Author Archives: Andi

Selecting the Proper Brushless DC Motor

You may have an application that requires high-speed, but quiet operation with low EMI generation and long operating life. For such applications, BLDC or brushless DC motors are what you must be looking at. Among many advantages of these motors, high-speed operation is a special one. As there are no brushes or commutator in the motor, the bearing friction is the only factor limiting their rotational speed.

Absence of brushes and commutator also means there is no arcing within the BLDC motor to cause erosion or EMI. The last factor makes these motors suitable for use in RF applications. With windings on the stator, BLDC motors show superior thermal characteristics over conventional motors and are consequently more efficient. Because the stator is connected to the case, heat dissipation is fast. All such factors means a BLDC motor has virtually non-existent maintenance problems.

The major downside to all the above good characteristics of BLDC motors is their higher cost. BLDC motors can easily cost about twice as much as simple brushed motor and this puts the BLDC technology out of reach for many applications. Apart from the cost of the basic motor, there is the added cost of the control or drive electronics. If not integrated within the motor itself, you will need to find space for mounting the electronics outside, but nearby. You cannot separate the drive and the motor with long cables, as the noise introduced will cause malfunctioning.

A brushless motor also must overcome starting friction, just as brushed motors do. Again, starting friction does not depend on speed, but is the sum total of torque losses. Dynamic friction, proportional to speed, defines the torque losses in BLDC motors. Viscous friction in the ball bearings cause dynamic friction and eddy currents in the stator, originated by the rotating magnetic field of the magnet, adds to it. Nevertheless, the speed-torque curve of a BLDC motor demonstrates excellent linearity.

Directly connecting to a DC supply will not operate a BLDC motor, unlike a brushed DC motor. This is because brushless technology makes use of electronic commutation. Although there is no physical commutator or brushes, the operating principal remains the same, with the permanent magnet rotor initiating motion by chasing a revolving magnetic field induced by a current in the stator windings. A PWM or pulse width modulated signal is necessary to create the on/off signal, which actually creates the motion.

A comparator normally generated the PWM signal, which is a voltage generated because of a sinusoidal command signal superimposed with a saw toothed carrier or chopper frequency. If the command is greater than the carrier frequency, the PWM signal will be high. This is because the low chopping frequency gives the current more time to gain amplitude. The current density governs the rate at which the motor accelerates or decelerates.

To avoid ripples and a shortened motor life, it is important that the switching frequency is high enough. This is usually done by controlling the discrete on/off steps with six semiconductor switches. These send the amplified current through the correct phases, with the necessary switching being done by the semiconductor switches.

Researchers Create a Highly Sensitive Magnetic Sensor

Scientists at the National University of Singapore have constructed a new hybrid type of magnetic sensor that is more responsive that the existing varieties. This innovation holds promise for the creation of cheap and compact sensors and detectors in areas like information technology, electronics, health sciences and automotive industry.

Professor Yang Hyunsoo, who has directed the design of the device, has explained the findings in the September 2015 issue of the periodical Nature Communications.

Using the concept of magneto resistance

Just as electric resistance develops when an electric current passes through a conductor, a similar feature called magneto resistance comes into being when certain substances are placed in a magnetic field. Scientists at the university have utilized this newly discovered feature in developing the magnetic field sensor.

Although the feature is exhibited by all magnetic materials, the university team has been on the lookout for an ideal material, which would be particularly receptive to low and high fields, while remaining immune to temperature variations. In other words, the magneto resistance should vary appreciably with any change in the magnetic field but should be stable when the temperature changes.

Graphene and boron nitride combination

The scientists tried out several groupings of different materials. These trials led to a hybrid arrangement comprising graphene and boron nitride that suggests great potential as a sensing device. The team experimented with the material placed at various angles with the field and at different temperatures. According to Dr. Kalon Gopinadhan of the university, a two-layer structure of the two materials shows a sizeable response to small changes in magnetic fields. The researchers found that the hybrid structure was 200 times more receptive than sensors currently in use.

A significant gain of using this sensor is that the combination shows very high sensitivity at and around 127 degree Celsius, the temperature at which most electronics function. The sensor is small and can be easily fitted into other devices. Furthermore, the manufacturing cost of graphene is very low as compared to that for existing sensors made from indium antimonide.

Complying with industry requirements

The demand for reliable magneto resistance is expected to rise steadily. Indium antimonide sensors used in the automotive industry suffer a change in properties due to temperature changes caused by the air conditioning or the sun’s heat and do not function reliably. Cars and other vehicles use several sensor systems in interlocks, flow meters and position sensors that make use of complicated temperature correction circuitry to offset the errors. The new hybrid sensor eliminates the necessity of these rectification procedures.

Professor Yang declares that the graphene and boron nitride combination is prepared to take on the current sensors in the market. Apart from finding use in applications like hard drives, thermal switches and magnetic field detectors, they can be incorporated in flexible electronics, as well.

The university team has applied for a patent for the innovation. They now plan to scale up their production in order to turn out wafers of several sizes to meet the demands of the sensor industry.

Raspberry Pi and the Smart Video Car

As kids, nearly everyone has played with a battery-operated car controlled by a remote. Now, you can have the same with the Smart Video Car, but with vastly enhanced features. Additionally, you can control the Smart Video Car from your PC, because running the car is the versatile, single board computer, the Raspberry Pi, or RBPi.

You are in luck if you already have an RBPi B+ or the RBPi 2 with you, as the car comes as a complete learning kit, but without the RBPi. The car operates on 7-12V DC, supplied by two 18650 rechargeable lithium batteries. Since the RBPi cannot operate with such high voltages, a step-down DC-DC converter module is included. The module steps the battery voltage down to 3.3V, suitable for the RBPi to operate satisfactorily.

The kit contains all the multiple parts needed to put the car together. The driver module is based on the IC L298N, from ST Microelectronics, which works as a full-bridge motor controller. That means you can run the car backwards as well. To let the PC control the car wirelessly, the kit includes a USB WLAN stick or Wi-Fi Adapter. To know where your Smart Video Car is at any moment, you can check out the video it sends to your PC or smartphone through its webcam in real-time. The webcam is a part of the kit.

Using the PC, you have complete control of your Smart Video Car. Apart from forward or backward motion, you can turn the car left or right to avoid any obstacles in its path. An additional feature is you can control the camera independently to turn it vertically and horizontally. This way, you can capture the image from different directions.

SunFounder, the manufacturer, supplies all the necessary instructions, diagrams, descriptions and code in a complete manual along with their kit. A Tower Pro Micro Servo SG90 drives two front wheels of the car kit to make it turn left or right, while the other two rear wheels are active wheels. Two Gear Reducers drive the rear active wheels. A 12-bit PWM driver with 16 channels drives the L298N driver module for DC motor.

If you are just beginning to learn the RBPi code and application, this is a great kit to start. However, the kit also teaches you about basic components and modules in electronics. You can then use this knowledge for furthering your application and explore in different fields.

As SunFounder provides the entire code including all the necessary parts, anyone can assemble the kit referring only to the user guide. Building this Smart Video Car can be a fascinating experience and an enjoyable one. If you are running Linux on your PC, you can realize the car control very easily. You can even use Linux running on a virtual machine with equal ease.

The kit uses MJPG-streamer to capture images and transmit video in real-time. If you have a Firefox or Google Chrome browser running on your PC or smartphone, you can easily view the video on the browser and at the same time control the Smart Video Car.

Get 37 Sensors for Your Raspberry Pi

If you have a bunch of school kids rearing to have a go at the most popular single board computer, the Raspberry Pi or RBPi, then this 37-sensor kit is something that can keep them happy for hours on end. Fans of the open source RBPi will relish the different kinds of experiments they can try out with the funny and completed modules in this new kit.

The modules in the kit connect to your RBPi and send it all kinds of different signals from the physical world. Using these modules by connecting them to the RBPi is very simple as the manufacturer of the kit provides detailed information and usage guidelines for all the sensors in the kit.

The latest kit from SunFounder comes with the sensors neatly packed in a plastic box, along with the 168-page user manual. The improved Fritzing breadboard and the sensors are suitable for the RBPi Model B+ and RBPi2. The kit also contains the detailed material list of each module. Users get the improved code in Python and C along with the Fritzing images. That certainly helps the user to learn to use the sensors for their individual applications.

You must have your own RBPi for using the sensors in this kit, as the kit itself does not come with the RBPi. Moreover, the 40-pin GPIO expansion board included with the kit is for the RBPi B+. The most interesting part of the kit is the 16×2 LCD module and the Breadboard. Using these and the several sensors you can try out about 35 experiments listed in the kit.

The experiments cover a mixture of analog and digital electronics. For example, you can learn about how a relay works, how a mercury tilt-switch functions or how to make an active or a passive buzzer sound the alarm. Those interested in remote sensing will find the Hall sensor fascinating, along with the sound sensor and the gas sensor. With the Ultrasonic Ranging Module, you can easily measure distances without approaching the distant object.

For those interested in temperature measurements, there is the DS18820 Temperature Sensor and the Thermistor module. The RTC-DS1302 module will help in measuring in real time, while the Barometric-BMP180 and the Humidity sensor will help in determining or predicting the weather.

Experiments in light interest many. For them, the kit includes dual color LEDs, RGB LEDs, and Auto-Flash LED modules. Photo-interrupter modules, IR obstacle modules, IR remote control module and the IR receiver modules will help those interested in communication with light beams.

Control experiments that are more sophisticated are also possible. For example, those interested in Analog to Digital and Digital to Analog conversion and control will find the AD/DA Converter PCF8591 module to be useful. Other modules such as the Rotary Encoder module, the Joystick PS2 module, the MPU6050 module hold promises of still further sophistication.

The kit is suitable for all types of beginners, learners and the more initiated. It is an attempt to allow users to learn the basics of analog and digital electronics. Users can then move over to experimenting with different types of sensors and learn about controlling their physical world.

What You Need To Know About EMI Antennas

Any electronic device, system or subsystem generates EMI or ElectroMagnetic Interference and is susceptible to EMI generated by others. To allow them to coexist and cooperate, all such electronic devices, systems or subsystems must confirm to specific standards, which limit the amplitude and frequency range of EMI generated and tolerated by each of them.

Testing for such radiated emissions and immunity involves EMI chambers and OATS or Open Area Test Sites. To check for EMI generated, these chambers or OATS will have several types of antenna that can handle a wide range of frequencies. As visits to a full-compliance lab are expensive and time intensive, you may want to do pre-compliance tests, for which, it is a simple matter to set up a temporary antenna in a conference room or basement. This helps in troubleshooting and correcting EMI problems beforehand.

Several factors decide the nature of the antenna you should be using for your tests. The choice for the tests mostly ranges among radiated emissions, radiated immunity, pre-compliance, full compliance, frequency range, power and size of the antennas. The most common EMI test people perform is for checking radiated emissions. Here too, the antenna you use will depend on frequency, size, gain and your budget.

For pre-compliance tests, the most popular antenna is the hybrid. This is also called by names such as Combilog, Biconilog, Bi-log and others. Hybrids are so favored because of their wide frequency range, which easily covers different ranges from 30 MHz to 7 GHz, depending on the model. This is a very big advantage, as you do not need to switch antennas in between the tests, which you have to do if you were using log-periodic or biconical.

For a lab, where precision is more important, using multiple antennas gives an advantage in the performance. Typically, a lab might use a horn antenna for frequencies above 1 GHz, a log-antenna from 1 GHz to 200 MHz and a biconical antenna for frequencies below 200 MHz. However, for pre-compliance tests, hybrids or Bi-log antennas are adequate for makeshift labs.

The size of the antenna you can use depends on the space you have in your makeshift lab. Larger antennas cover a wider frequency range along with better sensitivities as compared to those offered by smaller antennas. Some designs of hybrid antennas come with bent elements, which help to fit them in limited spaces. In general, hybrid antennas are larger than most dedicated antennas.

Antennas are available that allow you to use them for both radiated immunity as well as radiated emission tests. However, for immunity tests, it is important to limit the power you drive into an antenna to get the required field strength. Typically, immunity testing requires larger antenna sizes as compared to those necessary for measurements of emissions alone.

Hybrid antennas usually combine a log-periodic element with a biconical element. This extends the frequency range the antenna covers as compared with that covered by single-type antenna. For example, one of the newest hybrid antennas covers the entire range of 26 MHz to 3 GHz, while being able to handle signal power up to 300 W for immunity tests.

What is Digital Signal Processing?

Initially, when DSP or Digital Signal Processing was introduced over thirty years ago, it involved standalone processing. A single micro-controller handled all the parameters for processing the analog signal and transforming it to its digital value. Evolution in this area has introduced multicore processing elements that now extend the DSP’s range of applications.

Simultaneously, evolvement of software development tools for the DSP now allows expansion for accommodating diverse programmers. Therefore, on one hand you can have voice and image recognition with small, low power, but smart devices, while on the other, it is possible to have real-time data analytics with the multiple core high-performance compute platforms. This way, DSPs offer nearly endless opportunities for achieving low-power processing efficiencies.

Although initial DSPs processed only audio, engineers quickly adapted DSP technology for a wide variety of applications. Today, DSPs are available as standalone or as part of an SoC or System-on-Chip offering full software programmability including all the benefits of software-based products.

DSPs take already digitized signals from the real world, such as audio, video, pressure, temperature or position for further mathematical manipulations. Engineers design DSPs for performing quick mathematical operations such as add, subtract, multiply and divide.

This processing of the signals enables displaying, analyzing or converting information to a signal of another type to be useful. In the real world, several analog products are available to detect and manipulate signals such as pressure, temperature, light or sound. These signals are then passed on to converters such as ADCs or Analog to Digital Converters, which transform the analog signals into a digital format of 1’s and 0’s.

The DSP takes over this stream of digitized information and processes it further. The processed digital information goes back for use in the real world. The DSP does this in one of two ways. It feeds the information in the digital format to instruments capable of handling it. Where that is not possible, the digital signal passes through a second converter or DAC, the Digital to Analog Converter and this converts the digital signal to analog. All this happens at very high speeds.

An MP3 player is a very simple illustration of the concept of DSP. The analog audio, during the recording phase, passes through a receiver containing a microphone and an amplifier. An ADC then converts this analog signal into digital information, before passing it over to a DSP. The DSP processes the digital signal further as defined by its internal algorithm and encodes it as MP3, before saving the file to memory.

While playing back the recorded information, the DSP decodes the file from memory and a DAC converts the digital signal to an analog form. That makes it suitable to output the signal through an amplifier and speaker system. If necessary, the DSP handles other functions such as level control and equalization including user interfacing.

A computer can also use information from a DSP. The computer can use this information to control security, home theater systems, telephones and for compressing video. Compressed signals are more efficient when transmitting. Additionally, the computer can easily manipulate or enhance the signals to improve their quality.

Predict Solar Eclipses with Wolfram on Raspberry Pi

Wolfram Research shows how the Wolfram language, used on a Raspberry Pi or RBPi, can help visualize solar eclipses. With this combination, you can view past and present solar eclipses. The most astounding aspect is the solar eclipses you visualize can be not only total or partial, but also as if seen from Earth, Mars or Jupiter.

Depending on your present geographical location, you may or may not be able to witness a solar eclipse. To recapitulate, solar eclipses are events where the Moon blots out the Sun to observers on the Earth. The Moon may be so positioned it blocks out the entire Sun or a part of it. If the Moon blocks out a part of the Sun, the incident is termed a partial eclipse. In a total eclipse, an observer on the Earth will only see the corona of the Sun as a halo around the Moon as it covers the Sun entirely.

By mathematically tracking heavenly bodies, it is possible to predict when a solar eclipse is likely, if it will be visible from a specific location and whether it will be partial or total. Usually, the media drums up a small hype of the event, predicting local weather conditions, telling people how and when to observe the eclipse while including other relevant details. However, this is only if the eclipse is visible in your area.

For people on the Wolfram Community, geographical hurdles do not exist. Novices, experienced users and developers from all over the world share data and knowledge. The Community discusses the latest solar eclipse with anticipation, observation and data analysis. They also participate in the computations for future and extraterrestrial eclipses.

For example, consider the total solar eclipse that occurred on March 20, 2015. Before the event, Jeff Bryant and Fransisco Rodriguez from Wolfram explained how the community could compute the geographical locations from where the eclipse would be totally or partially visible. Fransisco used GeoEntities to highlight with green those countries that would witness at least partial solar eclipse on the date.

Although they predicted the visibility of the solar eclipse, neither Jeff or Fransisco was able to see even the partial solar eclipse, as the former is in the US and the latter in Peru. In their prediction, the intense red area shows the regions from where the total eclipse would be visible, while the lighter red areas depict regions of visibility of the partial eclipse. Another total solar eclipse is predicted in the next decade, of which, at least a partial phase will be visible from almost all countries of the world.

Wolfram now has a new language function, the TimeLinePlot. This is a great way to visualize a chronological event such as a solar eclipse. With TimeLinePlot, you can specify the last few years and the next few years to plot territories and countries from where a total solar eclipse will be visible. TimeLinePlot complies with ISO 3166-1 when depicting territories and countries. Using the incredible powers of computational info-graphics, Wolfram predicts a spectacular total solar eclipse spanning the US from coast to coast on August 21, 2017.

Phosphorene Challenges Graphene as a Semiconductor

Though silicon has been the basis of semi-conductors for decades, it is facing stiff competition from other materials that promise to deliver several extras to consumers who like to enjoy more flexibility with their gadgets.

For some time, graphene, a one atom thick allotrope of carbon has been under consideration for use in electronic devices because its thin structure allows electrons to travel across it much more rapidly than they would do across silicon. However, graphene has severe limitations, as its conductivity is a little too high to be of much use in electronic devices, which need semi-conductors or materials with medium levels of conductivity. Another newly developed material dubbed phosphorene, which can form identical thin layers and is a semiconductor as well, offers a wider scope in electronics.

Phosphorene particulars

Scientists at the Technical University of Munich (TUM) have prepared a semiconducting material with black phosphorus in which a few phosphorus atoms have been swapped by arsenic atoms. Replacement of the phosphorus atoms with arsenic has caused the band gap to reduce to 0.15eV, which makes the material an effective semiconductor.

Phosphorene or black arsenic phosphorus can form very thin layers like graphene. Unlike silicon, which is hard and brittle, phosphorene is easy to manipulate into different kinds of structures and shapes. This makes possible a great range of electronic devices with considerable mechanical flexibility.

Scientists at TUM have built on technology that allows the fabrication of phosphorene with the application of high pressure. This reduces the production costs considerably. The research workers have been able to fine-tune the band gap exactly according to specific requirements by tweaking the arsenic concentration. According to Tom Nilges, who is heading the research team at TUM this has enabled them to produce a wide range of materials with diverse electronic properties that were not possible earlier.

Field Effect Transistors

American scientists from Yale University and the University of Southern California (USC) have collaborated with the researchers at TUM to build devices like field effect transistors with phosphorene. A group headed by Dr. Liu and Professor Zhou of the Electrical Engineering Department at USC has studied the transistor characteristics.

Infrared Detectors

Further exploration of the material by the scientists revealed that the material when heavily doped with arsenic could be used for infrared detection. For instance, when the arsenic concentration is as high as 83%, the band gap in phosphorene is about 0.15eV. This fact makes it an effective sensor for infrared rays of long wavelengths. Researchers expect that the new substance can be effectively used as Light Detection and Ranging (LIDAR) sensors, which find use in applications for tracing dust particles and pollutants in the atmosphere and as distance sensors in vehicles.

Anisotropic behavior

Another noteworthy feature of phosphorene is its anisotropic nature. Electronic and optical properties of the material were studied using ultra-thin films in two mutually perpendicular, x- and y-axes. It was observed that the properties were different in the two directions.

Phophorene has an edge over other newly discovered thin-layered semiconductors because it is very easy to peel off layers from a parent black phosphorus crystal.

Let Raspberry Pi Track Bats for You

If you live in an area that has fruit trees around, it is likely bats share your space. Bats are furry mammals that flit about at night, feasting on insects and fruits. Although they are not gifted with good eyesight, they locate prey and avoid obstacles using echolocation. They are expert fliers and it is difficult to observe them since they are so silent.

Although humans cannot hear bats, it does not mean these creatures make no noise. In fact, using the process of echolocation, bats produce a considerable amount of sound. However, humans cannot hear them because the sound bats produce has a frequency range beyond human hearing capabilities. Depending on age, humans can hear sounds produced in the frequency range between 20 Hz and 15-20 KHz. Bats can hear and produce sound up to about 110 KHz. That is why a Raspberry Pi or RBPi is necessary to collect process and graphically represent bat calls.

An analysis of bat calls shows the sounds they produce are quite loud and not limited to just one tone. Different breeds of bats produce a variety of sounds, differing just as bird chirping does. For example, their tone may sweep down from a high frequency to a low one, or move around a specific frequency.

Holger and Henrike Korber from Germany have used an RBPi to make a bat detection device. To collect the sound produced by bats, they use an inexpensive microphone of high sensitivity capable of responding to high frequencies. The algorithm they use allows not only a graphical representation of the calls, but also identification of the bat species as well. Additionally, the software allows manipulation of the calls to bring them into frequencies within the human hearing range and create histories of bat activity.

On their site, which translates to Bat Conservation in English, the Korbers offer a list of bat literature. If you can know the German language, you will find a treasure of information on echolocation and acoustic identification of bat species. To read in English, pass the page through Google Translate.

Details of their new WLAN-Raspi-Bat detector are available here. The detector, based on the RBPi Model B+, is wirelessly connected to an external notebook. That allows easy manipulation of the configuration and wireless recording of data. The RBPi bat project uses a UMTS stick for WLAN communication and a modified image of the RBPi OS.

The WLAN-Raspi-Bat detector sends SMS text messages automatically and at freely configurable times. For example, this could be just after the RBPi has booted or just before it shuts down. As the detector is portable, it is important to save on power consumption and data space on the SD Card. To keep the arrangement simple, the Korbers use a simple clock timer to start and shut down the RBPi. As bats venture out only at night, the RBPi can sleep during the day along with the bats.

As the detector communicates wirelessly, there are numerous applications. For example, it is able to operate at locations hard to access, such as in trees up to the canopy and in buildings with difficult access.

How Gesture Sensors are Revolutionizing User Interface

Imagine a scenario where you control almost everything by simply waving your arms and not by punch any buttons or touching a screen. Welcome to the complicated world of gesture controls. Mechanical buttons and switches are subject to the risk of reliability – they also need protection from the environment. When replaced with electrical controls, such as resistive or capacitive displays and buttons, these do bypass the problems faced by mechanical switches. However, to operate, they still need the physical touch of the operator.

By using optical sensors, it is easy to avoid the reliability risk, mechanical complexity and the requirement for physical touch. You can find optical sensors being used as proximity detectors in many applications such as in water and soap dispensers. Apart from the ease of operation, optical sensors provide the primary potential in recognizing user gestures, thereby reducing system complexity and enhancing user functionality. Today, gesture sensors have evolved to revolutionize user interface controls. They offer the ideal combination of functionality, performance and ease of implementation.

For instance, gesture sensor TMG3992 and others offer simple digital interfaces and do not demand significant processing or memory bandwidth to operate. Being interrupt driven, such sensors interact with the system only when they encounter a recognized event. Simple electrical and software designs are enough to implement two and four direction gesture sensing applications. The sensors work easily from behind plastic or glass transparent to infrared light. That means there is no added complexity or reliability risk in incorporating gesture sensors in electronic devices, as most use plastic housings transparent to infrared.

Gesture sensors help the industry in myriad ways. For example, heavy industries use gloves that limit options for user interface. Operators need specialty gloves to operate most capacitive touchscreens, as they do not respond to commonly used gloves. On the other hand, there are no restrictions for gesture sensors to operate with any type of gloves.

Gesture sensors are eminently suitable for recreational applications such as cold weather or aerial sports and industrial applications such as clean room manufacturing, chemical industries and construction. For example, a skier may keep his or her hands warm within gloves and yet operate a smartphone or manipulate a self-mounted camera with ease.

Touchscreens do not work in environments under water. However, divers can make full use of gesture sensors. It is true water attenuates infrared light and restricts the working distance, so you need additional power. However, multiple benefits overcome this minor restriction. Using gesture sensors such as the TMG3992 and similar greatly simplifies the user interface as underwater cameras can do the job, while the TMG3992 replaces several mechanical buttons and switches for a smaller and more reliable interface.

Smartphone designers and manufacturers already include several user interface options offering multiple solutions for different tasks. However, in many situations – such as exercising or cooking – it is inconvenient to touch the phone while performing the tasks. Gesture controls provide the user different ways of interacting with the phone – such as when checking notifications and scrolling through them. For example, the user can identify a caller and select from a variety of options – answer the call with the speaker enabled, ignore the call without a response or ignore the call with a pre-defined text message.