Category Archives: Electronics History

What is a capacitor used for?

Just as a bucket holds water, a capacitor holds charge. In fact, the world’s first capacitor was in the shape of a jar and was aptly named the Leyden jar. However, the latest capacitors do not look anywhere close to a jar. In its simplest form, a capacitor has two conductive plates separated by a dielectric. This helps maintain an electric charge between its plates. Depending on the type, different materials are used for the dielectric, such as plastic, paper, air, tantalum, polyester, ceramic, etc. The main purpose of the dielectric is to prevent the plates from touching each other.

The Leyden jar was invented in the 18th century, at the Netherlands University. It was a glass jar coated with metal on both the inside as well as the outside, with the glass effectively acting as the dielectric. The jar was topped off with a lid. A hole on the lid had a metal rod passing through it, with its other end connected to the inner coat of metal. The exposed end of the rod culminated in a metal ball. The metal ball and rod was used to charge the inner electrode of the jar electrically. Experiments in electricity used the Leyden jar for hundreds of years.

A capacitor can be used in a number of different ways, such as for storing digital data and analog signals. The telecommunication equipment industry uses variable capacitors to adjust the frequency and tuning of their communications equipment. You can measure a capacitor in terms of the voltage difference between its plates, as the two plates hold identical but opposite charge. However, unlike the battery, a capacitor does not generate electrons, and therefore, there is no current flow if the two plates are electrically connected. The electrically connected plates rearrange the charge between them, effectively neutralizing each other.

A naturally occurring phenomenon, lightning, works very similar to a capacitor. The cloud is one of the plates and the earth forms the other. Charge slowly builds-up between the cloud and the earth. When this creates more voltage than the air (the dielectric) can bear, the insulation breakdown causes a flow of charges between the two plates in the form of a bolt of lightning.

As there is only a dielectric between the two plates, a capacitor will block direct current but will allow alternating current to flow within its design parameters. If you hook up a capacitor across the terminals of a battery, there will not be any current flow after the capacitor has charged. However, alternating current or AC signal will flow through, impeded only by the reactance of the capacitor, which depends on the frequency of the signal. As the alternating current fluctuates, it causes the capacitor to charge and discharge, making it appear as if a current is flowing.

Capacitors can dump their charge at high speed, unlike batteries. That makes capacitors eminently suitable for generating a flash for photography. This technique is also used in big lasers to get very bright and instantaneous flashes. Eliminating ripples is another feather in the capacitor’s cap. The capacitor is a good candidate for evening out the voltage by filling in the troughs and absorbing the crests.

How did the diode get it’s name?

Although most diodes are made of silicon nowadays, it was not always so. Initially, there were two types – thermionic or vacuum tube and solid state or semiconductor. Both the types were developed simultaneously, but separately, in the early 1900s. Early semiconductor diodes were not as capable as their vacuum tube counterparts, which were extensively used as radio receiver detectors. Various types of these thermionic valves were in use and had different functionalities such as double-diode triodes, amplifiers, vacuum tube rectifiers and gas-filled rectifiers.

The diode gets its name from the two electrodes it has. Both the thermionic as well as the semiconductor type possess the peculiar asymmetric property of conductance, whereby a diode offers low resistance to flow of current in one direction and high resistance in the other. Similar to its vacuum counterpart, several types of semiconductor diodes exist.

The first semiconductor diode was the cat’s whisker type, made of mineral crystals such as galena and developed around 1906. However, these were not very stable and did not find much use at the time. Different materials such as selenium and germanium are also used for making these devices.

In 1873, Frederick Guthrie discovered that current flow was possible only in one direction and that was the basic principle of the thermionic diodes. Guthrie found that it was possible to discharge a positively charged electroscope when a grounded piece of white-hot metal was brought close to it. This did not happen if the electroscope was negatively charged. This gave him proof that current can flow only in one direction.

Although Thomas Edison rediscovered the same principle in 1880 and took out a patent for his discovery, it did not find much use until 20 years later. In 1900s, John Ambrose Fleming used the Edison effect to make and patent the first thermionic diode, also called the Fleming valve. He used the device as a precision radio detector.

To put it simply, a diode functions as a one-way valve. It allows electricity to flow in one direction while blocking all current flow in the reverse direction. The semiconductor diode has an anode (A, p-type or positive) and a cathode (K, n-type or negative). Since the cathode is more negatively charged compared to the anode, electric current will not flow if the cathode and anode are charged to the same or very similar voltage.

This property of the diode allowing current to flow in only one direction is utilized during rectification, when alternating current is changed to direct current. Such rectifier diodes are mostly used in low current power supplies. For turning a circuit on or off, you need a switching diode. If you are working with high-frequency signals, band-switching diodes are useful. Where a constant voltage is necessary, there are zener diodes.

Diodes are also used for various purposes such as the production of different types of analog signals, microwave frequencies and even light of various colors. When current passes through Light Emitting Diodes or LEDs, it emits light of a specific wavelength. Such diodes are used for displays, room lighting and for decoration.

What is IFTTT? How can you use it?

Kevin Andersson has a lot to look forward to when he wakes up every morning. As soon as he puts his feet on the ground, all the lights in his home turn on. When he steps on to the weighing scale, the coffee maker activates itself to prepare a mug of steaming coffee.

Kevin has made all these events possible by installing a motion sensor in his bedroom and connecting it to the lighting arrangement with the help of an internet service known as IFTTT, which is the acronym for “If This, Then That”.

Since Kevin is a programmer by profession, you would naturally believe that he put his superior programming ability to use to bring about this high level of automation in his home. Strangely enough, he made all this possible without writing any kind of code. He just invested in some hardware items, linked them up and made use of the IFTTT service available on the web so that the gadgets could communicate with each other.

A Sneak Peek into Internet Services

Most of the services made possible by the IFTTT are for use on the Internet only. For instance, you can automatically save snaps you get onto in Facebook in your Dropbox folder. This is very handy indeed. IFTTT used with Gmail becomes a seriously powerful tool.

You can do other cool and trendy things like uploading only certain photos on Flickr. Although Siri works with only the default apps of Apple, you can integrate Siri with the apps you use on IFTTT.

Connecting Real World Devices

You may not find these applications available on the net amazing enough, since you may take the Internet for granted as most people do. However, the fact that IFTTT services can hook up your everyday home devices and make them perform remarkable tasks like preparing your coffee without your needing to step into the kitchen is amazing indeed!

The services can link many of your home gadgets like Belkin WeMo devices used for sensing motion, home lighting system made available by Phillips and a variety of equipment to suit your specific needs.

What exactly is IFTTT?

If This, Then That implies a cause and effect relationship. If a situation triggers an event, a certain result occurs. Say for example, if the stock price of a certain product rises above a specific mark, the stock market will send you a Google alert. Here the rising of the stock above a particular value is the trigger or the cause and the alert sent to you by the market is the effect or the result.

Linden Tibbets and his brother Alexander, the brains behind IFTTT conceived of the project in terms of how people react to ordinary objects in the home and the office like doorknobs and cell phones. Often, people use these objects in ways the designer did not intend. For instance, you may use your phone as a paperweight because you can judge from its looks that it is heavier than a sheet of paper. Tibbets and his brother have extended this idea into the digital world so that IFTTT allows individuals to use Internet applications in modes the developers of the packages did not expect.

How do photovoltaic cells work?

Your calculator probably has a darkish colored panel just above the display. The panel is made up of solar cells that power up your calculator if there is enough light. You may also have seen some solar panels, which people use for charging up their cell phones. Earlier, these solar cells or photovoltaic cells were exclusively used to power the electrical systems of satellites. However, they are now commonly used in less exotic ways as well.

How do photovoltaic cells convert light to electricity? For this, you must understand the way these cells are constructed. A photovoltaic cell has two silicon plates bonded together. Pure silicon is an insulating material and is unable to conduct electricity. This is because of the atomic structure of silicon, which has place for eight electrons in the outermost shell of its atoms. However, there are only four electrons present.

Therefore, when silicon atoms come together, they share their electrons. Each atom shares one electron with its neighbor and they become a pair. That means at any time, four atoms surround each silicon atom, bringing up its catch of electrons to eight on the outer shell. Since all the electrons are now bound up, there is none left free to move about and carry electric charge.

To make the silicon plates able to carry electric charge, one of the two plates must have some free electrons and the other plate must have some holes or lack of electrons. This is done by the process of doping. While making the plates, one of them is given a few phosphorus atoms as impurities. Since phosphorus has five atoms in the outermost shell of its atom, when combining with the silicon atoms, one of its electrons remains unpaired. This makes the silicon plate with the phosphorus impurity have excess electrons and this is called the n-type silicon.

Likewise, the other plate is doped with boron, which has only three electrons in the outermost shell of its atoms. This leaves the combination of silicon and boron atoms with a deficit of electrons and this is called the p-type silicon. This is like a hole, which will readily grab a wandering electron to fill up its vacant space.

Light is essentially a barrage of energetic particles called photons. Photons impart their energy to the surface where they land, which is why you feel warm when you stand in sunlight. If light or photons are allowed to fall on the n-type silicon plate that has extra electrons, they receive the excess energy from the photons. The extra energy allows them to dislodge themselves from their original positions and wander off until they come to the other plate with the holes, where they are eagerly absorbed.

However, the n-type silicon plate that supplied the electrons now has a deficiency of electrons that it must fill up. For electrons to flow, the circuit must be externally completed. This is usually done by connecting a load to the solar cell through external wires. The plate makes up its deficiency of electrons by borrowing them from the connecting wire. In essence, photons drive the electrons through the entire circuit, and that makes the current flow through the solar cell and the load connected to it.

As soon as light falling on the solar cell is removed, the running electrons lose their drive, and the flow of current stops. Although the output from each cell is usually very tiny, by combining them in series and parallel, an impressive amount of power can be generated.

Transistors: What Is The Difference Between BJT, FET And MOSFET?

BJTs, FETs and MOSFETs are all active semiconductor devices, also known as transistors. BJT is the acronym for Bipolar Junction Transistor, FET stands for Field Effect Transistor and MOSFET is Metal Oxide Semiconductor Field Effect Transistor. All three have several subtypes, and unlike passive semiconductor devices such as diodes, active semiconductor devices allow a greater degree of control over their functioning.

Depending on their subtypes, operating frequency, current, voltage and power ratings, all the three types of transistors come in a large variety of packages, and all of them are susceptible to ESD or Electro Static Discharge. That means when you handle these devices, you must take adequate precaution against static charges destroying them.

he basic construction of a BJT is two PN junctions producing three terminals. Depending on the type of junctions, the BJT can be a PNP type or an NPN type. The three terminals are identified as the Emitter or E, the Base or B and the Collector or C. BJTs usually function as current controlling switches. The three terminals can be connected in three types of connections within an electronic circuit – Common Base configuration, Common Emitter configuration and Common Collector configurations. All the three connections have their own functions, merits and demerits. The BJT is Bipolar because the transistor operates with both types of charge carriers, Holes and Electrons.

The FET construction does not have a PN junction in its main current carrying path, which can be made from an N-type or a P-type semiconductor material with high resistivity. A PN junction is formed on the main current carrying path, also called the channel, and this can be made of either a P-type or an N-type material. The three leads of a FET are the Source (S), Drain (D) and Gate (G), with Source and Drain forming the ends of the channel and the Gate controlling the channel conductivity. Unlike the BJT, the FET is a unipolar device since it functions with the conduction of electrons alone for the N-channel type or on holes alone for a P-channel type.

The input impedance at the gate of an FET is very high, unlike the BJT, which comparatively has much lower impedance. Additionally, the conductivity of the channel depends on the voltage applied to the Gate, essentially making it a voltage-controlled device, unlike the BJT, which is current-controlled. The voltage applied to the Gate controls the width of the channel, allowing the FET to carry current between the Drain and Source pins. The Gate voltage that cuts off the current flow between Drain and Source is called the pinch off voltage and is an important parameter.

The MOSFET is a special type of FET whose Gate is insulated from the main current carrying channel. It is also called the IGFET or the Insulated Gate Field Effect Transistor. A very thin layer of silicon dioxide or similar separates the Gate electrode and this can be thought of as a capacitor. The insulation makes the input impedance of the MOSFET even higher than that of a FET. The working of the MOSFET is very similar to the FET.

You can read more about transistors in depth here.

How do battery powered pico-projectors work?

Once upon a time, very long ago, the projector world was ruled by the intense light of arcs. As they were rather unwieldy, xenon lamps took their place. With the unrelenting march of innovation, the era of OHPs or overhead projectors that could project images of transparencies, came into existence. These soon became obsolete as computers evolved and could be directly connected to projectors with LCD screens. The latest in line is the Pico-projector, which uses tiny batteries and the light from LEDs to project large displays.

Although Pico-projectors are small – as small as mobile phones, and sometimes even smaller – they can project large displays, sometimes up to 100 inches. Even though their brightness and resolution is not up to the mark of their bigger brethren, Pico-projectors are relatively new in the innovation chain, and as the market expands, they are expected to develop further.

Several companies have developed their own methods of producing battery-powered Pico-projectors. Of them, the three major technologies are DLP or Digital Light Processing, LCoS or Liquid Crystal on Silicon and LBS or Light Beam Steering. DLP and LCoS use a white light source and a system of filtering techniques to create different color and brightness of each pixel. On the other hand, LBS uses a small liquid crystal display to control the amount of light going to each pixel.

Digital Light Processing or DLP is pioneered by Texas Instruments (TI). Their idea is to use tiny mirrors on a chip to direct the light. Each mirror controls how much light goes onto each pixel of the display. The mirror can be turned on or turned off on command many times a second, and the on to off time ratio defines the brightness of the pixel. For color, there is a color wheel in front of the light source, splitting the beam into red, green and blue. Each mirror controls all the three light beams.

Liquid Crystal on Silicon or LCoS, as the name suggests, uses an LCD to control the amount of light reaching the pixel of the display. For color, two techniques are used. One is the Color Filter where three sub pixels are used, and they each have their own color, Red, Green and Blue. The other is the FSC or Field Sequential Color that requires a fast LCD and a color filter to split the image into RGB, the three main colors sequentially. The LCD is refreshed three times, once for each color. For LCoS, the light source could be an LED or a diffused Laser.

Laser Beam Steering or LBS creates the image one pixel at a time. The technique uses three directed laser beams, red, green and blue. The three beams are combined using optics and are guided using mirrors. So that the eye does not notice the pixel-by-pixel design, the image is scanned at over 60Hz.

LBS has some advantages over the other two techniques. The size is small and power consumption lowest, as the darker pixels require less energy, while the black pixel does not require any energy at all. The image from an LBS system is always focused, even on curved surfaces. On the other hand, lasers are expensive, cause random intensity patterns and are a concern for eye safety.

What Are Inductors and How Do They Work

An inductor or an induction coil is a tightly woven coil of wire. Now, you would not expect an ordinary piece of wire to show any special property on passage of current through it. A coil with several loops or turns however, exhibits a remarkable property when current passes through it. The current through the coil creates a magnetic field in the immediate space surrounding the coil. The field stores electrical energy during the passage of current and for a very short while, even if you cut off the current.

Another amazing fact of an inductor coil is that if you place the coil in a varying magnetic field, a current starts to flow through it. The amount of current depends upon the rate at which you change the field.

Bulb and Coil Experiment

You can make out this amazing property of an inductor coil from a simple experiment. Consider a simple circuit with a battery, bulb and a switch. The bulb glows when you close the switch while it stops glowing the moment you open or release the switch.

If you now include a coil of wire wound around an iron bar across the bulb, the bulb will light up as you close the switch. However, instead of glowing at a constant brightness, the intensity of the light changes from bright to dim. If you now open the switch, the bulb does not turn off immediately as you would expect. Instead, the brightness gradually decreases before turning off completely.

Explaining the Observations

You can attribute this curious behaviour to the inductor coil placed across the bulb. When you close the switch, current flows from the battery through the bulb, causing it to glow. At the same time, current flows through the inductor coil too. This generates a magnetic field in the space surrounding the coil. The magnetic field varies in the short time the current builds up. The changing magnetic field induces a current to flow through the coil. However, according to the rules of electricity, this current is opposite to the original current sent by the battery. Hence, the effective current through the coil increases with time, while decreasing that passing through the bulb. This causes the bulb to reduce its glow from bright to dim.

When you open the switch, the magnetic field falls. During the fall of the field, the induced current causes the voltage across the inductor to rise for a moment. This causes the bulb to brighten up briefly. When the current reduces to zero, the bulb turns off.


The physical quantity associated with this property is called inductance. The value of this quantity is measured in Henrys. Inductance depends upon four features, which include the number of turns in the coil, the degree of overlap, area of the cross section of the wire and the material of the core inside the coil.

You can increase the inductance by increasing the number of turns and the cross section area of the coil. You may also increase the value by increasing the degree of overlap i.e. by using a tightly wound coil.

Uses of Inductors

You must have wondered how traffic signalling works. Traffic light sensors make use of inductors, which form filter circuits along with capacitors. Inductors are essential components in electronic circuits and devices like receivers, transmitters, oscillators and voltage regulators, as well.

Raspberry Pi and Laika

Raspberry Pi and Laika – A Powerful Combination for Robotics

Some of you may recall Laika, the first dog in space, and the first animal to orbit the Earth. In 1957, Laika gave up her life to prove that living beings can survive being launched into orbit.

This platform, aptly named the Laika Explorer, presents a powerful robotics control for your Raspberry Pi (Raspberry Pi). With Laika Explorer and using C, Python or Scratch programming, you can control switches, lamps, motors, robots and more from your Raspberry Pi.

The Laika Explorer is a simple platform, and you can start with the Scratch programming language for controlling the hardware in a matter of minutes. You only need to download the drivers, plug in the USB cable and you are ready to go, building up your hardware and software skills.

The Laika Explorer provides you with:

— Inputs to connect sensors, switches and other input devices – 2x analog and 4x digital;
— Outputs for controlling LEDs, motors, sounders and other output devices – 7x digital;
— Control for motors, drive forward, reverse and brake – 2x H-bridge motor drivers;
— Interaction between hardware and software – 4x switches;
— Diagnostics for digital outputs – 7x indicator LEDs

All the above are available on one PCB. You connect this PCB to your Raspberry Pi using a USB lead, and start the control by using one of the three programming languages – C, Python or Scratch. If you buy the Inventor’s kit, you get a laser cut, custom designed Perspex base to mount the Explorer board and the Raspberry Pi (the Pi is not included with the kit). Some motors, LEDs, potentiometers, wiring, etc., are thrown in. The USB connection will give you access to all the hardware control on the Laika Explorer board.

By sending a Scratch Broadcast, you transfer data to the Explorer board and to the seven digital outputs. Each output is capable of handling 500mA, although not at the same time. Each output is also protected by a back-emf diode, which means you can connect small motors, relays and solenoids, without having to worry about blasting the output driver transistors.

The dual h-bridge motor driver on the Explorer board is very useful in driving two motors individually. The two motors can be independently driven either in backwards, forwards or in braked condition. Both channels can each handle 1.5A continuously, or 3A if you want to drive one bigger motor with the outputs tied together.

The two analog inputs on the Explorer board provide 10-bit resolution. This makes it possible to use variable resistors or potentiometers to give precise control.

In practice, you do not need Scratch running on your Raspberry Pi to control the connected Laika Explorer. You can run a special Python script on your Raspberry Pi, allowing use of Scratch to communicate with the Laika Explorer over a network connection. Therefore, now you can control your Raspberry Pi robot through your Wi-Fi connection.

What does the future look like for Laika? Well, it is quite exciting as of now, with other modules in development. One such module is the multiple radio transceivers (868MHz for EU and 915MHz for US) forming a mesh network extension option, an exciting option for home automation to control lights, music and more through Raspberry Pi and Laika.

How does a smartphone camera autofocus?

How does the camera of a super slim smartphone autofocus?

As long as cell phones were over 10 mm thick, manufacturers had no problem of getting the camera to autofocus. Of the 2 billion cameras manufactured for the phone and tablet market, nearly half of them autofocus. Usually, one of more of the lenses in the camera are moved in or out using a linear actuator, while an algorithm calculates a figure of merit for the sharpness of image for that location of the lens. The best focus for the scene is achieved by repeating this procedure.

This was going fine, until form factors started to get thinner. Manufacturers made thinner phones, and people took this as a paramount design consideration. As the 5 mm form factor was approached, compressing an 8-13 M Pixel auto focus camera that would still produce high fidelity images became a challenge. In addition, the requirement of speed, power and performance also changed, and altogether, forced manufacturers to abandon the old method of Voice Coil Motor in favor of a MEMS linear actuator.

The Voice Coil Motor (VCM) operated using the principle of electromagnetism. This is the same technology used in loudspeakers to produce sound from electricity. When electricity passes through a coil, it produces a magnetic field that reacts with a permanent magnet to either repel or attract the coil. The movement of the coil is restricted such that it can only move along its axis. Springs attached to the coil help to bring it back to its rest position once the electricity in the coil stops flowing.

The main disadvantage of the VCM is the hysteresis of its stroke. Usually, the coil does not return to its original position after a displacement and this prevents rapid tracking of focal distances in a VCM controlled camera lens. Other disadvantages are the high requirement of power for operating the VCM and de-centering and lens-tilting while operating. All these problems became increasingly acute with increasing image sensor resolution, decreasing pixel dimensions and f-numbers. Moreover, with the VCM technology now over 100 years old, the opportunities for further cost reduction are virtually nil.

This paved the way for a competing technology with a commercial opportunity that can deliver improved performance at a reasonable cost. This is the MEMS or Micro-Electro-Mechanical-System that uses components from one to 100 micrometers in size.

The MEMS technology for autofocus integrates the three functions of a linear actuator. It provides a linear vertical movement, has a spring to provide the restoring force and uses an electrostatic comb as a drive to displace the lens. The MEMS technology saves on power since it does not use electromagnetism.

The comb drive is more like interlocking fingers, only the fingers never touch. The electrostatic charge developed when a DC voltage is applied, develops an attractive force causing the combs to be drawn to each other. The lens, which is attached in the center, completes the silicon MEMS autofocus actuator.

The MEMS technology allows only one lens to move very precisely, while the other lenses are locked in the most optimal position. This approach offers an excellent image quality over the entire focal range within the 5 mm allowed in a thin smartphone.

How Professional Grade Capacitors Are Used In the Automotive Industry

The challenging conditions faced by automobiles have compelled component manufacturers in the automotive industry to come up with superior capacitors. Two of these advanced capacitors are professional grade capacitors of tantalum and niobium oxide.

A capacitor is comprised of two conducting plates separated by a dielectric (insulating) medium. One plate maintains a positive charge while the other maintains a negative charge.

Benefits of Professional Grade Tantalum Capacitors

A tantalum capacitor has a pellet of tantalum as the positive end separated from the negative conductor by a dielectric, which in this case is a thin layer of tantalum oxide formed on the tantalum pellet surface.

Professional grade variety of tantalum capacitors has several advantages over standard tantalum capacitors. Manufacturers adopt strict design specifications to construct the capacitors and use thicker and better dielectrics. In addition, the manufactures check the devices for high surge current and burn-in procedures.

The use of these capacitors results in a low failure rate of 0.5% in 1000 hours. In addition, the leakage current is almost 75% less than that in conventional tantalum capacitors. Manufacturers make professional grade capacitors available with low and standard equivalent series resistances (ESR). This makes these components suitable for several types of control circuits in automobiles.

The low ESR capacitors are particularly useful in airbag modules, engine control modules and power supply modules.

Functioning at High Temperatures

Automotive engineering requires placing electronic components close to sources of heat like engines, gearboxes, AC circuits and headlights. The temperatures in these regions may be in the region of 175°C. Since tantalum capacitors can function over a wide temperature range from -55°C to +175°C, they are suitable for use in these regions.

Niobium Capacitors

How The Automotive Industry Uses Capacitors

Before deciding on a tantalum or niobium oxide capacitor in a particular automotive circuit, the industry thinks about the nature of the circuit and the device using it. The first factor, which is the maximum voltage drop across the load in the circuit, determines the voltage rating of the capacitor. The second factor is the applied DC voltage. The applied voltage must be 50% of the rated voltage for the capacitors. This takes care of an unexpected surge in voltage. The third factor is the maximum value of the operating temperature. The capacitor selected must be able to withstand the temperature of the operating device.

A circuit operating under high temperature conditions (up to 125°C) can expect to see additional voltage surges. It is crucial that capacitors employed can endure these issues.