Monthly Archives: March 2015

Choose the color of your led

To indicate the hue of a specific type of light source, the standard procedure is to measure its color temperature in degrees Kelvin. For example, for suggesting realistic colors of lights in a 3D scene, you can use a Color Temperature chart. Typically, the white balance of a video camera or a film stock is used as the base for relating visible colors. For this, two settings are used most commonly. The first is the indoor color balance, set at 3200K and the other is the daylight color balance, set at 5500K.

Measuring the hue of light as a ‘temperature’ was started by the British Physicist William Kelvin in the late 1800s. When heating a block of carbon, he noticed that it glowed and produced a range of different colors at different temperatures. Beginning from a black cube, it first produced a dim red light, moving to a bright yellow as the temperature increased. Eventually, it glowed with a bright blue-white at the highest temperature.

To honor William Kelvin, the unit of measurements of color temperature is degrees Kelvin, a variation on degrees Centigrade. Unlike the Centigrade scale, which starts at the temperature of freezing water, the Kelvin scale starts at -273 degree Centigrade, also known as ‘absolute zero’. However, when attributing color temperatures to different types of lights, it is usual to correlate them based on visible colors matching a standard black body. Therefore, the stated color temperature is not the actual temperature at which a filament is burning.

Now, an LED, available as a simple chip on board or COB package, can be tuned for its color temperature. The LED manufacturer Everlight has introduced this as the world’s first color-temperature tunable LED.

Immediately following brightness dimming, the next most desirable feature for users of LEDs is to be able to tune the warmth of the light output. For example, some people prefer a ‘warm’ colored light to a ‘cool’ type of illumination. Accordingly, manufacturers generally implement this feature by using multiple LEDs ranging from cool white to warm white, placing them behind a diffuser.

Everlight provides a very compact solution with its CHI3030 27V/29W series. They have packaged the LEDs behind concentric layers of phosphors. This offers different color temperatures of white as setting a precise color-temperature mix is simple now – just light up the required numbers of warn white or cool white LEDs.

Consuming 29W at 27V, the 30x30mm COB CHI3030 from Everlight is the largest such multi-chip solution for a tunable temperature LED. You can select from among different tunable ranges such as 4745-7050K for the KY Cool-White series to the 2500-5700K for the KH Warm-White series. The typical luminous flux output from the LEDs is 2990 lumens for the 5700K cool white and 2760 lumens for the 2700 warm white. Everlight makes similar other series of LEDs with fewer concentric phosphor rings that operate down to 9W.

Everlight expects such color-temperature tunable LEDs to see mainstream use within the next few years. Adding such extra color tuning flexibility allows manufacturers to calibrate their products easily and precisely at low costs.

Let Raspberry Pi do your Calling and Answering

In certain projects or experiments where you are monitoring an entity such as temperature or pressure, it is impractical to be physically present for any length of time. However, it may be important for you to know when the measured entity breaches a high or a low set point. For example, if something is not working out as it should – say temperature or humidity too high – you may wish to start or control another activity rather quickly to compensate.

In such cases, the handy, credit card sized single board computer, the Raspberry Pi or RBPi can be of immense help. RBPi can call, sms or inform you via web-interface, in case things are tending to go beyond their limits. Although sms and web-interface work equally well, for cases that are more important a call gets more attention than the others do.

When receiving a call, you expect the other party to speak up. Programs such as eSpeak and Festival endow an RBPi with capabilities of synthesized speech. Both tools allow you to cache speech as wav-files. eSpeak is more adjustable and creates wav files a bit faster than Festival; however, their performance is similar. You can select any one of the programs depending on your preference and install it with a ‘sudo apt-get install …’ command.

For making calls, it is simpler to use a sip/voip based system. Here again, you can select between two capable tools – PJSIP or Linphone. Of the two, Linphone is difficult to include into an application script. PJSIP has a command line interface and provides a powerful api that you can use within your own sip-based project. However, you will need to download and compile it for Raspbian.

After compilation, you may find some echo or jitter when making normal calls to another phone. To get rid of these, you will need two other tools – sipcall and sipserv. Sipcall will help you to make a completely automated call to a specified number using a text to speech converter. That makes it very useful when using via bash-scripts. For example, you can ask it to check the state of a sensor and place a call if a critical threshold is reached. On the other hand, Sipserv is more like a service, where you make a call to query information and/or execute a command via phone. Of course, your sip-provider must support inbound DTMF. Both tools are available here, but you will need the pkg-config-package tool to compile them.

The original author has also created simple bash-scripts that can check the actual load and place a call if the load is found too high. For stopping/starting the service available, he has provided a simple configuration and a bash-script that you can use for Sipserv. Readme files and general info is available for the user. For more details, refer here.

Although the tools are rather ‘proof of concept’ than a final product, they work well. The author permits changes and extensions to his original work and invites suggestions on any improvements, more especially for the current sound problems of echo and jitter.

Superconduction at nanowire levels

Superconduction At Nanowire Levels

Passing electricity through any conductor generates heat. Even the best conductor such as a copper wire offers some resistance to electrons passing through it. As electrons move through the ordinary conductor, they occasionally collide with its atoms and this releases energy as heat.

Cooling ordinary materials to very low temperatures changes the scenario drastically. Cold temperature dampens the Brownian motion of their atoms, allowing electrons to zip past with very few collisions. Therefore, very low voltage difference is required to pump electrons through ordinary materials when they are at cryogenic temperatures.

For example, Niobium Nitride, which is the base for several superconducting circuits, has a relatively high operating temperature of 16 degree Kelvin. This is equivalent to -257 degree Celsius and is achieved with liquid Helium. Within a superconducting chip, the liquid Helium circulates through a system of pipes in an insulating housing, much like Freon circulating inside a household refrigerator.

Although superconducting materials offer huge benefits, cooling to extremely low temperatures is very expensive and many researchers are working across the globe to make the process commercially viable. Researchers at MIT claim to have developed a circuit design that can help to make simple superconducting devices with extremely low electrical resistance much cheaper.

According to the researchers at MIT, chips made using the technology would make them 50-100 times more energy efficient compared to today’s chips. Although their working would not top the speed of current chips, recovering results of calculations that Josephson junctions perform would be made much simpler.

The current research at MIT has the cryotron as its basis. Cryotron or the Cryotron Computer, an experimental computing circuit, was developed by the MIT professor Dudely Buck in the 1950s. Although, the cryotron attracted a great deal of interest at the time as the possible future for a new generation of computers, the Integrated Circuit eclipsed it.

Current research at MIT in this field has resulted in the development of the nanocryotron. Researchers have tested superconducting circuits made with nanocryotron in light detectors and have been successful in registering the arrival of a single photon or light particle. They also wired several of these circuits together to produce the half-adder, a fundamental component of digital arithmetic. This square-centimeter chip has the nTron adder and performs computations using the new superconducting circuit.

A system using liquid-Helium for cooling is sure to increase the power consumption of a superconducting chip. However, given that this increase starts at about one percent of the energy required for a conventional chip, the overall savings can potentially be enormous. For example, making single-photon detectors would become very cost-effective – this being an essential component in any information system exploiting the computational speedup promised by quantum computing.

The nanocryotron or, as the researchers prefer to call it, the nTron, is an individual layer of Niobium Nitrate on an insulator. The device gets its name from its pattern that looks much like a capital ‘T’. The junction of the base and the crossbar tapers to a narrow region, forming a switch to control the current flow through the crossbar by injecting a current in the base.

What is eco-friendly electronics?

Imagine an easy and non-polluting way of disposing of your old electronic gadgets that have outlived their usefulness. E-waste or waste from electronic products is a ticking time bomb that threatens to engulf us. For instance, about 85% of e-waste is discarded as landfills, releasing several toxins into the environment. Although only 2% of America’s trash in landfills is e-waste, it equals 70% of the overall toxic waste, with lead as the major element. Every year, worldwide, disposal of e-waste is nearing 50 million metric tons of which, only 12.5% is currently recycled.

To combat the menace of e-waste, SINTEF, a research organization in Scandinavia, is making progress in developing electronic components that can dissolve in water. The components are printed on silicon wafer and they contain extremely thin circuits, which are only a few nanometers thick. Being made of a combination of silicon, magnesium or silicon with magnesium additives, these circuits are water-soluble and disappear after a few hours.

Final working products are usually protected with a coating that prevents external fluids from reaching the inside of the packaging and degrading the circuit. Therefore, the requirement is that the circuit be designed to complete its job before that can happen. For example, a circuit package designed to operate in seawater and fitted with sensors to detect oil spills may have a film that remains in place for the few weeks when detection is due.

At present, SINTEF is not manufacturing final products, but only demo products that demonstrate how electronic components can have properties that make them degradable. As their project enters its second year, SINTEF is searching for an active industry partner and additional funding to carry their research further. However, they are confident eco-friendly electronics has a future of its own.

Apart from eco-friendly electronics, researchers are also working on electronic devices that are biodegradable. Such a device, when implanted in the body for different uses such as pain management or for combating infection, will dissolve over time after its objective is met. While several countries, especially America, has made colossal contributions towards resolving the issue of waste and building relations to medical applications, SINTEF s trying to find alternative approaches to this problem.

Other researchers are also working along similar lines. For example, the world’s only ‘biodegradable’ drone, built with biodegradable material, starts to break down upon impact in the event of a crash – eventually leaving no evidence of its existence. This drone was designed and built by a team of students from the Spelman college, Brown University and Stanford University, in collaboration with Ecovative Design for IGEM, a New York based biomaterials company.

Such an aerial vehicle, unmanned and made from biological materials, is ideal for venturing into sensitive areas, while leaving no trace of its existence in the event of a crash. Scientific expeditions with such drones will not contaminate the environment. It will be easy for covert military drones to conceal the fact that they have been spying.

In fact, the biological prototype drone may use a plant-root-like material such as mycelium. This is a part of a fungus, often used as a lightweight and sustainable material for packaging wine or for use in surfboard cores. Several other biological materials are being developed for making all parts of the drone biodegradable – including the sensors.

Integrate your Raspberry Pi to the Hackable Roomba

You do not find many robots in the consumer arena, unless it is the AVA 500, the telepresence robot from iRobot. Users can simply specify where they want AVA 500 to be and it automatically navigates to the destination without requiring any human intervention. It has advanced mapping technology combined with a real-time view of the environment. Another simpler consumer robot is Roomba, from the same company, iRobot.

iRobot has turned the highly successful Roomba 600 robot into a hackable Create 2 version. This is very useful for K12 and college level STEM education, because Create 2 can be programmed via a laptop, an onboard Arduino or a Raspberry Pi (RBPi). Although both AVA 500 and Roomba are Linux based, unlike the more sophisticated AVA 500, Roomba 600 was a modest, vacuuming robot, based on a simple Motorola HC12 micro-controller.

Create 2, the modified Roomba 600, is not meant for vacuuming, as iRobot has eliminated all the internal vacuuming equipment. That leaves Create 2 with plenty of space inside for adding custom hardware components. You can easily put in an RBPi there, using pre-programmed routines to control the bot. Other alternate methods of direct control are tethering Create 2 to a laptop via the serial Mini-Din port using a serial-to-USB cable.

Based on the original Roomba 600, Create 2 is a round, 3.58-Kilo robot, measuring 340 mm in diameter and 92 mm in height. The market has several models of the Roomba robot, but Roomba 600 is the cheapest. iRobot offers 3D printing files that help you in adding electronics and peripherals to Create 2. They provide instructions for replacing the bin with a cargo tray that you can 3D print. They also supply a faceplate drill template.

Rechargeable batteries on the Create 2 allow a three-hour run before needing a recharge. As with the original Roomba 600, Create 2 will also return to its charging dock when it is time for a recharge. Sensors, such as IR transceivers on Create 2 enable it to escape cul-de-sacs and move around obstacles.

To interface with the Motorola MCU and related components, Create 2 comes with a programming environment, the Roomba OI or Open Interface. With the Roomba OI, a user can program the behavior, sounds, movements and read its sensors. The OI provides several commands for the sensors, cleaning, song, actuator and mode settings.

RBPi Model A is the most suitable for controlling Create 2 as you can run it off the serial connector of the robot. Power requirements for the Model A and its camera are just within the headroom of the on-board thermal resettable fuse of Create 2. It is also possible to work with RBPi models A+, B or B+; however, you will have to power them independently.

The RBPi will need an SD card of at least 4GB, pre-installed with the Raspbian Linux. Other hardware that you will require are an RBPi camera board, a switching DCDC converter, a micro-USB male cable, a 5V to 3.3V level converter and a USB to Wi-Fi module. iRobot provides several programming samples and starter projects with varying levels of difficulty.

New Generation BLDC Motor Drives

The introduction of Li-ion batteries and brushless DC or BLDC motors has opened up a new market for battery powered motor driven products. You will find brushless motors powered with rechargeable batteries being used in products such as uninterruptible power supplies, wheelchairs, e-bikes and other small electric vehicles and in small tools such as leaf blowers, chainsaws and drills. To take advantage of the integration of BLDC motors with Li-ion batteries for providing power requires updated MOSFET bridge drivers.

Although batteries such as lead-acid, Ni-MH and Ni-Cd are more popular, Li-ion batteries with their high energy density offer significant advantages over other battery technologies. Li-ion batteries typically offer two to three times the energy density as compared to what other conventional battery technologies currently offer. With higher energy density, users can make do with smaller battery packs that lead to lighter and more compact hand-held tools. Wheelchairs and e-bikes can operate for longer times without any increase in the physical size of their original battery pack.

However, there are some disadvantages associated with the high energy density of Li-ion batteries. It is customary to think of batteries as voltage sources, but for Li-ion batteries, this is not the case. Li-ion batteries have a significantly high internal inductance that generates considerable ripples on its voltage as a consequence of driving the motor with PWM or Pulse Width Modulation methods. Although this can be easily offset by adding sufficient capacitance across the MOSFET bridge, there can be enclosure limitations leading to prohibitive cost increases.

Low capacitance on the MOSFET bridge can lead to significant voltage ripples. For example, the ripple voltages found on a typical 18-20V Li-ion battery under heavy load can range from 5V at minimum to 36V at the maximum. Additionally, the battery voltage is likely to fall to an abysmally low value when the motor is overloaded to a stall or locked rotor condition. Therefore, presence of a controller is necessary to decide on how to react to such extreme operating conditions.

Compared to conventional brushed DC motors, BLDC motors offer significant advantages. For example, brushes limit the speed of a brushed DC motor, but the BLDC motor has no such limitations; the design of its rotor decides its maximum operating speed or RPM. Most applications do not require the full speed of the motor and a transmission with a gear reduction is used to bring down the motor speed to the desired RPM. A BLDC motor can rotate at significantly higher RPMs compared to the speed of a brushed motor. Therefore, the required torque at the output of the device can be achieved easily with a smaller BLDC motor and a corresponding transmission gear ratio.

As BLDC motors do not have brushes, they do not produce EMI as the brushed motors do. Additionally, the absence of brushes leads to lower maintenance and an increase in the efficiency of BLDC motors. On average, a BLDC motor is 1.5 times or more efficient than a brushed motor is. However, the drive electronics adds complexity to the application of a BLDC motor, requiring ICs to reduce component count, real estate and BOM costs, especially where space is a constraint.