Monthly Archives: November 2014

Is solid state memory better than magnetic memory?

Moore’s Law, or more specifically, Gordon Moore, predicted in 1965 that transistor density in chips would double about every two years. For the past 50 years, this observation has held true and is the fundamental driving force behind most advances in technology leading to computers becoming smaller, faster, cheaper and more reliable. Typically, Moore’s Law has resulted in solid-state memory becoming smaller and cheaper. However, the ever-increasing need for greater storage capacity has had manufacturers sacrificing reliability and performance in some cases. Apparently, the solid-state memory area presents a major dichotomy.

The solid-state memory arena has seen exponential growth in the past 15 years. Many have not even seen a floppy disk as it was replaced almost overnight by the thumb drives. These solid-state drives also made ZIP drives disappear shortly thereafter. With the increase in digital storage in smartphones, CD players and CD drives became obsolete.

There is no doubt that solid state media is superior to the mechanical, rotating magnetic memory media, which we commonly known as the Hard Disk Drive, in most applications. However, surprising as it may seem, the solid-state media has some characteristics that do not allow it to follow Moore’ Law, making it less than optimal for some types of applications.

For example, flash memory is known to have a limited life, as it wears out over time. With the technological improvements we have been witnessing year-over-year, one would assume that flash endurance has gradually improved; however, reality says otherwise. In the ancient days (read 8 years ago), SLC NAND memory was rated to give 100,000 write/erase cycles. Currently manufactured SLC NAND memory has a life of 50,000 write/erase cycles. In the case of MLC NAND memory, the reduction is even more dramatic. Older MLC NAND memories had a life of about 10,000 write/erase cycles, current MLC NAND memories are limited to 3,000 write/erase cycles.

That means newer flash memories wear out more quickly, and in addition, do not perform as well. This can be attributed in part to the stronger EDC or Error Detection and Correction requirements for newer flash. This is evident from the decreasing write/erase cycles and the increasing ECC or Error Correcting Code requirements following a reduction in the NAND flash lithography.

This reduced lifespan may not be so much of a problem for many consumer devices. For example, MLC NAND memory within a cell phone is likely to outlast the mobile phone itself; assuming an original owner lifespan of two years.

Industrial devices using solid-state media would face a different story. Typically, devices manufactured for industrial use have an expected lifetime of 10, 15 or more years. That makes endurance of solid-state media in such devices very critical.

Although flash lifespan is measured in cycles of write/erase, interestingly, only the erase operation counts against the life of flash memory. That means, you could use up the flash simply by erasing it repeatedly, while not writing anything to it at all. It does not matter whether you write a small or a large amount of data; what matters is how many times you erased it.

What are Zener, Schottky and Avalanche Diodes?

Diodes are very commonly used semiconductor devices. They are mostly used as rectifiers for converting Alternating to Direct current. Their special characteristic of allowing current flow in only one direction makes them indispensable as rectifiers. Apart from rectification, various types of diodes are available for different purposes such as for generating light, microwaves, infrared rays and for various types of switching at high speeds.

For example, the power supply industry has been moving towards high speed switching because higher speed reduces the volume of magnetics used, which ultimately reduces the bulk and price of the units. For switching at high frequencies, diodes are also required to react at high speeds. Schottky diodes are ideal for this purpose, as their switching speeds approach nearly zero time. Additionally, they have very low forward voltage drop, which increases their operating efficiency.

As their switching speed is very high, Schottky diodes recover very fast when the current reverses, resulting in only a very small reverse current overshoot. Although the maximum average rectified currents for Schottky diodes are popularly in the range of 1, 2, 3 and 10 Amperes, Schottky diodes that can handle up to 400A are also available. The corresponding maximum reverse voltage for Schottky diodes can range from 8 to 1200V, with most popular values being 30, 40, 60 and 100 Volts.

Another very versatile type of diode used in the power supply industry is the Zener diode. All diodes conduct current only when they are forward biased. When they are reverse biased, there is only a very small leakage current flowing. As the reverse voltage increases to beyond the rated peak inverse voltage of the diode, the diode can breakdown irreversibly and with permanent damage.

A special type of diode, called the Zener diode, blocks the current through it up to a certain voltage when reverse biased. Beyond this reverse breakdown voltage, it allows the current to flow even when biased in the reverse. That makes this type of diode very useful for generating reference voltages, clamping signals to specific voltage levels or ranges and more generally acting as a voltage regulator.

Zener diodes are manufactured to have their reverse breakdown voltage occur at specific, well-defined voltage levels. They are also able to operate continuously in the breakdown mode, without damage. Commonly, Zener diodes are available with breakdown voltage between 1.8 to 200 Volts.

Another special type of diode called the Avalanche diode is used for circuit protection. When the reverse bias voltage starts to increase, the diode intentionally starts an avalanche effect at a predetermined voltage. This causes the diode to start conducting current without damaging itself, and diverts the excessive power away from the circuit to its ground.

Designers use the Avalanche diode more as a protection to circuits against unwanted or unexpected voltages that might otherwise have caused extensive damage. Usually, the cathode of the diode connects to the circuit while its anode is connected to the ground. Therefore, the Avalanche diode bypasses any threatening voltage directly to the ground, thus saving the circuit. In this configuration, Avalanche diodes act as clamping diodes fixing the maximum voltage that the circuit will experience.

Power Your Smartphone by Your Sweat

Anyone can power a smartphone by manually running a small electric generator. Without a doubt, some will sweat in the process. However, this technology is somewhat different. Here, a small tattoo will detect whether you are sweating (for whatever reasons) and generate power directly from your sweat.

Researchers at the University of California in San Diego have developed a sensor to monitor a person’s progress when he or she is exercising. Although this is not something new, but the sensor is in the form of a temporary tattoo and it also doubles as a bio-battery. It can detect when the person is perspiring and produce power from it.

According to one of the researchers, Wenzhao Jia, when a person sweats, one of the naturally occurring chemicals is lactate. The sensor detects and responds to lactate, which is a very important indicator of how the person is progressing with the exercise. That is because with more intense exercise, the body produces increasing amounts of lactate. With strenuous physical activity, the body activates a process called glycosis, which produces energy and lactate.

Professional athletes test their performance by monitoring the levels of lactate they produce. This is one of the ways they evaluate their training program and their fitness. Moreover, some conditions cause abnormally high lactate levels in the body such as lung or heart diseases. Doctors measure the lactate levels during exercise testing of their patients. However, lactate testing is intrusive because it needs blood samples of the person to be collected at different times during exercising and then analyzed. Therefore, the current process is inconvenient.

The team led by Joseph Wang, of which Jia is a member, has developed a faster, easier and more comfortable way of measuring lactate during exercise. They imprinted the biosensor onto a temporary tattoo paper. The sensor has an enzyme that strips electrons from the lactate produced during the workout and generates a weak electrical current.

In practice, the tattoo is applied to the upper arm of the person exercising. When the person exercises on a stationary bicycle, it is easy to monitor the performance against increasing resistance levels. The researchers were able to monitor 10 health volunteers for 30 minutes and checked the lactate levels in their sweat over time and with changes in intensity of their exercise.

One of the startling discoveries from the research was that different people produced different amounts of electricity. Surprisingly, people who exercised less than once per week and hence were less fit produced more power as compared to moderately fit people who exercised between one and three times per week. Those who were the most fit, working out more than three times per week, produced the least amount of power.

According to the researchers, less-fit people become fatigued sooner and glycosis kicks in earlier for them. Therefore, they produce more lactate because of their increased fatigue. In the low-fitness group, the maximum amount of energy produced by a person was 70μW for every square cm of skin. Although the power generated is not very high, the researchers are confident of eventually increasing it to power small gadgets.

e-whisker: how about a hairy robot?

No matter how quietly you approach a cat from behind, it is sure to detect your presence almost always. It is not its acute sense of hearing or smell that helps the cat, but its whiskers. They can sense the tiniest air turbulence caused by your movements. In fact, such tactile feedback gathered by most animals and insects with their whiskers and antennae makes it very efficient to coordinate their movements at striking speeds.

Such high-speed reflexes are possible because the feedback from the sensors is directly coupled to the insects’ locomotive actions and does not have to pass through much processing. Actually, there is absolutely no central processing or environmental data analytics to impede the information from multiple data sources.

Several insects and certain mammals use their antennae and whiskers – the hair-like tactile sensors – to monitor wind turbulences and for navigating around obstacles in tight spaces. Researchers at Berkeley Lab found this a new source of inspiration and they came up with e-whiskers or electronic whiskers. These e-whiskers are based on flexible polymer fibers with high aspect ratio, coated with a mixture of silver nano-particles and carbon nanotubes.

According to the lead researcher Ali Javed of the Materials Sciences Division of Berkley Lab, tests of these whiskers show they are ten times more sensitive compared to all previously reported resistive or capacitive pressure sensors. In addition, by changing the composition of the whiskers, researchers could manipulate their characteristics.

For example, a change the ratio of the nanoparticles and the nanotubes resulted in a change in resistance from a minimal 10% to around 260% with the application of a 2.4% strain on the whiskers. Scientists monitored the resistivity change by hooking up the e-whiskers arrays to a computer. The carbon nanotubes give the e-whiskers their excellent bendability with their conductive network matrix. On the other hand, the silver nanoparticles contribute to the conductivity of the coated fibers giving them the high mechanical strain sensitivity. That makes the e-whiskers so sensitive to pressures as low as 1Pa, representing 8%.

When scientists increased the weight content of the silver nanoparticles, the strain sensitivity of the e-whiskers was enhanced. This can be explained as the change in the distance between the silver nanoparticles in the film directly affecting the probability of electrons tunneling through neighboring conductive nanoparticles. As compressive and tensile stresses cause the gaps between the nanoparticles to become smaller and larger compared with the relaxed state, the e-whisker is able to detect the direction of bending.

Scientists at Berkley Lab built the e-whisker by patterning it with a micro-etched silicon mold with trenches which were 15mm long, 250µm wide, and 250µm deep. They then coated the fiber with the carbon nanotube and silver nanoparticle composite and cured it. The researchers claim that the whiskers can be made smaller still – they would have to use the MEMS processes for that.

With this e-whisker array of seven vertically placed fibers, scientists demonstrated mapping a weak wind flow (1m/s) in three dimensions as a proof-of-concept. More applications are planned for the future.

Add-On Board on Raspberry Pi Can Control Entire Building

If you thought that the tiny credit card sized single board computer, the inexpensive Raspberry Pi or RBPi was only good for home automation and no more, you may be surprised to learn that it can do a lot more – control an entire building, for instance. Of course, it will need assistance in the form of an add-on board, such as the UniPi.

Very often, people have used the RBPi for automatically controlling their sprinkler systems, the lighting in their house or even for guarding their homes while they are away on a holiday. Commercial systems have often used the RBPi as a prototype. A Czech startup with the same name, the UniPi, is now offering a baseboard and an add-on board for building automation that you can use with your RBPi.

The RBPi plugs into the UniPi baseboard via its 26-pin expansion connector. With this combination of the UniPi and RBPi, you can control the entire functions of a modest sized building. For example, it can read signals from different sensors such as humidity, temperature and/or status of alarms and switches to control gates, sprinklers, curtains, doors, lights and more.

To help with the sensors and control, UniPi is also offering a passive sensor hub that comes along with a free temperature sensor and an optional waterproof temperature sensor, should you need one. The UniPi baseboard has 14 opto-isolated digital inputs that can read sensor signals from 5 to 20V and show the status with LEDs. The board can read 0-10V signals on two analog inputs and output 0-10V on another analog output. On-board is a 12V power supply, along with eight changeover relays, which can switch 5A at 230VAC. That makes UniPi adequate for controlling power to sensor devices for an entire building.

For reading sensors, the UniPi is equipped with a single-channel 1-Wire interface. That makes it convenient to connect hundreds of humidity and temperature sensors. UniPi even allows the second I2C port of the RBPi and its UART to be extended with 5V level converters and provides ESD protection for them. Power loss does not affect the timing of the board as it has an RTC or real-time clock module for keeping time. UniPi is compatible with the RBPi model B Rev2 and it is possible to configure it for the Rev1 model as well. However, UniPi does not mention the possibility of compatibility with the latest model of the RBPi, the 40-pin model B+.

On their website, UniPi offers numerous tutorials based on C/Python libraries for people wanting to develop UniPi applications on the Linux-based RBPi. For example, there is the Webiopi, which is specifically useful for connectivity with the Python Internet of Things. Additionally, there is the Wiringpi library for GPIO interfacing and other libraries for Adafruit.

UniPi is offering its baseboard with on RJ45 connector for the 1-Wire interface and two RJ11 connectors – one for the UART and the other for the external I2C. It has one P1 header and another P5 header along with a 2.1mm standard power connector and an RBPi power jumper.