Monthly Archives: March 2014

Special heat sinks for heavily populated boards

Designers have to manage airflow carefully when solving the task of cooling heavily populated PCBs or Printed Circuit Boards. For effective cooling, the movement of airflow along the board is important. Two factors play a crucial role when selecting and qualifying heat sinks for dense PCB applications. The first factor is thermal resistance and the other pressure drop.

Thermal resistance is the increase in temperature in degrees Celsius for every watt and it measures how effectively the heat sink transfers heat from the heat-generating device to the ambient environment. A better heat sink has a lower thermal resistance. In other words, a better heat sink offers lower resistance to heat flow, such that it can cool hotter objects faster. Another way to say the same thing is heat sinks with lower thermal resistance cool hot devices before they reach their maximum allowed temperature. For any heat sink, its thermal resistance value depends on the airflow over the heat sink. Faster airflow results in lowering the thermal resistance values.

Pressure drop, the other factor, is the resistance the air faces while moving through the fins of the heat sink. This is the difference in the airflow speed as it enters the array of fins of the heat sink to the airflow speed of the air as it exits the array. If the pressure drop is more, it means the heat sink is taking up more air for its own heat removal, leaving less air for the other devices on the board. Therefore, with heavily populated boards, designers must balance the low-pressure drop and the low thermal resistance for a heat sink. This requires a good understanding of the relationship among pressure drop, airflow, heat sink fin-density and heat sink performance.

The performance of a heat sink is highly dependent on the speed of the air stream approaching the heat sink. Air, being a bad conductor of heat, tends to move slowly while circulating on the surface of the heat sink. A faster air stream pushes the hot air away from the heat sink and lets in cooler air, resulting in better heat removal. For heat sinks that have many fins, air remains trapped within the fins because the low speed of the incoming air does not move the hot air away from the fins. Therefore, to enable a densely populated heat sink perform efficiently, forced air cooling is necessary; this improves thermal resistance more than 100 times in certain heat sinks, compared to natural convection cooling – that is, cooling without airflow.

When the board contains only one heat sink, the selection is simple as the thermal resistance of the heat sink is the predominant factor. For multiple heat sinks on a board, the allocation of available airflow along the board takes predominance. All heat sinks on a densely populated board, apart from affecting the device that each resides on, also affects the neighboring devices. Therefore, for proper selection of a heat sink depends on both its thermal resistance and its pressure drop.

Possibilities of harvesting triboelectricity

Although we already harvest energy from many sources, new sources are always welcome. Ignoring the up-front costs, harvesting energy is often free, convenient and eases problems of several types of practical installation and replacement. Energy harvesting requires three fundamental stages: a reliable source of energy, the harvesting electronics or the converter and a load where the energy can be gainfully employed.

Apart from finding a reliable source of energy, there is one other factor before the energy goes into the converter and load. This factor is the transducer, which will allow the energy to be gathered with reasonable efficiency and reliability. Suitable transducers examples are blades for airflow, piezo-based components for vibrations or a water-driven vehicle using temperature gradient for propulsion.

Currently we use several potential sources of energy for harvesting. Prominent among them are solar radiation, temperature difference, sound, vibration, airflow and motion. One of the most common sources that have been very hard and baffling to capture is static electricity generated from friction (also referred to as Electro Static Discharge or ESD). Generally famous for the damage it causes, triboelectricity it may finally have been tamed by the work done at the Georgia Institute of Technology.

Although a precursor to generating and collecting static electricity does exist in the form of the Van De Graaff generator, the team from GIT has developed polymer materials, which are inexpensive and flexible. In addition, these materials are very good at developing a charge through rubbing and holding it until it is extracted as current flow. Static electricity is easy to generate – simply walking on carpet is good enough – and hold – that is, until you touch the doorknob – but very tricky to extract.

The team generates power from triboelectricity by sliding two materials together and then separating them to create a gap in between. Although this may be interesting, the next question could be a tricky one – how much harvestable energy does this mechanism offer?

The GIT press release cites power outputs of the order of 300W, which is of course, significant. However, there is another side to energy harvesting. This concerns power delivery to the load. Although energy collection may happen in dribbles on the generation side, when releasing energy it to the load, it has to be done in the form of power, which is the rate at which energy is expended.

The reason for this is not hard to fathom. All loads require a minimum threshold or power to function. The 300W generated may translate into barely meaningful power levels at the load. When energy levels to be harvested are on the low side, it may actually be difficult to collect enough power after accounting for acceptable losses.

The team from Georgia Tech has done something impressive and intriguing. They claim that the materials they have developed have a volume power density of more than 400KW per cubic meter and the efficiency figure is more than 50%. In addition, the team says that their material is suitable for generating energy from contact with flowing water. That is an interesting proposition, opening up new opportunities where sinks and faucets could become the hidden sources for charging mobiles and or lighting up the kitchen.

Newly launched APT Power Transducers measure three phase current & voltage

NK Technologies, the San Jose, CA based American company has introduced an APT power transducer that is able to measure three phase currents and voltages. As per the industry norms, it generates an analog signal in proportion to the watts used. The product utilizes current transformers to measure load amperage and transducers to measure the line voltage, which can read up to 600 VAC. The power transducer is a compact unit and can be used in very widely different applications in multiple places. NK Technologies has been focusing on innovations in the area of cost effective current sensing products.

The APT power transducers can be configured in multiple ways. They accept 5-Ampere secondary current transformers. Alternatively, they also accept the safer ProteCT low voltage output sensors. Irrespective of the type of current, by generating an accurate signal and helping to locate where there is excess consumption of energy, it permits reduction in demand through intervention. The users have the option of 4-20 mA, 0-5 or 0-10 VDC outputs. The APT power transducers are compatible with most of the automation systems. Significantly, the compatibility is due to the industry standard analog output.

This product has been developed with the user in mind and taking into consideration various applications. The APT power transducers are externally powered. This power transducer gives improved reliability in places where there are significant variations in voltage and current, where the power sags, as well as where there are fluctuations in voltage, which is very common,. This helps in adopting cost effective measures used overall in time and energy so that there is stability in the system. The APT power transducers are designed to meet these conditions. NK Technologies have introduced this transducer after extensive testing in their factory and after field trials with varying conditions of current and voltage.

The APT power transducers are easy to install whatever the location. This is because of its compact DIN mounted housing. The terminals in the transducers are clearly labeled, which enables easy and quick installation. The design is such that the cabinet depth is reduced significantly and it makes a low profile. The terminals are made safe for the person handling the transducer; the terminals are considered finger friendly. Effectively, it means that the connectors are safe and secure. World-renowned agencies such as the UL, CE and CUL, which everyone considers as rigorous and stiff in quality certification, have approved the APT power transducers.

With wide-ranging and need-based features and top class quality, the APT power transducers command worldwide acceptance. The company is at the forefront of Agency listings, Certifications and International Registrations for its manufacturing facility. This process has paved the way for innovation and customer requirements. The company offers warranty for all its products and along with it, a customer support considered the best in the industry. APT power transducers are all set to give the customer a new tool that is effective in terms of both cost and operational efficiency.

This 10 Watt blasting gun has intense illumination

The LED light application has now covered almost the entire gamut of all human activity. Larsen Electronics recently announced the launch of 10W LED blasting gun light designed to produce intense illumination up to 860 Lumens. The major highlight of this product is that it is IP-66 watertight, which gives it the capability to withstand the rigors of heavy-duty environmental applications. Larson Electronics has christened the product as BLG-LEDP1X10W blasting gun light and it is extremely durable in media blasting applications. This LED light can be mounted on any standard blasting gun stand with utmost ease for immediate use.

The mounting system is specifically designed to be easily setup and used on the barrel of any standard blasting gun. The system comes with the hardware needed for the mounting along with its protective lens cover. It can be easily removed or replaced, even when wearing gloves. This product is helpful in blasting environments such as sand, baking soda or coal slag. The lens may wear out in due course of time as it is exposed to blasting, but is easily replaceable. A slot provided at the bottom of the lens allows cleaning of particles when the lens is changed. The LED mounted on the blasting gun system can last for a considerable length of time.

With a 120-277V AC encapsulated transformer and 100-ft cable attached to it, the LED light operates on 24V DC. The step-down transformer converts 120-277V AC to 24V DC and provides the power needed for this LED light unit. It produces light of high intensity, about 860 Lumens. The light beam covers 600 feet and the manufacturer is assuring a lifetime of 50,000 hours. Meeting the IP66 watertight standards, the LED gun light is not only for heavy-duty applications, but also for aggressive use in the difficult terrains of atmospheric variations. Unlike other blasting gun lights, BLG-LEDP1X10W blasting gun light by Larson Electronics is lightweight but at the same time produces an intense light, which is brighter and produces more intense illumination when compared to the incandescent lights.

The gun lamp consumes only 10-Watts and the overall dimension of the unit is 3×3.8×4-inches, with IP 66 ingress protection and spot/flood light configuration. This LED light unit is mounted on the clamp on top of the blasting gun. The protective lens is made of quick-change polycarbonate. This unit comes without the blasting gun mount as the mount is to be procured separately.

BLG-LEDP1X10W from Larsen Electronics is seen as a new dimension to the illumination designed with the users in mind. It gives not only a viable lighting technology, but also durability in very rough and abusive work areas. It is durable while at the same time it generates an intense light of 860 Lumens. It is to be noted that this unit will replace all the instances where incandescent lamps were being used so far. With more innovations expected, LED lighting technology is all set to take over totally in all locations on a global basis.

Pairing your Raspberry Pi with an SPI OLED

OLEDs are interesting because they produce very crisp and brighter displays than is possible with the regular Liquid Crystal Displays. Being made of thin films of organic molecules, OLEDs use less power than conventional Light Emitting Diodes and LCDs. Driving OLEDs from your Raspberry Pi (RBPi) can be a great project to learn about these nifty solid-state displays and the processes that drive them.

Adafruit offers a lovely little monochrome SPI OLED module with a resolution of 128×32, driven by a SSD1306 driver chip. You can refer to excellent tutorials, libraries and guides on the website if you are driving this display from an Arduino. Although other OLED modules support I2C interface, this module supports only SPI, has pixel and text drawing functions, without any geometric drawing functions.

Although very small, only about 1-inch diagonal, the display is very readable because of the very high contrast of the OLED display. It has 128×32 individual white pixels, and the controller chip can turn each one of them on or off individually. No backlights are needed, as the OLED display produces its own light. This feature enhances the contrast and reduces the power consumption as well. The SSD1306 driver chip of the display communicates over the SPI bus, and requires four to five pins from the RBPi.

The OLED and its driver require a power supply voltage of 3.3V and logic levels of 3.3V for communication. If you are using this with the 5V supply of the RBPi, a 3.3V regulator should be used to power the display. On average, the display consumes about 20mA from the 3.3V supply, but this actually depends on how much of the display is lit. OLEDs usually require a high-voltage drive for the good contrast, but since this switched capacitor charge pump is already built-in into the display, this is one of the easiest OLED modules to interface.

Apart from the SPI specifications of the module, there is also a D/C pin, which controls the Data/Command going into the module. When you pull the D/C pin HIGH (connect it to VDD), the signals present at the pin are treated as data. When you pull it LOW (connect it to VSS), the signals present at the D/C pin are treated as command and are transferred to the command register.

What this essentially means is the opcode and the argument bytes that follow it are treated as a single command, even though this is a multi-byte command. For example, the command for setting the contrast control consists of a one-byte opcode followed by a one-byte contrast value. Therefore, the D/C pin has to be pulled LOW for the entire sequence when sending this command. Similarly, when sending image data, the D/C pin has to be pulled HIGH, which will enable the data to be moved into the image memory buffer.

The project is simplified when you use the following software – Occidentalis 0.2 for boot image, WiringPi-Python for accessing the GPIO pins and Py-Spidev for accessing the python bindings to the spidev Linux kernel driver. For further details, refer here.

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.

Make a time clock with the Raspberry Pi

People working on projects are usually required to keep their time records up to date. However, those who are more engrossed with the technicalities of their work, find that they slip on their time keeping chores. If you fall into that category, let your Raspberry Pi (RBPi) help you out. Along with the tiny single board computer, you will additionally need one RGB LED, an OLED character display and a rotary encoder. Your time will be logged directly into a Google Docs spreadsheet.

The purpose-built time clock has several off-the-shelf components. For the RBPi, use the Occidentalis 0.2 operating system. The 128×32 OLED display uses SPI interface and this OS has the interface bundled in.

The time clock is very simple to operate. When you start it up, it will pull in a list of jobs from a specified Google Docs spreadsheet. To scroll through the list of jobs, simply rotate the knob on the rotary encoder. When you want to record time for specific project, just locate it by rotating the knob and click it. That starts the clock ticking on the spreadsheet. For logging off, simply click once again.

Use any case suitable for the RBPi or make your own. Since the HDMI, audio and video ports will not be used it is acceptable if the case does not provide access to these ports. For those who like to do things professionally, designing the carriage for the RBPi on OpenSCAD could be great fun. Printing the carriage on a Makerbot Replicator will give the required professional touch. Since the RBPi board does not have any mounting holes, you may have to put in edge-clips for holding it. Having posts at the corners of the board will make a snug fit.

Although the documentation of the RBPi mentions some ground pins as DNC or Do Not Connect, using them as extra grounds can be very convenient, just make sure you are using the proper ground pins.

Using the GPIO pin 5 of the RBPi for the push button can be of dual advantage. This keeps the pin 5 available for a Safe Mode boot, for example, when there is a recent firmware release. Simply hold the knob down when booting up and your RBPi comes up in the safe mode. Additionally, there is no chance of the pin being accidentally held low, such as could be the case if it was used for one of inputs to the quadrature encoders.

Use the software from here. The PWM library drives the RGB LED and the RgbLed class animates its color transition loops. The rotary encoder uses the RotaryEncoder.Worker class for polling through the encoder GPIOs and for keeping the application code as simple as possible.

Since the application code utilizes the CPU only to around 20%, its temperature rise is within safe range. The color-coding gives idea of the state of the machine. When no time is being logged, the LED shows purple. As time is logged against a task, the LED pulses slowly and turns blue. When rapidly flashing, you know that the spreadsheet on the Google Docs is being updated.

A new 32 HD motor for rough operations

Maxon Precision Motors, Inc. based in Fall River, MA, has successfully designed a new 32 HD motor for rough and abusive operations. Known as the EC-4pole 32 HD motor with part number 397798, the motor is considered ideal for operating in conditions existing in deep drilling. Exploration in gas and oil fields is known by the name “downhole drilling” and according to deep drilling technology, it is possible to recover oil and gas even from depths of 2500 meters or more. This 32 HD motor is being offered for this application as it has been specifically designed for the purpose. According to the company, this 4-pole power motor uses a winding technology that is the best among the same class of motors in the field.

The performance in terms of the volume rate, in proportion to its weight along with the quality and security it is able to generate, is excellent due to the motor providing inertia free motion. The durability of the motor is astoundingly long. This factor alone has been the main feature for this motor, which has enabled the motor to cater to the application of deep drilling in a very significant manner. With wide ranging options for different types, as required by the user, the motor is able to meet the requirements for the purpose.

The motor has a power rating of 220W in air and graduates to 480W in oil due to the high heat flow that is generated in the process. The motor functions in an ambient temperature range reaching up to 200°C and more, with atmospheric pressures of up to 1700 bar. The notable aspect of this motor is its capability to bear vibration up to 25Grms along with impacts up to 1,000G. That means an impact that is effectively 1000 times the acceleration due to gravity at the earth’s surface. The operational efficiency of the motor is exceptionally high. The manufacturer claims an efficiency of 89% in air and 80% in oil.

The EC-4pole 32 HD motor from Maxon is 3-phase AC operated at a nominal voltage of 48V. The nominal speed of the motor is 5710RPM with the starting current at 47.5A, for an efficiency of 89%. It weighs only 860grams and the rotation is clockwise. The motor rotor produces inertia of 128 gcm² with a mechanical time constant of 2ms. The terminal resistance of the motor is 1.01 Ω. The maximum permissible speed is 12000RPM and the motor can take up a maximum axial load of 16N.

Maxon Precision Motors, with a global reputation in the field, expects the EC-4pole 32 HD motor to perform well in the field meeting the rigorous standards set for the deep drilling applications. With a wide range of options available to meet the specific needs, the 32HD motor will be able to function in rough operating conditions, where the depth is more than 2500meters. This motor makes it possible to recover gas and oil at a high level of efficiency. This highly durable motor performs in spite of multiple vibrations and severe impacts it undergoes.

Learn about metal film resistors

Resistors are a common passive item in any electronic assembly. They are used for restricting the amount of current flowing in a circuit; acting much as a valve does in a water pipeline. The most commonly in use are carbon, thick metal and thin metal film resistors. The film forms the resistive material of the resistor.

The axial resistor is usually a cylindrical conductive film on a non-conductive ceramic carrier. Two leads projecting from both ends of the resistance help in connecting the item electrically within a circuit. Although the appearance of a metal film resistor is very similar to that of a carbon film resistor, the former has much better properties of stability, accuracy and reliability.

A cylindrical ceramic core of high purity forms the base of a metal film resistor. Manufacturers mostly use a method known as sputtered vacuum deposition to deposit a thin metal layer on this ceramic base. This combination is then kept at a low temperature for a long period, which results in very good accuracy for the resistor. Mostly, the resistance material used is nickel chromium (NiCr), however, for special applications, other alloys such as tin and antimony, tantalum nitride with platinum and gold are used as well.

The thickness of the metal film strongly governs the stability of the resistance. Typically, a metal thickness of 50-250nm is a good compromise between better stability and lower resistance value. For connecting to the circuit, two end caps with connecting leads are pressed on to the two ends of the resistor body.

To obtain the desired resistance a laser beam cuts a spiral slot in the thin metal layer. This is a more modern method as compared with grinding techniques and sandblasting used earlier for trimming the resistance value. Once the final value of the resistance is achieved, several layers of paint are placed on the resistor body, with each layer being baked individually.

Apart from providing a high dielectric strength, the coating protects against ingress of moisture and mechanical stresses. Color code bands on the body mark the resistor value along with the tolerance band. Metal film resistors are available with standard tolerances of 2, 1, 0.5. 0.25 and 0.1%, with the TCR or temperature coefficient of resistance lying between 50 and 100 ppm/K.

Metal film resistors demonstrate good properties for TCR, stability and tolerance. Because these resistors have a low voltage coefficient, they feature high linearity and low noise properties. Therefore, if any of your circuits need low noise, tight tolerance and low temperature coefficient properties, be sure to use metal film resistors. For example, active filters and bridge circuits use metal film resistors.

Metal film resistors show good reliability when operated from 80 percent down to 20 percent of their specified power rating. Although reliability generally increases if the resistor is derated 50 percent, going below 20 percent of the power rating at elevated humidity conditions usually diminishes reliability. Moreover, metal film resistors are more easily damaged by power overloads and voltage surges, as compared to carbon composition or wire-wound resistors.