Embedded Sensor Innovation at MIT

During his June 5 keynote address at they 2013 Sensors Expo in Chicago, Joseph Paradiso presented details about some of the innovative embedded sensor-related projects at the MIT Media Lab, where he is the  Director of the Responsive Environments Group. The projects he described ranged from innovative ubiquitous computing installations for monitoring building utilities to a small sensor network that transmits real-time data from a peat bog in rural Massachusetts. Below I detail a few of the projects Paradiso covered in his speech.

DoppleLab

Managed by the Responsive Enviroments group, the DoppelLab is a virtual environment that uses Unity 3D to present real-time data from numerous sensors in MIT Media Lab complex.

The MIT Responsive Environments Group’s DoppleLab

Paradiso explained that the system gathers real-time information and presents it via an interactive browser. Users can monitor room temperature, humidity data, RFID badge movement, and even someone’s Tweets has he moves throughout the complex.

Living Observatory

Paradiso demoed the Living Observatory project, which comprises numerous sensor nodes installed in a peat bog near Plymouth, MA. In addition to transmitting audio from the bog, the installation also logs data such as temperature, humidity, light, barometric pressure, and radio signal strength. The data logs are posted on the project site, where you can also listen to the audio transmission.

The Living Observatory (Source: http://tidmarsh.media.mit.edu/)

GesturesEverywhere

The GesturesEverywhere project provides a real-time data stream about human activity levels within the MIT Media Lab. It provides the following data and more:

  • Activity Level: you can see the Media Labs activity level over a seven-day period.
  • Presence Data: you can see the location of ID tags as people move in the building

The following video is a tracking demo posted on the project site.

The aforementioned projects are just a few of the many cutting-edge developments at the MIT Media Lab. Paradiso said the projects show how far ubiquitous computing technology has come. And they provide a glimpse into the future. For instance, these technologies lend themselves to a variety of building-, environment-, and comfort-related applications.

“In the early days of ubiquitous computing, it was all healthcare,” Paradiso said. “The next frontier is obviously energy.”

Microcontroller-Based Heating System Monitor

Checking a heating system’s consumption is simple enough.

Heating system monitor

Determining a heating system’s output can be much more difficult, unless you have this nifty design. This Atmel ATmega microcontroller-based project enables you to measure heat output as well as control a circulation pump.

Heating bills often present unpleasant surprises. Despite your best efforts to economise on heating, they list tidy sums for electricity or gas consumption. In this article we describe a relatively easy way to check these values and monitor your consumption almost continuously. All you need in order to determine how much heat your system delivers is four temperature sensors, a bit of wiring, and a microcontroller. There’s no need to delve into the electrical or hydraulic components of your system or modify any of them.

A bit of theory
As many readers probably remember from their physics lessons, it’s easy to calculate the amount of heat transferred to a medium such as water. It is given by the product of the temperature change ΔT, the volume V of the medium, and the specific heat capacity CV of the medium. The power P, which is amount of energy transferred per unit time, is:

P= ΔT × CV × V // Δt

With a fluid medium, the term V // Δt can be interpreted as a volumetric flow Vt. This value can be calculated directly from the flow velocity v of the medium and the inner diameter r of the pipe. In a central heating system, the temperature difference ΔT is simply the difference between the supply (S) and return (R) temperatures. This yields the formula:

P = (TS – TR) × CV × v × pr2

The temperatures can easily be measured with suitable sensors. Flow transducers are available for measuring the flow velocity, but installing a flow transducer always requires drilling a hole in a pipe or opening up the piping to insert a fitting.

Measuring principle
Here we used a different method to determine the flow velocity. We make use of the fact that the supply and return temperatures always vary by at least one to two degrees due to the operation of the control system. If pairs of temperature sensors separated by a few metres are mounted on the supply and return lines, the flow velocity can be determined from the time offset of the variations measured by the two sensors…

As the water flows through the pipe with a speed of only a few metres per second, the temperature at sensor position S2 rises somewhat later than the temperature at sensor position S, which is closer to the boiler.

An ATmega microcontroller constantly acquires temperature data from the two sensors. The time delay between the signals from a pair of sensors is determined by a correlation algorithm in the signal processing software, which shifts the signal waveforms from the two supply line sensors relative to each other until they virtually overlap.The temperature signals from the sensors on the return line are correlated in the same manner, and ideally the time offsets obtained for the supply and return lines should be the same.

To increase the sensitivity of the system, the return line sensor signals are applied to the inputs of a differential amplifier, and the resulting difference signal is amplified. This difference signal is also logged as a function of time. The area under the curve of the difference signal is a measure of the time offset of the temperature variations…

Hot water please
If the heating system is also used to supply hot water for domestic use, additional pipes are used for this purpose. For this reason, the PCB designed by the author includes inputs for additional temperature sensors. It also has a switched output for driving a relay that can control a circulation pump.

Under certain conditions, controlling the circulation pump can save you a lot of money and significantly reduce CO2 emissions. This is because some systems have constant hot water circulation so users can draw hot water from the tap immediately. This costs electricity to power the pump, and energy is also lost through the pipe walls. This can be remedied by the author’s circuit, which switches on the circulation pump for only a short time after the hot water tap is opened. This is detected by the temperature difference between the hot water and cold water supply lines…

Circuit description
The easiest way to understand the schematic diagram is to follow the signal path. It starts at the temperature sensors connected to the circuit board, which are NTC silicon devices.

Heating system monitor schematic

Their resistance varies by around 0.7–0.8% per degree K change in temperature. For example, the resistance of a KT110 sensor is approximately 1.7 kΩ at 5 °C and approximately 2.8 kΩ at 70 °C.

The sensor for supply temperature S forms a voltage divider with resistor R37. This is followed by a simple low-pass filter formed by R36 and C20, which filters out induced AC hum. U4a amplifies the sensor signal by a factor of approximately 8. The TL2264 used here is a rail-to-rail opamp, so the output voltage can assume almost any value within the supply voltage range. This increases the absolute measurement accuracy, since the full output signal amplitude is used. U4a naturally needs a reference voltage on its inverting input. This is provided by the combination of R20, R26 and R27. U5b acts as an impedance converter to minimise the load on the voltage divider…

Thermal power

PC connection
The circuit does not have its own display unit, but instead delivers its readings to a PC via an RS485 bus. Its functions can also be controlled from the PC. IC U8 looks after signal level conversion between the TTL transmit and receive lines of the ATmega microcontroller’s integrated UART and the differential RS485 bus. As the bus protocol allows several connected (peer) devices to transmit data on the bus, transmit mode must be selected actively via pin 3. Jumper JP3 must be fitted if the circuit is connected to the end of the RS485 bus. This causes the bus to be terminated in 120 Ω, which matches the characteristic impedance of a twisted-pair line…

[Via Elektor-Projects.com]

CC269: Break Through Designer’s Block

Are you experiencing designer’s block? Having a hard time starting a new project? You aren’t alone. After more than 11 months of designing and programming (which invariably involved numerous successes and failures), many engineers are simply spent. But don’t worry. Just like every other year, new projects are just around the corner. Sooner or later you’ll regain your energy and find yourself back in action. Plus, we’re here to give you a boost. The December issue (Circuit Cellar 269) is packed with projects that are sure to inspire your next flurry of innovation.

Turn to page 16 to learn how Dan Karmann built the “EBikeMeter” Atmel ATmega328-P-based bicycle computer. He details the hardware and firmware, as well as the assembly process. The monitoring/logging system can acquire and display data such as Speed/Distance, Power, and Recent Log Files.

The Atmel ATmega328-P-based “EBikeMeter” is mounted on the bike’s handlebar.

Another  interesting project is Joe Pfeiffer’s bell ringer system (p. 26). Although the design is intended for generating sound effects in a theater, you can build a similar system for any number of other uses.

You probably don’t have to be coerced into getting excited about a home control project. Most engineers love them. Check out Scott Weber’s garage door control system (p. 34), which features a MikroElektronika RFid Reader. He built it around a Microchip Technology PIC18F2221.

The reader is connected to a breadboard that reads the data and clock signals. It’s built with two chips—the Microchip 28-pin PIC and the eight-pin DS1487 driver shown above it—to connect it to the network for testing. (Source: S. Weber, CC269)

Once considered a hobby part, Arduino is now implemented in countless innovative ways by professional engineers like Ed Nisley. Read Ed’s article before you start your next Arduino-related project (p. 44). He covers the essential, but often overlooked, topic of the Arduino’s built-in power supply.

A heatsink epoxied atop the linear regulator on this Arduino MEGA board helped reduce the operating temperature to a comfortable level. This is certainly not recommended engineering practice, but it’s an acceptable hack. (Source: E. Nisley, CC269)

Need to extract a signal in a noisy environment? Consider a lock-in amplifier. On page 50, Robert Lacoste describes synchronous detection, which is a useful way to extract a signal.

This month, Bob Japenga continues his series, “Concurrency in Embedded Systems” (p. 58). He covers “the mechanisms to create concurrently in your software through processes and threads.”

On page 64, George Novacek presents the second article in his series, “Product Reliability.” He explains the importance of failure rate data and how to use the information.

Jeff Bachiochi wraps up the issue with a article about using heat to power up electronic devices (p. 68). Fire and a Peltier device can save the day when you need to charge a cell phone!

Set aside time to carefully study the prize-winning projects from the Reneas RL78 Green Energy Challenge (p. 30). Among the noteworthy designs are an electrostatic cleaning robot and a solar energy-harvesting system.

Lastly, I want to take the opportunity to thank Steve Ciarcia for bringing the electrical engineering community 25 years of innovative projects, essential content, and industry insight. Since 1988, he’s devoted himself to the pursuit of EE innovation and publishing excellence, and we’re all better off for it. I encourage you to read Steve’s final “Priority Interrupt” editorial on page 80. I’m sure you’ll agree that there’s no better way to begin the next 25 years of innovation than by taking a moment to understand and celebrate our past. Thanks, Steve.

CC268: The History of Embedded Tech

At the end of September 2012, an enthusiastic crew of electrical engineers and journalists (and significant others) traveled to Portsmouth, NH, from locations as far apart as San Luis Obispo, CA,  and Paris, France, to celebrate Circuit Cellar’s 25th anniversary. Attendees included Don Akkermans (Director, Elektor International Media), Steve Ciarcia (Founder, Circuit Cellar), the current magazine staff, and several well-known engineers, editors, and columnists. The event marked the beginning of the next chapter in the history of this long-revered publication. As you’d expect, contributors and staffers both reminisced about the past and shared ideas about its future. And in many instances, the conversations turned to the content in this issue, which was at that time entering the final phase of production. Why? We purposely designed this issue (and next month’s) to feature a diversity of content that would represent the breadth of coverage we’ve come to deliver during the past quarter century. A quick look at this issue’s topics gives you an idea of how far embedded technology has come. The topics also point to the fact that some of the most popular ’80s-era engineering concerns are as relevant as ever. Let’s review.

In the earliest issues of Circuit Cellar, home control was one of the hottest topics. Today, inventive DIY home control projects are highly coveted by professional engineers and newbies alike. On page 16, Scott Weber presents an interesting GPS-based time server for lighting control applications. An MCU extracts time from GPS data and transmits it to networked devices.

The time-broadcasting device includes a circuit board that’s attached to a GPS module. (Source: S. Weber, CC268)

Thiadmer Riemersma’s DIY automated component dispenser is a contemporary solution to a problem that has frustrated engineers for decades (p. 26). The MCU-based design simplifies component management and will be a welcome addition to any workbench.

The DIY automated component dispenser. (Source: T. Riemersma, CC268)

USB technology started becoming relevant in the mid-to-late 1990s, and since then has become the go-to connection option for designers and end users alike. Turn to page 30 for Jan Axelson’s  tips about debugging USB firmware. Axelson covers controller architectures and details devices such as the FTDI FT232R USB UART controller and Microchip Technology’s PIC18F4550 microcontroller.

Debugging USB firmware (Source: J. Axelson, CC268)

Electrical engineers have been trying to “control time” in various ways since the earliest innovators began studying and experimenting with electric charge. Contemporary timing control systems are implemented in a amazing ways. For instance, Richard Lord built a digital camera controller that enables him to photograph the movement of high-speed objects (p. 36).

Security and product reliability are topics that have been on the minds of engineers for decades. Whether you’re working on aerospace electronics or a compact embedded system for your workbench (p. 52), you’ll want to ensure your data is protected and that you’ve gone through the necessary steps to predict your project’s likely reliability (p. 60).

The issue’s last two articles detail how to use contemporary electronics to improve older mechanical systems. On page 64 George Martin presents a tachometer design you can implement immediately in a machine shop. And lastly, on page 70, Jeff Bachiochi wraps up his series “Mechanical Gyroscope Replacement.” The goal is to transmit reliable data to motor controllers. The photo below shows the Pololu MinIMU-9.

The Pololu MinIMU-9’s sensor axes are aligned with the mechanical gyro so the x and y output pitch and roll, respectively. (Source: J. Bachiochi, CC268)

DIY 10.1˝ Touchscreen Home Control System

Domotics (home automation) control systems are among the most innovative and rewarding design projects creative electrical engineers can undertake. Let’s take a look at an innovative Beagle Board-based control system that enables a user to control lights with a 10.1˝ capacitive touchscreen.

Domotics control system

The design features the following modules:

• An I/O board for testing purposes
• An LED strip board for controlling an RGB LED strip
• A relay board for switching 230-VAC devices
• An energy meter for measuring on/off (and also for logging)

ELektor editor and engineer Clemens Valens recently interviewed Koen van Dongen about the design. Van Dongen describes the system’s electronics and then demonstrates how to use the touchscreen to control a light and LED strip.

As Valens explains suggests, it would be a worthwhile endeavor to incorporate a Wi-Fi connection to enable cellphone and tablet control. If you build such system, be sure to share it with our staff. Good luck!

CircuitCellar.com is an Elektor International Media website.

DIY Internet-Enabled Home Control System

Why shell out hundreds or thousands of dollars on various home control systems (HCS) when you have the skills and resources to build your own? You can design and implement sophisticated Internet-enabled systems with free tools and some careful planning.

John Breitenbach did just that. He used a microcontroller, free software, and a cloud-based data platform to construct a remote monitoring system for his home’s water heater. The innovative design can email or text status messages and emergency alerts to a smartphone. You can build a similar system to monitor any number of appliances, rooms, or buildings.

An abridged version of Breitenbach’s article, “Internet-Enabled Home Control” (Circuit Cellar 264, July 2012), appears below. (A link to the entire article and an access password are noted at the end of this post.) Breitenbach writes:

Moving from the Northeast to North Carolina, my wife and I were surprised to find that most homes don’t have basements. In the north, the frost line is 36˝–48 ˝ below the surface. To prevent frost heave, foundations must be dug at least that deep. So, digging down an extra few feet to create a basement makes sense. Because the frost line is only 15 ˝ in the Raleigh area, builders rarely excavate the additional 8’ to create basements.

The lack of basements means builders must find unique locations for a home’s mechanical systems including the furnace, AC unit, and water heater. I was shocked to find that my home’s water heater is located in the attic, right above one of the bedrooms (see Photo 1).

Photo 1: My home’s water heater is located in our attic. (Photo courtesy of Michael Thomas)

During my high school summers I worked for my uncle’s plumbing business (“Breitenbach Plumbing—We’re the Best, Don’t Call the Rest”) and saw firsthand the damage water can do to a home. Water heaters can cause some dramatic end-of-life plumbing failures, dumping 40 or more gallons of water at once followed by the steady flow of the supply line.

Having cleaned up the mess of a failed water heater in my own basement up north, I haven’t had a good night’s sleep since I discovered the water heater in my North Carolina attic. For peace of mind, especially when traveling, I instrumented my attic so I could be notified immediately if water started to leak. My goal was to use a microcontroller so I could receive push notifications via e-mails or text messages. In addition to emergency messages, status messages sent on a regular basis reassure me the system is running. I also wanted to use a web browser to check the current status at any time.

MCU & SENSOR

The attic monitor is based on Renesas Electronics’s YRDKRX62N demonstration kit, which features the RX62N 32-bit microcontroller (see Photo 2). Renesas has given away thousands of these boards to promote the RX, and the boards are also widely available through distributors. The YRDK board has a rich feature set including a graphics display, push buttons, and an SD-card slot, plus Ethernet, USB, and serial ports. An Analog Devices ADT7420 digital I2C temperature sensor also enables you to keep an eye on the attic temperature. I plan to use this for a future addition to the project that compares this temperature to the outside air temperature to control an attic fan.

Photo 2: The completed board, which is based on a Renesas Electronics YRDKRX62N demonstration kit. (Photo courtesy of Michael Thomas)

SENSING WATER

Commercial water-detection sensors are typically made from two exposed conductive surfaces in close proximity to each other on a nonconductive surface. Think of a single-sided PCB with no solder mask and tinned traces (see Photo 3).

Photo 3: A leak sensor (Photo courtesy of Michael Thomas)

These sensors rely on the water conductivity to close the circuit between the two conductors. I chose a sensor based on this type of design for its low cost. But, once I received the sensors, I realized I could have saved myself a few bucks by making my own sensor from a couple of wires or a piece of proto-board.

When standing water on the sensor shorts the two contacts, the resistance across the sensor drops to between 400 kΩ and 600 kΩ. The sensor is used as the bottom resistor in a voltage divider with a 1-MΩ resistor up top. The output of the divider is routed to the 12-bit analog inputs on the RX62N microcontroller. Figure 1 shows the sensor interface circuit. When the voltage read by the analog-to-digital converter (ADC) drops below 2 V, it’s time to start bailing. Two sensors are connected: one in the catch pan under the water heater, and a second one just outside the catch pan to detect failures in the small expansion tank.

Figure 1: The sensor interface to the YRDK RX62N board

COMMUNICATIONS CHOICES

One of my project goals was to push notifications to my cell phone because Murphy’s Law says water heaters are likely to fail while you’re away for the weekend. Because I wanted to keep the project costs low, I used my home’s broadband connection as the gateway for the attic monitor. The Renesas RX62N microcontroller includes a 100-Mbps Ethernet controller, so I simply plugged in the cable to connect the board to my home network. The open-source µIP stack supplied by Renesas with the YRDK provides the protocol engine needed to talk to the Internet.

There were a couple of complications with using my home network as the attic monitor’s gateway to the world. It is behind a firewall built into my router and, for security reasons, I don’t want to open up ports to the outside world.

My Internet service provider (ISP) occasionally changes the Internet protocol (IP) address associated with my cable modem. So I would never know what address to point my web browser. I needed a solution that would address both of these problems. Enter Exosite, a company that provides solutions for cloud-based, machine-to-machine (M2M) communications.

TALKING TO THE CLOUD

Exosite provides a number of software components and services that enable M2M communications via the cloud. This is a different philosophy from supervisory control and data acquisition (SCADA) systems I’ve used in the past. The control systems I’ve worked on over the years typically involve a local host polling the hundreds or thousands of connected sensors and actuators that make up a commercial SCADA system. These systems are generally designed to be monitored locally at a single location. In the case of the attic monitor, my goal was to access a limited number of data points from anywhere, and have the system notify me rather than having to continuously poll. Ideally, I’d only hear from the device when there was a problem.

Exosite is the perfect solution: the company publishes a set of simple application programming interfaces (APIs) using standard web protocols that enable smart devices to push data to their servers in the cloud in real time. Once the data is in the cloud, events, alerts, and scripts can be created to do different things with the data—in my case, to send me an e-mail and SMS text alert if there is anything wrong with my water heater. Connected devices can share data with each other or pull data from public data sources, such as public weather stations. Exosite has an industrial-strength platform for large-scale commercial applications. It provides free access to it for the open-source community. I can create a free account that enables me to connect one or two devices to the Exosite platform.

Embedded devices using Exosite are responsible for pushing data to the server and pulling data from it. Devices use simple HTTP requests to accomplish this. This works great in my home setup because the attic monitor can work through my firewall, even when my Internet provider occasionally changes the IP address of my cable modem. Figure 2 shows the network diagram.

Figure 2: The cloud-based network

VIRTUAL USER INTERFACE

Web-based dashboards hosted on Exosite’s servers can be built and configured to show real-time and historical data from connected devices. Controls, such as switches, can be added to the dashboards to push data back down to the device, enabling remote control of embedded devices. Because the user interface is “in the cloud,” there is no need to store all the user interface (UI) widgets and data in the embedded device, which greatly reduces the storage requirements. Photo 4 shows the dashboard for the attic monitor.

Photo 4: Exosite dashboard for the attic monitor

Events and alerts can be added to the dashboard. These are logical evaluations Exosite’s server performs on the incoming data. Events can be triggered based on simple comparisons (e.g., a data value is too high or too low) or complex combinations of a comparison plus a duration (e.g., a data value remains too high for a period of time). Setting up a leak event for one of the sensors is shown in Photo 5.

Photo 5: Creating an event in Exosite

In this case, the event is triggered when the reported ADC voltage is less than 2 V. An event can also be triggered if Exosite doesn’t receive an update from the device for a set period of time. This last feature can be used as a watchdog to ensure the device is still working.

When an event is triggered, an alert can optionally be sent via e-mail. This is the final link that enables an embedded device in my attic to contact me anywhere, anytime, to alert me to a problem. Though I have a smartphone that enables me to access my e-mail account, I can also route the alarm message to my wife’s simpler phone through her cellular provider’s e-mail-to-text-message gateway. Most cellular providers offer this service, which works by sending an e-mail to a special address containing the cell phone number. On the Verizon network, the e-mail address is <yourcellularnumber>@vtext.com. Other providers have similar gateways.

The attic monitor periodically sends heartbeat messages to Exosite to let me know it’s still working. It also sends the status of the water sensors and the current temperature in the attic. I can log in to Exosite at any time to see my attic’s real-time status. I have also configured events and alarms that will notify me if a leak is detected or if the temperature gets too hot…

The complete article includes details such about the Internet engine, reading the cloud, tips for updating the design, and more.  You can read the entire article by typing netenabledcontrol to open the password-protected PDF.

CC264: Plan, Construct, and Secure

Circuit Cellar July 2012 features innovative ideas for embedded design projects, handy design tips with real-world examples, and essential information on embedded design planning and security. A particularly interesting topic covered in this issue is the microcontroller-based home control systems (HCS). Interest in building and HCSes never wanes. In fact, articles about such projects have appeared in this magazine since 1988.

Circuit Cellar 264 (July 2012) is now available.

Turn to page 18 for the first HCS-related article. John Breitenbach details how he built an Internet-enabled, cloud-based attic monitoring system. Turn to page 36 for another HCS article. Tommy Tyler explains how to build a handy MCU-based digital thermometer. You can construct a similar system for your home, or you can apply what you learn to a variety of other temperature-sensing applications. Are you currently working on a home automation design or industrial control system? Check out Richard Wotiz’s “EtherCAT Orchestra” (p. 52). He describes an innovative industrial control network built around seven embedded controllers.

John Breitenbach's DIY leak-monitoring system

The wiring diagram for Tommy Tyler's MCU-based digital thermometer

The rest of the articles in the issue cover essential electrical engineering concepts and design techniques. Engineers of every skill level will find the information immediately applicable to the projects on their workbenches.

Tom Struzik’s article on USB is a good introduction to the technology, and it details how to effectively customize an I/O and data transfer solution (p. 28). On page 44, Patrick Schaumont introduces the topic of electronic signatures and then details how to use them to sign firmware updates. George Novacek provides a project development road map for professionals and novices alike (p. 58). Flip to page 62 for George Martin’s insight on switch debouncing and interfacing to a simple device. On page 68, Jeff Bachiochi tackles the concepts of wireless data delivery and time stamping.

Jeff Bachiochi's hand-wired modules

I encourage you to read the interview with Boston University professor Ayse Kivilcim Coskun on page 26. Her research on 3-D stacked systems has gained notoriety in academia, and it could change the way electrical engineers and chip manufacturers think about energy efficiency for years to come. If you’re an engineer fascinated by “green computing,” you’ll find Coskun’s work particularly intriguing.

Special note: The Circuit Cellar staff dedicates this issue to Richard Alan Wotiz who passed away on May 30, 2012. We appreciate having had the opportunity to publish articles about his inventive projects and innovative engineering ideas and solutions. We extend our condolences to his family and friends.

Circuit Cellar Issue 264 (July 2012) is now available on newsstands. Go to Circuit Cellar Digital and then select “Free Preview” to take a look at the first several pages.

Tech Highlights from Design West: RL78, AndroPod, Stellaris, mbed, & more

The Embedded Systems Conference has always been a top venue for studying, discussing, and handling the embedded industry’s newest leading-edge technologies. This year in San Jose, CA, I walked the floor looking for the tech Circuit Cellar and Elektor members would love to get their hands on and implement in novel projects. Here I review some of the hundreds of interesting products and systems at Design West 2012.

RENESAS

Renesas launched the RL78 Design Challenge at Design West. The following novel RL78 applications were particularly intriguing.

  • An RL78 L12 MCU powered by a lemon:

    A lemon powers the RL78 (Photo: Circuit Cellar)

  • An RL78 kit used for motor control:

    The RL78 used for motor control (Photo: Circuit Cellar)

  • An RL78 demo for home control applications:

    The RL78 used for home control (Photo: Circuit Cellar)

TEXAS INSTRUMENTS

Circuit Cellar members have used TI products in countless applications. Below are two interesting TI Cortex-based designs

A Cortex-M3 digital guitar (you can see the Android connection):

TI's digital guitar (Photo: Circuit Cellar)

Stellaris fans will be happy to see the Stellaris ARM Cortex -M4F in a small wireless application:

The Stellaris goes wireless (Photo: Circuit Cellar)

NXP mbed

Due to the success of the recent NXP mbed Design Challenge, I stopped at the mbed station to see what exciting technologies our NXP friends were exhibiting. They didn’t disappoint. Check out the mbed-based slingshot developed for playing Angry Birds!

mbed-Based sligshot for going after "Angry Birds" (Photo: Circuit Cellar)

Below is a video of the project on the mbedmicro YouTube page:

FTDI

I was pleased to see the Elektor AndroPod hard at work at the FTDI booth. The design enables users to easily control a robotic arm with Android smartphones and tablets.

FTDI demonstrates robot control with Android (Photo: Circuit Cellar)

As you can imagine, the possible applications are endless.

The AndroPod at work! (Photo: Circuit Cellar)

Living & Working Off the Grid

Interested in engineering your own solar panel system installation? If so, you’ve likely begun researching photovoltaic technology, construction materials, and test equipment on the Internet. Have you been satisfied with the information you’ve found? Probably not. There’s simply a scarcity of reliable electronics engineering advice out there about serious solar panel installation projects. Enter Circuit Cellar. Over the past several years, we’ve published articles by professional engineers about their own installations.

Three panels are wired in series and run into the MPPT controllers. Their capacity is 170 W each, 510 W total, to charge the batteries and put off running the generator. (Source: George Martin CC218)

So, before you get sidetracked with another 3-minute video or bullet-point tutorial, do yourself a favor and read columnist George Martin’s two-part article series “Living and Working Off the Grid.” Here’s an excerpt from Part 1:

“First, I’m an engineer—and an electrical one at that (except my degree is so old that it reads “DC ONLY!”). In addition, my neighbors in New Mexico already have systems up and running. Jeff and Pat live up the road in a handmade log home. Jeff is a former engineer for General Motors (Pontiac GTO, Avanti, and Saturn to his credit). That makes for some interesting discussions about how electronics will revolutionize the car industry, but I digress. He’s a mechanical engineer who doesn’t fully embrace all of this electrical stuff. He has a minimal system with four panels of about 150 W each. Another neighbor’s system has about 3 kW of panels. Armed with the idea that it could be done, I started to match up equipment with our requirements.

The equipment I selected falls into four main categories: solar panels, inverters, charge controllers, and batteries. In fact, you could consider each independently and not get too far off an ideal system. There are, however, some areas of concern when mating equipment from different manufactures, so I stayed with one manufacturer for the control devices.

SOLAR PANELS

Solar panels convert solar energy into electrical energy. Again, there is a lot of literature available about how this is accomplished. But what about some hard code conversion details? Standard test conditions require a temperature of 25°C and an irradiance of 1,000 W/m² with an air mass of 1.5 (AM1.5) spectrum. They correspond to the irradiance and spectrum of sunlight incident on a clear day on a sun-facing 37° tilted surface with the sun at an angle of 41.81° above the horizon. This condition approximately represents solar noon near the spring and autumn equinoxes in the continental U.S. with the surface of the cell aimed directly at the sun. Thus, under such conditions, a solar cell with a 12% efficiency and a 100 cm2 (0.01 m2) surface area can be expected to produce approximately 1.2 W of power.[1] This gives you an idea of what’s involved in rating and selecting solar panels. Look at the University of Western New Mexico’s weather site for solar radiation and you’ll get a feeling for the actual solar radiation for the area.

There is another consideration when selecting a panel, namely cost per watt. If you start looking, you will find panels of different wattages and different prices. In March 2004, I started a spreadsheet listing panels from 125 to 195. Note pricing from March 2004, purchased equipment in 2005, installed in 2006–2007, and operational in October 2007. Then, I added the costs different suppliers were charging for each panel and calculated a price/watt number.

My results range from $4.35 to $4.76 per watt. I estimated that I would need 3,000 W of panels, and came up with $13,320 for the cost of the BP Solar SX 170B.

More polysilicon is currently being used in solar panel manufacturing than all other usages combined, so this is big business. It also seems that the larger-power-rating panels command a higher price per watt. It is sort of like the CPU business where chips are speed graded and priced accordingly.

My cost estimates are a bit old, so you’ll need to run the numbers with today’s prices. Let me add that I found solar panels to be in tight supply, so when you begin your design, look to secure the panels at a good price early in the game.

The 3,000 W in my design was derived from the sun’s availability in the winter. Figure 2 represents the solar radiation for an actual cloudless winter day.

Figure 2: The actual solar radiation recorded by Western New Mexico University in Silver City about 30 miles to the west of the house site. (Source: George Martin CC 216)

The peak radiation is 600 W/m2. Let’s estimate that the shape of the curve is a sine function so that the area under the curve is its average value (2/pi, or 0.6366 times the peak value) multiplied by its width. So, that is 600 W/m2 × 0.6366 × 8 h (9 A.M. to 5 P.M.), or 3,055.7 Wh/m2. Therefore: Close to 10 kWh per day is good enough for the workshop, but not enough for the house when it’s built. And 3 kW of panels is what one neighbor is using.

We also need to account for cloudy days. The energy to run the workshop would need to come from the battery or backup generator. Another concern is hot summer days when the panel efficiency drops because of the heat. But the days are longer in the summer. Actually, it’s still a 24-hour day, but there is more available sunlight each day. I don’t have test results for summer generation (because I’m writing this in February 2008 after getting the system put together in October 2007), so stay tuned. The last point to watch out for in panel selection is cold weather open-circuit voltage going into the charge controller.

In the cold, with no current drawn, the open-circuit voltage of the solar panel will rise. If several panels are connected in series (for efficiency), this voltage may damage the input to the charge controller. This is a well-known situation and your equipment dealer will be able to guide you in this area.

INVERTERS

I must confess that I find inverters boring. They are not as exciting as solar panels, charge controllers, or even batteries. I thought I would not find much difference in available inverters and that probably was due to my lack of enthusiasm. I selected inverters from OutBack Power Systems. I wanted the inverter/charge controller combination to be from one manufacturer. As I looked at the literature, OutBack seemed to have covered all of the issues for my installation. I ended up with two OutBack VFX3648 inverters (see Photo 2).

Photo 2: The placement of the Outback System next to the feed into the normal house distribution panel. (Source: George Martin CC216)

They are 3.6 kW (continuous) with connections for a 48-V battery and vented. You will find vented and sealed inverters. I selected vented because they typically have a larger power rating and I’m not in a harsh environment.

Also, the inverters are located in an area that is protected from the elements. Another option is a fan on the inverter. The fan also gives you more capacity, but what will you do when the fan fails, and you know it will? Our system is a normal 220-V home application. So, there are two inverters, one for each phase. OutBack has a neat option that includes a transformer to supply the second phase so the second inverter can remain in a low-power operating mode. When the power requirements become large enough, the main inverter will signal the second (slave) inverter to start up and handle the increased load. This is a good setup for our application. We can install a normal commercial heating/cooling system and power up only the second inverter when the load is calling for it.

Click here to read the entire article series.

 

Radiant Floor Heating Zone Controller Project

Even if you aren’t interested in designing a radiant floor zoned heating system, you can study this innovative project and apply what you learn to any number of building control and automation applications. Dalibor Zaric’s Radiant Floor Heating Zone Controller is built around an NXP Semiconductors LPC2134 ARM processor that’s connected to an Echelon Pyxos chip. The project won Second Place in Echelon’s 2007 “Control Without Limits” design competition.

The heat zone controller system (Source: Echelon & Dalibor Zaric)

Zaric provides the following details in his project documentation:

“• Power supply to unit is 24VAC and controller has switching power supply to provide 24VDC for Pyxos network as well 5V for logic, there is 3.3V linear regulator as well.

• There are four relay with 24VAC output to power up thermoelectric zone valve on radiant floor heating manifold. These outputs are protected with 1.85A self resetting fuse to prevent overloading. This block has as well 24VAC/DC dry contact to provide a call for heat to boiler or optional zones pump.

• Pyxos power supply filter and Pyxos chip provides Pyxos network connection for future sensors and thermostats. Pyxos thermostat will be more cost effective than regular LONWorks sensors/thermostats.

• RS-485 driver will provide future Modbus connection for local touch screens or smart home systems with Modbus connections. There is end of line resistors enabled with the dip switches beside connector.

• 3150 Neuron board with 64K flash provides LONWorks connection to the controller.”

 

The heat zone controller diagram (Source: Echelon & Dalibor Zaric)

For more information about Pyxos technology, visit www.echelon.com.

This winning project, as well as others, was promoted by Circuit Cellar based on a 2007 agreement with Echelon.

 

Solid-State Lighting Solutions Project

Electronics system control, “green design,” and energy efficiency are important topics in industry and academia. Here we look at a project from San Jose-based Echelon Corp.’s 2007 “Control Without Limits” design competition. Designers were challenged to implement Pyxos technology in innovative systems that reduced energy consumption. Daryl Soderman and Dale Stepps (of INTELTECH Corp.) took First Prize for their Solid State Lighting Solutions project.

The Pyxos chip is on the board (Source: Echelon & Inteltech)

So, how does it work? Using the Pyxos FT network protocol, this alternative lighting project is a cost-effective, energy-efficient solution that’s well-suited for use in residential, commercial, or public buildings. You can easily embed the LED lighting and control system—which features SSL lighting, a user interface, motion detectors, and light sensors—in an existing network. In addition, you can control up to five zones in a building by using the system’s fully programmable ESB-proof touchpad.

Another view of the Pyxos chip is on the board (Source: Echelon & Inteltech)

 

For more information about Pyxos technology, visit www.echelon.com.

This winning project, as well as others, was promoted by Circuit Cellar based on a 2007 agreement with Echelon.