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What Is An Electronic Load And Where Do You Use It?

Power supply manufacturers need to test their products dynamically. Instead of using fixed-resistor banks of different sizes, electronic loads allow them to simulate easily and quickly various power states. Using an electronic load, large ranges of power sources such as converters, inverters, UPSs and electromechanical sources such as batteries and fuel cells may be tested. For varying loads, electronic loads are easier to use and provide a much higher throughput compared to fixed-resistors.

For example, a handheld device may have to be tested for sleep, power conservation and full power modes. These are easier to test using a single electronic load, but may require several combinations of fixed-resistors. Additionally, an electronic load may be programmed to represent closely a real environment for a power source. This may take the form of modulation to improve the performance of power supplies by providing a faster transient response as compared to a standard power supply.

An electronic load usually consists of a bank of power transistors, power MOSFETs or IGBTs mounted on a suitably sized heat sink, and cooled with fans. An electronic circuit governs the amount of current that the power devices can draw from the power supply on test. To protect the power devices from damage, electronic loads usually have a pre-settable power limit. The manufacturer usually provides a power curve for the safe operation of an electronic load. The user must be aware of the simultaneous maximum voltage and current that can be applied to the electronic load to ensure the electronic load is not overpowered.

It is important to select a suitable electronic load for the testing. For example, a power supply rated for 12V and 30A, may never be operated at 12V and 30A continuously. While testing, the operator may run it at 12V and 5A and then at 3V and 30A. That means an electronic load of 90-100W is sufficient to test the supply.

To improve the performance of a power supply, an electronic load may be used as a high-speed current modulator. In such cases, only a fraction of the power rating of the power supply is required. When the current is modulated to the highest level, the voltage across the load is likely to be very low. As the current is modulated off, the voltage rises to its maximum. Usually, if the modulation of the current is from zero to some maximum, the load power required is one-quarter of the operating voltage times the current rating with some margin added.

Electronic loads are very useful for dynamically testing power sources. In this form of testing, the current is quickly pulsed between two states, simulating a possible sleep mode and a full power mode of a device. This pulsing can be as fast as 20,000 times a second.

Another requirement that electronic loads are adept at is low voltage testing. Although most electronic loads will refuse to operate when the applied voltage is below 1V, there are some models, which perform comfortably down to 0.6V. This is a very useful feature when testing fuel cells where the operation at low voltages is crucial.

Home Protection with Raspberry Pi

Planning to go on a vacation, but afraid of who will look after your home for you? Worry not, for the mighty Raspberry Pi (RBPi) is here. Not only will RBPi look after your entire house, it will send you an email of what is happening in your home and let you see it on your mobile or on a PC. How cool is that?

Most alarm systems incorporate three primary sensors. The first is a temperature sensor to detect the rise in temperature in case of a fire. The second is an intrusion detection sensor to detect if an intruder has gained access to the insides of the house and third is a motion detection sensor. Apart from these primary sensors, you may add smoke detectors and cameras according to your necessity.

The software consists mainly of a database to store all the events with a time stamp, a dashboard to display the status of the sensors, configure them and to program the alarm system. The Raspberry Pi also acts as a web-server to send email alerts and to display the dashboard on a remote computer or Smartphone.

Depending on the size of the home, its vulnerability and the number of sensors being used, you could divide the area into a number of zones. This makes it easier to arm the sensors belonging to a specific zone. For example, a door and few windows of your home may be facing a busy street during the day and you may decide not to arm the sensors in this zone in the daytime. As night falls, the street gets deserted and you may want the sensors in that zone to be armed for the night.

Dividing the home into zones also has the advantage of knowing in which area or areas the alarm has been triggered. The camera for that zone can then be switched on to assess the situation visually.

Since RBPi runs on Linux, and Linux multitasks very well, the software runs in the background. The software is programmed to wake up RBPi about once every minute and check in on each of the armed sensors in all the zones. If there is no activity, it simply updates the logs for the database and the dashboard and goes back to sleep.

If a sensor trips, or generates an activity, Raspberry Pi records it in its logs, and sends you an email with the details. The dashboard then indicates the alarm condition in the zone where the alarm originated. You have a choice of turning off the alarm after checking it out.

You can login to the server from a remote PC using a username and a password. The web-browser will display the dashboard and a green button lets you know that the RBPi is running your home alarm software and is transmitting the information from the sensors. If the alarm system goes down for some reason, or there is a problem with the connectivity between the Raspberry Pi and your computer, this green button will turn red within a minute. You can now proceed to test, arm or disarm the sensors in each zone. For details of software and setup, refer here.

Sensing humidity using advanced technology

An approaching thunderstorm creates a very stuffy environment with oppressively heavy moisture in the air. The presence of water in the air is termed as humidity and this largely affects human comfort. The amount of water vapor influences many physical, chemical and biological processes. In industries, measuring and controlling humidity is critical since it can affect not only the health and safety of personnel, it can affect the business cost of the product as well.

Sleep apnea leads to repeated cessation of breathing during sleep. People, who suffer from sleep apnea, have to wear a mask to prevent nasal collapse. The mask is connected to a Positive Airway Pressure machine that sends pressurized air through the nasal passage of the patient, to prevent it from collapsing. It is important to monitor the humidity of the air the patient receives, keeping it at the appropriate level of comfort to allow the patient to sleep comfortably.

Traditionally, humidity or relative humidity was measured with the wet and dry bulb hygrometers. This method is neither accurate nor convenient in the industrial environment. With advancement in technology, solid-state devices are now available, which measure humidity with very high accuracy, repeatability and interchangeability. Solid-state humidity sensors are generally of two types, capacitive and resistive.

In resistive type humidity sensors, the resistance of the element changes responding to variations in humidity in the environment. The construction is in the form of two intermeshed printed combs, made of a thick film conductor of a precious metal such as gold or ruthenium oxide. The two combs form two electrodes, the space between them being filled with a polymeric film. This film has movable ions whose movement is governed by humidity. The film thus acts like a sensing film whose resistance changes with change in humidity.

The capacitive type of humidity sensor has an Alumina substrate on which the lower electrode is formed using either gold or platinum. A dielectric polymer layer such as thermoset polymer is then deposited on the lower electrode. This layer is sensitive to humidity. On top of this polymer layer, a top electrode is placed, and this is also made of gold or platinum. The top layer is porous and allows water vapor to pass through into the sensitive PVA layer. Moisture enters or leaves the sensing layer until the vapor content is in equilibrium with the environment. This sensor is therefore a type of capacitor whose capacitance changes with the change in humidity.

The arrangement of a hygroscopic dielectric material sandwiched between two pairs of electrodes, forms a capacitor whose value is governed by the dielectric constant of the hygroscopic material and the sensor geometry. At normal room temperatures, the value of the dielectric constant of water vapor is about 80, which is much larger than the constant of the sensor dielectric material. Therefore, as the sensor absorbs water vapor from the environment, it results in an increase in the capacitance of the sensor.

Both the resistive type and capacitive type of humidity sensors are available in the form of small surface mount SMD packages, and pre-calibrated to simplify, speedup manufacturing and reduce the cost for Original Equipment Manufacturers.

Digital Isolators vs Optocouplers

Industrial equipment may need to operate in a region of strong electromagnetic fields. There can be a sudden surge in the voltage applied to the equipment, which may be hazardous to the user and the gear. It is crucial that you incorporate a reliable isolation system to take of these issues.

Until very recently, the optocoupler was the only practical choice in providing safety isolation for manufacturers of medical and industrial isolated systems. The arrival of digital isolator has however, changed the situation greatly.

Digital isolators offer several advantages over optocouplers. They are more reliable, cheaper and have greater power efficiency compared to the optocouplers.

It is important that you understand the three vital aspects of an isolation system. These are the insulation material, the structure and the method of transfer of data.

Insulation Material

Typical insulation materials are silicon dioxide wafers and thin film of polymers. Optocouplers use polymer films. Digital isolators make use of a particular form of polymer called polyimide. This material serves to increase the efficiency of isolation systems.

Silicon Dioxide is not a very suitable material as an isolator. While you may increase the thickness of polyimide to increase the insulation, you cannot adopt the same method for silicon dioxide. Wafers thicker than 15 micrometers may crack during processing.

Structure

Digital isolators use either transformers or capacitors to transfer data across the isolation barrier. A transformer system has two coils placed side by side. Current flowing through a coil (called the primary coil) gives rise to a magnetic field in the space surrounding the coil. This induces a current to flow in the other coil (called the secondary coil).

A capacitor consists of two metal plates with the space between the plates filled with a non-conductor.

Optocouplers use light emitting diodes (LED) for data transmission.

Transfer of Data

The LED in an optocoupler turns on for logic high state and turns off for logic low state. The device consumes a significant amount of power when the LED is on. Digital isolators do away with this undesirable aspect. The sophisticated circuitry in the system encodes and decodes data at a rapid pace so that the transmission of data involves less power consumption.

A digital isolator using a transformer for data transmission transfers the data from the primary coil to the secondary coil during the pulses of current driving the transformer.

A digital isolator may use radio frequency signals as well, in a fashion similar to the way an optocoupler uses light from an LED. However, since a logic high state causes a continuous transmission of radio frequency signals, this method uses more power.

Digital isolators with capacitors have an advantage in that they consume lower currents for creating coupling electric fields for data transmission.

Ensuring the Correct Combination

It is important to use the right insulating material and the apt method for data transfer depending upon the application.

Since polymers provide more than adequate insulation, they are suitable in most applications. Polyimide insulation is particularly suitable for equipment used in healthcare and heavy industries.

Concerning data transfer, capacitor isolation is adequate for situations requiring just functional and not safety isolation. Isolation systems making use of transformers will serve the purpose of safety as well as functional isolation.

How to measure temperature with a Raspberry Pi

Looking for another project to make with a Raspberry Pi? You can use your Raspberry Pi to measure temperature. Not only at a single point, but also at maximum of 20 points simultaneously. Of course, you will need 20 individual sensors for doing that. Raspberry Pi will poll all the 20 sensors one after the other, and read the temperature from each of the sensors.

If you are wondering how complicated it would be to wire up 20 sensors to the Raspberry Pi, you can relax, since you need only three wires in all. One of the wires will carry power to the sensors, one wire will be the ground or return path and the third wire is a unique 1-wire interface to control the sensor and to read the temperature measured by it.

This wonder sensor is a High-Precision 1-Wire Digital Thermometer, DS18S20, with a measurement range of -55°C to +125°C (-67°F to +257°F), a thermometer resolution of 9-bits and an accuracy of ±0.5°C from -10°C to +85°C. Maxim Integrated makes this thermometer and the smallest size is a little larger than a matchstick head (TO-92).

Not only can this tiny fellow read the temperature, it stores them in its non-volatile memory and can present them either as °C or as °F. You can set temperature limits in its memory and DS18S20 will tell you when the temperature it is monitoring goes beyond the programmed limits. You can use this thermometer with the Raspberry Pi to control thermostats, industrial systems, consumer products or any thermally sensitive system.

At this point, you may be wondering if there is only one single wire for all the 20 sensors, how is the Raspberry Pi able to differentiate the twenty temperature readings. Maxim has programmed each of the sensors with a unique serial number, and when Raspberry Pi wants to read the temperature from a specific sensor, it simply asks for it by the serial number of that sensor. Only the sensor whose serial number the Raspberry Pi queries, sends the temperature data, all the others remain silent.

The Raspbian Linux distribution that you are using in your Raspberry PI already has all necessary kernel modules installed for accessing the 1-wire bus. The programming details are rather simple and you can refer to them here.

What else can you do with a DS18S20 and Raspberry Pi? You may be measuring temperature at a remote place, or there is no space for the extra power supply to the DS18S20. So, instead of supplying power separately, you could make DS18S20 “steal” power from the 1-Wire bus. For this, you must connect the VDD pin of the DS18S20 to ground. According to the datasheet, do not use the parasitic mode for measurements above 100°C, as the DS18S20 will not be able to sustain communications.

If you have programmed temperature limits for some of the DS18S20s, they will raise a flag if the temperature they are sensing goes beyond the set points. By polling for the flags, Raspberry Pi can know, which sensor is sensing temperatures beyond its set point.

Energy Harvesting – How & Why

What Is Energy Harvesting – Why Is It Needed?

The process of extracting small quantities of energy from one or more natural, inexhaustible sources, accumulation and storage for subsequent use at an affordable cost is called Energy Harvesting. Specially developed electronic devices that enable this task are termed Energy Harvesting Devices.

The world is facing acute energy crisis and global warming, stemming from rapid depletion of the traditional sources of energy such as oil, coal, fossil fuels, etc., which are on the verge of exhaustion. Not only is the global economy nose-diving, but the damage to the environment is also threatening our very existence. Natural calamities like earthquakes, tsunamis, droughts, floods, storms, etc., have become the order of the day. Economic growth is generating a spiraling demand for energy, goading us to tap alternative sources of energy on a war footing. Our very existence on the planet Earth is at stake, and we must find immediate solutions to meet the energy needs for survival.

Alternative Energy Sources Available

There are many, almost inexhaustible, sources of energy in nature. In addition, these energy forms are available almost free, if available close to the place where required. Sources include: Solar Energy, Wind Energy, Tidal Energy, Energy from the waves of the ocean, Bio Energy, Electromagnetic Energy, Chemical Energy, and so on.

Recent Advances in Technology

The sources listed above provide miniscule quantities of energy. The challenge before us is to gather the miniscule amounts and generate meaningful quantities of energy at affordable cost. Until very recently, this has remained an unfulfilled challenge.

Today, research and innovation has resulted in creation of more efficient devices to capture minute amounts of energy from these sources and convert them into electrical energy. Besides, better technology has led to lower power consumption, and hence higher power efficiency. These have been the major propelling factors for better, more efficient energy harvesting techniques, making it a viable solution. These solutions are considered to be more reliable and relatively maintenance free compared to traditional wall sockets, expensive batteries, etc.

Basic Building Blocks of an Energy Harvesting System

An Energy Harvesting System essentially consists of:

a) One or more sources of renewable energy (solar, wind, ocean or other type of energy)
b) An appropriate transducer to capture the energy and to convert it into electrical energy (such as solar cells for use in conjunction with solar power, a windmill for wind power, a turbine for hydro power, etc.)
c) An energy harvesting module to accumulate, store and control electrical power
d) A means of conveying the power to the user application (such as a transmission line)
e) The user application that consumes the power

With advancement in technology, various interface modules are commercially available at affordable prices. Combined with the enhanced awareness of the efficacy of Energy Harvesting, more and more applications and utilities are progressively using alternative sources of energy, which is a definite sign of progress to effectively deal with the global energy crisis.

Optional addition of power conditioning systems like voltage boosters, etc., can enhance the applications, but one must remember that such devices also consume power, which again brings down the efficiency and adds to cost.

Do surge protectors save energy?

Most modern electronic gadgets are not meant to be switched off. Rather, they are placed in a state of suspended animation called standby. Gadgets in standby perform some basic background functions until their user recalls them for full functionality. The benefit to the user is an instant response from the unit against having to wait for it to resuscitate.

However, all this comes at a price. Units in standby mode need power, however small, to keep them ticking. For those powered from a battery, need to replace or re-charge their batteries more often. Those drawing power from the utilities’ outlet, consume a tiny amount of power in the standby mode, and if the design of the gadget is not proper, this may amount to energy up to one-tenth of their normal consumption when fully operating. Multiply this with the number of such gadgets all over the house or office, and you will notice the standby consumption forms a substantial chunk of the yearly electricity bill.

People use surge protectors to save their expensive electronic gadgets from going bust with high-voltage surges appearing on the power outlets in homes and offices. These are long strips of connectors allowing plug-in of multiple gadgets. Equipment connected to these strips are saved from the marauding surges because the strip has a device called an MOV inside it followed up with a fuse. The MOV shunts the high-voltage surges and prevents them from reaching the plugged-in equipment.

Apart from the connectors, MOV and fuse, the surge protector strip also has a master switch with which all the gadgets connected to the strip can be switched on or off. Irrespective of the individual gadgets being in full operation or in standby, flipping the master switch to the off position cuts off power to all equipment connected to that strip. This essentially means none of the equipment can draw any more power, not even for their standby operation.

Switching off all equipment from the wall outlet with their individual switches can be a daunting task, especially if there are a number of gadgets connected and the wall outlet switches are difficult to access. After a few days of diligence, people usually give the switching off routine a miss and the equipment remain in a standby mode, consuming their share of energy.

Since surge protectors have a master switch, it is simpler to switch off a number of gadgets at a time, and thereby, cut down on the consumption of standby power. For example, you may have a TV, a few computers, a printer and a few battery chargers hooked up to one surge protector strip. When leaving at the end of the day, switching off individually would be troublesome. However, flipping the master switch on the surge protector strip may not be a big deal.

Therefore, the proactive user is actually saving the energy by remembering to flip the switch on the surge protector strip. If the user forgets to flip the switch, the surge protector strip does not save any energy.

Protection with Surge Protectors – Why and How

If you have once had your TV, audio system and other electronic equipment destroyed by a voltage surge during a thunderstorm, you will surely know how to prevent this from happening once again. For preventing such drastic accidents, it is common to use a device called the surge protector, and to have the maximum protection, it is important to know why it is required and how it works.

Most people know of a surge protector as a long strip of electrical power connectors, which power sensitive electronic gadgets. However, two components inside the strip provide the actual protection. One of them is the Metal Oxide Varistor (MOV), and the other is the familiar fuse. The combination of an MOV and the fuse protects your electronic gadgets by limiting the voltage delivered.

Normally, all households and offices experience power surges many times during the day, including at night. The surges are generated when nearby appliances are switched on or off. Appliances such as microwave ovens, air conditioners, refrigerators and pumps switch on and switch off periodically. When they switch, they create a disturbance in the electrical supply lines, causing either a voltage dip or a voltage spike, or both. Since all electronic gadgets have a limit to the level of voltage they can withstand, any spike over and above the limit will have a damaging effect.

A thunderstorm is another factor generating a power surge. Even if lightning does not strike a home directly, it is enough if it hits a power line nearby. The power lines feeding a home can carry this surge in and can cause massive damages. Using a surge protector largely prevents all this.

The MOV inside a surge protector has a special property. As long as the voltage across it does not cross its specified limit, the MOV remains a passive device, with a very high resistance. When a surge arrives, and is above the voltage limit, the MOV lowers its resistance immediately. This causes a massive current to flow through the MOV. The increased current also flows through a fuse, which precedes the MOV, causing the fuse to blow and cutting off any further supply to the MOV and any connected gadget. In the absence of a fuse, or the fuse not blowing because of improper rating, the MOV may burn out allowing further spikes to be passed on to the gadget.

An MOV has a specific voltage rating and the spike expected at the point of use defines the rating selected. The telephone industry uses a special type of surge protection, known as Gas Discharge Tube or GDT, at specific points where the telephone lines enter a building. A GDT operates at a much higher voltage as compared to an MOV, and offers protection from higher voltage surges.

For working satisfactorily, an MOV and a GDT both need a good electrical earthing and a proper earth-wire connection.

11 secret controls on your iPhone headphones

If you have any Apple brand device, chances are you have at least one pair of their headphones laying around. If you use them on a regular basis, here are some tips to get the most from your Apple headphones:

During phone calls:
1 – Incoming calls: Tap the center button to answer a call
2 – Ignore a call: Long-press the center button to ignore the call – you should hear 2 ‘beeps’ and you will know that the caller was successfully sent to voice mail
3 – Swapping calls: Tap the center button once to swap calls – Hold the center button down for about 2 seconds to end the new call
4 – Disconnecting/Hanging up: Tap the center button once again to hang up

When listening to music:
5 – Toggle pause/play: Single tap the center button
6 – Skip a song: Double tap the center button
7 – Return to the previous song: Triple tap the center button
8 – Fast forward a song: Tap the center button two time; long-press the second tap
9 – Rewind a song: Tap the center button three times; long-press the third tap.

Using the camera function:
10 – Shutter Release: Tap the volume-up button to snap a picture. This trick will help you get very steady shots.

For Siri users (iPhone 4S and above):
11 – Activate Siri: Long-press the center button

Remember – any Apple device that utilizes their headphones and have these functions (i.e. iPad and iPod) can also take advantage of these features. Do you know of any headphone tricks that we’ve missed? Send them our way!

How to wipe a hard drive clean

If you are donating, disposing of or selling anything that contains a hard drive, chances are that drive should be wiped clean before it leaves your hands. Even if the hard drive has failed, special equipment can read a hard drive which could expose your private and confidential information to the next owner.

So what should you do before your dispose of your equipment with a hard drive? There are several methods that are recommended by the experts. Here is an explanation of two of them:

1 – Destruction:
According to the National Institute of Standards and Technology Special Publication 800-88, “Destruction of media is the ultimate form of sanitization.” Some methods to destroy a hard drive include pulverization, incineration, melting, and shredding however it should be noted that it is recommended that you never burn a hard drive, put a hard drive in a microwave, or pour acid on it in an effort to destroy it. Those methods should be avoided. What IS recommended is that you drive a nail through the hard drive, being sure to pierce the hard drive platter. This can be accomplished with a hammer and nails or even a drill. If you use this method to destroy the hard drive, drive several nails through or drill through it several times. Another method is to remove the hard drive platter and sand it to erase the data.

Destroying the hard drive ensures that you or anyone else will never be able to use the hard drive again. Should you want someone to be able to use the hard drive again, you might consider another option which is data destruction software.


2 – Data Destruction Software:
Sometimes called hard drive eraser software or disk wipe software, data destruction software is a way to remove your personal data off of a drive without permanently destroying the drive. While not a fool proof method (user error comes into play here), it is the easiest way to wipe a drive clean. Data destruction software overwrites a hard drive in a particular way to make extracting data from it very difficult, if not impossible. Most computer users should be able to safely wipe their hard drive clean using this type of software.

There are other methods available however they are generally expensive. Either of the two methods outlined above should suffice for the average computer user that would just like to wipe a drive clean before disposing of it.