DIY Green Energy Design Projects

Ready to start a low-power or energy-monitoring microcontroller-based design project? You’re in luck. We’re featuring eight award-winning, green energy-related designs that will help get your creative juices flowing.

The projects listed below placed at the top of Renesas’s RL78 Green Energy Challenge.

Electrostatic Cleaning Robot: Solar tracking mirrors, called heliostats, are an integral part of Concentrating Solar Power (CSP) plants. They must be kept clean to help maximize the production of steam, which generates power. Using an RL78, the innovative Electrostatic Cleaning Robot provides a reliable cleaning solution that’s powered entirely by photovoltaic cells. The robot traverses the surface of the mirror and uses a high voltage AC electric field to sweep away dust and debris.

Parts and circuitry inside the robot cleaner

Cloud Electrofusion Machine: Using approximately 400 times less energy than commercial electrofusion machines, the Cloud Electrofusion Machine is designed for welding 0.5″ to 2″ polyethylene fittings. The RL78-controlled machine is designed to read a barcode on the fitting which determines fusion parameters and traceability. Along with the barcode data, the system logs GPS location to an SD card, if present, and transmits the data for each fusion to a cloud database for tracking purposes and quality control.

Inside the electrofusion machine (Source: M. Hamilton)

The Sun Chaser: A GPS Reference Station: The Sun Chaser is a well-designed, solar-based energy harvesting system that automatically recalculates the direction of a solar panel to ensure it is always facing the sun. Mounted on a rotating disc, the solar panel’s orientation is calculated using the registered GPS position. With an external compass, the internal accelerometer, a DC motor and stepper motor, you can determine the solar panel’s exact position. The system uses the Renesas RDKRL78G13 evaluation board running the Micrium µC/OS-III real-time kernel.

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Water Heater by Solar Concentration: This solar water heater is powered by the RL78 evaluation board and designed to deflect concentrated amounts of sunlight onto a water pipe for continual heating. The deflector, armed with a counterweight for easy tilting, automatically adjusts the angle of reflection for maximum solar energy using the lowest power consumption possible.

RL78-based solar water heater (Source: P. Berquin)

Air Quality Mapper: Want to make sure the air along your daily walking path is clean? The Air Quality Mapper is a portable device designed to track levels of CO2 and CO gasses for constructing “Smog Maps” to determine the healthiest routes. Constructed with an RDKRL78G13, the Mapper receives location data from its GPS module, takes readings of the CO2 and CO concentrations along a specific route and stores the data in an SD card. Using a PC, you can parse the SD card data, plot it, and upload it automatically to an online MySQL database that presents the data in a Google map.

Air quality mapper design (Source: R. Alvarez Torrico)

Wireless Remote Solar-Powered “Meteo Sensor”: You can easily measure meteorological parameters with the “Meteo Sensor.” The RL78 MCU-based design takes cyclical measurements of temperature, humidity, atmospheric pressure, and supply voltage, and shares them using digital radio transceivers. Receivers are configured for listening of incoming data on the same radio channel. It simplifies the way weather data is gathered and eases construction of local measurement networks while being optimized for low energy usage and long battery life.

The design takes cyclical measurements of temperature, humidity, atmospheric pressure, and supply voltage, and shares them using digital radio transceivers. (Source: G. Kaczmarek)

Portable Power Quality Meter: Monitoring electrical usage is becoming increasingly popular in modern homes. The Portable Power Quality Meter uses an RL78 MCU to read power factor, total harmonic distortion, line frequency, voltage, and electrical consumption information and stores the data for analysis.

The portable power quality meter uses an RL78 MCU to read power factor, total harmonic distortion, line frequency, voltage, and electrical consumption information and stores the data for analysis. (Source: A. Barbosa)

High-Altitude Low-Cost Experimental Glider (HALO): The “HALO” experimental glider project consists of three main parts. A weather balloon is the carrier section. A glider (the payload of the balloon) is the return section. A ground base section is used for communication and display telemetry data (not part of the contest project). Using the REFLEX flight simulator for testing, the glider has its own micro-GPS receiver, sensors and low-power MCU unit. It can take off, climb to pre-programmed altitude and return to a given coordinate.

High-altitude low-cost experimental glider (Source: J. Altenburg)

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! 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.


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)


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


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.


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


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> 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.

Build a Microcontroller-Based Mail Client

Does the sheer amount of junk mail that fills your Inbox make you hate everything about e-mail? If so, it’s time to have a little fun with electronic mail by building a compact microcontroller-based mail client system. Alexander Mann designed a system that uses an Atmel ATmega32 and a Microchip Technology ENC28J60 Ethernet controller to check continuously for e-mail. When a message arrives, he can immediately read it on the system’s LCD and respond with a standard keyboard.

Mann writes:

My MiniEmail system is a compact microcontroller-based mail client (see Photo 1). The silent, easy-to-use system doesn’t require a lot of power and it is immune to mail worms. Another advantage is the system’s short start-up time. If you want to write a quick e-mail but your PC is off, you can simply switch on the miniature e-mail client and start writing without having to wait for your PC to boot up and load the necessary applications. All you need is an Ethernet connection and the MiniEmail system.

Photo 1: The complete MiniEmail system includes an LCD, a keyboard, and several connections. (A. Mann, Circuit Cellar 204)


The hardware for the MiniEmail system is inexpensive. It cost me about $50. The LCD is the most expensive part. To keep things simple, I left the system’s power supply, 5- to 3.3-V conversion crystals, and latch out of Figure 1.

Figure 1: This is a block diagram of MiniEmail’s hardware. The arrows indicate the directions of data flow between the devices. The rounded boxes indicate parts that do not sit on the circuit board.

The main components are an Atmel ATmega32 microcontroller and a Microchip Technology ENC28J60 Ethernet controller. Because a mail client is a piece of complex software, you need a fast microcontroller that has a considerable amount of program space. The MiniEmail system uses almost all of the ATmega32’s features, including the SPI, internal EEPROM and SRAM, counters, USART interface, sleep modes, all 32 I/O lines, and most of the 32 KB of program memory. The ENC28J60 is a stand-alone Ethernet controller that provides basic functionality for transmitting frames over an Ethernet connection. It has 8 KB of built-in SRAM, which can be divided into transmit and receive buffers as desired, and it provides several interrupt sources (e.g., when new packets have arrived). The ATmega32 also has 128 KB of external SRAM connected as well as an LCD, which is a standard module with a resolution of 128 × 64 pixels.

Take a look at the ATmega32’s pin connections in Figure 2. Ports A and C are used as 8-bit-wide general I/O ports, one of which is latched using an NXP Semiconductors 74HC573.

Figure 2: Here’s the complete schematic for the MiniEmail. The LF1S022 is the RJ-45 connector for the Ethernet connection.

The two ports provide data connections to the LCD and SRAM (U3). For the SRAM, you need three additional wires: write (*RAM_WR), read strobe (*RAM_RD), and the seventeenth bit of the address (ADDR16). The LCD connector (CON1) uses five additional wires (for the signals CS1, CS2, DI, EN, and RW). CS1 and CS2 are taken from the general I/O port A (DATA6 and DATA7) and determine which of the two halves of the LCD is selected (i.e., the two controllers on the LCD module you are talking to). RW (where you can use ADDR16 again) sets the direction of the LCD access (read or write). DI describes the type of instruction sent to the LCD. EN is the enable signal for read and write cycles. For the keyboard, you need only two pins: KEY_DATA and KEY_CLOCK. The clock signal must be connected to an external interrupt pin, INT1. One additional wire is needed to switch the latch (LE).

You are left with eight I/O pins on the ATmega32’s ports B and D. RXD and TXD are connected to a MAX232, an RS-232 level converter that also provides the negative supply voltage needed for the LCD (LCD_VOUT in Figure 2). The ATmega32’s USART functionality is used as a debugging interface. It isn’t needed for normal operation.


The firmware for this project is posted on the Circuit Cellar FTP site. I wrote the firmware in C language with a few small parts of inline assembler. I used the open-source software suite WinAVR, which includes the GNU GCC compiler with special libraries for AVR devices and avrdude, a tool for the in-system programming of AVR microcontrollers…


The user interface consists of three control elements: menus, edit fields, and an elaborate text editor. A special screen (the Mail Menu) enables you to quickly browse through your mailbox. After power-up, the system displays a greeting message. After a short while, the Main menu appears (see Photo 2).

Photo 2: This is a screenshot of MiniEmail’s main menu. In the upper-right corner, a clock shows the current time, which is retrieved from the Internet. An arrow to the left of the menu items indicates the selected item. (A. Mann, Circuit Cellar 204)

The Compose Mail, Check Mailbox, and Configuration submenus form a hierarchical menu structure. When the other items listed beneath the respective menu titles in the diagram are activated (e.g., start the text editor), they enable you to input data, such as a username and password, or retrieve mail from the mail server. “Standby” is the only action that is accessible directly from the main menu. All other actions are grouped by function in the submenus.


With respect to the firmware, sending mail is much easier than reading it, so let’s first focus on the Compose Mail menu. The first item in the menu starts the text editor so you can enter the body of your letter. You then enter the recipient’s mailing address and the subject of your e-mail, just like you would do when sending e-mail from your PC. Additional fields, such as CC or BCC are not included, but since this requires only one more line in the header of the mail, it is not difficult. Your e-mail also needs a reply address, so the recipient knows who sent the mail. The reply address is normally the same for all of the messages you write. The text you enter in this edit field is stored in the ATmega32’s EEPROM, so you don’t have to type it every time you write a letter. After you select the last menu item, “Send” initiates the dispatch of the mail and displays a message that indicates whether or not it was successful.


What makes this part more sophisticated is the ability to handle not only one e-mail at a time, but also fetch mail from the server. The system can determine which messages are new and which messages have been read. It can also extract data such as the sender, subject, or sent date from the header of the mail and then display the information.

The amount of mail the firmware can handle is limited by the size of the external SRAM. The maximum number of e-mails is currently 1,024. (If you’ve got more mail, you will be so busy answering it that you won’t have time to build your own MiniEmail client—or you should delete some old mail). Note that 1,024 is the number of unique identifiers that the system can remember. The server assigns a unique identifier to each piece of mail. The system uses the identifiers to keep track of which letters are new on the server, which have already been read, and which have been marked for deletion.

All of the header data for all of the 1,024 messages cannot be held in SRAM at once; only the most recent (about 50) mail headers are held. When you want to browse through older e-mails, the firmware automatically reconnects to the server and fetches the headers of the next 50 e-mails.

When you select Check Mailbox in the main menu, you get to a submenu where you can retrieve and read mail. Before you can collect your mail, you must enter your username and password, which can be stored in EEPROM for your convenience. The firmware then retrieves the headers and displays the Mail Menu, where you can browse through your e-mail. Apart from the size and the date, the first 42 characters of the subject and the mail sender are shown. In the first row, additional icons indicate (from left to right) whether a message is new, has been marked for deletion, or has been read. You can view the content of the selected message by pressing Return. When the mail is fetched from the server, it is prepared for viewing. The header and HTML tags, as well as long runs of the same character, are stripped from the mail and base64 decoding (used to encode 8-bit characters) is performed, so the content of the message is as readable as plain text. Binary attachments (e.g., images) can’t be handled. Following this, the mail is viewed in the text editor (with editing disabled).

A similar action is performed when you press “r” in the Mail Menu. In that case, you can edit the text so you can add your reply. Leaving the text editor will bring you back to the Send Mail menu, where the reply address and subject will be filled in so your mail will be clear for take-off. To delete a message, simply press D to mark it for deletion….


I hadn’t imagined how many details would need to be considered when I started this project more than a year ago. It has been a very interesting and challenging project. It has also been a lot of fun.

The MiniEmail system provides all of the basics for communicating via email, but such a project is never really finished. There are still dozens of items on my to-do list. Fortunately, the ATmega32 can be replaced with a new member of the AVR family, the Atmel ATmega644, which is pin-compatible to the ATmega32 and has twice the flash memory (and internal SRAM). That will provide enough space for many of my new ideas. I want to get rid of the static IP address, add CC and BCC fields, use a bigger display or a smaller (variable-width) font, improve the filtering and display of mail content and attachments, and add an address book (it would be best in combination with an additional external EEPROM with an SPI, such as the AT25256).

This project proves, rather impressively, that the ATmega32 and the ENC28J60 are a powerful combination. They can be used for many useful Internet applications. My e-mail client system is surely one of the most exciting. I can think of many other interesting possibilities. At the moment, my MiniEmail assembly serves as an online thermometer so I can check my room’s temperature from anywhere in the world…

Mann’s entire article appears in Circuit Cellar 204, 2007. Type “miniemailopen”  to access the password-protected article.