Monthly Archives: June 2015

Happy Gecko MCU Only Sips Power

The EMF32 micro-controller series from Silicon Labs, apart from featuring a smart interface, is also ultra-low power and USB enabled. Going by the name of Happy Gecko, this micro-controller is based on the ARM Cortex M0+ core. It uses autonomous peripherals and an advanced system for managing energy usage. That keeps the total energy usage in most applications so low that the controller can source power comfortably for a year from energy-harvesting arrangements or from a single battery.With the CPU core operating at speeds close to 25MHz, the core peripherals include comparators, 1Msps, 12-bit ADC, a current DAC, counter/timers, GPIO and serial buses such as I2C and USB. It supports encrypted firmware updates over USB with an onboard AES acceleration engine. Users have different memory options for up to 8KB of RAM and 64KB of Flash in a series of pin-compatible family members.

The designers of Happy Gecko have employed a variety of techniques for keeping its energy consumption to the minimal levels. Not only does its circuit design feature only 130uA for every MHz when active, the MCU can trade power for functionality through five energy modes. Therefore, developers have the ability to choose the mode consuming the lowest amount of power at any given time.

Apart from intelligent peripherals, the MCU also offers a peripheral reflex system with six channels. That allows several routine functions to execute without involving the CPU. For instance, an onboard comparator is available to monitor an input voltage, triggering an ADC to take sample as the signal crosses a threshold. The ADC in turn, stores the value in memory using a DMA channel. All this happens without the CPU coming out of its sleep mode. When the CPU needs to be active, its high clock rate ensures that it accomplishes the necessary actions in minimal time and it can return to its sleep mode quickly. Only 2µs are necessary to wake up the CPU from its slumbering state.

For the Happy Gecko, the low-energy USB interface is its key feature. However, this operates only as an endpoint device. That means the device does not require an external USB crystal and automatically synchronizes its internal oscillator to the incoming data. The endpoint device has its own dedicated RAM and an integrated PHY layer with a 5V LDO regulator and resistor. The interface remains in its low power mode, waking up only when it detects activity on the bus different from the idle time following a USB start-of-frame.

Silicon Labs offers a starter kit for the Happy Gecko. This is mbed-compatible and comes with a built-in USB debugger. The internal current measurement makes it very easy for developers to correlate the energy use of the CPU with their code.

Silicon Labs also offers an IDE to support the CPU, called the Simplicity Studio. The IDE features a pin out design tool that makes it easy to handle the configurable IO pins of the device. It also has a real-time energy profiler for synchronizing code to the minimal energy consumption of the micro-controller.

Efficient Control of Motors at Low Speeds

When a motor is operating at high electrical frequency or high mechanical speed, the back EMF signal generated by the rotating rotor presents an efficient feedback technique for a sensor less motor control.

However, generation of the back EMF requires a minimum frequency and that makes it difficult to control motors running at low speeds. The process of continuously estimating the rotor flux angle at zero and very low speeds, together with stably moving between low-speed and high-speed estimators helps to improve the effectiveness of starting the motor under load without using sensors.

TI or Texas Instruments’ InstaSPIN-FOC software called FAST helps to make this estimation at very low speeds, sometimes below 1Hz. Although the initial rotor flux angle is unknown, FAST estimates this using sensor less techniques. Until it has measured enough back EMF, this estimate remains unpredictable and the estimated angle is incorrect.

However, FAST feeds the control system applicable to the motor and induces motor movement. Enough back EMF is generated with only a small amount of rotor movement and the algorithm can then converge on a reasonable estimate for the angle very quickly. This allows a controlled high-torque drive at low-speeds with excellent operation. Although the start-up performance may not be consistent, this method can start the motor with enough torque for rotor movement.

With increase in the starting load, the torque requirement goes up. The amount of torque the system can generate depends on the current through the motor and the alignment angle between the magnetic fields of the stator and the rotor. For ensuring generation of enough current, the speed controller must necessarily have a maximum output larger than the rated current required to generate the necessary torque.

For example, a motor starting under full load may require 4A of current to produce the necessary torque to move. This requires setting the speed controller’s maximum current output to 6A. When started, the motor will draw a current of 6A in its first electrical cycle for moving the rotor. With FAST providing a valid angle within this first cycle, the control system will quickly regulate the current usage to the required level of 4A.

However, even when there is a stable feedback angle, the rotor may not necessarily align itself properly for generating the maximum torque. In reality, you are simply sweeping the stator field and waiting until the rotor field locks on and synchronizes. If the stator field is not oriented properly, the motor may fail to generate enough torque or even produce torque in the opposite direction. Control systems can improve this situation only by starting with a better starting angle.

The simplest way to control the initial alignment is to inject a DC current in a field-oriented control system. This defines the orientation of the rotor flux. A large enough DC current injected will move the rotor and the load to a known angle. Even though the forced angle is still emulated, the orientation will be proper for correct starting and the rotor will be in the best position for produce torque. The DC current injection may be done manually or programmed through FAST.

High Efficiency Hybrid Solar Cells

Normally, a modern silicon solar cell exhibits a maximum theoretical efficiency of about 33.7 percent. A majority of the sunlight falling on the solar cell – more than 66 percent – is not converted to electricity and is simply wasted in heating up the cell. Now, a new type of solar cells may be able to boost this efficiency to 95 percent or more.

The University of Cambridge Cavendish Laboratories is researching on a new type of high-efficiency hybrid solar cell. The UK researchers are using an organic formulation to put in as a layer on top of a standard silicon solar cell. This layer will help the solar cell to reach its target of the hard-to-believe 100 percent efficiency.

The top layer of special organic formulation coating on the solar cell helps to absorb high-energy light and produce pairs of triplets. Inorganic solar cells underneath can efficiently absorb these triplets. Generally, the cells cannot convert the high-energy radiation into electricity and these radiations only serve to heat up the solar cells. The organic film on top of the solar cells converts the wasted energy into a form that the underlying solar cell can turn into useful electricity.

With an increase in efficiency brought about by the Cavendish Laboratory hybrid approach, solar energy harvesting farms can be reduced in size significantly, while still producing the same amount of electricity.

According to Maxim Tabachnyk, Scholar, and Akshay Rao, research fellow at Gates Cambridge, and other members of the Cavendish Laboratory at the University, they have developed a film to convert wasted energy into useful form. The traditional solar cell is unable to convert high-energy light and wastes it as heat because of the fundamental limit of the solar cell’s power conversion efficiency.

The researchers coated the silicon solar cells with a special organic layer. This layer functions to distribute the energy of the incoming high-energy photons into two triplet excitons that in turn transfer their electrons on to the silicon cells.

The researchers had to first characterize the ultra-fast processes occurring at the organic/inorganic interface. For this, they directed ultra-short laser pulses into organic pentacene and studied the effect with laser spectroscopy. By following the transfer of energy taking place within a femtosecond (a billionth of a billionth of a second), they confirmed the presence of two electrons for each high-energy photon. Normally, only one electron is generated per photon.

After proving the concept that each high-energy photon can generate two electrons, the researchers had to find an alternative candidate to replace pentacene, which is not a suitable candidate to produce electrons suitable for silicon to absorb. They have now found a suitable organic material that can produce electrons with excitation higher than the band gap or the minimum absorption energy of silicon. The organic material is cheap and can be printed or even sprayed on as ink on top of traditional silicon solar cells.

According to Tabachnyk, normal solar cells harvest only the bright single-spin excitation electrons produced by the photons. The organic layer extends the ability of the cells by allowing them to harvest additional electrons from high-energy photons producing dark spin-triplet excitations.

What is a Raspberry Pi?

Raspberry Pi or RBPi, the fully functioning, tiny, single board computer costing next to nothing, has been a runaway success. However, a perennial question doing the rounds is – why would anyone want one when there is such a glut of PCs, tablets and smartphones? This article discusses the answer while exploring the RBPi doing real things.

Why is the RBPi Special?
Being an ARM-based single board computer, the RBPi, though unexceptional, is not particularly powerful. However, it is amazingly cheap and that makes it an almost disposable computer.

Several low-cost embedded systems platforms such as the Arduino are available on the market. However, unlike others, the RBPi is a complete general-purpose computer. For a very low cost, the RBPi offers the complete package of a Linux-based machine that challenges the computing power of a desktop machine of a few years ago. Apart from using it as a desktop personal machine, you can also use the RBPi as a server, a dedicated device running in kiosk mode, or for physical computing – its digital IO pins control other hardware.

The RBPi is cheap enough for one to use it to do a single job. To be equally multipurpose, other platforms would need machines that are more expensive. For example, a single RBPi can work equally well as a wall clock, a weather station, a digital photo frame, etc. Earlier, one would be using multiple temperature sensors and running long cables to a single data-collecting machine. The same job can now be handled more efficiently with an RBPi in each location, individually enabled with Wi-Fi and sending their data to another RBPi acting as a central server.

Therefore, the low cost of the RBPi is changing the optimal architecture of several projects.

Types of RBPi Available

At present, all RBPi models are based on the Broadcom BCM2835 system on a chip. This is actually a combination of a version 6 ARM architecture CPU and a VideoCore IV GPU. That makes it roughly as powerful as a 300MHz Pentium II processor typically used in the year 1999. The actual distinction between the different models is primarily based on the amount of RAM and the interfaces offered. All modes come with an HDMI and an audio port.

The initial Model A started with 256MB, while the later Models B and B+ have 512MB each. However, Linux and most applications for Linux are not as memory hungry as Windows, so the RBPi & Linux constitutes an efficient and economical combination.

Although RBPi operates on a capable Linux operating system, there are no hard disk drives and no disk interfaces either. Instead, the RBPi relies on an SD card interface that supplies the 8-32GB Operating System and file system storage.

While the Model A started with a single USB port interface, the Model B comes with a 100MHz network port and two USB ports. The latest Model B+ has one 100MHz network port and four USB ports. Therefore, you can connect a mouse and a keyboard to the Model B+ and still have two more USB ports left for connecting other appliances.

Silver Nanowire Conductors Improve Touchscreen Products

The next generation of flexible wearable devices is getting help from an unexpected quarter – the silver nanowire, which is proving to be cost-effective for producing touchscreen products.

As wearables grow in popularity, designers struggle with offering flexible products. So far, notebooks and tablets needed to have tough, flat surfaces that were able to survive frequent wear and tear. Although designers have been largely successful in mastering this technology, wearable products pose a different challenge. Humans attaching wearables to their bodies want flexible products that can follow the curvature of their body part. Touch-enabled products are taking a leap forward with the use of materials such as silver nano-wires.

Apart from the mind-boggling reduction in electronic devices, wearability is the next best thing already happening in personal computing devices. That also means an evolution in the human interface. Therefore, people prefer flexibility, not only for the display glass and the electronics, but for the interface as well. In turn, this is leading to virtually unlimited design flexibility along with durability and portability.

With flexible touch comes flexible ergonomics. For example, phone screens are now unbreakable – when dropped, they flex rather than shatter. Therefore, it is now possible to roll up a seven-inch tablet and carry it in the pocket. A display could easily wrap around the arm or a huge public display could wrap around a pillar or a building, just as easily as a neon light can.

The clunky boxes that passed for consumer electronic devices are no longer in vogue. Today, consumers prefer ever-thinner laptops and tablets. Even kiosks and monitors therein are now sleeker and aesthetically more pleasing. This is leading to a greater demand for thinner and lighter components. Additionally, electronic components with lower mass are more durable and rugged.

Apart from being thin, light, visible in different ambient light conditions, highly responsive, touchscreens also need to be brighter, stronger, more sensitive, consume lower power and most importantly, be lower in cost. Since most touchscreens are of the capacitive type, they typically have a see-through conductor as a screen. This very thin layer of material has to conduct electricity while remaining lucid. The transparency allows light from the display underneath to shine through the screen. At present, Indium Tin Oxide or ITO is the legacy material used for the conducting screen, but this has limited flexibility, transparency and conductivity, when compared to silver nano-wires.

Touch interfaces made of silver nanowires are showing great promise on all accounts. This material will help to make forthcoming generations of touch interfaces more responsive, whether they are small or large. They will also be brighter and be visible in all ambient lighting. All this requires more transparency, higher transmission ability and higher conductivity – things that silver nano-wires can easily deliver.

Applications for transparent conductors are not limited to LCDs alone. They are required for OLEDs, shutters for 3D TVs, thin-film photovoltaic cells and future products that the world can only imagine for now. With better light transmission, higher conductivity and no side effects such as pattern or moire-fringe visibility, silver nano-wires are set to introduce all these and more at a lower cost than the traditional technologies presently can.

Focus Stacking with the Raspberry Pi

If you are into photography, a flatbed scanner and the popular single board computer, the Raspberry Pi or RBPi, can help you to focus stacking images in macro photography. After re-purposing an old flatbed scanner, David Hunt is using it as a macro-rail controlled by the SBC, RBPi.

Those who shoot macro photography are aware of the common issue of depth of focus limitation that shows up as the depth of field limitation in the photograph. Depending on the magnification you are trying to achieve and the camera settings, the depth of focus can be as small as 0.5mm. One solution is to stack together several images of a subject, with each image focusing on a different part of the object.

To do this with commercial solutions may set you back by as much as $600. The difficulty lies in moving the camera closer to the subject in extremely small increments, but with great accuracy. The sharp parts of the images are combined together using free software such as CombineZM, resulting in a completely sharp image of the subject right from front to back.

David Hunt decided to solve the problem with an old flatbed scanner that was lying in his attic gathering dust. Capable of 2400 dpi, the scanner had not been used for over a couple of years.

Even the drivers available for it worked only on Windows XP. Although accurate enough, David was doubtful if the machine would be capable of moving a 3Kg camera and lens combination. He decided to use the stepper motor and drive the scan element in very small increments, with the camera attached to it – it would be ideal for macro photography.

Scanners typically come with a nice flat platform on which a camera can be placed. Driving the platform forward and back requires a stepper motor that has its own drive electronics and has to be driven externally. The drive is slow, so it will let the camera remain steady while it moves. A camera with a shutter release mechanism will be useful, as you will have to take a number of snaps.

H-bridge stepper motor drives are efficient and easy to use. David used a drive capable of handling 2 DC motors or 1 stepper motor with two coils. For powering the motors and the drive, David used 3x AA type batteries. Therefore, he was able to connect four GPIO pins from the RBPi to control the drive and the motor. However, driving the motor through opto-couplers would have provided more safety for the RBPi.

The binary sequence of 1000, 0100, 0010 and 0001, when repeated, will drive the motor forward one-step at a time. The same sequence, repeated in reverse, will allow the motor to move back one-step at a time. David programmed the RBPi to generate these sequences repeatedly while he added an additional circuit for releasing the camera shutter between each movement of the platform.

With the above contraption, David can move his camera forward towards the subject in the smallest increments of 0.02mm, and take images at each increment.

Different Types of Interface Pressure Measurement Techniques

Precise measurement of interface pressure and force between two surfaces is always a challenge to engineers. However, several specific technologies exist for sensors dealing with interface force and pressure. Parameters such as form factor, precision and environment influence the selection and capabilities of such sensors.

A variety of applications requires measurement of pressure. These range from product development to medical research. Typically, pressure is the measurement of applied force over an area. With two objects held in contact, both exert force on the other. Therefore, the average interface pressure is the total force divided over the interface area. However, this interface pressure may not be distributed uniformly, creating the necessity of measuring localized interface pressure.

For measuring the force or interface pressure, chiefly three technologies are considered suitable – load cells, pressure indicating films and tactile pressure mapping systems. Although each sensing technology has some overlapping information, they all provide unique values when solving problems. Additionally, as the shape of the target becomes increasingly uneven, the ability of the sensor to match the overlap with the surfaces applying the force also becomes critical.

Load Cell

A load cell is the most common force or pressure sensor with which most engineers are familiar. The load cell has many varieties, the most useful being strain gages, piezo-electric elements and variable capacitance. Load cells may be utilized in multiple form factors depending on the force applied and the mechanics of the application. For example, measuring the deformation of a beam for qualifying the force of the load applied relies on load cells. Such compression, S- or Z-beam and shear beam load cells are all dependent on strain gages. Most reliable load cells utilize a full bridge of strain gages bonded on to the load-bearing structures.Force applied to the load cell deforms the structure and places a mechanical stress on the strain gages. This changes the resistance of the strain gages affecting their output signal. With calibration, the output voltage can correlate to the force applied on the load.

Pressure Indicating Film

These are useful when measuring interface pressure between two surfaces. A layer of polyester hides a color developing material layered next to tiny microcapsules containing staining ink. These microcapsules are designed to break under different pressures. With pressure applied to the film, the microcapsules rupture. This distributes the ink at the places where the pressure is applied. With more force being applied to a location, more microcapsules rupture increasing the intensity of color on the film. This gives an image of the force applied across the sensing area. Films are available for different sensitivities of pressure.

Tactile Pressure Sensor

Tactile pressure sensors are made of piezo-electric material. Two pieces of flexible polyester with printed silver conductors on each piece sandwich a unique piezo-resistive ink. The result is an extremely thin sensor, about a tenth of a millimeter thick. A signal is transmitted via the silver electrodes through the piezo-resistive ink. As pressure increases on the sensing area, the resistance of the ink changes and the data collected maps the pressure applied.

Different Types of Feedback Encoders

All closed loop systems use feedback to control speed and or position. This plays an important role in keeping equipment operating accurately and smoothly. When using feedback for the best benefits in an application, it is important to understand how feedback works, because a variety of devices as well as models is available for the purpose. The most popular among them are tachometers, Hall sensors, encoders and resolvers.

Tachometers
Tachometers are rotating electromagnetic devices. Typically, these are connected to the shaft of a motor, rotating when the shaft rotates and generating a voltage as a signal. The faster a tachometer shaft rotates, the larger is the magnitude of the voltage output. Therefore, the output signal is directly proportional to the speed of the motor shaft. The polarity of the output voltage indicates the direction of rotation, clockwise or counter clockwise.

Usually, analog or DC tachometers provide direction and speed information. When fed to a meter, this information can be used in servo control for stabilization. DC tachometers are the simplest of feedback encoders.

Hall Sensors
Hall sensors are solid-state electronic devices and they can sense or detect magnetic fields. The output of the sensor changes or flips whenever a magnet comes close to a Hall sensor. Therefore, a Hall sensor provides a digital output as either a high or a low voltage.

Hall sensors are used for brushless motor applications, providing information about rotor position. This works as an electronic commutation, with the controller using the information to turn on or off specific power devices applying power to the stator windings.

Encoders
Encoders are simple mechanical-to-electrical conversion devices and turn mechanical rotary motion into velocity or position information for systems controlling motion. Encoders can be rotary, digital, optical or incremental types.

In its most basic form, and encoder consists of a light source, a mask, a coded disk and a photo sensor along with related electronics. After passing through the mask and the coded disk, light from the source is detected by the sensor. As the encoder shaft rotates, light is alternately passed through or blocked, making an alternating light and dark pattern.

The associated electronics converts this into an electrical signal representing high or low corresponding to light passing through or being blocked. The resolution desired for the application governs the number of lines etched on the coded disk. By counting the number of pulses, the position of the shaft relative to its starting position is known.

There are two types of encoders, classified as incremental and absolute. Absolute encoders generate a specific address for each shaft position throughout the 360-degree rotation of the shaft.

Free Your Smart Phone and Let it Fly

You may not feel very enthusiastic about Lily, the flying camera-drone that follows you around, but a PhoneDrone is bound to change your point of view. Using your smartphone as its brains, the PhoneDrone lends it wings and allows it to fly along a predetermined path.

This is a perfectly logical situation as a smartphone already contains the necessary sensory and computing power that a drone needs. Most smartphones run on a powerful multicore processor along with several sensors on-board, so why pay for all these things over again when buying a drone. The people at PhoneDrone were also led by the same reasoning and the result is a drone that utilizes its owner’s smartphone for its brains. Users have to dock their phone into the device for each use. Not only does this approach help to keep the price down, it also makes the user exercise caution not to crash the thing.

The Indiana-based company, xCraft, has designed the PhoneDrone, which can accommodate not only iPhones 4s and above, but also the most popular Android phones as well. This same company had earlier produced the fixed-wing/hovering X PlusOne drone. Users can fly the latest PhoneDrone, a quadcopter, in a few different fashions.

By using another mobile device, users can control their flying mobile through Wi-Fi and at the same time, watch live streaming video from the camera on the PhoneDrone. A free app allows users to enter a flight path for the PhoneDrone to follow autonomously. When transporting the device, the propeller arms of the PhoneDrone will fold back.

The user can also impose a follow-me mode with the second mobile device, if required. The phone in the aircraft locks on to the signal of the hand-held device and will automatically pilot the drone to position it above the hand-held device as it moves. A folding mirror on the drone allows the camera of the phone to shoot straight ahead, down or anywhere in between. The battery in the drone gives a flight time of 20-25 minutes. According to xCraft, they are working on an ultrasonic type of collision-avoidance system.

At present, xCraft is raising product funds via Kickstarter for their PhoneDrone project. You can pledge US$199 for the product, which will be yours as soon as xCraft is ready to go.

Others have also tried their hands at making drones with brains based on smartphones. Notable among them are the University of Pennsylvania and the Vienna University of Technology. However, their attempts were mostly one-off. Qualcomm and UPenn have also combined the drone and phone earlier. They had used the electronics of the Android smartphone and its software to fly the drone. All the sensors required for providing navigational information for the drone are already present on the smartphone – accelerometer, GPS, gyroscope and others.

The present trend is to utilize the camera on the phone itself and use its visual input to steer the phone. The user has to install an app on the phone to achieve this. In future, expect more hobbyists to substitute smartphones for hardware at the heart of several other types of machinery such as drones.

ArdHat for Connecting Raspberry Pi to the Real World

Many users of the tiny, inexpensive, Linux-based single board computer, the Raspberry Pi or RBPi, would like to connect it to the outside world, but do not know how. According to Maker Jonathan Peace, ArdHat is most suitable for connecting the barebones Unix platform to the real world. Therefore, he calls it the “missing link that connects the Raspberry Pi with the real world.”

Onboard the ArdHat is an Arduino-compatible embedded MCU, the ATmega328P. Its specialty is very quick response to all real-time events, allowing the RBPi to take care of the rest of the heavy lifting. HATs or Hardware Attached on Tops are most suitable for the RBPi Model B+. These HATs conform to specified standards and make life easier for users. One significant feature of HATs is an onboard system to allow the RBPi B+ identify the connected HAT and automatically configure its GPIOs and drivers for the plugged-in board.

Real-world systems need low-power operation, real-time performance and environmental protection and awareness, all of which the ArdHat provides. As a super-compact RBPi compatible HAT, the ArdHat enhances and protects the RBPi for applications in the real world, while being accessible to everyone possessing an Arduino.

You can have the ArdHat in four different models – two with long-range radio modules and the other two without the radio. All four are packed with analog sensors, user interface controls, a real-time clock, 5V Arduino shield capability, supply monitoring, a wide operating range of voltages that includes automotive, full power/sleep management and high current outputs for driving peripherals. All these are accessible from the AVR chip on-board the ArdHat or the RBPi.

Those looking for more power can also choose between the ArdHat-W and the ArdHat-I. The first has a 15Km long-range ISM wireless node, while the latter has a 10-DOF inertial measurement unit. Both make the boards ready for IoT right out of the box.

Apart from a flat top design that allows plenty of space for placing a battery or a prototyping board, the ArdHats accept several Arduino shields. Users can also buy an optional high-capacity 1800mAh battery, especially tailored to plug-in directly into the JST standard connector. The whole arrangement fits snugly between the shield headers of the board’s flat top design.

Among the smart power management feature of the ArdHat is a power switch and charge control. That allows the RBPi to run on several types of power supplies, including LiPo batteries to automotive supplies. Therefore, the HAT can simply connect to systems operating on 5V and drive them – smart LEDs, quadcopters and servos.

Other than protecting the RBPi from external power outages and voltage spikes, the TopHat enclosure offers a physical safeguard as well. Made of laser-cut Perspex, the enclosure allows access to pins of the Arduino shield for teaching and experimental purposes. At the same time, the enclosure protects the delicate circuitry of the RBPi circuit board.

The scheduler and applications for the ArdHat are entirely open-source. Using the Arduino IDE, users can modify and update even the preloaded sketch of the real-time software on the ArdHat.