How to Select Current Sensors?

To select an appropriate AC current sensor for an application, you must know the operational frequency range and the current rating the sensor will encounter. Additional considerations that you will need to decide are the type of the sensor, its mounting (through-hole or surface mount), turns ratio, and the overall dimensions.

Sensor type refers to a sensor only configuration, where a conductor integral to the application forms the primary. Another type could be a complete current transformer where the primary is included as a winding. Engineers typically use current sensors to measure and control the load current in control circuits, safety circuits, and power supplies. Power supplies usually require accurate control of current, and this requires sensing the magnitude of the current accurately.

Irrespective of whether you are using the sensor or transformer, the highest flux density handled is dependent on the worst-case current and frequency faced by the device. However, note that exceeding 2000 Gauss will mean most AC current sensors output will be non-linear. Therefore, the current through the sensor and its output voltage will no longer remain proportional, as the magnetic core of the sensor saturates at very high flux densities. To keep the flux density below the saturation limit, it is necessary to use higher secondary turns.

For instance, in wire-through-the-hole style of current transformers, looping additional primary turns through the hole can dramatically reduce the turns ratio, provided the wire diameter and the hole size permit. Increasing the primary turns allows the use of a higher input current transformer to provide higher output voltage across the terminating resistor on the secondary.

Manufacturers of current transformers offer online tools to help designers select the right current sensor or current transformer for specific application conditions. Initially, the user has to select the type of sensor—a transformer or a sensor only. The next selection is the preferred mounting style—SMT or Through-hole. The online tool also requires other parameters such as the maximum sensed current expected in amperes, the input frequency in kHz, the duty cycle of the primary current waveform as a percentage, and the desired output voltage corresponding to the expected maximum input current.

The tool then calculates the required terminating resistance based on the maximum input current, the number of secondary turns and the output voltage—basing the calculations on a single-turn primary. Next, the tool calculates the maximum flux density of the secondary, making sure it does not exceed 2000 Gauss. It does this by taking into account the output voltage, the duty cycle, secondary turns, and the frequency of operation.

The result lists all part numbers of the manufacturer that meet these input conditions, typically including a graph of the output voltage versus the sensed current for the calculated terminating resistance.

To select an appropriate current sense transformer for your application, you require knowledge of the maximum current, frequency, and duty cycle of the sensed current, including the output voltage you require. Using this information, the online selector tools will provide you with the appropriate terminating resistor value and a list of current sensors that meet the conditions of the application.

ASUS Tinker Board Competes with the Raspberry Pi

With the advent of the Raspberry Pi (RBPi), the popularity of single board computers (SBCs) has risen rapidly over the last five years. The RBPi has easy software and a low price that has won it a vibrant community consisting of not only coding hobbyists, but also teachers and children, whose minds and hearts it has captured. This success of the RBPi has led to scores of other vendors pitching in with their SBCs. Among them, ASUS is the latest with its Tinker Board SBC, challenging the RBPi.

The Tinker Board from ASUS offers an SBC with somewhat higher premium hardware compared to that offered by the RBPi. According to ASUS, its Tinker Board tries to meet the demands of enthusiasts who are looking for better performance. Although their efforts are commendable and they have created a great piece of hardware, the real hurdle they have yet to overcome are the software and support.

If you are not careful with the Tinker board, at first glance you might mistake it for a more colorful RBPi. However, the tweaks exhibited by the Tinker Board design makes it feel more like a premium product. For instance, icons covering the board depict its various functions, such as they clearly differentiate between the display and the camera connectors.

Color-coding on the Tinker Board helps identify most of the pins on the general-purpose input/output (GPIO) header. For instance, the +5 V pins are all colored red, while the ground pins are black. Moreover, ASUS has maintained the same pin configuration for the GPIO as that followed by RBPi. Therefore, transferring your projects over to the Tinker Board is very easy. The Tinker Board comes with a stick-on heatsink. This is really helpful as, under load, its SOC runs far hotter than that of the RBPi does.

The Tinker Board sports a faster system-on-chip, the Rockchip RK3288, a quad-core running at a maximum frequency of 1.8 GHz. Not only is this faster than that of the RBPi3, the Tinker Board also has double the RAM. On the ASUS site, they have benchmarks to show the speed of the Tinker Board as far above its competitor, the RBPi. Comparatively, the site claims double the CPU power and GPU performance over that of the RBPi.

Apart from the faster chip and the extra RAM, ASUS has also added the Gigabit Ethernet connector in place of the 10/100 Ethernet of the RBPi. The Tinker Board also has an uprated sound chip and an upgradable Wi-Fi antenna. According to ASUS, the performance of the USB storage is superior and the operation of the SD card is faster. ASUS attributes this to the dedicated controller of the Gigabit Ethernet, which does not allow any reduction in LAN speed during USB data transfers. Comparatively, the RBPi has a USB-to-Ethernet bridge, which makes the two functions interdependent.

However, unlike the Tinker Board, the RBPi has a website full of useful information. The RBPi also has the NOOBS installer, which simplifies installation of a number of operating systems. Comparatively, the website of the Tinker Board has two images, one for the Debian-based Tinker OS, and another based on Android.

Inertial Sensing for Automation

In any type of industry, whether it is automotive, unmanned aerial vehicles, energy, logistics, agriculture, or manufacturing, automation brings increasing promises of great gains in terms of efficient utilization of resources, achieving accuracy, and safety. To achieve these gains it is necessary to identify the appropriate sensing technologies that will enhance the contextual knowledge of the equipment’s condition.

As the location or position of an equipment is a valuable input, precision inertial sensors provide accurate location information and help in maintaining accurate positioning. Where mobility is a factor, it is necessary to couple both the location and the contextual sensor information with the application. Operating in a harsh or complex environment often requires determination of position as a critical value. This is where inertial sensors help to make a difference.

Over the years, machinery has evolved from making simple passive movements, to functioning with embedded controls, and now it is moving towards fully autonomous operations, with sensors playing the enabling role. Earlier, for supporting offline analysis or process control, sensors working in isolation were adequate. However, obtaining real-time benefits requires increasingly sophisticated sensor types, while efficient processing requires important advances in sensor fusion. Therefore, increasingly intelligent sensor systems are coming up catering to complex systems on multiple platforms that require the knowledge of states the system has held in the past.

Inertial sensors used with smart machines serve two special functions, one for equipment stabilization or pointing, and other for equipment navigation or guidance. Most systems consider GPS as the most suitable for navigation. However, potential blockages cause significant concerns for many industrial systems. Some systems transition to inertial sensing when GPS is blocked, but this requires the inertial systems to be of sufficient quality to provide the same precision, as did the GPS.

Inertial sensors provide the feedback mechanism in case of servo loop or stabilization for maintaining a reliable positioning such as the antenna pointing angle, construction blade, crane platform, camera, UAV, or farming implement. For all these, the purpose is not only to provide a useful function, but also to deliver a safety mechanism or critical accuracy, even when the environment is incredibly difficult.

In reality, sensor quality matters when good performance is desired. Engineers use sensor fusion for making some correction, for instance, when correcting the temperature drift of sensors, or compensating an accelerometer when correcting for gravitational effects on a gyroscope. In such cases, this helps only in the calibration of the sensor to the environment, but does not improve the ability of the sensor to maintain performance between the calibration points. With a poor quality sensor, the accuracy falls off quickly, as the performance of the sensor rapidly drifts without expensive or extensive calibration points.

Even when using high quality sensors, some amount of calibration is desirable, especially when the aim is to extract the highest possible performance from the device. However, the most cost-effective method of calibration depends on the intricate details of the sensor, along with a deep knowledge of motion dynamics. This makes the compensation or calibration step an embedded necessity for the manufacturer of the sensor.

Specifying Fiber Optic Sensors

The industry prefers fiber optic sensors as they work well in tight spots and in applications that have a high degree of electrical noise. Fiber optic sensors are useful in machines, fixtures, and conveyors for sensing part presence as an important component of industrial automation. The industry often requires controlling sequence and error-proofing assembly based on the presence or absence of a part. In many cases, it is simply impossible to know whether a part is where it should be or the holder is empty as expected. Therefore, verification is only possible by using a presence sensor.

Sensors come in many varieties, including magnetic, capacitive, inductive, and photoelectric. Depending on the application, each type of sensor has its own merits and demerits. Among all the sensors available in the market, photoelectric sensors offer the broadest types and technologies, and suitable for the widest range of applications.

The family of photoelectric sensors includes a large variety of light-emission types that includes lasers of class 1 and 2, visible, and infrared. They also include different sensing technologies such as through-beam, reflective, suppression, background, and diffuse. Different housing configurations are also available such as fiber optics and photo eye. We will focus on specifying and applying fiber-optic sensors, as these offer the most advanced capabilities with options for configuration, and are most suitable for use in tight spots that the photo-eye sensor finds too small.

Fiber-optic sensors are also known as fiber photoelectric sensors, and comprise of two parts—the amplifier and the fiber cable. The amplifier is the electronic part and is actually a fiber photoelectric amplifier. The fiber-optic cable includes the optic sensor head and the fiber cable to transmit light to and from the amplifier.

All photoelectric sensors work with a simple technique. A light emitter produces the source signal and a receiver detects the signal. A large variety of technologies is available for sensing and measuring the light transmitted to the receiver. For instance, standard photo-eyes look for the presence or absence of light, whereas background suppression sensors sense the angle of the returning beam. Other type of sensors measure the time taken by the light to return, thereby providing a measure of distance it traveled.

Simple photo-eyes such as those used in reflective and diffuse units house the emitter and receiver in the same optical sensor head, while through-beam units house them in two optical sensor heads. On the other hand, fiber-optic sensors have all the electronics in a single housing, with a fiber cable connecting the separate emitter and receiver to the electronic housing. Light from the emitters and that coming to the receivers travels through the fiber cables, similar to high-speed data traveling through fiber-optic networks.

The above segregation means the technician has to mount only the sensor head on the machine, while routing the integrated fiber-optic cable and plugging it into the amplifier placed in a safe place such as a control enclosure to protect it from the harsh manufacturing environment.

A large variety of options is available for both fiber-optic cables and amplifiers. These range from basic to advanced, suitable for meeting the demands of increasing functionality, including advanced logic and communication capabilities.

Using Raspberry Pi to Monitor the Environment

Many cities in the world are plagued with poor quality of air caused mostly by pollution form old diesel cars. This is true of Peru also, and James Puderer is using Raspberry Pis (RBPis) fitted in several taxis to monitor the air quality. James fitted the RBPis in the hollow vinyl roof sign almost all taxicabs use in Peru.

James uses the RBPi along with various Adafruit technologies, such as the BME280 sensor for temperature, humidity, and pressure. He has created a retrofit setup powered by a battery and GPS antenna that fits snugly into the hollow of the vinyl sign.

The completed air-quality monitor collects data on latitude, longitude, pressure, temperature, humidity, and airborne particle count. The data enters a data logger, which then pushes it on to the Google IoT Core, from where any computer may access it remotely.

At the Google IoT Core, Google Dataflow processes the data and turns it into a BigQuery table. Any user can then visualize the measurements the monitor collects, using several online tools available to study them and organize to figures depending on the results he or she expects to achieve. For instance, James uses Google Maps to analyze the data and produce a heat map of the local area that includes air quality.

On his project page, James provides the complete build process for the air quality monitor using the RBPi. This includes the technical ingredients and the code he developed. He also urges others to make their own air quality monitors for their local environment. His plans include designing an additional 12 V power hookup, which will enable connecting the air quality monitor to the battery of the vehicle. He also plans to include functioning lights when the air quality monitor is inside the sign, and companion apps for the drivers to use.

Others have also used the RBPi with sensors to track the world around it. This includes the Human Sensor costume series by Kasia Kolga. The dresses react to the air pollution by lighting up. Kasia created the Human Sensor in collaboration with Professor Frank Kelly and other environmental scientists at the King’s College, London.

Linked to an RBPi and a GPS watch, a small aerosol monitor is hidden within each suit of the Human Sensor costumes. These components work together and gather the pollution data at their location. Although the suits store their collected information to submit it later, in future the suits will be relaying the data in real time to a website for the public to access.

The RBPi works to control the LEDs attached to the suit. In reaction to the air conditions detected by the monitor, the RBPi flashes the LEDs, makes them pulse, or produce patterns and colors that morph accordingly.

Depending on the negative or positive effect of the air around the monitor, the suit’s LED system responds to the absence or presence of pollutant particles. For instance, when the wearer walks past a grassy clearing in a local park, the suit will glow in green colors to match it. As soon as the wearer goes behind the exhaust fumes of a car, the suit will pulsate with red light.

What is USB Type-C Interface?

All new electronic devices are now coming with the USB-C interface, and this is revolutionizing the way people charge the devices. So far, most electronic devices had the micro-USB type-B connectors. With the USB Type-C connector, it is immaterial what orientation you use for the charging cable—the non-polarized connector goes in either the right side up or upside down. The connecting system is smart enough to figure out the polarity as a part of the negotiation process, and supports bidirectional power flow at a much higher level.

Earlier, the USB connectors handled only the 5 VDC fed into them. The USB-C port can take in the default 5 V, and depending on the plugged in device, raise the port voltage up to 20 V, or any mutually agreed on voltage, and a preconfigured current level. The maximum power delivery you can expect from a USB-C port is 20 V at 5 A or 100 W. This is more than adequate for charging a laptop. No wonder, electronic device manufacturers are opting for incorporating the USB-C into their next-generation products.

With the increasing power delivery through the USB Type-C ports, the computer industry has had to raise the performance requirement of the voltage regulator. Unlike the USB Type-B and the USB Type-A fixed voltage ports, the USB Type-C is a bidirectional port with a variable input, and an output range of 5-20 VDC. This adjustable output voltage feature allows manufacturers of notebooks and other mobile devices to use USB Type-C ports to replace the conventional AC/DC power adapters and USB Type-B and A terminals. Manufacturers are taking advantage of these features and incorporating dual or multiple USB Type-C ports into their devices.

However, using the current system architecture for implementing dual or multiple USB Type-C ports, leads to a complicated situation. It is unable to meet many requirements of the customers. As a solution, Intersil has proposed a new system architecture using the ISL95338 buck-boost type of regulator, and the ISL95521A, which is a combo battery charger. Use of these devices simplifies the design of the USB-C functions and fully supports all features. Applied on the adapter side, manufacturers can implement a programmable power supply, and it offers an adjustable output voltage that matches the USB-C variable input voltage.

In the proposed design, Intersil offers an architecture with two or more ISL95338 devices in parallel. Each of them interfaces a USB Type-C port to the ISL95521A battery charger. As this architecture eliminates several components from the conventional charging circuit, including individual PD controllers, ASGATE and OTG GATEs, it saves manufacturers significant costs. For charging a battery, power is drawn directly from the USB-C input to the ISL95521A, and the multiple ISL95338s offer additional options.

For instance, the user can apply two or more USB-C inputs with different power ratings for charging the battery fast. Therefore, the battery charge power is now higher than that supplied by a single USB-C input power. It also means there is no need for adding external circuitry to determine the different power rating operations of the paralleled ISL95338 voltage regulators.

Beemo Works With Raspberry Pi

Even adults watching Adventure Time wish to own a personal BMO, the quirky living game system from the Be More episode of the show. Although based on the GameBoy, BMO is a digital friend calling out through the nostalgia lens of our childhood times. Now Bob Herzberg has created Beemo, a BMO for his daughter and her friends.

In building the living little boy, Beemo, Herzberg used the popular single board computer Raspberry Pi (RBPi), which be runs on battery power, a USB battery pack. Although his body is made from laser-cut MDF wood, Beemo uses am 8-inch HDMI monitor. Herzberg had to 3-D print the arms and legs, attached them to the body, which he sanded, sealed, and painted. Adding some vinyl lettering completed the look. Adding a small wireless keyboard meant Beemo could be remotely controlled.

To interface the gaming button on the panel, Herzberg had to create a custom PCB, and he laser-cut the special acrylic buttons to mount them. These he connected to the IO header on the RBPi to make them work. Another PCB functions as a holder for the USB sockets. This allows Beemo to have USB ports on the front panel. Beemo works comfortably for a continuous 8-hour period on his battery.

Herzberg’s daughter created the custom animations that he then transformed into MP4 video files—giving Beemo most of his personality. The remote keyboard operations turn the animations on. Some BMOs are given an internal microphone and a speaker. The BMO translates the user’s voice using Google Voice API, and maps it to an appropriate response, allowing the user to have a conversion with BMO.

Herzberg also used the RBPi camera module. Some BMO makers use servos to make the camera pop out for taking a snap. This type is called the GoMO and it can take pictures. Actually, there is a whole family of MOs—GoMO, CMO, XMO, UMO, and a few others. Although people like to think of the retractable camera as a ghost detecting equipment, Beemo simply likes to take nice photos.

Playing games with Beemo is very simple. You only have to load one of the emulators Raspbian supports. Raspbian is the operating system that makes RBPi run. Herzberg faced some real challenges when creating Beemo. He had to use different materials and techniques to fabricate the enclosure. However, the presence of the RBPi inside meant bringing Beemo to life was much simpler.

While Beemo may not be able to hop around and sing as the BMO in Adventure Time did, he can certainly play a huge number of retro games, because of the RBPi within him. As Herzberg was familiar with the Atari 800 emulator, having written games for that platform earlier, he used the front panel USB ports for connecting gamepads. Of course, the D-pad and front panel buttons are also equally useable.

Herzberg uses the RBPi A+ as the heart of his project. He has split 256 MB of the RAM between the CPU and the GPU. He also uses the composite video and stereo outputs on the 4-pole jack internally. By modifying the config.txt file, he was able to shut off HDMI output completely.

Control the OpenGarage from Anywhere

All of us have our forgetful moments such as not having closed the garage door after leaving home, and that has us worried and stressed until we can get back. At times like this, we miss the advantage a remote garage door would have given us. Although automated garage door openers are readily available, they use proprietary software, which we may not be able to tailor to our requirements.

OpenThings now offer OpenGarage, an intuitive and easy-to-use garage door monitoring and controlling device. Apart from monitoring the door status remotely, the user can also close or open it from anywhere. Apart from this, you can also check the history, receive notifications, and even use the automation feature to auto-close the door. Now, even if you have forgotten to close your garage door, with OpenGarage, you can access, monitor, and control it from your office, home, or while traveling on the road. OpenThings offers a free app for use on your mobile, and it allows you to remain in contact with OpenGarage always and from anywhere.

However, the greatest advantage of OpenGarage is it is an open-source product. That means you can easily access the complete software code, and customize it to fit your own specific need. As it is a Wi-Fi enabled gadget, OpenGarage has a built-in ultrasonic distance sensor and a relay. You can modify it to use it as a sump pump controller by monitoring the water level in the sump, or use it as a parking sensor for making sure the car is parked at the required safe distance.

If you do not want to use OpenGarage to control a garage door, you can connect more sensors to it, such as humidity and temperature sensors, and use it as a Wi-Fi enabled weather data logger. The instruction video OpenThings provides makes it very quick and easy to install OpenGarage.

There are several advantages of using OpenGarage and its accompanying app. Apart from the ease of accessing, monitoring, and controlling your garage door remotely, using the intuitive OpenGarage UI on your mobile means you do not need to carry an extra remote control unit. The app shows the present status of the door on your screen, and you can always toggle it open or close.

OpenThings places updates for their device and app on the OpenGarage Github repository. That makes it easy to use the web interface for updating the firmware in the device—simply click on the update button at the bottom of the page.

Sometimes the update may fail due to various reasons. You can then do a factory reset by holding the button on the device—keeping it pressed for about 5 seconds—then follow the steps for setup. If this step also does not work, simply use a USB cable to flash the new software, following the instructions.

OpenThings has designed the OpenGarage app to enable control over several units that may be required in a multi-garage setup. Therefore, not only is this web-connected door opener useful for individuals alone, it is useful for commercial garages as well.

Do Air Conditioners Need Inverters?

With the economy jumping around and the cost of electricity traveling north, consumers now prefer to buy appliances that guarantee payback through long-term savings. As old gadgets, especially air-conditioners become non-functional, more and more users are replacing them with appliances using inverter compressor technology. This not only uses energy more effectively, it saves the user from paying large electricity bills.

While regular air-conditioners consume a fixed amount of energy depending on the temperature setting, those using the inverter compressor technology consume only the power necessary for the cooling—ensuring maximum savings of electricity, while offering maximum comforts to the consumers.

With rivers running dry in most parts of the world, dams are no longer producing enough electricity to sustain entire cities. That is forcing people to purchase environmentally friendly products that utilize electricity effectively. When the temperature difference is low, such as during the night, a regular air-conditioner does not reduce its power intake, but those using the inverter technology automatically slow down the compressor so that it consumes less power. When the compressor speed varies with temperature difference, and it consumes electricity only as needed, energy requirement reduces by as much as 30-50%.

While the inverter technology is more expensive, equipment using the technology pay back over time with savings through lower power consumption. Acting as heat pumps, air-conditioners with inverter technology are highly efficient at utilizing lower energy compared to their regular counterparts.

Another advantage in using the inverter technology is the relatively quiet nature of its operation. Regular home appliances such as air-conditioners and refrigerators are notorious for their noisy operation, especially noticeable at night, when the ambient noise levels are lower. As the inverter technology is quieter, users can enjoy better sleeping times.

As the compressor speed adjusts itself with temperature fluctuations, the device using the inverter technology runs with greater stability, ensuring the durability and a longer life span for the device.

For the more technically oriented, inverter technology works with DC motors of the compressor in a refrigerator or air-conditioner, controlling the speed of the motor, thereby continuously regulating the temperature. The inverter units usually have a variable-frequency drive for controlling the speed of the compressor motor, resulting in better control of the cooling or heating output.

In practice, the drive converts the incoming AC into Direct Current and using pulse width modulation creates the desired frequency for operating the motors. A micro-controller does all this including sampling the ambient temperature to control the speed of the compressor.

Compared to the regular air-conditioners and refrigerators, the inverter units have increased the efficiency of operation, extended the life of various parts, and have avoided the sharp fluctuations in temperature.

With a quieter operation, lower operating costs, and requiring lower maintenance, inverter air-conditioners units are better than regular constant speed air-conditioners are. Although these new type of air-conditioners are more expensive, they balance this with their lower energy bills. Although it depends on the actual usage, the payback time is usually two years on average. Modern air-conditioners are typically split units, with the heat exchanger placed outside for higher efficiency.

What is a Hygrobot?

In the future, tiny robots such as the hygrobot will be able to avoid the need for batteries and electricity to power them. Like a worm or a snake, moisture will power these tiny wriggly robots.

Hygrobots actually inch forward by absorbing humidity from their surrounding environment. Created by researchers at the Seoul National University, South Korea, these tiny robots can twist, wriggle forwards and back, and crawl just as snakes or worms do. The researchers envisage these hygrobots being useful for a variety of applications in the future, which could include delivering drugs within the human body.

According to the researchers, they received the inspiration for hygrobots from observing plants, and they have described their findings in the journal Science Robotics. Using hydroexpansion, plants change their shape and size when they absorb water from the air or ground. For instance, pinecones know when to close and when to open, depending on whether the air is wet or dry, and this helps them to disperse seeds more effectively. Even earlier, plants have provided inspiration for robots—researchers created robots in imitation of algae.

Although hygrobots are not made of plant cellulose, they mimic the mechanism the plants use. As moisture is available almost everywhere, using it as a source of power for operating robots makes sense. Unlike batteries, moisture is non-toxic, and does not have the tendency to explode. This is an important consideration, as microbots, for instance the spermbot, are usually required to operate within the human body.

One can visualize the motion of hygrobots by observing the Pelargonium carnosum seed bristle—a shrub-like plant found in Africa. The hygrobot mimics the motion of the bristles, as it has two layers made of nanofibers. While one layer absorbs moisture, the other does not.

Placing the bot on a wet surface causes the humidity-absorbing layer to swell up, making the bot move up and away from the wet surface. This allows the layer to lose moisture and dry up, and the bot comes back down—the cycle repeating itself—allowing the bot to move. The researchers demonstrated a hygrobot coated with antibodies crawling across a bacteria-filled culture plate. It could sterilize the entire plate without requiring any artificial power source.

This is how the researchers imagine the bots of the future will deliver drugs within the human body, propelling themselves using only the moisture of the skin. Other than responding only to water vapor, researchers say they could equip them with sensors that respond to other gases as well.

However, this is not the first instance of scientists working with tiny robots. Last year, researchers had created a hydrogel bot for biomedical applications that a magnet could activate. It was able to release localized chemo doses for treatment of tumors.

Not only medical, military, and industrial applications will also benefit from light and agile microbots that do not require additional power inputs to operate. Hygrobot, the biologically inspired bilayer structure harnessing energy from the environmental humidity uses ratchets to move forward. The hygroscopically responsive film quickly swells and shrinks lengthwise in response to a change in humidity.