Author Archives: Andi

Comparing Wireless Standards 802.11ad & 802.11ah

Wireless LAN standards were first set up for serving the needs of laptops and PCs in homes and offices. These were IEEE 802.11a and b, and these later served to allow connectivity in different places such as in shopping malls, Internet cafes, hotels and airports. The main functionality of the standards was providing a wireless link to a wired broadband connection for email and Web browsing.

Initially, speed of the broadband being a limited factor, a relatively slow wireless connection was enough. Therefore, 802.11a offered up to 54Mb/s at 5GHz and 802.11b up to 11Mb/s at 2.4GHz, with both frequencies being in the unlicensed spectrum bands. To reduce interference from other equipment, both standards were heavily encoded using forms of spread-spectrum transmission. In 2003, a new standard 802.11g used the 2.4GHz band maintaining the maximum data rate of 54MB/s.

However, by this time, people started realizing the need for higher throughput, especially with increased data sharing amongst connected devices in the home or small office. By 2009, a new standard, 802.11n came up, which improved the single channel data rate to over 100Mb/s. The new standard also introduced spatial streaming or MIMO, multiple inputs, multiple outputs. The new modems had up to four separate transmit and receive antennas, carrying independent data that was aggregated in the modulation/demodulation process.

However, new WLAN usage models were continually raising the demand on throughput, such as projection to TV or projectors, streaming from camcorders to displays, video streaming around the house, airplane docking, public safety mesh and more. Catering to these VHT or very high throughput demands made it necessary to generate two new standards 802.11ac (an extension of 802.11n) and 802.11ad.

Standard 802.11ac runs in the 5GHz band, providing a minimum of 500Mb/s on a single link and 1Gb/s overall throughput. On the other hand, 802.11ad provides up to 6.7Gb/s using a spectrum of about 2GHz at 60GHz, but at short range. Operation at high frequencies limits the transmission range and obstacle penetrating capacity of the signals.

With the proliferation of local sensor networks working on low power, billions of IoT or Internet of Things and M2M or machine-to-machine device connections, a new standard is now deemed necessary. This new standard is the 802.11ah, working in the license-exempt 1GHz band and its final version is expected in 2016.

Standard 802.11ah is a down-clocked version of the 802.11ac standard. While adding some enhancements in the MAC and PHY layers, the new standard offers advantages such as power savings, multiple station support, better coverage and mobile reception.

For the standard 802.11ah, three main use-case categories are under consideration. These are Wi-Fi extended range networks, backhaul networks for sensors and meter data and sensor networks. The standard 802.11ah extends the transmission range with 1 and 2MHz mandatory modes, allows ultra-low power consumption, thereby offering multi-year battery life for large scale sensor networks and is optimized for long sleep times while handling small packet sizes.

Therefore, with 802.11ah, you can have several devices such as light sensors, temperature sensors and smart meters set up throughout the home, enabling your home devices and appliances to be considered smart.

Why is WAM Better than QAM?

Almost all wired and wireless applications today use the QAM or Quadrature Amplitude Modulation. These include the Fiber infrastructure, Wireless Backhaul, DSL modems, Cable modems, Cable TV, Satellite TV, Wi-Fi, Cellular and numerous other communication systems.

QAM systems use two AM or Amplitude-Modulated signals combined into a single channel – increasing the effective data rate while using the same amount of bandwidth. A QAM signal has two carriers, each with the same frequency, but differing in phase by 90 degrees. The term quadrature arises from the difference of one quarter of a cycle. If you call one of the amplitude-modulated signals the in-phase signal, the other becomes the quadrature signal.

Typically, the quadrature signal, multiplied with a sine wave, is subtracted from the in-phase signal multiplied with a cosine wave. The resulting signal is then amplified and transmitted over the air, wires or cables.

At the destination, a reversal of operations takes place by multiplying the in-phase output by a cosine wave and the quadrature output by a sine wave. Filtering them individually leaves only the lower frequencies. As these operations are entirely reversible, they ensure the preservation and exact recovery of the originally transmitted data.

Proliferation of communications devices and systems is putting considerable stress on bandwidth availability. For the past 40 years, QAM has completely dominated the advanced communication systems. Consequently, there are over seven billion connected devices using QAM technology.

Lately, a new Wave Amplitude Modulation or WAM technology is challenging this dominance of QAM. MagnaCom, who has patented and trademarked the WAM technology, claims the use of WAM can enhance nearly all wired and wireless applications. Additionally, WAM being backward compatible to legacy QAM systems, its use will not require any changes to the RF, radio or the antenna.

WAM technology uses a purely digital modulation scheme and is scalable. While using the same analog and RF circuits that QAM does, WAM needs no redesign and consumes only about one square millimeter space in modern semiconductor design. As the WAM technology is scalable, designers can now implement a smaller and lower cost solution.

Speaking technically, WAM represents a multi-dimensional signal construction technique working in the Euclidean domain. For the first time, designers can break the orthogonal signal construction. This provides an optimal handling of nonlinear distortion, increasing the system capacity. Overall, there is significant improvement over the legacy QAM systems.

The benefits of using WAM include a system gain advantage of over 10dB, while increasing the distance covered by over four times at half the power. This results in double the spectrum savings, offering better noise tolerance, major increase in speed and easier design at lower costs. Additionally, there is no need to replace any of the existing QAM equipment, as WAM is entirely backward compatible with QAM.

Compared to QAM, the new technology modulates information differently resulting in major system benefits. The use of spectral compression allows WAM to improve spectral efficiency by enabling an increase of the signaling rate. This allows reduction of complexity to a lower order. The use of nonlinear signal shaping by WAM offers inherent diversity of time and frequency domains, resulting in a lower cost and lower power design of the transmitter.

The Rezence Standard for Wireless Charging

Typical wireless charging technologies depend on magnetic induction to transfer power from a ‘mat’ to the specially designed mobile device under charge. However, Rezence holds forth the concept of spatial freedom, which extends the wireless power applications to go beyond the mat to any surface and into almost any mobile device. Unlike magnetic induction, Rezence works on the principles of magnetic resonance. With Rezence, the wireless charging ecosystem has a number of unique benefits.

The Rezence standard allows superior charging range. This amounts to a true drop and go charging experience, with charging taking place through almost any surface and through several objects such as clothing and books. The new standard is able to charge many devices simultaneously even when they have different power requirements – including Bluetooth handsets, laptops, tablets and smartphones.

The Rezence standard is an ideal choice for charging in situations involving kitchen appliances, retail and automotive applications. Rezence powered charging surfaces do not conflict with metallic objects such as coins and keys. Additionally, use of this new technology minimizes the hardware requirements of the manufacturer as it leverages the existing Bluetooth Smart v4.0 technology. Therefore, users can have Smart Charging Zones in the future.

The world already has multiple wireless power standards. Ultimately, the consumer will decide the most popular wireless power technology it will use. Presently, wireless power is undergoing the same process of certification and testing that other technologies such as 4G, 3G, Bluetooth and Wi-Fi have had to go through. Although technology selection and adoption is primarily a market-based mechanism, development of standards is a process separate and distinct from the former.

The Rezence standard is actually the released version 1.0 of the A4WP specifications, released in January 2013. Only when an outside standards organization accepts a specification, it is truly considered a standard. Therefore, organizations, including the A4WP, sometimes use the two terms interchangeably – as a matter of semantics.

Other organizations, including A4WP, are technically at the stage of development of the specifications. Additionally, A4WP is working actively with standard bodies around the world to ensure their technology will be adopted regionally as well.

Various organizations have promoted their wireless power technologies over several years. However, most of the older technologies have proven to be impractical in real-world applications. For example, they work well for single devices when these are positioned perfectly on a charging mat. Moreover, the charging range remains limited and the inability to handle differing power requirements at the same time makes this technology impractical.

When working with wireless power system design, heating and power absorption are dependent upon metal thickness and magnetic field strength. The older wireless inductive charging systems mostly use 115 KHz, at which frequency common household objects such as metal stickers, paper clips and even coins have higher power absorption and consequently, heat up. The Rezence system, with its operating frequency of 6.78 MHZ, does not cause similar heating up of common metal objects.

Therefore, unlike the older charging systems, in the Rezence method of charging, common metal objects do not heat up to create a hazard or trigger the termination of the charging process.

Get VGA from your Raspberry Pi

Those of you who use the single board computer, the Raspberry Pi or RBPi, know that it has two video outputs. It offers high definition video via the HDMI port and a composite video via the RCA port. For viewing the output of the RBPi on a VGA monitor, one must use an HDMI to VGA adapter or similar. However, there is a simpler and cheaper method now available – the Gert VGA 666.

The Gert VGA 666 is a breakout/add-on board, useful only for the RBPi Model B+. The board does not work on other RBPi Models such as A and B, as it requires the additional GPIO pins that are only available on the Model B+. Gert van Loo has designed this Gert VGA 666 board and has released it as an open source hardware design. Incidentally, Gert van Loo was associated with the initial design of the original RBPi and is one of the architects of the BCM2835 chip that forms the heart of the RBPi.

The Gert VGA 666 is a useful and neat solution for attaching a VGA monitor/screen to your RBPi. Additionally, this works out much cheaper than buying a converter or adapter for converting HDMI to VGA. A parallel interface from the GPIO pins drives the hardware natively for the VGA connection, using the same CPU load as the HDMI connection does. Users have the added advantage of setting up a dual screen, one for HDMI and the other for VGA. This is possible as the RBPi can drive both interfaces at the same time. With no CPU load, you can expect a VGA video display with resolution of 1080p60 or 640×480.

You can buy this adapter in the form of a kit, comprising the PCB for Gert VGA 666, a 40-pin header connector for the GPIO, a 15-pin female VGA connector, 20 through-hole resistors and two Pi supply stickers. When assembled and fitted on the RBPi, the board uses up nearly all the GPIO pins on the Model B+. Therefore, it will not be possible to use any other add-on boards at the same time when using the VGA adapter.

The decision to offer the adapter as a kit stems from the requirement of meeting EMC compatibility regulations. A fully assembled board would be required to meet most EMC regulations. However, these regulations do not cover the kit, as it is a homemade electronic product.

After soldering the board, plug it into the RBPi and power up the combination. However, the adapter does not work directly and you will need an intermediate solution for video output. You can use either an HDMI or a DVI-D monitor. If that is not available, use a composite monitor or TV via the RCA port. However, using the composite video means you will need to program the NOOBS on the RBPi.

After booting, you must install the necessary drivers for the Gert VGA 666 adapter. This requires an Internet connection, preferably via an Ethernet connection. If you simply plug in the Ethernet cable, Raspbian will automatically start to use it.

Adding Memory to the Raspberry Pi

Although the memory onboard the Single Board Computer Raspberry Pi or RBPi is sufficient for most applications, some may feel the necessity of expanding the storage capacity. The options provided on the RBPi are limited, as the USB ports often engage a keyboard, a mouse or a game controller and the SD card slot holds only a single device.

The most obvious option for expanding the storage capacity on the RBPi is through the USB ports. However, tying up ports with a USB hard disk drive or flash drive can run into difficulty if you need the port for plugging in another USB device. One way of getting around this problem is by using powered USB hubs. It is important to realize the RBPi cannot supply enough power for driving the hub.

Using a powered USB hub makes it easy to add USB devices to your RBPi, including additional storage. However, you must consider a few things when expanding storage on your RBPi. In reality, there are only two common USB storage options available – flash drive and hard disk drive. Nevertheless, you may also consider a card-expanding trick for the Raspbian operating system for your RBPi. These are the three primary options available for expanding storage on your SBC. Apart from this, you may also consider using secondary storage devices such as networked drives, USB DVD-r drives and NAS drives.

The SD card in the RBPi acts as the main storage option – use an SDHC card for best results. It is a boot device acting as the general storage and from which the operating system also runs. You may think of the SD card as a replacement for the HDD of a regular desktop computer, more like an SSD or Solid State Drive, as it has no moving parts and uses very low energy.

By default, Raspbian, the standard Operating System of the RBPi, is designed to run from a 2 GB SD card. Therefore, when you flash the Raspbian image, the SD card will have a partition of 2 GB, with the balance of the card memory remaining unused.

To get around this, you must use the expand file system feature included in the raspi-config screen in Raspbian. This enables expanding the size of the partition to the maximum capacity of the SD card.

When you insert your flash drive into a USB port of the RBPi, you may be surprised it does not have the same effect as it does in a regular Ubuntu or Windows computer. It is not enough to insert the flash drive, Raspbian expects you to mount the device manually before you can use it as an additional USB storage device. However, before you can mount it, you must know the exact device name that Raspbian has assigned to the drive.

For this, the command necessary is: sudo ls /dev/sd*. The command “sudo” gives you temporary administrative status, “ls” allows listing the devices and “/dev/sd*” lists the devices seen by Raspbian. With this command, you will know the number Raspbian has assigned for your drive.

Now, you can mount the USB flash drive and use it as an additional storage device with the command: sudo mount -t vfat /dev/[USB DEVICE NUMBER] /mnt/usb.

RS-485 – The Wired Communication Standard

TIA/EIA-485 is a popular wired communication standard published by the TIA/EIA or the Telecommunications Industry Association/Electronics Industries Association. This standard is also known as the RS-485 and uses differential signaling enables the standard to transmit data over long distances for factory automation and in noisy industrial environments.

This is because differential signaling allows rejection of common mode noise, while the twisted pair cable ensures the most received interference comes as common mode. When used over long distances, the standards improve the chances for ground potential differences, while the wide CMR or common mode range of the standard ensures that the network operates satisfactorily, even when there are large common mode voltages present.

In practice, both the transmitter and the receiver have non-inverting and inverting pins. Bidirectional communication over a single cable can use half-duplex devices, where the corresponding Receiver and Transmitter terminals connect to the same IC pins. Networks can also use two cables for bidirectional communication, and employing full-duplex devices, only, the Receiver and Transmitter terminals now must connect to separate pins.

The number of transceiver models available in the market is huge, and that makes it a challenge picking out the best and most cost-effective device for a specific application. That requires considering the common design considerations, examining the electrostatic discharge (ESD) protection and comparing the Human Body Model. Other important points to be considered are the over voltage protection (OVP) and data skew in case of high-speed transmissions.

Requirements of RS-485

Although the published standard for the RS-485 is over 14 pages long, the most important requirements are:

The differential output voltage generated must be over ±1.5V, while the receiver must be capable of detecting signals with a minimum of ±200mV. This combination makes sure the devices can tolerate attenuation from long cables and there is a robust noise margin available.

As the standard allows multiple drivers on the bus, each transmitter must have an enable pin giving it tri-state output capability. This ensures true bidirectional transmission over a single cable.

Transmitters must have high output current capability to drive long cables and cables with double termination, especially for high-speed bidirectional transmission.

The CMR should be at least -7V to +12V. This allows using RS-485 over networks of 1220 m or 4000 feet. Long distances can involve ground potential differences and a high CMR helps to tolerate them in noisy environments. Additionally, devices with different supply voltages can also communicate on the same bus because of a large CMR.

The receiver input resistance must be over 12KΩ. According to the standard, there can be 32 devices on a bus.

The Basic RS-485 Transceiver

People often use less expensive RS-485 transceivers for simple, short, low-node-count networks. This works because short networks do not involve much CMV or common mode voltage and OVP, and they can work with the CMR specified by the standard.

When there are less than 32 modes in the network, fractional unit load devices are not necessary. Moreover, when cables are not frequently connected and disconnected, ESD protection is also not necessary. However, most basic devices now include the ±8 to ±15 KV Human Body Model for ESD protection.

Solid State Drives – Why Are They So Fast?

For most people, an HDD or hard disk drive inside their computer is the flat broad box that stores their Operating System, files, documents, and other essentials. So far, not many users were aware of the inner workings of their HDD. Lately, with speeds of computers going up many folds, people have started looking at alternatives for the HDD – the SSD or the Solid State Drive.

Whatever else you change in your computer system, the general experience remains the same. For example, you may get a new display, add more RAM or install a new graphics card. Barring a few moments of exhilaration, you do not experience the constant euphoria that you get when you replace your regular HDD with an SSD.

An SSD suddenly transforms your computer into a high-speed demon. Additionally, you get this feeling every time you use the computer. Even if you do not realize this increase in speed with an SSD, you will appreciate it as soon as you have to revert to operating a computer with a regular HDD. It is truly amazing the way this new technology is helping to transform our computer experience.

To understand the functioning of SSDs, it is necessary to know the computer’s inner structure or architecture regarding its memory. A computer’s memory architecture is actually made up of three sections: the cache, the temporary memory and the actual memory storage itself.

The CPU or the Central Processing Unit of a computer is intimately connected to the cache memory and accesses it almost instantaneously. As the computer operates, the CPU uses the cache memory as a sort of scratch pad for all its interim calculations and procedures.

The temporary memory, also known as the RAM or Random Access Memory of a computer is the place where the CPU stores information related to all the active programs and running processes. Although the CPU can access the RAM at high speeds, the access is slower than that for cache memory.

For permanent storage, your computer uses the memory within the HDD or the SSD. These may be programs, documents, configuration files, movie files, songs, and many more. Unlike cache and RAM, an HDD or an SSD retains its contents even when the computer has been shut down.

When people replace their HDD with an SSD, their computer operates at a higher speed even when they have not updated their cache or RAM. This is fundamentally because of the difference in the way of working of an HDD and an SSD.

An HDD is essentially an electromagnetic device. Inside, there is a motor to spin the several magnetic platters stacked one on top of the other. Before the CPU can read data from the magnetic plates, they have to spin until the right sector comes under the reading heads, which then move in to read from the exact location. All this mechanical movement takes time.

On the other hand, the SSD, being an all-electronic device, involves no mechanical movements. It uses a grid of electrical cells to store and retrieve data. Moreover, these cells are further separated into sections called pages. Further, pages are clumped together to form blocks. All this contributes to the fantastic speed of an SSD.

A New Operating System for the Raspberry Pi

The Single Board Computer, the Raspberry Pi or RBPi runs on a version of the popular operating system Linux – the Raspbian. Although there are other versions of Linux equally capable of running on the RBPi, another operating system is in the making. Not ready yet, the Tizen 3.0, is being ported for the RBPi Model 2.

While not attracting a lot of attention, Tizen is another Linux-based operating system into which huge resources are being pumped to make it more popular for the RBPi. The Linux Foundation is providing all the guidance for its development along with help from a number of companies led by Samsung.

Samsung is pushing for the adoption of Tizen, which, until now, it has implemented only on some low-end devices including a watch. Samsung wants Tizen as a replacement for the Android OS developed by Google, mainly because it has to pay royalties to Google. Hence, Tizen 3.0 for the RBPi 2 is an important step for Samsung.

However, the trouble is the community is not very aware of Tizen. The main issue is people do not even know of its existence. By making it available for the RBPi, an SBC already in use by over a million people, Samsung expects to make Tizen more popular.

The Open Source Group of Samsung is currently attempting to port Tizen 3.0 to the RBPi 2. Their goal is to run a fully functional Tizen 3.0 on the RBPi 2. They have chosen the RBPi 2 as their base system, as this is the most popular SBC that more than five million people are using.

Although Tizen 3.0 is presently working on the RBPi 2, there are still a number of issues that Samsung has yet to sort out. For example, installation of applications is one of the biggest issues they need to overcome. However, one can assess the speed of the porting process, as the developers have already managed to enable the 3D acceleration on the platform. However, there is still no indication of when Tizen 3.0 may be available in a stable form, and Tizen 3.0 is still in Beta stages.

In its stable form, Tizen 3.0 will ship with Linux Kernel 4.1 and Wayland in place of the familiar X-windowing system. Linux Foundation, the developers of the open source Linux operating system, aims to run it on phones, tablets, watches, and in-vehicle entertainment systems. They claim Tizen 3.0 will bring some interesting changes.

Although many companies are still evaluating their choices, some of them have chosen to support Tizen as they are looking for alternatives to Android. They know it is not an easy task to move people away from Android, just as Microsoft has discovered to their chagrin.

The Linux Foundation is building Tizen for various profiles and is making the current iteration for the TV and Mobile. It will support 64-bit systems and provide a replacement for the X-server in the form of Wayland. Additionally, Tizen will come with Chromium-efl, a generic policy manager, in place of Webkit2.

Detecting Plunger Movement in DC solenoids

DC solenoids are used in many applications that require movement of a part to be arrested in some way, to be released when an event occurs. An example of such an application would be the garage door. A solenoid keeps the garage door locked down until a signal reaches it to release the door – to allow a vehicle to go in or out – a simple operation as long as the door operates as intended. However, there may be times when the door does not, and one of the reasons could be the solenoid failing to activate.

If the solenoid is easily accessible, the movement of its plunger or parts attached to it can indicate whether it is functioning as intended. However, some solenoids must be located at remote locations that are difficult to reach and therefore, pose difficulties for visual fault diagnosis. However, there is a way to remotely sense whether there is proper plunger movement when the solenoid is switched on.

Many types of valves, relays and contactors use electromechanical solenoids. Typically, these operate from 12-24 V DC and 110-230 V AC systems, consuming power ranging from 8-20 Watts. Electromechanical solenoids consist of a movable iron or steel slug named the plunger or armature, and an electromagnetically inductive coil wound around it.

During actuation, when the plunger has to be pulled into the coil, the solenoid needs high current. Once actuated, the solenoid can hold the armature in the pulled-in position with only about 30% of its nominal current – this is called the hold current. If the solenoid coil consistently operates at the nominal current, high power dissipation raises the temperature of the coil and plunger. Therefore, immediately after the plunger has moved, reducing the current to the hold current helps to reduce power consumption and minimize the temperature rise in the solenoid. This is another reason to detect the plunger movement in a solenoid.

Two popular methods used to detect plunger movement depend on one, Hall sensors and two, on excitation current profile. However, Hall sensors cannot detect faulty or slow movement of the plunger, while the excitation current profile depends on the working temperature of the solenoid. Therefore, these are not particularly suitable for detecting faulty operation of solenoids.

A third and more reliable method of detecting plunger movement in solenoids depends on the current profile from the Back EMF generated by the movement. The solenoid operates when an excitation voltage energizes the solenoid coil. Current passing through the coil causes a distribution of magnetic flux through the plunger. The current increases until the magnetic flux is strong enough to move the plunger.

As soon as the plunger starts to move, its movement produces a magnetic flux in opposition to the main magnetic flux. This induces back EMF in the solenoid coil opposing the excitation voltage – momentarily reducing the current through the coil. Note that this reduction happens only because of the plunger movement and not because of anything else.

Temperature does not affect the dip seen in the current due to plunger movement. Hence, this method is a reliable indication of detecting plunger movement in solenoids.

Raspberry Pi Can Keep Your Plants Happy

Those who like indoor plants know how important it is to maintain a proper atmosphere for the plants to grow happily. Only a few parameters are important – air humidity, air temperature and soil moisture apart from adequate sunshine. However, it is rare for people to be able to monitor the health and well-being of their flora personally, given the busy schedules.

That is where a single board computer such as the Raspberry Pi or RBPi can help. Being flexible in setting up and connecting to the various sensors necessary, this SBC not only looks after the plants, but also alerts you with SMS and via email whenever the situation differs from the normal. This project also has an app, Plant Friends, for your Android phone, so that you are up to date on the real-time and historical parameter data on your plants. The project consists of three main components – the sensor nodes, the base station and the app.

You need a sensor node for each plant. Each of these sensor nodes consist of an Arduino clone called Moteino fitted with an RF transceiver, a battery meter, a temperature sensor, a humidity sensor and a sensor for soil moisture. The sensor nodes collect the readings from all the sensors and transmit the data using the transceiver to the base station. The sensors and the base station are connected via the 915MHz ISM band.

For this project, users must be slightly above the beginner level. Some basic experience with Arduino hardware and Arduino IDE will be necessary – for installing libraries, making LEDs blink, etc. Additionally, experience in wielding a soldering iron is also necessary. On the RBPi side, it is essential to be familiar with the basic knowledge of the SBC and with installing the Raspbian OS.

The Plant Friends system has several advantages. It reminds you to water your plants and sends you an alert via email and/or SMS. It works for multiple plants at the same time, even if they are in different rooms of your home. Since wires are a minimum and all components of the system are of a reasonable size, you can move the plants and the system freely about the home.

The entire system consumes low power and therefore runs on batteries. Typically, battery swaps are necessary every 4 to 6 months. The electronics is low-maintenance as it is housed in a moisture-proof enclosure. The best part of the system is the Android app, as it allows monitoring from anywhere in the world.

An RBPi, model B, is used for the project, although a model A will work equally well. However, model B has more RAM and an Ethernet port, which may be necessary for flexibility. A USB Wi-Fi adapter helps to connect to the internet.

For each sensor node, you will need a holder for four AA type rechargeable batteries. In addition, you will need a combined sensor for temperature and humidity. For sensing the moisture in the soil, you may use a soil probe consisting of a PCB with exposed traces. However, ensure there is no lead involved.