Category Archives: Guides

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.

How to solder like a pro

Manual soldering is a skill that gets better with practice. For those who are starting out for the first time, manual soldering can be risky, unless they take proper care and follow safety instructions. Manual soldering involves application of heat locally by a soldering iron, whose tip may reach temperatures as high as 400°C. Soldering materials are sometimes toxic, especially if using lead based solders. Some very useful information about soldering can be found here.

One of the best tips to follow for both starters and experienced people is to don safety glasses before starting to solder. This is something that should become a habit for everyone who is soldering, because hot solder entering the eye can be dangerous. A wire, bent the wrong way, can easily flick hot solder into the air. When cutting a component leg, the cut piece can travel at high speeds. Safety glasses will save the eyes from all these flying missiles.

For most people, soldering skills will not be very good at first, but will certainly improve over time. There is no magic in making perfect solder joints every time, you will simply get used to how to hold things, when the iron is hot enough and the feel for how long you need to apply the heat on.

One basic question that comes up often is whether people ought to use leaded solder or unleaded solder. Leaded solder is composed of Tin (Sn) and Lead (Pb), typically in the ration 60:40, with lead being added to bring down the melting point of the composition to about 180°C. However, Lead being unsuitable to human health, has led to creation of unleaded or lead-free solders. The composition of lead-free solder varies, but in general, these have a higher melting point, nearer to 240°C.

The lower melting point of leaded solder makes it easier for soldering work, and beginners find it easier to practice with. Unleaded solder also has a more corroding effect on the tip of the soldering iron, so you need to change the tip more frequently if you are doing a lot of soldering with unleaded solder. For fine electronics soldering, it is preferable to use a thin gauge of solder wire such as 0.7mm in diameter. Thicker solder is intended for heavier electrical work.

For solder to melt and flow easily, a chemical compound is used; this is called Flux. Usually, the solder wire has a hollow core, in which flux is filled. As you heat the solder wire, flux melts first and helps solder to melt and flow. However, melting flux releases fumes that although not harmful in small quantities, it is advisable to avoid breathing in.

Soldering should preferably be done in a large, well-ventilated room. If that is not possible, a fume extractor or even a fan should be used to draw the fumes away. The tip of the soldering iron should be kept clean and well wetted with solder. This keeps the tip in good condition for a longer time, preventing pitting. For cleaning the tip, use a wet sponge or some wire wool. Wire wool can be used to clean the surfaces to be soldered, resulting in faster and better-soldered joints.

REX – a brain for robots

Not to be confused with Tyrannosaurus the king of beasts, REX is a complete development platform for sophisticated robotic applications. While most robotic designers use the Arduino platform as a base for their robots, Mike Lewis and Kartik Tiwari were not impressed with the available hardware. Their design, REX, is specifically targeted towards robots. REX poses no wiring hassles, has built-in battery inputs and has a robot programming environment that it boots up directly into.

The duo felt people who designed robots needed a new and more advanced platform. When using a single microcontroller for handling multiple sensors, motors and other electronics, problems start arising. The situation worsens as you plan on adding increasingly sophisticated tasks such as speech recognition and computer vision. The Arduino is, by default, not a multitasking platform and is intended for running a single task at a time. However, robotics essentially requires multiple tasks to be running at any given time.

Therefore, REX came up with a 32-bit ARM Cortex-A8 processor core running at 1GHz, an 800 MHz DSP core and 512 MB of RAM. The board runs on the Alphalem Operating System and boasts of a host of features such as built-in drivers for sensors and other similar devices, a task manager to allow launching multiple processes and support for several programming languages such as C, C++ and Python. The Arduino-style programming environment facilitates developing your own robot applications.

REX is a low-cost robot development platform that targets advanced robotics. Although simple robotics can be handled by the Arduino project and is fairly straightforward, REX is geared towards handling the extra functionality required where you need voice recognition and computer vision. Being simple and low-cost, the REX platform helps make more advanced robotics projects more accessible to the average hobby roboticist.

At the core of REX is the ADE or Alphalem Development Environment, consisting of scripts or programs written in C++, which form an Application Programming Interface for communicating with devices connected to REX using the I2C expansion ports. Apart from the built-in drivers that the Alphalem team selected for REX for driving sensors and actuators, the ADE also has a process management system for running multiple programs in parallel for efficient robot control. This, the team claims is the most useful features that REX offers to robotic designers.

Physically, REX is about the size of a standard pack of playing cards, small and compact. This palm-sized, single board computer is priced at $99 for its basic model, which includes the DSP, camera, microphone inputs and preloaded OS. You can use REX to control small simple robots easily.

However, this is not to mean that REX cannot handle complicated stuff. In fact, REX is extremely powerful and is able to handle a huge range of sensors such as speech recognition and machine vision. This allows it to be used for some very complicated robotic activities.

Incidentally, the name for the project was earlier AlphaOne, to commemorate Apple’s first PC. However, Mike, as the product engineer, proposed that the name should be changed to REX since he had a Jurassic Park mug on his desk.

What is a brushless DC motor?

Most electrical appliances have an electric motor that rotates to displace an object from its initial position. Various motors are available in the market such as servomotors, induction motors, stepper motors, DC motors (both brushless and brushed), etc. The choice of a motor depends on the requirements of an application. Most new designs favor brushless DC motors, also referred to as BLDC motors.

The working principle of brushless DC motors is similar to that of brushed DC motors, but their construction is very close to that of AC motors. Like all motors, a brushless DC motor too has a stator and a rotor as its major parts.

The stator of a brushless DC motor, similar to the stator of an induction AC motor, is made up of laminated CRGO steel sheets stacked up to carry the windings. The stator windings follow one of two patterns, star and delta. Motors with stators wound in star pattern produce high torque at low RPM compared to motors whose stators are wound in a delta pattern. For motors required to run at very high speeds, the stator core has no slots, as this lowers the winding inductance.

Lack of slots in the lamination stack means the stator has no teeth, which reduces the cogging torque. Teeth in the stator align with the permanent magnets in the rotor, holding the rotor in a stationary position. When starting to move, additional torque, known as the cogging torque is required to make the rotor break free. However, slotless cores are more expensive as a larger air gap is necessary and that means more winding to compensate.

A typical brushless DC motor has its rotor made out of permanent magnets. The number of poles in the rotor depends on the requirements of the application, as more number of poles gives better torque. However, this reduces the maximum possible speed. Torque produced in a brushless DC motor also depends on the flux density of the material of the permanent magnet; higher flux density material produces higher torque.

Brushless DC motors are popular due to several advantages they offer over other types of motors. Compared to brushed type of motors, a BLDC motor produces higher torque because it has no brushes where power may be lost. Lack of brushes also means higher operating life and lower maintenance. Compared to AC motors, the rotor construction is simpler as it has no windings.

The cost to performance ratio of brushless DC motors is the lowest among all the types of motors available. One reason for this is the stator of a BLDC motor is on its outer periphery, which makes it dissipate a larger amount of heat. Additionally, commutation of brushless DC motors is simpler through electronic switches. That makes it easier to control the speed of BLDC motors.

Whether you are looking at single-speed, adjustable speed, position control or low-noise applications, brushless DC motors are the clear winners over all other types. As they are easier to control, maintaining speed of brushless DC motors is simpler with variations in load. A brushless DC motor generates very low amounts of EMI and audible noise.

How noise affects touch screens

Although not understood explicitly, touch-screens in devices are susceptible to noise. The offending noise sources may be both internal as well as external. Most common sources of noise affecting touch-screens are display and charger noise. Cheap chargers entering the market are inherently noisy, and this affects the functioning of touch-screens. In addition, as devices get thinner, display noise increases.

In addition, many other items of everyday use generate noise that may cause interference. This includes the AC mains, radio signals and the ballasts used for fluorescent lights. When noise is present, low-performance capacitive touch systems may distort the position reported and this may impact the overall system reliability and accuracy.

Injected noise causes large amounts of jitter (highly variable touch coordinates reported for a stationary finger), false touches reported even for no touch on the screen, non-recognition of a finger actually touching the screen and sometimes a complete lock up of the device. For example, noise may prevent you from being able to unlock your phone, since your finger touch is no longer reported or you dial wrong numbers because of jitter and false-touch reporting.

A user experience of touch interface quality is directly dependent on how well a touch-screen controller combats interference from noise. Poor touch performance when noise is present can make customers unhappy, resulting in an increase in returns. However, since noise may be of different types, touch-screen controllers must be able to detect, differentiate and combat noise, especially the two sources most problematic to users – chargers and displays.

The proliferation of Switch Mode Power Supply or SMPS type chargers has reduced the size, weight and cost of mobile chargers. However, this has also led to the market being flooded with chargers that prioritize cost over performance, using lower grade components and not using certain components that would assist in reducing common-mode noise.

High amplitude, high frequency, common-mode noise emanating from chargers is a major problem resulting in degradation of touch performance of capacitive touch-screen devices. Some manufacturers have addressed this problem of noisy chargers by providing limited functionality when a device is plugged into such a charger. Others may show a message on the screen that the charger is not supported when it is not the approved charger for the device. Online forums reveal customer dissatisfaction of touchscreen performance due to noisy chargers is quite prevalent.

Common-mode noise causes fluctuations of both, the power and ground supplies of the charger voltage, relative to earth ground, but keeping the same voltage differential between them. Such fluctuations affect the performance of the touchscreen only when the finger of the user touches the screen. Since the potential of a finger of the user is roughly the same as that of earth ground, and the charger’s ground and power lines are fluctuating relative to it, the resulting noise enters the touchscreen through the finger.

Manufacturers aggressively pursuing thinner form factors for touch-screen devices has led to displays coupling more noise into the touch-sensors because of their proximity. Earlier, touch-screens had an air-gap or a shield layer for protection. With devices getting thinner, such shields and air-gaps have disappeared and the touch sensor is now laminated directly atop the display.
This increases the capacitance, while the sensor electrodes are closer to the noise producing VCOM layer of the display, increasing the coupling.

Get ready to talk to your gadgets

Google has many things always in the development stages so that they will remain at the forefront of action for internet users and smart phone users. Expectations are high that gadgets in the future will have voice-interface so that users can command different devices verbally. Talking to gadgets will be possible and Google is making sure that it is a part of such breathtaking developments. Smartphones will be the mode for talking to these gadgets and Google is gearing up to provide the necessary tools for the user for home activity from any location. The recent takeover of Nest Labs, which makes smoke detectors and thermostat controllers, by Google at an estimated deal of $3.2 billion, is thought to be precisely for that purpose.

Speaking to kitchen gadgets is likely to become a reality in the near future. The process is known as the “Internet of Things” and is likely to be in the thick of daily routine activities. When launched, it will totally change the nature of human activity at home and will enhance the popularity of the smartphone. According to the research company Gartner, Inc., the Internet is likely to be linked to more than 26 million objects suitable for verbal command and interface. Additionally, connectivity to PC, smartphones and tablets will substantially add to this figure. Tony Fadell is the founder of Nest Labs, and he is an Apple veteran who assisted in designing the iPhone and the iPod.

According to Forrester Research analyst, Frank Gillett, the reason Google bought Nest is “to learn about this world where even more information is going to be accessible by computers.” Nest has already been successful in offering thermostats to users for controlling the cooling and heating of devices at home. Nest, in the last few years, sold their products in the USA, Canada and the UK; it has been well received.

Google has not made any disclosures about the type of activity lined up for Nest for the immediate future. Angela McIntyre, the Gartner analyst, believes that, “They need to gather as much information as they can to understand the context in how we live our lives”, in order to take over all the activities which are routine and have no need for physical presence at home to perform it. It is likely that the mapping software from Google could be utilized to map out the home layout. This will be essential for delegating tasks to a robot if employed at home. It could also lead to navigation of the entire home from a remote place by a smartphone.

Although, at present, it is known that Google’s main source of revenue is from advertising and search requests, there is no doubt that the acquisition of Nest Labs is in the direction of involving with people’s personal activities in a more significant manner without in any way sacrificing their privacy. On the whole, Google could be of assistance with these new tools for people not at home to perform activities through the internet and smart phones even from remote places.

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.

Gardening with the Raspberry Pi

Many of you may be garden enthusiasts and would welcome the idea of automating some of the maintenance requirements of your plants. For example, keeping tabs on the quantity of water that is required by the plants based on the moisture in the soil, the available sunlight and the environmental temperature might be easy for an experienced gardener. However, gardeners who have just started gardening find it a difficult equation to balance. Even an experienced gardener may have to depend on a novice if taking leave from his garden for a few days.

With a Raspberry Pi (RBPi), most of the above gardening issues can be fixed. The Raspberry Pi can take care of the garden’s watering requirements based on a few environmental measurements. This can bring relief to an experienced gardener forced to leave his beloved plants for a few days. The novice gardener can quit worrying if he is starving his plants or drowning them in water. This is how Devon approached the problem with his Raspberry Pi.

Avid gardening enthusiasts know that too much water to a plant can be as bad as too little. For the Raspberry Pi to determine how much water should be delivered to the plant, it is necessary to know how much moisture is present in the soil in the first place. That, combined with the temperature and the amount of available light can let Raspberry Pi control the pump that delivers the water to the garden.

Since Raspberry Pi is not capable of measuring analog signals that most sensors put out, an Analog to Digital Converter attachment is necessary. For this, using the MCP3008 ADC is a good choice since it allows eight sensors to be used at a time. For sensing the amount of sunlight available, a Light Dependent Resistor or LDR is useful. To measure the ambient temperature with some amount of precision, a temperature sensor such as the TMP35 or TMP37 will do. For sensing humidity in the soil, a homemade humidity sensor using a few long metal nails will be fine.

All the sensors will need a DC voltage supply and a return ground connection, with the signal from each sensor going to one of the channels of the ADC. The 3.3VDC from the Raspberry Pi board is good enough for the sensors. While only one temperature sensor and one LDR is enough, you may need more than one humidity sensor, depending on how big your garden is.

The humidity sensors check the resistance of the soil between a pair of probes inserted into the ground. As the soil dries up, the resistance increases between the two probes of the humidity sensor. If several such probes are placed at different places in the garden, the Raspberry Pi has a fairly good idea of the state of dryness of the soil in the garden.

The final and most important part of the entire system is the pump that delivers water to the garden. Using a tank and a submersible pump eliminates a whole bunch of issues that many gardeners face. You can experiment with drip-irrigation also if you like the idea. Devon has kindly shared the software and the code used, and you can download them 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.

What is IFTTT? How can you use it?

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

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

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

A Sneak Peek into Internet Services

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

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

Connecting Real World Devices

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

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

What exactly is IFTTT?

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

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