About Mary Wilson

Mary Wilson is Circuit Cellar's Managing Editor. You can reach her at mwilson@circuitcellar.com and @mgeditor_cc.

Remote Control and Monitoring of Household Devices

Raul Alvarez, a freelance electronic engineer from Bolivia, has long been interested in wireless device-to-device communication.

“So when the idea of the Internet of Things (IoT) came around, it was like rediscovering the Internet,” he says.

I’m guessing that his dual fascinations with wireless and the IoT inspired his Home Energy Gateway project, which won second place in the 2012 DesignSpark chipKIT challenge administered by Circuit Cellar.

“The system enables users to remotely monitor their home’s power consumption and control household devices (e.g., fans, lights, coffee machines, etc.),” Alvarez says. “The main system consists of an embedded gateway/web server that, aside from its ability to communicate over the Internet, is also capable of local communications over a home area wireless network.”

Alvarez catered to his interests by creating his own wireless communication protocol for the system.

“As a learning exercise, I specifically developed the communication protocol I used in the home area wireless network from scratch,” he says. “I used low-cost RF transceivers to implement the protocol. It is simple and provides just the core functionality necessary for the application.”

Figure1: The Home Energy Gateway includes a Hope Microelectronics RFM12B transceiver, a Digilent chipKIT Max32 board, and a Microchip Technology ENC28J60 Ethernet controller chip.

Figure 1: The Home Energy Gateway includes a Hope Microelectronics RFM12B transceiver, a Digilent chipKIT Max32 board, and a Microchip Technology ENC28J60 Ethernet controller chip.

Alvarez writes about his project in the February issue of Circuit Cellar. His article concentrates on the project’s TCI/IP communications aspects and explains how they interface.

Here is his article’s overview of how the system functions and its primary hardware components:

Figure 1 shows the system’s block diagram and functional configuration. The smart meter collects the entire house’s power consumption information and sends that data every time it is requested by the gateway. In turn, the smart plugs receive commands from the gateway to turn on/off the household devices attached to them. This happens every time the user turns on/off the controls in the web control panel.

Photo 1: These are the three smart node hardware prototypes: upper left,  smart plug;  upper right, a second smart plug in a breadboard; and at bottom,  the smart meter.

Photo 1: These are the three smart node hardware prototypes: upper left, smart plug; upper right, a second smart plug in a breadboard; and at bottom, the smart meter.

I used the simple wireless protocol (SWP) I developed for this project for all of the home area wireless network’s wireless communications. I used low-cost Hope Microelectronics 433-/868-/915-MHz RFM12B transceivers to implement the smart nodes. (see Photo 1)
The wireless network is configured to work in a star topology. The gateway assumes the role of a central coordinator or master node and the smart devices act as end devices or slave nodes that react to requests sent by the master node.

The gateway/server is implemented in hardware around a Digilent chipKIT Max32 board (see Photo 2). It uses an RFM12B transceiver to connect to the home area wireless network and a Microchip Technology ENC28J60 chip module to connect to the LAN using Ethernet.

As the name implies, the gateway makes it possible to access the home area wireless network over the LAN or even remotely over the Internet. So, the smart devices are easily accessible from a PC, tablet, or smartphone using just a web browser. To achieve this, the gateway implements the SWP for wireless communications and simultaneously uses Microchip Technology’s TCP/IP Stack to work as a web server.

Photo 2: The Home Energy Gateway’s hardware includes a Digilent chipKIT Max32 board and a custom shield board.

Photo 2: The Home Energy Gateway’s hardware includes a Digilent chipKIT Max32 board and a custom shield board.

Thus, the Home Energy Gateway generates and serves the control panel web page over HTTP (this page contains the individual controls to turn on/off each smart plug and at the same time shows the power consumption in the house in real-time). It also uses the wireless network to pass control data from the user to the smart plugs and to read power consumption data from the smart meter.

The hardware module includes three main submodules: The chipKIT Max 32 board, the RFM12B wireless transceiver, and the ENC28J60 Ethernet module. The smart meter hardware module has an RFM12B transceiver for wireless communications and uses an 8-bit Microchip Technology PIC16F628A microcontroller as a main processor. The smart plug hardware module shows the smart plugs’ main hardware components and has the same microcontroller and radio transceiver as the smart meter. But the smart plugs also have a Sharp Microelectronics S212S01F solid-state relay to turn on/off the household devices.

On the software side, the gateway firmware is written in C for the Microchip Technology C32 Compiler. The smart meter’s PIC16F628A code is written in C for the Hi-TECH C compiler. The smart plug software is very similar.

Alvarez says DIY home-automation enthusiasts will find his prototype inexpensive and capable. He would like to add several features to the system, including the ability to e-mail notifications and reports to users.

For more details, check out the February issue now available for download by members or single-issue purchase.

A Visit to the World Maker Faire in New York

If you missed the World Maker Faire in New York City, you can pick up Circuit Cellar’s February issue for highlights of the innovative projects and hackers represented there.Veteran electronics DIYer and magazine columnist Jeff Bachiochi is the perfect guide.

“The World Maker Faire is part science fair and part country fair,” Bachiochi says. “Makers are DIYers. The maker movement empowers everyone to build, repair, remake, hack, and adapt all things. The Maker Faire shares the experiences of makers who have been involved in this important process… Social media keeps us in constant contact and can educate, but it can’t replace the feeling you can get from hands-on live interaction with people and the things they have created.

Photo 1: This pole-climbing robot is easy to deploy at a moment’s notice. There is no need for a ladder to get emergency communication antennas up high where they can be most effective.

Photo 1: This pole-climbing robot is easy to deploy at a moment’s notice. There is no need for a ladder to get emergency communication antennas up high where they can be most effective.

“It should be noted that not all Maker Faire exhibitors are directly involved with technology. Some non-technological projects on display included the ‘Art Car’ from Pittsburgh, which is an annual revival of an old clunker turned into a drivable art show on wheels. There was also the life-size ‘Mouse Trap’ game, which was quite the contraption and just plain fun, especially if you grew up playing the original game.”

Bachiochi’s article introduces you to a wide variety of innovators, hackers, and hackerspaces.

“The 721st Mechanized Contest Battalion (MCB) is an amateur radio club from Warren County, NJ, that combines amateur (ham) radio with electronics, engineering, mechanics, building, and making,” Bachiochi says. “The club came to the Maker Faire to demonstrate its Emergency Antenna Platform System (E-APS) robot. The robot, which is designed for First Responder Organizations, will turn any parking lot lamppost into an instant antenna tower (see Photo 1).”

The keen and growing interest in 3-D printing as a design tool was evident at the Maker Faire.

“Working by day as an analog/mixed-signal IC design engineer for Cortina Systems in Canada, Andrew Plumb needed a distraction. In the evenings, Plumb uses a MakerBot 3-D printer to create 3-D designs of plastic, like thousands of others experimenting with 3-D printing,” Bachiochi says. “Plumb was not satisfied with simply printing plastic widgets. In fact, he showed me a few of his projects, which include printing plastic onto paper and cloth (see Photo 2).”

Photo 2: Andrew Plumb showed me some unique ideas he was experimenting with using one of his 3-D printers. By printing the structural frame directly on tissue paper, ultra-light parts are practically ready to fly.

Photo 2: Andrew Plumb showed me some unique ideas he was experimenting with using one of his 3-D printers. By printing the structural frame directly on tissue paper, ultra-light parts are practically ready to fly.

Also in the 3-D arena, Bachiochi encountered some innovative new products.

“It was just a matter of time until someone introduced a personal scanner to create digital files of 3-D objects. The MakerBot Digitizer Desktop 3-D Scanner is the first I’ve seen (see Photo 3),” Bachiochi says. “It uses a laser, a turntable, and a CMOS camera to pick off 3-D points and output a STL file. The scanner will create a 3-D image from an object up to 8″ in height and width. There is no third axis scanning, so you must plan your model’s orientation to achieve the best results. Priced less than most 3-D printers, this will be a hot item for 3-D printing enthusiasts.”

Bachiochi’s article includes a lengthy section about “other interesting stuff” and people at the Maker Faire, including the Public Laboratory for Open Technology and Science (Public Lab), a community that uses inexpensive DIY techniques to investigate environmental concerns.

Photo 3: The MakerBot Digitizer Desktop 3-D Scanner is the first production scanner I’ve seen that will directly provide files compatible with the 3-D printing process. This is a long-awaited addition to MakerBot’s line of 3-D printers. (Photo credit: Spencer Higgins)

Photo 3: The MakerBot Digitizer Desktop 3-D Scanner is the first production scanner I’ve seen that will directly provide files compatible with the 3-D printing process.  (Photo credit: Spencer Higgins)

“For instance, the New York chapter featured two spectrometers, a you-fold-it cardboard version and a near-infrared USB camera-based kit,” Bachiochi says. “This community of educators, technologists, scientists, and community organizers believes they can promote action, intervention, and awareness through a participatory research model in which you can play a part.”

At this family-friendly event, Bachiochi met a family that “creates” together.

“Asheville, NC-based Beatty Robotics is not your average robotics company,” Bachiochi says. “The Beatty team is a family that likes to share fun robotic projects with friends, family, and other roboticists around the world. The team consists of Dad (Robert) and daughters Camille ‘Lunamoth’ and Genevieve ‘Julajay.’ The girls have been mentored in electronics, software programming, and workshop machining. They do some unbelievable work (see Photo 4). Everyone has a hand in designing, building, and programming their fleet of robots. The Hall of Science is home to one of their robots, the Mars Rover.”

There is much more in Bachiochi’s five-page look at the Maker Faire, including resources for finding and participating in a hackerspace community. The February issue including Bachiochi’s articles is available for membership download or single-issue purchase.

Photo 4: Beatty Robotics is a family of makers that produces some incredible models. Young Camille Beatty handles the soldering, but is also well-versed in machining and other areas of expertise.

Photo 4: Beatty Robotics is a family of makers that produces some incredible models. Young Camille Beatty handles the soldering, but is also well-versed in machining and other areas of expertise.

Build an Inexpensive Wireless Water Alarm

The best DIY electrical engineering projects are effective, simple, and inexpensive. Devlin Gualtieri’s design of a wireless water alarm, which he describes in Circuit Cellar’s February issue, meets all those requirements.

Like most homeowners, Gualtieri has discovered water leaks in his northern New Jersey home after the damage has already started.

“In all cases, an early warning about water on the floor would have prevented a lot of the resulting damage,” he says.

You can certainly buy water alarm systems that will alert you to everything from a leak in a well-water storage tank to moisture from a cracked boiler. But they typically work with proprietary and expensive home-alarm systems that also charge a monthly “monitoring” fee.

“As an advocate of free and open-source software, it’s not surprising that I object to such schemes,” Gualtieri says.

In February’s Circuit Cellar magazine, now available for membership download or single-issue purchase, Gualtieri describes his battery-operated water alarm. The system, which includes a number of wireless units that signal a single receiver, includes a wireless receiver, audible alarm, and battery monitor to indicate low power.

Photo 1: An interdigital water detection sensor is shown. Alternate rows are lengths of AWG 22 copper wire, which is either bare or has its insulation removed. The sensor is shown mounted to the bottom of the box containing the water alarm circuitry. I attached it with double-stick foam tape, but silicone adhesive should also work.

Photo 1: An interdigital water detection sensor is shown. Alternate rows are lengths of AWG 22 copper wire, which is either bare or has its insulation removed. The sensor is shown mounted to the bottom of the box containing the water alarm circuitry. I attached it with double-stick foam tape, but silicone adhesive should also work.

Because water conducts electricity, Gualtieri sensors are DIY interdigital electrodes that can lie flat on a surface to detect the first presence of water. And their design couldn’t be easier.

“You can simply wind two parallel coils of 22 AWG wire on a perforated board about 2″ by 4″, he says. (See Photo 1.)

He also shares a number of design “tricks,” including one he used to make his low-battery alert work:

“A battery monitor is an important feature of any battery-powered alarm circuit. The Microchip Technology PIC12F675 microcontroller I used in my alarm circuit has 10-bit ADCs that can be optionally assigned to the I/O pins. However, the problem is that the reference voltage for this conversion comes from the battery itself. As the battery drains from 100% downward, so does the voltage reference, so no voltage change would be registered.

Figure 1: This is the portion of the water alarm circuit used for the battery monitor. The series diodes offer a 1.33-V total  drop, which offers a reference voltage so the ADC can see changes in the battery voltage.

Figure 1: This is the portion of the water alarm circuit used for the battery monitor. The series diodes offer a 1.33-V total drop, which offers a reference voltage so the ADC can see changes in the battery voltage.

“I used a simple mathematical trick to enable battery monitoring. Figure 1 shows a portion of the schematic diagram. As you can see, the analog input pin connects to an output pin, which is at the battery voltage when it’s high through a series connection of four small signal diodes (1N4148). The 1-MΩ resistor in series with the diodes limits their current to a few microamps when the output pin is energized. At such low current, the voltage drop across each diode is about 0.35 V. An actual measurement showed the total voltage drop across the four diodes to be 1.33 V.

“This voltage actually presents a new reference value for my analog conversion. The analog conversion now provides the following digital values:

EQ1Table 1 shows the digital values as a function of battery voltage. The nominal voltage of three alkaline cells is 4.75 V. The nominal voltage of three lithium cells is 5.4 V. The PIC12F675 functions from approximately 2 to 6.5 V, but the wireless transmitter needs as much voltage as possible to generate a reliable signal. I arbitrarily coded the battery alarm at 685, or a little above 4 V. That way, there’s still enough power to energize the wireless transmitter at a useful power level.”

Table 1
Battery Voltage ADC Value
5 751
4.75 737
4.5 721
4.24 704
4 683
3.75 661

 

Gaultieri’s wireless transmitter, utilizing lower-frequency bands, is also straightforward.

Photo 2 shows one of the transmitter modules I used in my system,” he says. “The round device is a surface acoustic wave (SAW) resonator. It just takes a few components to transform this into a low-power transmitter operable over a wide supply voltage range, up to 12 V. The companion receiver module is also shown. My alarm has a 916.5-MHz operating frequency, but 433 MHz is a more popular alarm frequency with many similar modules.”

These transmitter and receiver modules are used in the water alarm. The modules operate at 916.5 MHz, but 433 MHz is a more common alarm frequency with similar modules. The scale is inches.

Photo 2: These transmitter and receiver modules are used in the water alarm. The modules operate at 916.5 MHz, but 433 MHz is a more common alarm frequency with similar modules. The scale is inches.

Gualtieri goes on to describe the alarm circuitry (see Photo 3) and receiver circuit (see Photo 4.)

For more details on this easy and affordable early-warning water alarm, check out the February issue.

Photo 3: This is the water alarm’s interior. The transmitter module with its antenna can be seen in the upper right. The battery holder was harvested from a $1 LED flashlight. The box is 2.25“ × 3.5“, excluding the tabs.

Photo 3: This is the water alarm’s interior. The transmitter module with its antenna can be seen in the upper right. The battery holder was harvested from a $1 LED flashlight. The box is 2.25“ × 3.5“, excluding the tabs.

Photo 4: Here is my receiver circuit. One connector was used to monitor the signal strength voltage during development. The other connector feeds an input on a home alarm system. The short antenna reveals its 916.5-MHz operating frequency. Modules with a 433-MHz frequency will have a longer antenna.

Photo 4: Here is my receiver circuit. One connector was used to monitor the signal strength voltage during development. The other connector feeds an input on a home alarm system. The short antenna reveals its 916.5-MHz operating frequency. Modules with a 433-MHz frequency will have a longer antenna.

 

Places for the IoT Inside Your Home

It’s estimated that by the year 2020, more than 30 billion devices worldwide will be wirelessly connected to the IoT. While the IoT has massive implications for government and industry, individual electronics DIYers have long recognized how projects that enable wireless communication between everyday devices can solve or avert big problems for homeowners.

February CoverOur February issue focusing on Wireless Communications features two such projects, including  Raul Alvarez Torrico’s Home Energy Gateway, which enables users to remotely monitor energy consumption and control household devices (e.g., lights and appliances).

A Digilent chipKIT Max32-based embedded gateway/web server communicates with a single smart power meter and several smart plugs in a home area wireless network. ”The user sees a web interface containing the controls to turn on/off the smart plugs and sees the monitored power consumption data that comes from the smart meter in real time,” Torrico says.

While energy use is one common priority for homeowners, another is protecting property from hidden dangers such as undetected water leaks. Devlin Gualtieri wanted a water alarm system that could integrate several wireless units signaling a single receiver. But he didn’t want to buy one designed to work with expensive home alarm systems charging monthly fees.

In this issue, Gualtieri writes about his wireless water alarm network, which has simple hardware including a Microchip Technology PIC12F675 microcontroller and water conductance sensors (i.e., interdigital electrodes) made out of copper wire wrapped around perforated board.

It’s an inexpensive and efficient approach that can be expanded. “Multiple interdigital sensors can be wired in parallel at a single alarm,” Gualtieri says. A single alarm unit can monitor multiple water sources (e.g., a hot water tank, a clothes washer, and a home heating system boiler).

Also in this issue, columnist George Novacek begins a series on wireless data links. His first article addresses the basic principles of radio communications that can be used in control systems.

Other issue highlights include advice on extending flash memory life; using C language in FPGA design; detecting capacitor dielectric absorption; a Georgia Tech researcher’s essay on the future of inkjet-printed circuitry; and an overview of the hackerspaces and enterprising designs represented at the World Maker Faire in New York.

Editor’s Note: Circuit Cellar‘s February issue will be available online in mid-to-late January for download by members or single-issue purchase by web shop visitors.

Arduino MOSFET-Based Power Switch

Circuit Cellar columnist Ed Nisley has used Arduino SBCs in many projects over the years. He has found them perfect for one-off designs and prototypes, since the board’s all-in-one layout includes a micrcontroller with USB connectivity, simple connectors, and a power regulator.

But the standard Arduino presents some design limitations.

“The on-board regulator can be either a blessing or a curse, depending on the application. Although the board will run from an unregulated supply and you can power additional circuitry from the regulator, the minute PCB heatsink drastically limits the available current,” Nisley says. “Worse, putting the microcontroller into one of its sleep modes doesn’t shut off the rest of the Arduino PCB or your added circuits, so a standard Arduino board isn’t suitable for battery-powered applications.”

In Circuit Cellar’s January issue, Nisley presents a MOSFET-based power switch that addresses such concerns. He also refers to one of his own projects where it would be helpful.

“The low-resistance Hall effect current sensor that I described in my November 2013 column should be useful in a bright bicycle taillight, but only if there’s a way to turn everything off after the ride without flipping a mechanical switch…,” Nisley says. “Of course, I could build a custom microcontroller circuit, but it’s much easier to drop an Arduino Pro Mini board atop the more interesting analog circuitry.”

Nisley’s January article describes “a simple MOSFET-based power switch that turns on with a push button and turns off under program control: the Arduino can shut itself off and reduce the battery drain to nearly zero.”

Readers should find the article’s information and circuitry design helpful in other applications requiring automatic shutoff, “even if they’re not running from battery power,” Nisley says.

Figure 1: This SPICE simulation models a power p-MOSFET with a logic-level gate controlling the current from the battery to C1 and R2, which simulate a 500-mA load that is far below Q2’s rating. S1, a voltage-controlled switch, mimics an ordinary push button. Q1 isolates the Arduino digital output pin from the raw battery voltage.

Figure 1: This SPICE simulation models a power p-MOSFET with a logic-level gate controlling the current from the battery to C1 and R2, which simulate a 500-mA load that is far below Q2’s rating. S1, a voltage-controlled switch, mimics an ordinary push button. Q1 isolates the Arduino digital output pin from the raw battery voltage.

The article takes readers from SPICE modeling of the circuitry (see Figure 1) through developing a schematic and building a hardware prototype.

“The PCB in Photo 1 combines the p-MOSFET power switch from Figure 2 with a Hall effect current sensor, a pair of PWM-controlled n-MOFSETs, and an Arduino Pro Mini into

The power switch components occupy the upper left corner of the PCB, with the Hall effect current sensor near the middle and the Arduino Pro Mini board to the upper right. The 3-D printed red frame stiffens the circuit board during construction.

Photo 1: The power switch components occupy the upper left corner of the PCB, with the Hall effect current sensor near the middle and the Arduino Pro Mini board to the upper right. The 3-D printed red frame stiffens the circuit board during construction.

a brassboard layout,” Nisley says. “It’s one step beyond the breadboard hairball I showed in my article “Low-Loss Hall Effect Current Sensing” (Circuit Cellar 280, 2013), and will help verify that all the components operate properly on a real circuit board with a good layout.”

For much more detail about the verification process, PCB design, Arduino interface, and more, download the January issue.

The actual circuit schematic includes the same parts as the SPICE schematic, plus the assortment of connectors and jumpers required to actually build the PCB shown in Photo 1.

Figure 2: The actual circuit schematic includes the same parts as the SPICE schematic, as well as the assortment of connectors and jumpers required to actually build the PCB shown in Photo 1.

Multi-Zone Home Audio System

Dave Erickson built his first multi-zone audio system in the early 1990s using C microprocessor code he developed on Freescale MC68HC11 microprocessors. The system has been an important part of his home.

“I used this system for more than 15 years and was satisfied with its ability to send different sounds to the different rooms in my house as well as the basement and the deck,” he says. “But the system needed an upgrade.”

In Circuit Cellar’s January and February issues, Erickson describes how he upgraded the eight-zone system, which uses microprocessor-controlled analog circuitry. In the end, his project not only improved his home audio experience, it also won second place in a 2011 STMicroelectronics design contest.

Several system components needed updating, including the IR remote, graphic LCD, and microprocessor. “IR remotes went obsolete, so the IR codes needed to change,” Erickson says. “The system was 90% hand-wired and pretty messy. The LCD and several other parts became obsolete and the C development tools had expired. Processors had evolved to include flash memory and development tools evolved beyond the old burn-and-pray method.”

“My goal was to build a modern, smaller, cleaner, and more efficient system,” he says. “I decided to upgrade it with a recent processor and LCD and to use real PC boards.”

Photo 1: Clockwise from the upper left, the whole-house system includes the crosspoint board, two quad preamplifiers, two two-zone stereo amplifiers, an AC transformer, power supplies, and the CPU board with the STMicroelectronics STM32VLDISCOVERY board.

Photo 1: Clockwise from the upper left, the whole-house system includes the crosspoint board, two quad preamplifiers, two two-zone stereo amplifiers, an AC transformer, power supplies, and the CPU board with the STMicroelectronics STM32VLDISCOVERY board.

Erickson chose the STMicroelectronics STM32F100 microprocessor and the work incentive of a design contest deadline (see Photo 1).

“STMicroelectronics’s excellent libraries and examples helped me get the complex ARM Cortex-M3 peripherals working quickly,” he says. “Choosing the STM32F100 processor was a bit of overkill, but I hoped to later use it to add future capabilities (e.g., a web page and Ethernet control) and possibly even a simple music server and audio streaming.”

In Part 1 of the series, Erickson explains the design’s audio sections, including the crosspoint board, quad preamplifiers, modular audio amplifiers, and packaging. He also addresses challenges along the way.

Erickson’s Part 1 provides the following overview of the system, including its “analog heart”—the crosspoint board:

Figure 1 shows the system design including the power supplies, front-panel controls, and the audio and CPU boards. The system is modular, so there is flexibility in the front-panel controls and the number of channels and amplifiers. My goal was to fit it all into one 19”, 2U (3.5”) high rack enclosure.

The CPU board is based on a STM32F100 module containing a Cortex-M3-based processor and a USB programming interface. The CPU receives commands from a front-panel keypad, an IR remote control, an encoder knob, RS-232, and external keypads for each zone. It displays its status on a graphic LCD and controls the audio circuitry on the crosspoint and two quad preamplifier boards.

The system block diagram shows the boards, controls, amplifiers, and power supplies.

The system block diagram shows the boards, controls, amplifiers, and power supplies.


Photo 2 shows the crosspoint board, which is the analog heart of the system. It receives line-level audio signals from up to eight stereo sources via RCA jacks and routes audio to the eight preamplifier channels located on two quad preamplifier boards. It also distributes digital control and power to the preamplifiers. The preamplifier boards can either send line-level outputs or drive stereo amplifiers, either internal or external to the system.

My current system uses four line-level outputs to drive PCs or powered speakers in four of the zones. It also contains internal 40-W stereo amplifiers to directly drive speakers in the four other zones. Up to six stereo amplifiers can reside in the enclosure.

Photo 2: The crosspoint board shows the RCA input jacks (top), ribbon cable connections to the quad preamplifiers (right), and control and power cable from the CPU (bottom). Rev0 has a few black wires (lower center).

Photo 2: The crosspoint board shows the RCA input jacks (top), ribbon cable connections to the quad preamplifiers (right), and control and power cable from the CPU (bottom). Rev0 has a few black wires (lower center).

DIYers dealing with signal leakage issues in their projects may learn something from Erickson’s approach to achieving low channel-to-channel crosstalk and no audible digital crosstalk. “The low crosstalk requirement is to prevent loud music in one zone from disturbing quiet passages in another,” he says.

In Part 1, Erickson explains the crosspoint and his “grounding/guarding” approach to transmitting high-quality audio, power, and logic control signals on the same cable:

The crosspoint receives digital control from the CPU board, receives external audio signals, and distributes audio signals to the preamplifier boards and then on to the amplifiers. It was convenient to use this board to distribute the control signals and the power supply voltages to the preamplifier channels. I used 0.1” dual-row ribbon cables to simplify the wiring. These are low-cost and easy to build.

To transmit high-quality audio along with power and logic control signals on the same cable, it is important to use a lot of grounds. Two 34-pin cables each connect to a quad preamplifier board. In each of these cables, four channels of stereo audio are sent with alternating signals and grounds. The alternating grounds act as electric field “guards” to reduce crosstalk. There are just two active logic signals: I2C clock and data. Power supply voltages (±12 and 5 V) are also sent to the preamplifiers with multiple grounds to carry the return currents.

I used a similar grounding/guarding approach throughout the design to minimize crosstalk, both from channel to channel and from digital to analog. On the two-layer boards, I used ground planes on the bottom layer. Grounded guard traces or ground planes are used on the top layer. These measures minimize the capacitance between analog traces and thus minimize crosstalk. The digital and I2C signals are physically separated from analog signals. Where they need to be run nearby, they are separated by ground planes or guard traces.

To find out more about how Erickson upgraded his audio system, download the January issue (now available online) and the upcoming February issue. In Part 2, Erickson focuses on his improved system’s digital CPU, the controls, and future plans.

MCU-Based Projects and Practical Tasks

Circuit Cellar’s January issue presents several microprocessor-based projects that provide useful tools and, in some cases, entertainment for their designers.

Our contributors’ articles in the Embedded Applications issue cover a hand-held PIC IDE, a real-time trailer-monitoring system, and a prize-winning upgrade to a multi-zone audio setup.

Jaromir Sukuba describes designing and building the PP4, a PIC-to-PIC IDE system for programming and debugging a Microchip Technology PIC18. His solar-powered,

The PP4 hand-held PIC-to-PIC programmer

The PP4 hand-held PIC-to-PIC programmer

portable computing device is built around a Digilent chipKIT Max32 development platform.

“While other popular solutions can overshadow this device with better UI and OS, none of them can work with 40 mW of power input and have fully in-house developed OS. They also lack PP4’s fun factor,” Sukuba says. “A friend of mine calls the device a ‘camel computer,’ meaning you can program your favorite PIC while riding a camel through endless deserts.”

Not interested in traveling (much less programming) atop a camel? Perhaps you prefer to cover long distances towing a comfortable RV? Dean Boman built his real-time trailer monitoring system after he experienced several RV trailer tire blowouts. “In every case, there were very subtle changes in the trailer handling in the minutes prior to the blowouts, but the changes were subtle enough to go unnoticed,” he says.

Boman’s system notices. Using accelerometers, sensors, and a custom-designed PCB with a Microchip Technology PIC18F2620 microcontroller, it continuously monitors each trailer tire’s vibration and axle temperature, displays that information, and sounds an alarm if a tire’s vibration is excessive.  The driver can then pull over before a dangerous or trailer-damaging blowout.

But perhaps you’d rather not travel at all, just stay at home and listen to a little music? This issue includes Part 1 of Dave Erickson’s two-part series about upgrading his multi-zone home audio system with an STMicroelectronics STM32F100 microprocessor, an LCD, and real PC boards. His MCU-controlled, eight-zone analog sound system won second-place in a 2011 STMicroelectronics design contest.

In addition to these special projects, the January issue includes our columnists exploring a variety of  EE topics and technologies.

Jeff Bachiochi considers RC and DC servomotors and outlines a control mechanism for a DC motor that emulates a DC servomotor’s function and strength. George Novacek explores system safety assessment, which offers a standard method to identify and mitigate hazards in a designed product.

Ed Nisley discusses a switch design that gives an Arduino Pro Mini board control over its own power supply. He describes “a simple MOSFET-based power switch that turns on with a push button and turns off under program control: the Arduino can shut itself off and reduce the battery drain to nearly zero.”

“This should be useful in other applications that require automatic shutoff, even if they’re not running from battery power,” Nisley adds.

Ayse K. Coskun discusses how 3-D chip stacking technology can improve energy efficiency. “3-D stacked systems can act as energy-efficiency boosters by putting together multiple chips (e.g., processors, DRAMs, other sensory layers, etc.) into a single chip,” she says. “Furthermore, they provide high-speed, high-bandwidth communication among the different layers.”

“I believe 3-D technology will be especially promising in the mobile domain,” she adds, “where the data access and processing requirements increase continuously, but the power constraints cannot be pushed much because of the physical and cost-related constraints.”

Real-Time Trailer Monitoring System

Dean Boman, a retired electrical engineer and spacecraft communications systems designer, noticed a problem during vacations towing the family’s RV trailer—tire blowouts.

“In every case, there were very subtle changes in the trailer handling in the minutes prior to the blowouts, but the changes were subtle enough to go unnoticed,” he says in his article appearing in January’s Circuit Cellar magazine.

So Boman, whose retirement hobbies include embedded system design, built the trailer monitoring system (TMS), which monitors the vibration of each trailer tire, displays the

Figure 1—The Trailer Monitoring System consists of the display unit and a remote data unit (RDU) mounted in the trailer. The top bar graph shows the right rear axle vibration level and the lower bar graph is for left rear axle. Numbers on the right are the axle temperatures. The vertical bar to the right of the bar graph is the driver-selected vibration audio alarm threshold. Placing the toggle switch in the other position  displays the front axle data.

Photo 1 —The Trailer Monitoring System consists of the display unit and a remote data unit (RDU) mounted in the trailer. The top bar graph shows the right rear axle vibration level and the lower bar graph is for left rear axle. Numbers on the right are the axle temperatures. The vertical bar to the right of the bar graph is the driver-selected vibration audio alarm threshold. Placing the toggle switch in the other position displays the front axle data.

information to the driver, and sounds an alarm if tire vibration or heat exceeds a certain threshold. The alarm feature gives the driver time to pull over before a dangerous or damaging blowout occurs.

Boman’s article describes the overall layout and operation of his system.

“The TMS consists of accelerometers mounted on each tire’s axles to convert the gravitational (g) level vibration into an analog voltage. Each axle also contains a temperature sensor to measure the axle temperature, which is used to detect bearing or brake problems. Our trailer uses the Dexter Torflex suspension system with four independent axles supporting four tires. Therefore, a total of four accelerometers and four temperature sensors were required.

“Each tire’s vibration and temperature data is processed by a remote data unit (RDU) that is mounted in the trailer. This unit formats the data into RS-232 packets, which it sends to the display unit, which is mounted in the tow vehicle.”

Photo 1 shows the display unit. Figure 1 is the complete system’s block diagram.

Figure 1—This block diagram shows the remote data unit accepting data from the accelerometers and temperature sensors and sending the data to the display unit, which is located in the tow vehicle for the driver display.

Figure 1—This block diagram shows the remote data unit accepting data from the accelerometers and temperature sensors and sending the data to the display unit, which is located in the tow vehicle for the driver display.

The remote data unit’s (RDU’s) hardware design includes a custom PCB with a Microchip Technology PIC18F2620 processor, a power supply, an RS-232 interface, temperature sensor interfaces, and accelerometers. Photo 2 shows the final board assembly. A 78L05 linear regulator implements the power supply, and the RS-232 interface utilizes a Maxim Integrated MAX232. The RDU’s custom software design is written in C with the Microchip MPLAB integrated development environment (IDE).

The remote data unit’s board assembly is shown.

Photo 2—The remote data unit’s board assembly is shown.

The display unit’s hardware includes a Microchip Technology PIC18F2620 processor, a power supply, a user-control interface, an LCD interface, and an RS-232 data interface (see Figure 1). Boman chose a Hantronix HDM16216H-4 16 × 2 LCD, which is inexpensive and offers a simple parallel interface. Photo 3 shows the full assembly.

The display unit’s completed assembly is shown with the enclosure opened. The board on top is the LCD’s rear view. The board on bottom is the display unit board.

Photo 3—The display unit’s completed assembly is shown with the enclosure opened. The board on top is the LCD’s rear view. The board on bottom is the display unit board.

Boman used the Microchip MPLAB IDE to write the display unit’s software in C.

“To generate the display image, the vibration data is first converted into an 11-element bar graph format and the temperature values are converted from Centigrade to Fahrenheit. Based on the toggle switch’s position, either the front or the rear axle data is written to the LCD screen,” Boman says.

“To implement the audio alarm function, the ADC is read to determine the driver-selected alarm level as provided by the potentiometer setting. If the vibration level for any of the four axles exceeds the driver-set level for more than 5 s, the audio alarm is sounded.

“The 5-s requirement prevents the alarm from sounding for bumps in the road, but enables vibration due to tread separation or tire bubbles to sound the alarm. The audio alarm is also sounded if any of the temperature reads exceed 160°F, which could indicate a possible bearing or brake failure.”

The comprehensive monitoring gives Boman peace of mind behind the wheel. “While the TMS cannot prevent tire problems, it does provide advance warning so the driver can take action to prevent serious damage or even an accident,” he says.

For more details about Boman’s project, including RDU and display unit schematics, check out the January issue.

Amplifier Classes from A to H

Engineers and audiophiles have one thing in common when it comes to amplifiers. They want a design that provides a strong balance between performance, efficiency, and cost.

If you are an engineer interested in choosing or designing the amplifier best suited to your needs, you’ll find columnist Robert Lacoste’s article in Circuit Cellar’s December issue helpful. His article provides a comprehensive look at the characteristics, strengths, and weaknesses of different amplifier classes so you can select the best one for your application.

The article, logically enough, proceeds from Class A through Class H (but only touches on the more nebulous Class T, which appears to be a developer’s custom-made creation).

“Theory is easy, but difficulties arise when you actually want to design a real-world amplifier,” Lacoste says. “What are your particular choices for its final amplifying stage?”

The following article excerpts, in part, answer  that question. (For fuller guidance, download Circuit Cellar’s December issue.)

CLASS A
The first and simplest solution would be to use a single transistor in linear mode (see Figure 1)… Basically the transistor must be biased to have a collector voltage close to VCC /2 when no signal is applied on the input. This enables the output signal to swing

Figure 1—A Class-A amplifier can be built around a simple transistor. The transistor must be biased in so it stays in the linear operating region (i.e., the transistor is always conducting).

Figure 1—A Class-A amplifier can be built around a simple transistor. The transistor must be biased in so it stays in the linear operating region (i.e., the transistor is always conducting).

either above or below this quiescent voltage depending on the input voltage polarity….

This solution’s advantages are numerous: simplicity, no need for a bipolar power supply, and excellent linearity as long as the output voltage doesn’t come too close to the power rails. This solution is considered as the perfect reference for audio applications. But there is a serious downside.

Because a continuous current flows through its collector, even without an input signal’s presence, this implies poor efficiency. In fact, a basic Class-A amplifier’s efficiency is barely more than 30%…

CLASS B
How can you improve an amplifier’s efficiency? You want to avoid a continuous current flowing in the output transistors as much as possible.

Class-B amplifiers use a pair of complementary transistors in a push-pull configuration (see Figure 2). The transistors are biased in such a way that one of the transistors conducts when the input signal is positive and the other conducts when it is negative. Both transistors never conduct at the same time, so there are very few losses. The current always goes to the load…

A Class-B amplifier has more improved efficiency compared to a Class-A amplifier. This is great, but there is a downside, right? The answer is unfortunately yes.
The downside is called crossover distortion…

Figure 2—Class-B amplifiers are usually built around a pair of complementary transistors (at left). Each transistor  conducts 50% of the time. This minimizes power losses, but at the expense of the crossover distortion at each zero crossing (at right).

Figure 2—Class-B amplifiers are usually built around a pair of complementary transistors (at left). Each transistor conducts 50% of the time. This minimizes power losses, but at the expense of the crossover distortion at each zero crossing.

CLASS AB
As its name indicates, Class-AB amplifiers are midway between Class A and Class B. Have a look at the Class-B schematic shown in Figure 2. If you slightly change the transistor’s biasing, it will enable a small current to continuously flow through the transistors when no input is present. This current is not as high as what’s needed for a Class-A amplifier. However, this current would ensure that there will be a small overall current, around zero crossing.

Only one transistor conducts when the input signal has a high enough voltage (positive or negative), but both will conduct around 0 V. Therefore, a Class-AB amplifier’s efficiency is better than a Class-A amplifier but worse than a Class-B amplifier. Moreover, a Class-AB amplifier’s linearity is better than a Class-B amplifier but not as good as a Class-A amplifier.

These characteristics make Class-AB amplifiers a good choice for most low-cost designs…

CLASS C
There isn’t any Class-C audio amplifier Why? This is because a Class-C amplifier is highly nonlinear. How can it be of any use?

An RF signal is composed of a high-frequency carrier with some modulation. The resulting signal is often quite narrow in terms of frequency range. Moreover, a large class of RF modulations doesn’t modify the carrier signal’s amplitude.

For example, with a frequency or a phase modulation, the carrier peak-to-peak voltage is always stable. In such a case, it is possible to use a nonlinear amplifier and a simple band-pass filter to recover the signal!

A Class-C amplifier can have good efficiency as there are no lossy resistors anywhere. It goes up to 60% or even 70%, which is good for high-frequency designs. Moreover, only one transistor is required, which is a key cost reduction when using expensive RF transistors. So there is a high probability that your garage door remote control is equipped with a Class-C RF amplifier.

CLASS D
Class D is currently the best solution for any low-cost, high-power, low-frequency amplifier—particularly for audio applications. Figure 5 shows its simple concept.
First, a PWM encoder is used to convert the input signal from analog to a one-bit digital format. This could be easily accomplished with a sawtooth generator and a voltage comparator as shown in Figure 3.

This section’s output is a digital signal with a duty cycle proportional to the input’s voltage. If the input signal comes from a digital source (e.g., a CD player, a digital radio, a computer audio board, etc.) then there is no need to use an analog signal anywhere. In that case, the PWM signal can be directly generated in the digital domain, avoiding any quality loss….

As you may have guessed, Class-D amplifiers aren’t free from difficulties. First, as for any sampling architecture, the PWM frequency must be significantly higher than the input signal’s highest frequency to avoid aliasing….The second concern with Class-D amplifiers is related to electromagnetic compatibility (EMC)…

Figure 3—A Class-D amplifier is a type of digital amplifier (at left). The comparator’s output is a PWM signal, which is amplified by a pair of low-loss digital switches. All the magic happens in the output filter (at right).

Figure 3—A Class-D amplifier is a type of digital amplifier. The comparator’s output is a PWM signal, which is amplified by a pair of low-loss digital switches. All the magic happens in the output filter.

CLASS E and F
Remember that Class C is devoted to RF amplifiers, using a transistor conducting only during a part of the signal period and a filter. Class E is an improvement to this scheme, enabling even greater efficiencies up to 80% to 90%. How?
Remember that with a Class-C amplifier, the losses only occur in the output transistor. This is because the other parts are capacitors and inductors, which theoretically do not dissipate any power.

Because power is voltage multiplied by current, the power dissipated in the transistor would be null if either the voltage or the current was null. This is what Class-E amplifiers try to do: ensure that the output transistor never has a simultaneously high voltage across its terminals and a high current going through it….

CLASS G AND CLASS H
Class G and Class H are quests for improved efficiency over the classic Class-AB amplifier. Both work on the power supply section. The idea is simple. For high-output power, a high-voltage power supply is needed. For low-power, this high voltage implies higher losses in the output stage.

What about reducing the supply voltage when the required output power is low enough? This scheme is clever, especially for audio applications. Most of the time, music requires only a couple of watts even if far more power is needed during the fortissimo. I agree this may not be the case for some teenagers’ music, but this is the concept.

Class G achieves this improvement by using more than one stable power rail, usually two. Figure 4 shows you the concept.

Figure 4—A Class-G amplifier uses two pairs of power supply rails. b—One supply rail is used when the output signal has a low power (blue). The other supply rail enters into action for high powers (red). Distortion could appear at the crossover.

Figure 4—A Class-G amplifier uses two pairs of power supply rails. b—One supply rail is used when the output signal has a low power (blue). The other supply rail enters into action for high powers (red). Distortion could appear at the crossover.

The Future of Nanotube Computing

For decades, silicon-based transistors have been the workhorse of the semiconductor industry, achieving remarkable advances in computational power. While advances continue to be made, alternative technologies are being explored to increase computational power and efficiency beyond the limits of silicon.

Carbon nanotubes (CNTs) are nanocylinders of carbon atoms, approximately 1 nm in diameter. They have amazing electrical, thermal, and physical properties. CNTs can be used to form CNT field-effect transistors (CNFETs), which use CNTs as the channel material of the transistor, with traditional lithographically defined sources, drains, and gates. It has been projected that digital systems made from carbon nanotubes can achieve more than an order of magnitude benefit in energy delay product (a common metric to compare a circuit’s performance and energy efficiency) compared to competing technologies.

However, it has been impracticable to realize these system-level benefits due to the inability to manufacture CNT-based circuits. This limitation stems from substantial imperfections inherent with the CNTs, including mispositioned and metallic CNTs. Mispositioned CNTs cause erroneous connections in a circuit, metallic (rather than semiconducting) CNTs decrease Ion/Ioff ratio, both potentially resulting in incorrect logic functionality and power wastage.

The trivial solution to these obstacles is to grow 100% perfectly aligned and semiconducting CNTs. However, this is currently infeasible, and likely never will be. Thus, to overcome these inherent imperfections, our Stanford University research team uses the imperfection-immune design paradigm. This paradigm combines processing solutions and design “tricks” to overcome these imperfections in the very-large-scale integration (VLSI) compatible manner.

Max Shulaker, a graduate student at Stanford University and author of this essay, holds a wafer filled with CNTs. (Photo: Norbert von der Groeben )

Max Shulaker, a graduate student at Stanford University and author of this essay, holds a wafer filled with CNTs. (Photo credit: Norbert von der Groeben )

We begin by growing the CNTs highly aligned. This is accomplished by growing the CNTs on a crystalline quartz substrate. The CNTs grow along the crystalline boundary of the quartz and result in highly aligned growths—99.5% alignment. However, for VLSI applications, there are millions or billions of transistors, resulting in billions of CNTs. Thus 99.5% is insufficient.

In addition, we employ mispositioned CNT immune design, which is a technique that renders the circuits that we make 100% immune to any mispositioned CNTs that would be left on the wafer. An important point is that the design is not dependent on the exact placement of the individual CNTs. It works for any arbitrary configuration of CNTs, and thus is manufacturable and scalable to very-large-scale circuits.

To remove metallic CNTs, we break them down, much like a fuse. We turn off all semiconducting CNTs in the circuit and pulse a large voltage across the transistors. Only the metallic CNTs conduct current, and by passing enough current, eventually heat up to

Max M. Shulaker, who holds a wafer filled with carbon nanotubes (CNTs), is a PhD candidate at Stanford University where he earned his BS in Electrical Engineering. He is part of a Stanford research team that recently built the first functioning computer using CNTs. Max works on experimentally demonstrating nanosystems with emerging technologies. His current research focuses on realizing increased levels of integration for CNT-based digital logic circuits. (Photo credit: Norbert von der Groeben)

Max M. Shulaker, who wrote this essay for Circuit Cellar, holds a wafer filled with carbon nanotubes (CNTs). Max is a PhD candidate at Stanford University where he earned his BS in Electrical Engineering. He is part of a Stanford research team that recently built the first functioning computer using CNTs. Max works on experimentally demonstrating nanosystems with emerging technologies. His current research focuses on realizing increased levels of integration for CNT-based digital logic circuits. (Photo credit: Norbert von der Groeben)

the point where they break down, much like a fuse. The trick is being able to perform this breakdown at a chip  scale. Computers today have billions of transistors. It would be infeasible to breakdown each transistor one by one. VLSI-compatible metallic CNT removal (VMR) is a design technique that enables the breakdown to be performed at an entire chip scale.

The imperfection-immune design paradigm, coupled with CNT-specific fabrication processing resulting in high-yield devices, permits, for the first time, the realization of larger-scale digital systems using this very promising technology. Most recently, a basic computer was fabricated at Stanford University completely using CNFETs. The CNT computer was composed of tens of thousands of CNTs, demonstrating the ability to manufacture CNT circuits in a scalable, and thus manufacturable, manner. The computer executes the subtract and branch if negative (SUBNEG) instruction, which is Turing complete, adding to the computer’s generality. As a demonstration, the CNT computer concurrently counted integers and sorted integers, continuously swapping between the two processes. To demonstrate the computer’s flexibility, it also emulated 20 different instructions from the commercial MIPS instruction set.

The CNT computer, culminating years of work by a team of researchers at Stanford University led by Professors Subhasish Mitra and Philip Wong, demonstrates that CNTs are a manufacturable and feasible technology. Beyond CNTs, it is a step forward for the broader field of emerging nanotechnologies. While many alternatives to silicon are being explored, the CNT computer represents an initial demonstration of one of these emerging technologies coming to fruition.

Turn Your Android Device into an Application Tool

A few years ago, the Android Open Accessory initiative was announced with the aim of making it easier for hardware manufacturers to create accessories that work with every Android device. Future Technology Devices International (FTDI) joined the initiative and last year introduced the FTD311D multi-interface Android host IC. The goal was to enable engineers and designers to make effective use of tablets and smartphones with the Android OS, according to Circuit Cellar columnist Jeff Bachiochi.

The FTD311D “provides an instant bridge from an Android USB port(B) to peripheral hardware over general purpose input-out (GPIO), UART, PWM, I2C Master, SPI Slave, or SPI Master interfaces,” Bachiochi says.

In the magazine’s December issue Bachiochi takes a comprehensive look at the USB Android host IC and how it works. By the end of his article, readers will have learned quite a bit about how to use FTDI’s apps and the FT311D chip to turn an Android device into their own I/0 tool.

Bachiochi used the SPI Master demo to read key presses and set LED states on this SPI slave 16-key touch panel.

Bachiochi used the SPI Master demo to read key presses and set LED states on this SPI slave 16-key touch panel.

Here is how Bachiochi describes the FT311D and its advantages:

The FT311D is a full-speed USB host targeted at providing access to peripheral hardware from a USB port on an Android device. While an Android device can be a USB host, many are mobile devices with limited power. For now, these On-The-Go (OTG) ports will be USB devices only (i.e., they can only connect to a USB host as a USB device).

Since the USB host is responsible for supplying power to a USB peripheral device, it would be bad design practice to enable a USB peripheral to drain an Android mobile device’s energy. Consequently, the FT311D takes on the task of USB host, eliminating any draw on the Android device’s battery.

All Android devices from V3.1 (Honeycomb) support the Android Open Accessory Mode (AOAM). The AOAM is the complete reverse of the conventional USB interconnect. This game-changing approach to attaching peripherals enables three key advantages. First, there is no need to develop special drivers for the hardware; second, it is unnecessary to root devices to alter permissions for loading drivers; and third, the peripheral provides the power to use the port, which ensures the mobile device battery is not quickly drained by the external hardware being attached.

Since the FT311D handles the entire USB host protocol, USB-specific firmware programming isn’t required. As the host, the FT311D must inquire whether the connected device supports the AOAM. If so, it will operate as an Open Accessory Mode device with one USB BULK IN endpoint and one USB BULK OUT endpoint (as well as the control endpoint.) This interface will be a full-speed (12-Mbps) USB enabling data transfer in and out.

The AOAM USB host has a set of string descriptors the Android OS is capable of reading. These strings are (user) associated with an Android OS application. The Android then uses these strings to automatically start the application when the hardware is connected. The FT311D is configured for one of its multiple interfaces via configuration inputs at power-up. Each configuration will supply the Android device with a unique set of string descriptors, therefore enabling different applications to run, depending on its setup.

The FT311D’s configuration determines whether each application will have access to several user interface APIs that are specific to each configuration.

The article goes on to examine the various interfaces in detail and to describe a number of demo projects, including a multimeter.

Many of Bachiochi's projects use printable ASCII text commands and replies. This enables a serial terminal to become a handy user I/O device. This current probe circuit outputs its measurements in ASCII-printable text.

Many of Bachiochi’s projects use printable ASCII text commands and replies. This enables a serial terminal to become a handy user I/O device. This current probe circuit outputs its measurements in ASCII-printable text.

Multimeters are great tools. They have portability that enables them to be brought to wherever a measurement must be made. An Android device has this same ability. Since applications can be written for these devices, they make a great portable application tool. Until the AOAM’s release, there was no way for these devices to be connected to any external circuitry and used as an effective tool.

I think FTDI has bridged this gap nicely. It provided a great interface chip that can be added to any circuit that will enable an Android device to serve as an effective user I/O device. I’ve used the chip to quickly interface with some technology to discover its potential or just test its abilities. But I’m sure you are already thinking about the other potential uses for this connection.

Bachiochi is curious to hear from readers about their own ideas.

If you think the AOAM has future potential, but you want to know what’s involved with writing Android applications for a specific purpose, send me an e-mail and I’ll add this to my list of future projects!

You can e-mail Bachiochi at jeff.bachiochi@imaginethatnow.com or post your comment here.

 

Emerging Memory Technologies

Some experts predict it will be at least another decade before new memory technologies offer the low prices and wide availability to compete with NAND-based flash memory. Nonetheless, it’s worthwhile to look at potential NAND-flash successors, including phase-change RAM (PRAM), resistive RAM (ReRAM), and magnetoresistive RAM (MRAM).

In December’s Circuit Cellar magazine, now available online, Faiz Rahman describes and compares the newest memory technologies available for embedded systems.

“I cover only those devices that are now commercially available, but bear in mind that many other technologies are being hotly pursued in academic and corporate research labs worldwide,” says Rahman, an Ohio University visiting professor who received his PhD in Electrical Engineering from Imperial College, London.

For example, last summer MIT Technology Review reported on a startup company’s testing of crossbar memory. The new technology, according to an August 14, 2013, article written by Tom Simonite, can store data 40 times as densely as the most compact memory available and is faster and more energy-efficient.

Here are the commercially-available technologies Rahman considers and some of his insights. (For the full article with more details, including an update on manufacturers of the latest memory devices, check out the December issue.)

PHASE-CHANGE RAM
One of the most interesting memory types to emerge in recent years is one that stores data as order or disorder in small islands of a special material. The structural transition

The structure of phase-change RAM cells in reset and set states is shown.

The structure of phase-change RAM cells in reset and set states is shown.

between ordered and disordered phases is driven by controlled heating of the material island…

There have been several recent advances in phase-change RAM (PRAM) technology. Perhaps the most remarkable is the ability to control the cell-heating current precisely enough to create several intermediate cell-resistance values. This immediately increases the memory capacity as each cell can be made to store more than one bit. For example, if eight resistance values can be created and distinguished, then the cell can be used to store three bits, thus tripling the memory capacity. This is now a routinely used technique implemented with PRAM devices.

MAGNETORESISTIVE RAM
We have all wished for a computer with no start-up delay that could be ready to use almost as soon as it was powered up. Such a computer will need to use an inexpensive

A spin-torque magnetoresistive RAM cell’s structure includes a free layer, a tunnel barrier, and a fixed layer.

A spin-torque magnetoresistive RAM cell’s structure includes a free layer, a tunnel barrier, and a fixed layer.

but fast nonvolatile memory. This combination is difficult to come by, but proponents of magnetoresistive RAM (MRAM) think boot times could soon become outdated as this new memory becomes a mature product….

MRAM’s nonvolatility alone will not make it a potential game-changing technology. Its high-access speed is what makes it special. Unlike other nonvolatile memory (e.g., EEPROMs and flash), MRAM boasts typical access speeds of 35 ns and potentially as short as 4 ns, with further developments. This combined with MRAM’s extremely high endurance and data retention periods of more than 20 years even makes the technology suitable for use as CPU cache memories, which is a very demanding application.

One further advantage of MRAM is that its basic architecture—where the access transistor can be formed directly on top of the magnetic tunnel junction (MTJ)—enables very dense integration, greatly reducing the cost of storage per bit and making MRAM well suited for use in solid-state disks.

FERROELECTRIC RAM
In many ways, DRAM is an example of an ideal memory, if it weren’t for its volatility… The problem is that the charge stored in a DRAM cell tends to disappear due to self-discharge

A ferroelectric RAM cell’s organizational structure is shown.

A ferroelectric RAM cell’s organizational structure is shown.

after only a few milliseconds. This means that all DRAM chips have to be periodically read and every cell’s state must be restored every few milliseconds. The requirement for periodic “refresh” operations increases the power consumption of DRAM banks, in addition to endangering data integrity in the case of even short power supply dips.

Within this backdrop, ferroelectric RAM (FRAM) became a potential game changer when it was introduced in the early 1990s…The permanence of induced electrical polarization in ferroelectric capacitors endows FRAMs with their nonvolatility. To write a particular bit, a FRAM’s cell capacitor is briefly charged in one direction to polarize the ferroelectric material between its plates. The capacitor voltage can then be removed and the bit state will be retained in the directional sense of the dielectric material’s polarization. No charges may leak away, and the polarization can be maintained for many years making FRAM, in a sense, a nonvolatile analog of DRAM….

A big advantage of using FRAM in microcontrollers is that just one memory can be used for program, data, and information storage instead of having to use separate flash, SRAM, and EEPROM blocks, which has been the trend so far.

RESISTIVE RAM
Phase-change memory uses programmed heat-generating current pulses to affect memory cell resistance changes. However, resistive RAM (ReRAM)—a still developing memory breed—uses voltage pulses to make resistance changes. This memory technology

A typical resistive RAM cell’s structure is shown.

A typical resistive RAM cell’s structure is shown.

utilizes materials and structures where suitable voltages can alter memory cells’ resistive states so they can store one or more data bits, similar to PRAM.

There are strong hints that ReRAM is capable of very fast switching with symmetric read and write times of less than 10 ns. This comes with a remarkably low power consumption, which should make this technology ideal for many applications.

As if these attributes were not enough, ReRAM cells are very small and can be placed extremely close together, which results in high-density memory fabrics.

Rahman’s article also introduces manufacturers offering products with the latest memory technologies, but he declares no single memory device the best. Despite manufacturers extolling their particular products, those that succeed will need to be available in high volume and at low cost, he says. They also must offer high-storage densities, he says, a bar most new memory technologies struggle to reach.

DesignCon 2014 in Santa Clara

DesignCon 2014, an educational conference and technology exhibition for electronic design engineers in the high speed communications and semiconductor fields, will be held in late January at the Santa Clara Convention Center in Santa Clara, CA.

DesignCon is the largest gathering of chip, board, and systems designers in the world and focuses on signal integrity at all levels of electronic design, according to the website www.designcon.com.

The event features the conference, which runs Tuesday through Friday, January 28–31, and the expo on Wednesday and Thursday, January 29–30.

To see the schedule of planned speakers, tutorials, panel discussions, and other events, click here. Information about passes, prices, and registration can be found here.
For more details or assistance, call (415) 947-6135 or (888) 234-9476 or e-mail designconregistration@ubm.com

CC281: Overcome Fear of Ethernet on an FPGA

As its name suggests, the appeal of an FPGA is that it is fully programmable. Instead of writing software, you design hardware blocks to quickly do what’s required of a digital design. This also enables you to reprogram an FPGA product in the field to fix problems “on the fly.”

But what if “you” are an individual electronics DIYer rather than an industrial designer? DIYers can find FPGAs daunting.

Issue281The December issue of Circuit Cellar issue should offer reassurance, at least on the topic of “UDP Streaming on an FPGA.” That’s the focus of Steffen Mauch’s article for our Programmable Logic issue (p. 20).

Ethernet on an FPGA has several applications. For example, it can be used to stream measured signals to a computer for analysis or to connect a camera (via Camera Link) to an FPGA to transmit images to a computer.

Nonetheless, Mauch says, “most novices who start to develop FPGA solutions are afraid to use Ethernet or DDR-SDRAM on their boards because they fear the resulting complexity.” Also, DIYers don’t have the necessary IP core licenses, which are costly and often carry restrictions.

Mauch’s UDP monitor project avoids such costs and restrictions by using a free implementation of an Ethernet-streaming device based on a Xilinx Spartan-6 LX FPGA. His article explains how to use OpenCores’s open-source tri-mode MAC implementation and stream UDP packets with VHDL over Ethernet.

Mauch is not the only writer offering insights into FPGAs. For more advanced FPGA enthusiasts, columnist Colin O’Flynn discusses hardware co-simulation (HCS), which enables the software simulation of a design to be offloaded to an FPGA. This approach significantly shortens the time needed for adequate simulation of a new product and ensures that a design is actually working in hardware (p. 52).

This Circuit Cellar issue offers a number of interesting topics in addition to programmable logic. For example, you’ll find a comprehensive overview of the latest in memory technologies, advice on choosing a flash file system for your embedded Linux system, a comparison of amplifier classes, and much more.

Mary Wilson
editor@circuitcellar.com

Electrical Engineering and Artistic Expression

I think we’re on the verge of the next artistic renaissance. This time, instead of magnificent architecture, beautifully painted portraits, and the rise of humanism, I think engineering (specifically electrical engineering) will begin to define exciting new forms of artistic expression.

Cornell University graduate and electrical engineer Jeremy Blum in 2011 blog post

Regular Circuit Cellar readers will recognize Jeremy Blum as our November issue interview subject. Blum’s post sums up a philosophy that seems to be shared by some other recent EE graduates or aspiring electrical engineers. They view their work as art, or at least they like to occasionally work in art.

For example, Circuit Cellar’s January issue will feature an interview with Andrew Godbehere, an Electrical Engineering PhD candidate at the University of California, Berkeley. He has intertwined engineering and art more than once.

This is the central control belt pack worn by a dancer for CUMotive, the wearable accelerometer project. An Atmel Mega644V and an AT86RF230 were used inside to interface to synthesizer. The plastic enclosure has holes for the belt to attach to a dancer. Wires connect to accelerometers, which are worn on the dancer’s limbs.

This is the central control belt pack worn by a dancer for CUMotive, the wearable accelerometer project. An Atmel Mega644V and an AT86RF230 were used inside to interface to synthesizer. The plastic enclosure has holes for the belt to attach to a dancer. Wires connect to accelerometers, which are worn on the dancer’s limbs.

When he was Cornell student, he collaborated with Nathan Ward on a final project to translate a dancer’s movement into music. They created a central control belt pack for the dancer, which connected to four wearable wireless accelerometers to measure the dancer’s movements. Inside the belt pack, an ATmega 644V connected to an Atmel AT86RF230 wireless transceiver interfaced with a musical instrument digital interface (MIDI) and synthesizer.

When Godbehere graduated from Cornell and headed to UC Berkeley, his focus shifted to theoretical topics and robotic systems. But he jumped at a professor’s invitation to become involved in the “Are We There Yet?” art installation in 2011 at the Contemporary Jewish Museum in San Francisco.

During the four-month exhibit, visitors entered a nearly empty gallery to encounter recorded questions emanating from numerous floor speakers. A camera followed each visitor’s moves and robotic algorithms enabled it to determine which floor speaker to activate. The questions heard could range from “What Is My Purpose?” to “What’s Up Doc?”

How a visitor moved through the interactive installation triggered the combination of questions he or she heard.

Video documentary of “Are We There Yet?” 

Godbehere was the computer vision system engineer working with artists Gil Gershoni and Ken Goldberg, who is also a robotics and new media professor at UC Berkeley.

“We installed a color camera in a beautiful gallery in the Contemporary Jewish Museum… and a set of speakers with a high-end controller system from Meyer Sound that enabled us to ‘position’ sound in the space and to sweep audio tracks around at (the computer’s programmed) will,” Godbehere says. “The Meyer Sound System is the D-Mitri control system, controlled by the computer with Open Sound Control (OSC).

“The hard work was then to program the computer to discern humans from floors, furniture, shadows, sunbeams, and reflections of clouds. The gallery had many skylights, making the lighting very dynamic. Then, I programmed the computer to keep track of people as they moved and found that this dynamic information was itself useful in determining if detected color-perturbance was human or not.”

Behind the technology of “Are We There Yet?”

Can such art also have “practical” consumer applications? Godbehere says there are elements that can be used as an embedded system.

“I’ve been told that the software I wrote works on iOS devices by the startup company Romo, which was evaluating my vision-tracking code for use in its cute iPhone rover. Further, I’d say that if someone were interested, they could create a similar pedestrian, auto, pet, or cloud tracking system using a Raspberry Pi and a reasonable webcam.”

If you’re interested in learning more about Godbehere’s engineering and artistic work, be sure to check out the January issue of Circuit Cellar.

And if you have an opinion on electrical engineering and art, please post your comments below.