN Photodiode in the reverse bias mode to detect light intensity. In the presence of Laser / IR rays, the Photodiode conducts and provides base bias to T1. The NPN transistor T1 conducts and takes the reset pin 4 of IC1 to ground potential. IC1 is wired as an Astable oscillator using the components R3, VR1 and C3. The Astable operates only when its resent pin becomes high. When the Laser / IR beam breaks, current thorough the Photodiode ceases and T1 turns off. The collector voltage of T1 then goes high and enables IC1. The output pulses from IC1 drives the speaker and alarm tone will be generated.

IR Transmitter Circuit
Circuit Project: Photodiode Alarm circuit
A simple IR transmitter circuit is given which uses Continuous IR rays. The transmitter can emit IR rays up to 5 meters if the IR LEDs are enclosed in black tubes.

Doorbell For Deaf People

This circuit provides a delayed visual indication when a door bell switch is pressed. In addition, a DPDT switch can be moved from within the house which will light a lamp in the door bell switch. The lamp can illuminate the words "Please Wait" for anyone with walking difficulties.

Circuit diagram

Circuit Project: Doorbell for the Deaf

Notes:
The circuit uses standard 2 wire doorbell cable or loudspeaker wire. In parallel with the doorbell switch, S1, is a 1N4001 diode and a 12 volt 60mA bulb.

The bulb is optional, it may be useful for anyone who is slow to answer the door, all you need to do is flick a switch inside the house, and the bulb will illuminate a label saying Please Wait inside the doorbell switch or close to it.

The double pole double throw switch sends the doorbell supply to the lamp, the 22 ohm resistor is there to reduce current flow, should the doorbell switch, S1 be pressed while the lamp is on.

The resistor needs to be rated 10 watts, the 0.5 Amp fuse protects against short circuits.

When S2 is in the up position (shown as brown contacts), this will illuminate the remote doorbell lamp. When down, (blue contacts) this is the normal position and will illuminate the lamp inside the house. Switch S1 will then charge the 47u capacitor and operate the transistor which lights the lamp.

As a door bell switch is only pressed momentarily, then the charge on the capacitor decays slowly, resulting in the lamp being left on for several seconds. If a longer period is needed then the capacitor may be increased in value.

DIY Tremolo Effect

This tremolo effect circuit uses the XR2206 and the TCA730 IC which is designed as an electronic balance and volume regulator with frequency correction. The circuit is use full for stereo channels and it also has the ability to simulate the Lesley effect aka rotating loudspeaker effect.

 How does the tremolo effect circuit works
Balance and volume settings are done with a linear potentiometer for both channels. If this potentiometer is replaced with an AC voltage source, a periodic modulation of the input signal can be achieved. This AC voltage source comes from the function generator IC XR2206. This IC generates square, triangle and sine wave signals but for this project we use only the sine wave.

IC Tremolo effect circuit schematic

Circuit Project: DIY Tremolo Effect Circuit
The modulation voltage can be varied with P1 from 1 Hz up to 25 Hz. Resistor R3 sets the operation level of the sine wave generator. R5 and R6 set the DC voltage and the sine wave amplitude at the output. C2 is a ripple filter. The square wave output of the XR2206 drives T2 and a LED to optically display the frequency.

The modulating voltage reaches pin 13 of TCA730 via P3 and R10. This input functions as the volume control or in this case the volume modulation. The degree of the balance modulation (Lesley effect) can be varied with P2. A regulated power supply using 7815 IC is recommended. Do not use a non-stabilized power supply since the current variations would influence the modulation negatively.
Attach the 7815 IC to a good heat sink (about 10 cm2).

Invention Story of Electric Motor

Ever tried to count how many things around you have electric motor at its heart? The list is endless, starting from your clocks, cars, washing machines, DVD players, vacuum cleaners to hair dryers – most of the electric appliances around us have electric motor inside them. In case your heart is filled with gratitude for its inventor and you want to flip through the pages of the past to know how electric motor was invented, read on…

Like many other creations, this one was also a result of many brilliant and inquisitive minds. The foundation of electic motor invention was only laid after battery, magnetic fields from the electric currents and electromagnet made their way. Throughout the world, there were many inventors who passionately worked towards developing solutions in the electrical science field.

 The first electrical motor is known to have been a simple electrostatic motor fathered by Andrew Gordon in 1740s. Later in 1820, Andre-Marie Ampere discovered the Ampere’s force law – the principle that explained mechanical force production by interactions of magnetic field and electric current. This idea was further shaped into a reality by British chemist and physic, Michael Faraday. The man has been known for his electromagnetic induction discoveries and this certainly was one of the major breakthroughs in the field of electrical science.

Born in a poor family, this genius was an inquisitive soul from his childhood. To make his living, he used to work in bookbinding store in London. His passion for reading made him go through each book he bound. He was so fascinated by all this that he wanted to have a book of his own one day. Who would have thought that his passion and enthusiasm for reading would help him get a greater grip on his interest in the concept of force? This habit helped him while he was inventing at the later stage in his life. Using electromagnetic means, Faraday demonstrated conversion of the electrical into mechanical energy.  He did this by dipping a free hanging wire in the pool of mercury while placing a permanent magnet on it. On passing current through the wire, it rotated around magnet demonstrating that the passing current raised circular magnetic field around wire.

Though such a primitive motor was unfit for the practical use and could be merely used for demonstration in the physics classes by substituting mercury with brine, this laid foundation for this great invention. A curious mind and inspiration lead this man to build the basis of a great invention.

In 1827, Anyos Jedlik experimented with the electromagnetic coils and also solved many technical problems associated with the repeated rotation by introducing commutator. He called his device electromagnetic self rotator. A year after this, Anyos showcased his first machine that he claimed had three major components – rotar, commutator and a stator.

Some years later in 1832, William Sturgeon introduced first ever commutator DC electronic motor. Following the footsteps of Sturgeon, Thomas Davenport created a DC motor for commercial purpose. His machine could power the printing press as well as powered machines. But unfortunately because of high battery power cost involved Thomas became bankrupt. And due to these cost issues involved, the machine could not be used commercially.

1855 yet again Jedlik tried his hand at making the machine work and applied the same principles as his electromagnetic rotors.  Finally the first commercially booming machine was introduced by Zenobe Gramme in the year 1871. He introduced an anchor ring dynamo that took care of the double-T armature pulsating DC issue. Further in 1886, Frank Julian Sprague first feasible DC motor, this machine could maintain constant speed even under different loads.

After Francois Arago’s effort to put together rotating magnetic fields also known as Arago’s rotations in 1824, many other inventors made an effort to develop working AC motors in 1880s - Nikola Tesla and Galileo Ferraris developed rotating AC motors. But Ferraris’s motor was declared to be weak to make a commercial motor.

In the year 1888, Tesla presented a paper on alternating current transformers and motors. George Westinghouse bought Tesla’s patent and also hired him for developing them while CF Scott assisted him. Like many other glitches that make creation a bumpy task, the consistent speed of the AC induction was not considered to be suitable for the street cars. Westinghouse’s smart hires - the engineers working on its development adjusted it for powering mining operation in Colorado in the year 1891.

In the year 1886, an American industrialist named Sprague, introduced the first ever consistent speed DC motor. This allowed his company to issue world’s industrial electric motor catalogue. And soon in the year 1889-90, a Russian inventor and engineer Dolivo-Dobrovolsky introduced first ever cage-rotor versions of a three phased induction motor. Interestingly, these type of motors are used till date for the commercial purposed. Driven by his own invention, Dobrovolsky made a claim that motor by Tesla was unfit for practical use due to two phased pulsations.

Westinghouse was successful in achieving his first ever induction motor that could be used practically in the year 1892. He developed 60 hertz induction motor lien 1893 but all of these early motors were two phased motors. General Electric started producing three phased induction motors by the year 1891. In five years time, in 1896, Westinghouse and General Electric signed agreement for production of squirrel cage rotor.

In 1905, Alfred Zehden described linear induction motor that could be used in the lifts or trains in a patent form. And it took around thirty years from then for Kemper to build this linear induction motor for use 1935. This motor was further improvised by Laithwaite. He was the one to introduce first ever full sized working model of this induction motor.

It’s amazing to witness how conventional motors have progressed to be strong horse powered motors of today. Most of us would say we don’t see this wonder invention everyday just as we see other inventions around us. Think again! This underestimated invention is part of most of the electrical devices we use today. 

11 Qualities Google Looks For In Job Candidates

Google receives between 2.5 and 3.5 million job applications a year.
It only hires about 4,000 people.
Senior vice president of People Operations, Laszlo Bock presides over the ultra-selective process.In interviews with The New York Times, the Economist, and students on Google+, the hiring boss sheds light on how the search giant evaluates candidates.

We sifted through those interviews for the most surprising takeaways. Find them below.

  • Google doesn't look for experts
"We would rather hire smart, curious people than people who are deep, deep experts in one area or another," he says, noting that people with strong learning ability can generally find the right answers to unfamiliar questions. "But somebody who's been doing the same thing forever will typically just replicate what they've seen before."
  • Google does want people with high "cognitive ability."
"If you hire someone who is bright, and curious, and can learn, they're more likely to come up with a new solution that the world hasn't seen before," Bock explained in a Google+ Q&A. "This looking for cognitive ability stems from wanting people who are going to reinvent the way their jobs are going to work rather than somebody who's going to come in and do what everybody else does. We recruit for aptitude, for the ability to learn new things and incorporate them."

  • Google seeks out people with "grit."
Bock spoke with The Times about a time he was on a campus talking to a student double-majoring in computer science and math. The student was thinking about switching out of computer science — it was too difficult.

"I told that student they are much better off being a B student in computer science than an A+ student in English," he recalls. Taking computer science "signals a rigor in your thinking and a more challenging course load. That student will be one of our interns this summer."

As breakthrough research in education shows, grit — the ability to keep slogging through difficult work — is more important for success than raw IQ.

  • Google wants to know whether candidates can tackle difficult projects.
The company used to be famous for asking cranium-crashing brainteasers, like "what is the probability of breaking a stick into three pieces and forming a triangle?" But it found they weren't that helpful, and have since moved on.

Now, Google's interviews include questions about the candidate's concrete experiences, starting with queries like "give me an example of a time when you solved an analytically difficult problem."

By asking people to speak of their own experiences, Bock says, you get two kinds of information: "You get to see how they actually interacted in a real-world situation, and the valuable 'meta' information you get about the candidate is a sense of what they consider to be difficult."
  • Google wants candidates with analytical skills
Basic computer science skills will do, Bock says, since they signal "the ability to understand and apply information" and think in a formal, logical, and structured way. But there are options beyond CS. Bock says that taking statistics while he was in business school was "transformative" for his career.

"Analytical training gives you a skill set that differentiates you from most people in the labor market," he says.
  • Google expects people to meet ridiculously high standards.

"We don't compromise our hiring bar, ever," Bock says. Because of this, job listings stay open longer at Google than you'd expect, he says — they have to kiss a lot of frogs before finding The One.
But Google doesn't care about GPAs.

  • GPAs and test scores don't correlate with success at the company.

"Academic environments are artificial environments. People who succeed there are sort of finely trained; they're conditioned to succeed in that environment," Bock says.

While in school, people are trained to give specific answers. "It's much more interesting to solve problems where there isn't an obvious answer," Bock says. "You want people who like figuring out stuff where there is no obvious answer."
  • Google wants to know how much candidates have accomplished compared to their peers.
When Bock was explaining how to write resumes to Thomas Friedman at The Times, he said that most people miss that the formula for writing quality resumes is simple: "I accomplished X, relative to Y, by doing Z."

For example, Bock explained that a lot of people would just write, "I wrote editorials for The New York Times."

But a stand-out resume would be more specific about their accomplishments and how they compared to others. Bock gives a better example: "Had 50 op-eds published compared to average of 6 by most op-ed [writers] as a result of providing deep insight into the following area for three years."
  • Google looks for employees who know when to step up and take a leadership role.
Bock doesn't care for "traditional leadership." Did you take the fast track to becoming president of the chess club or vice president of sales?

"We don't care," he insists. "What we care about is, when faced with a problem and you're a member of a team, do you, at the appropriate time, step in and lead. And just as critically, do you step back and stop leading, do you let someone else? Because what's critical to be an effective leader in this environment is you have to be willing to relinquish power."
  • Google wants to see people who take ownership of projects.
With that sense of ownership, you'll feel responsible for the fate of a project, making you ready to solve any problem. But you also need to defer when other people have better ideas: "Your end goal," explained Bock, "is what can we do together to problem-solve. I've contributed my piece, and then I step back."
  • Google wants to see humility, too.
You need "intellectual humility" to succeed at Google, he says. "Without humility, you are unable to learn." This is a common problem among the well-educated; elite business school grads tend to plateau.

Read more: http://www.businessinsider.com/qualities-google-looks-for-in-job-candidates-2014-4#ixzz2zvZpY1fU