Author Archives: Andi

What are Zener, Schottky and Avalanche Diodes?

Diodes are very commonly used semiconductor devices. They are mostly used as rectifiers for converting Alternating to Direct current. Their special characteristic of allowing current flow in only one direction makes them indispensable as rectifiers. Apart from rectification, various types of diodes are available for different purposes such as for generating light, microwaves, infrared rays and for various types of switching at high speeds.

For example, the power supply industry has been moving towards high speed switching because higher speed reduces the volume of magnetics used, which ultimately reduces the bulk and price of the units. For switching at high frequencies, diodes are also required to react at high speeds. Schottky diodes are ideal for this purpose, as their switching speeds approach nearly zero time. Additionally, they have very low forward voltage drop, which increases their operating efficiency.

As their switching speed is very high, Schottky diodes recover very fast when the current reverses, resulting in only a very small reverse current overshoot. Although the maximum average rectified currents for Schottky diodes are popularly in the range of 1, 2, 3 and 10 Amperes, Schottky diodes that can handle up to 400A are also available. The corresponding maximum reverse voltage for Schottky diodes can range from 8 to 1200V, with most popular values being 30, 40, 60 and 100 Volts.

Another very versatile type of diode used in the power supply industry is the Zener diode. All diodes conduct current only when they are forward biased. When they are reverse biased, there is only a very small leakage current flowing. As the reverse voltage increases to beyond the rated peak inverse voltage of the diode, the diode can breakdown irreversibly and with permanent damage.

A special type of diode, called the Zener diode, blocks the current through it up to a certain voltage when reverse biased. Beyond this reverse breakdown voltage, it allows the current to flow even when biased in the reverse. That makes this type of diode very useful for generating reference voltages, clamping signals to specific voltage levels or ranges and more generally acting as a voltage regulator.

Zener diodes are manufactured to have their reverse breakdown voltage occur at specific, well-defined voltage levels. They are also able to operate continuously in the breakdown mode, without damage. Commonly, Zener diodes are available with breakdown voltage between 1.8 to 200 Volts.

Another special type of diode called the Avalanche diode is used for circuit protection. When the reverse bias voltage starts to increase, the diode intentionally starts an avalanche effect at a predetermined voltage. This causes the diode to start conducting current without damaging itself, and diverts the excessive power away from the circuit to its ground.

Designers use the Avalanche diode more as a protection to circuits against unwanted or unexpected voltages that might otherwise have caused extensive damage. Usually, the cathode of the diode connects to the circuit while its anode is connected to the ground. Therefore, the Avalanche diode bypasses any threatening voltage directly to the ground, thus saving the circuit. In this configuration, Avalanche diodes act as clamping diodes fixing the maximum voltage that the circuit will experience.

Power Your Smartphone by Your Sweat

Anyone can power a smartphone by manually running a small electric generator. Without a doubt, some will sweat in the process. However, this technology is somewhat different. Here, a small tattoo will detect whether you are sweating (for whatever reasons) and generate power directly from your sweat.

Researchers at the University of California in San Diego have developed a sensor to monitor a person’s progress when he or she is exercising. Although this is not something new, but the sensor is in the form of a temporary tattoo and it also doubles as a bio-battery. It can detect when the person is perspiring and produce power from it.

According to one of the researchers, Wenzhao Jia, when a person sweats, one of the naturally occurring chemicals is lactate. The sensor detects and responds to lactate, which is a very important indicator of how the person is progressing with the exercise. That is because with more intense exercise, the body produces increasing amounts of lactate. With strenuous physical activity, the body activates a process called glycosis, which produces energy and lactate.

Professional athletes test their performance by monitoring the levels of lactate they produce. This is one of the ways they evaluate their training program and their fitness. Moreover, some conditions cause abnormally high lactate levels in the body such as lung or heart diseases. Doctors measure the lactate levels during exercise testing of their patients. However, lactate testing is intrusive because it needs blood samples of the person to be collected at different times during exercising and then analyzed. Therefore, the current process is inconvenient.

The team led by Joseph Wang, of which Jia is a member, has developed a faster, easier and more comfortable way of measuring lactate during exercise. They imprinted the biosensor onto a temporary tattoo paper. The sensor has an enzyme that strips electrons from the lactate produced during the workout and generates a weak electrical current.

In practice, the tattoo is applied to the upper arm of the person exercising. When the person exercises on a stationary bicycle, it is easy to monitor the performance against increasing resistance levels. The researchers were able to monitor 10 health volunteers for 30 minutes and checked the lactate levels in their sweat over time and with changes in intensity of their exercise.

One of the startling discoveries from the research was that different people produced different amounts of electricity. Surprisingly, people who exercised less than once per week and hence were less fit produced more power as compared to moderately fit people who exercised between one and three times per week. Those who were the most fit, working out more than three times per week, produced the least amount of power.

According to the researchers, less-fit people become fatigued sooner and glycosis kicks in earlier for them. Therefore, they produce more lactate because of their increased fatigue. In the low-fitness group, the maximum amount of energy produced by a person was 70μW for every square cm of skin. Although the power generated is not very high, the researchers are confident of eventually increasing it to power small gadgets.

e-whisker: how about a hairy robot?

No matter how quietly you approach a cat from behind, it is sure to detect your presence almost always. It is not its acute sense of hearing or smell that helps the cat, but its whiskers. They can sense the tiniest air turbulence caused by your movements. In fact, such tactile feedback gathered by most animals and insects with their whiskers and antennae makes it very efficient to coordinate their movements at striking speeds.

Such high-speed reflexes are possible because the feedback from the sensors is directly coupled to the insects’ locomotive actions and does not have to pass through much processing. Actually, there is absolutely no central processing or environmental data analytics to impede the information from multiple data sources.

Several insects and certain mammals use their antennae and whiskers – the hair-like tactile sensors – to monitor wind turbulences and for navigating around obstacles in tight spaces. Researchers at Berkeley Lab found this a new source of inspiration and they came up with e-whiskers or electronic whiskers. These e-whiskers are based on flexible polymer fibers with high aspect ratio, coated with a mixture of silver nano-particles and carbon nanotubes.

According to the lead researcher Ali Javed of the Materials Sciences Division of Berkley Lab, tests of these whiskers show they are ten times more sensitive compared to all previously reported resistive or capacitive pressure sensors. In addition, by changing the composition of the whiskers, researchers could manipulate their characteristics.

For example, a change the ratio of the nanoparticles and the nanotubes resulted in a change in resistance from a minimal 10% to around 260% with the application of a 2.4% strain on the whiskers. Scientists monitored the resistivity change by hooking up the e-whiskers arrays to a computer. The carbon nanotubes give the e-whiskers their excellent bendability with their conductive network matrix. On the other hand, the silver nanoparticles contribute to the conductivity of the coated fibers giving them the high mechanical strain sensitivity. That makes the e-whiskers so sensitive to pressures as low as 1Pa, representing 8%.

When scientists increased the weight content of the silver nanoparticles, the strain sensitivity of the e-whiskers was enhanced. This can be explained as the change in the distance between the silver nanoparticles in the film directly affecting the probability of electrons tunneling through neighboring conductive nanoparticles. As compressive and tensile stresses cause the gaps between the nanoparticles to become smaller and larger compared with the relaxed state, the e-whisker is able to detect the direction of bending.

Scientists at Berkley Lab built the e-whisker by patterning it with a micro-etched silicon mold with trenches which were 15mm long, 250µm wide, and 250µm deep. They then coated the fiber with the carbon nanotube and silver nanoparticle composite and cured it. The researchers claim that the whiskers can be made smaller still – they would have to use the MEMS processes for that.

With this e-whisker array of seven vertically placed fibers, scientists demonstrated mapping a weak wind flow (1m/s) in three dimensions as a proof-of-concept. More applications are planned for the future.

Add-On Board on Raspberry Pi Can Control Entire Building

If you thought that the tiny credit card sized single board computer, the inexpensive Raspberry Pi or RBPi was only good for home automation and no more, you may be surprised to learn that it can do a lot more – control an entire building, for instance. Of course, it will need assistance in the form of an add-on board, such as the UniPi.

Very often, people have used the RBPi for automatically controlling their sprinkler systems, the lighting in their house or even for guarding their homes while they are away on a holiday. Commercial systems have often used the RBPi as a prototype. A Czech startup with the same name, the UniPi, is now offering a baseboard and an add-on board for building automation that you can use with your RBPi.

The RBPi plugs into the UniPi baseboard via its 26-pin expansion connector. With this combination of the UniPi and RBPi, you can control the entire functions of a modest sized building. For example, it can read signals from different sensors such as humidity, temperature and/or status of alarms and switches to control gates, sprinklers, curtains, doors, lights and more.

To help with the sensors and control, UniPi is also offering a passive sensor hub that comes along with a free temperature sensor and an optional waterproof temperature sensor, should you need one. The UniPi baseboard has 14 opto-isolated digital inputs that can read sensor signals from 5 to 20V and show the status with LEDs. The board can read 0-10V signals on two analog inputs and output 0-10V on another analog output. On-board is a 12V power supply, along with eight changeover relays, which can switch 5A at 230VAC. That makes UniPi adequate for controlling power to sensor devices for an entire building.

For reading sensors, the UniPi is equipped with a single-channel 1-Wire interface. That makes it convenient to connect hundreds of humidity and temperature sensors. UniPi even allows the second I2C port of the RBPi and its UART to be extended with 5V level converters and provides ESD protection for them. Power loss does not affect the timing of the board as it has an RTC or real-time clock module for keeping time. UniPi is compatible with the RBPi model B Rev2 and it is possible to configure it for the Rev1 model as well. However, UniPi does not mention the possibility of compatibility with the latest model of the RBPi, the 40-pin model B+.

On their website, UniPi offers numerous tutorials based on C/Python libraries for people wanting to develop UniPi applications on the Linux-based RBPi. For example, there is the Webiopi, which is specifically useful for connectivity with the Python Internet of Things. Additionally, there is the Wiringpi library for GPIO interfacing and other libraries for Adafruit.

UniPi is offering its baseboard with on RJ45 connector for the 1-Wire interface and two RJ11 connectors – one for the UART and the other for the external I2C. It has one P1 header and another P5 header along with a 2.1mm standard power connector and an RBPi power jumper.

Add a Real Time Clock to Your Raspberry Pi

The Linux-based credit card sized single board computer, the Raspberry Pi or the RBPi is designed to be low-cost and of small form factor. As such, many features that are available on normal computers, but considered superfluous here, have been left out. The real time clock is one among them. That makes the RBPi unable to keep time when its power supply has been removed.

Typically, the RBPi is expected to be connected to the Internet via the Wi-Fi or the Ethernet and to update its time automatically from the Network Time Protocol servers available globally. In the absence of an on-board RTC, when there is no Internet connection or when the power to the board is removed, the RBPi is unable to keep time. However, that can be easily rectified by adding a small RTC module running on DS1307 and a tiny coin battery. This allows the RTC to continue to keep time even when the RBPi does not have power supplied to it.

To make things easy, use Adafruit’s Breakout Board kit for the DS1307 RTC. This kit already has all the parts required, including the coin battery. Although the components can be purchased separately and assembled on a breadboard, the coin battery holder can pose a problem, as it is not breadboard-friendly. The kit on the other hand, has a dedicated place for the battery holder, making it more convenient to use.

To allow the RTC chip to communicate effectively with the RBPi, the two 2.2KΩ resistors on the kit must be left out. There is no need for these resistors since the RBPI already has two 1.8KΩ resistors on-board and they are connected to the 3.3V supply, as the RBPi needs them to be. Therefore, either do not solder the two resistors to the breakout board, or, if you have already soldered them in, remove or clip them out. The breakout board needs 5V, so connect the VCC on the board to the 5V pin of the RBPi.

Now, you will need to set up the I2C interface on the RBPi. For this, your RBPi must be running a kernel that includes the RTC and DS1307 modules. The latest version of the Raspbian OS already has the modules included, but older versions may not have them. Adafruit has a wonderful tutorial that will guide you for setting up and testing I2C on the RBPi, check it out here.

At the command line, you can run the command “sudo i2cdetect -y 0” to check your wiring. If you have a rev2 RBPi, enter the command “sudo i2cdetect -y 1”. Once you see ID #68 being displayed, you know that your wiring is correct, as this is the address of the DS1307. Once you get the kernel driver running, i2cdetect will show UU instead of 0x68, further confirming that everything is good.

The next step is to load up the RTC module and set it up as root. Follow the tutorial for doing that and you can check the time with the command line “sudo hwclock -r”. If you are using the module for the first time, the date will be Jan 1 2000 – set it to the current time, and you are done.

Of what use is spark erosion?

For many decades, people have been using Electro Discharge Machining (EDM) or Spark Erosion to successfully remove material from difficult to machine location or shapes. Toolmakers come across such difficult to machine surfaces and shapes occasionally. Therefore, most good tool making workshops are usually equipped with a Spark Eroder. Spark Erosion techniques and machines are not new – this knowledge has been around for nearly two-decades and more. EDM machines are equipped with current generators, with typical currents being in the range of 75A.

Modern EDM machines are computerized and numerically controlled. With such machines, it is a very simple affair to make a single set up to cut an array of cavities. For example, with a sparker, you can drill square holes very easily. These machines can be programmed to make an undercut or cut profiles with a precision measured in microns.

Workpieces are normally metallic and must be electrically conductive. In the tool making business, aluminum or steel blocks are usual. However, a workpiece could also be a machine with a broken drill bit, stud or a broken tap that has jammed tight in a hole. Machinists also use sparkers to work on car parts.

The other important part required in the spark erosion process is the electrode. Mold makers or toolmakers use any shape such as a simple cylinder or a polygon. Other more complex operations need a CNC milled brush head, convolute or a diaphragm. If you need to remove a drill bit jammed into a car part, the machinist would normally use a cylinder such as a copper tube of small diameter. After precisely mounting the electrode in the machine head, the machinist will align its movement in the direction of the travel for the head. The alignment of the electrode and the workpiece is a precision task often requiring the help of a Digital Readout or DRO.

To start the spark erosion process, the workpiece must be immersed in a dielectric liquid. Earlier EDM machinists used paraffin as the dielectric, but now liquids that have a much higher flashpoint have superseded paraffin. Moreover, these liquids are not only safer, but also kinder to the machinists’ hands, as he has to dip them often in the liquid.

The machine is switched on and the electrode is brought closer to the workpiece. For this motion control, the mechanism may be hydraulic or electronic. As soon as a critical distance is reached, a tiny spark jumps between the electrode and the workpiece. This is an electrical discharge creating extremely hot plasma and it melts a little part of the workpiece into a tiny pool. At the same time, a small part of the dielectric also vaporizes creating a bubble around the spark.

Seen on a microscopic scale, the pool and the bubble both get larger until the control electronics stops the spark. This collapses the bubble, whereby the surrounding dielectric rushes in and flushes away the molten workpiece. The process creates a large pit on the workpiece and a smaller one on the electrode. When repeated tens of thousands of times each second, the workpiece is slowly eroded away to the required depth.

Use Apples as Switches for Your Raspberry Pi

You may rightly question the logic behind using apples as switches for your Raspberry Pi, as against the usual hard plastic ones. Well, for one, we live in an analog world and there is much more fun in integrating items of daily use with your computer. For another, it pays to see the look of astonishment on someone’s face when picking an apple from a basket, if the computer were to reprimand him.

The tiny credit card sized single board computer, the ever-popular Raspberry Pi or RBPi can sense inputs with capacitive touch breakout boards. This is the basics of using several household objects as input sensors for the RBPi. You can use any conductive object, not only an apple, such as pencils (the graphite part), spoons and potatoes including any other fruits or vegetables that you may find handy.

Capacitive touch sensors detect the tiny amount of electric charge every human body carries. The breakout boards have a pad that is sensitive to touch. You can extend this pad to any object by attaching a wire, allowing the object to develop a sensitivity to touch. You will of course need to inform the RBPi of your intentions and to do that, put in some effort in programming it. Get help from this website.

With the hardware above and a few lines of Python, you will soon have a new way of controlling your projects and games that is fun and easy at the same time. There are three types of breakout boards that you can experiment with.

The first type is the momentary capacitive touch sensor. This detects as long as something continues to touch it. The sensor has an LED that glows when anyone touches the pad and remains lit until it detects the end of touch. This breakout board has a large touch-pad and a small copper hole near it. You can solder a piece of wire to the hole and extend it to a capacitive item such as a drawing you have made with pencil (graphite).

The second type of breakout board is the toggle type of capacitive touch sensor. The LED on the board comes on as soon as you touch its pad. The LED remains lit up even when you lift your finger off the pad. The LED will go off once you touch the pad again. Therefore, when you solder a piece of wire to the hole near the touch-pad and connect its other end to any conducting item such as a spoon, you can easily detect if someone has touched the spoon at least once.

The third breakout board is the most versatile of the lot. Surprisingly, it does not have any touch-pads, although it is named as a 5-pad capacitive touch sensor. Instead, it has five copper holes, so that you can connect five objects with five pieces of wire. Therefore, if you have five different fruits or vegetables, you can connect them up and the RBPi will help you to chart their individual responsive speeds against touch.

While the two boards will both need a 10K resistor each connected between the object and the board, the 5-pad touch sensor board does not require any resistors, as it has them on-board.

Why is Power Factor so Important?

The specifications of any electrical appliance working on AC supply, such as a refrigerator, a toaster, a fan, etc., list a minimum of three important parameters – Voltage, Wattage and PF. The voltage rating indicates the nominal operating voltage of the appliance, the wattage rating indicates the power the appliance will use when switched on. The third parameter, PF, stands for the Power Factor – usually a value between 0.6 and 1.0.

All electrical appliances consume power for operating or working such as for lighting, heating, motion, etc. The appliance transforms a major part of the consumed power into its intended activity and the rest is wasted as heat. The ratio of the power converted to useful work to the total power consumed is the efficiency of the appliance.

Of the power converted to useful work, only a part is used as true or real power and the balance as reactive power. Engineers express real power in W (Watts) and reactive power as VAR (Volt-Amperes-Reactive). The appliance converts the real power into actual work, while it needs the reactive power to sustain a magnetic field and this does not directly contribute to the actual work done by the appliance. Therefore, the real power is also called the working power, while the reactive power is called non-working power. The sum total of the working and non-working power of an appliance is called its apparent power, expressed as VA (Volt-Amperes) and is the product of the nominal operating voltage and the current consumed by the appliance when operating.

This phenomenon of reactive power is true mostly for inductive appliances such as motors, compressors or ballasts. Power Factor is the ratio of the real or working power to the apparent power – an indication of how effectively the appliance will be using electricity. The problem is, although you will be paying the electricity utility for the entire apparent power consumed, the appliance will be converting only the real power into useful work for you. Therefore, a higher PF rating for your appliance works to your advantage – choose one with PF as close to 1.0 as possible.

In reality, low PF is also a headache for the utility supplying you with power. This is best explained with an example. Let us assume you have an operation that requires 100KW to run properly. If you install a machine that has a PF of 0.8, it will chalk up 125VA on the Apparent Power meter, but will convert only 80% of its incoming power into useful work. Since the electricity utility will have to supply both active and reactive power to its consumers, the wasted power ends up heating the conductors of the distribution system, resulting in a voltage drop at the consumers end.

The simplest way of improving the power factor is to add capacitor banks to the electrical system. PF correction capacitors offset the reactive power used by inductive loads, thereby improving the power factor. That maximizes the current carrying capacity, improves the supply voltage, reduces transmission power losses and lowers electricity bills.

What is stretchable electronics?

Imagine carrying your solar panel rolled up like a grapefruit while going camping and stretching it to the size of a room on the spot. It will not break, since it is made from fracture-proof electronics that is super compliant. Well, for the moment, that is the dream of Professor Darren Lipomi, department of Nano engineering, University of California at San Diego.

Darren has a vision of self-repairing skins for sensors. A special super-thin layer of organic material will make up the stretchable skin, very similar to a thin layer of plastic. As this will be as pliable as foil, it will allow the semiconductor to conform to the object and stretch with movement. Such a new phase of bendable materials will influence change in the supply chain by turning flexible electronics into a layer similar to skin. Not only will this give a new meaning to the current phrase – mobile technology, to accommodate to the transition, OEMs will have to alter their manufacturing processes.

Darren is exploring different materials and types of electronics that have molecular structures for allowing conductive materials to function even when deformed or contorted in any direction for long durations. Of importance here, is the molecular level structural details of organic semiconductors. According to the scientists at the University of California, the super-thin film-like material, sometimes as thin as 100 nanometers, could be made to stretch without any loss in its electronic functions. Display light emitters need only be about one hundred billionth of a meter thick, according to Darren.

The professor is interested in solar panels, which he plans on making in the form of a thin, stretchable film on any object such as a piece of clothing or a tent. He describes this as an extremely large solar module that is fracture proof while generating electricity. He also envisions flexible commercial displays used in wearable devices such clothing and watches from Microsoft, Samsung, LG, Google, Apple and many others.

The professor’s research has identified several types of electronic materials that can stretch. However, he feels the major challenge here is to understand the way in which the molecular structure of the flexible materials influences the mechanical and electrical properties. This is especially true when moving from the laboratory material to a commercial product. Depending on the acceptance of the industry towards development of new processes and technology, Darren expects stretchable organic materials will find use in about 10-20 years.

The research is proceeding in two directions. One way is trying to obtain working electronic properties from films of highly amorphous nature. The other is trying to prepare stretchable fabrics or nanowires from processing solutions or by electro spinning. According to the researchers, the latter path forms the middle ground between molecular and composite approaches to elastic semiconductors.

This presents a challenge of representing high-performance molecular semiconductors that have predictable mechanical properties. A tight collaboration will be required from materials scientists, device engineers, synthetic chemists along with theorists – specializing in both the mechanical behavior of soft materials and the electronic structure calculations.

Raspberry Pi and Wolfram Alpha

If you are looking for something different from the regular Internet search that you get from Google, Yahoo or DuckDuckGo, try the new Computational Knowledge Engine Wolfram|Alpha (www.wolframalpha.com). In 2009, Stephen Wolfram Research released the new engine that could answer questions written in natural language.

When you try out Wolfram|Alpha, you may be surprised that the site does not actually work like the search engines you are so accustomed to. In fact, you may not see results to some of your simple queries. Regular search engines attempt to catalog the information on the Web, and that is exactly what Alpha does not do. Rather, the Wolfram engine is a computational knowledge engine.

Traditional search engines scour the web for sites to add them to their directories. They rank different pages up or down based on the algorithms built into them, judging them on several factors. If you have a public web site and it has links to it from other sites, chances are that traditional search engines will pick it up without any effort from your side.

It is different for Wolfram|Alpha. They rely on their own licensed databases where the content entered is tagged and cataloged by employees of Wolfram Research. To give an example of the scale of things we are dealing with, at the time of launch, Alpha servers had more than 10 trillion individual chunks of data. According to Wolfram Research, its employees vet all the information for accuracy before adding anything to the Wolfram|Alpha database.
Apart from the scientific search engine, Wolfram Research also has a piece of software called Mathematica, which is a highly respected program that helps people manipulate data in many ways. Now the company has released its Wolfram Language and this is the underlying platform for all its engines from Mathematica to Alpha. The best part is that you can run it on your tiny, credit card sized single board computer, the Raspberry Pi or RBPi.

Not only is Wolfram Language free to download and use, it runs on any platform and that includes RBPi and supercomputer clusters alike. You can run it locally or in the cloud to suit your requirements. According to Wolfram Research, its performance on the RBPi is somewhat faster than the NeXT cubes when Mathematica first shipped. Considering that the NeXT cubes were multi-thousand-dollar workstations, it is surprising what your tiny RBPi is capable of.

With the RBPi taking computing back to the level of hobbyists once again, the Wolfram Language and Mathematica take it to the next level for schoolchildren. In essence, the combination becomes a highly effective knowledge-driven computational device for kids to learn about programming computers at practically no major cost.

Wolfram Language claims to be ten times faster at development compared to other languages. This is because Wolfram Language aims to maximize the productivity of the programmer by automating most of the work and building as far as possible directly within the language. The programmer has to build only the unique parts of the code, while relying on the language for everything else. The result is concise readable code, which is easy to debug. Large systems can be simply built up incrementally with symbolic components.