What Is Emissivity? (EE Tip #133)

All objects radiate infrared energy. The warmer an object is, the faster the molecules in the object move about, and as a result the more infrared energy it radiates. The wavelength of this radiation lies roughly between 0.5 and 100 μm. This depends on the temperature: the higher the temperature, the shorter the wavelength of the radiated IR energy, as illustrated in Figure 1 for several different temperatures.Fig1-IR-Rad-Elektor

This means that an IR thermometer must be able to detect energy radiated in a specific spectrum in the IR band in order to be able to measure temperatures accurately over a wide temperature range. In addition, you should bear in mind that only perfect radiators (in technical terms, “black bodies”) actually radiate all of their thermal energy. With other types of objects, the amount of energy radiated also depends on factors other than the temperature of the object, such as the properties of the material and surface reflection. This is expressed by the emissivity or emission coefficient of the material, and it can strongly affect the accuracy of IR temperature measurements.

Emissivity (or the emission coefficient) is an indication of the extent to which the thermal infrared radiation emitted by an object is determined by the object’s own temperature. A value of 1 means that the infrared radiation is determined solely by the object’s own temperature. A value less than 1 indicates that the emitted radiation depends in part on factors other than the object’s own temperature, such as nearby objects or heat transmission.Table-Emissivity-Elektor

Simple IR thermometers usually have a fixed emission coefficient setting of 0.95. If the emissivity of the object to be measured differs from this, the resulting readings will be inaccurate. More expensive instruments have an adjustable emission coefficient setting.

The emissivity values of a number of materials are listed in the table. They have been compiled from lists provided by various manufacturers of IR thermometers. The emissivity of metals is strongly influenced by the processing undergone by the metal and the surface treatment.

When compiling the table, we noticed that every manufacturer states somewhat different values, which makes it rather difficult to derive the correct emissivity settings for an instrument from the table supplied with the instrument. The only sure way to determine the correct setting is to measure the temperature with a contact sensor.—By Harry Baggen (Elektor Netherlands Editorial), Elektor, April 2011

Q&A: Miguel Sanchez (Professor, Designer)

Miguel Sánchez (PhD, Computer Science) is Valencia, Spain-based computer scientist, embedded tech enthusiast, and professor who regularly challenges himself to design innovative microcontroller-based systems. Since 2005, Circuit Cellar has published six of his articles about projects such as a digital video recorder (Circuit Cellar 174) and a creative DIY image-processing system (Circuit Cellar 263).

This is a sample depth image projected in a 3-D space. It appeared in Sanchez’s article, “Image Processing System Development.” (Source: M. Sanchez, Circuit Cellar 263)

In the September issue of Circuit Cellar, Sánchez tells us about his background, his work at the Universitat Politècnica de València, his current interests, and his innovative designs. An abridged version of the interview follows.

NAN PRICE: How long have you been designing microcontroller-based systems?

MIGUEL SANCHEZ: I started using computers in 1978. I built my first microcontroller project in 1984 during my first year at Universitat Politècnica de València. I haven’t stopped designing embedded systems since then.

NAN: Tell us about the first microcontroller you worked with. Where were you at the time?

MIGUEL: Our university’s lab had Intel SDK-85 boards you could program in Hex using the built-in keyboard. I guess it wasn’t built well. You sometimes lost all your work while typing your code. I learned that schematics were available and a terminal monitor was built in too. So, I built my first microcontroller-based board around an Intel 8085 using the same software that was on the original ROM. But, I changed the serial port delay value so I could use 9,600 bps instead of the original 110 bps on the terminal port. This way, I could do the same labs as my mates, but I could do my work in 8080 Assembler, which was available in Control Program/Monitor (CP/M) computers. At the time, I had an Atari 1040 ST that could run CP/M on top of a Z-80 emulator. Assembly code could be uploaded to my board’s RAM memory and later executed using SDK-85 serial monitor code.

I used the 8085’s Wait signal to build an additional EEPROM socket in this same board that, with the aid of a 555 timer, was my first EEPROM programmer. I used the Wait signal to delay write operations. In fact, I used this programmer to change the original baud rate to the new one, as I originally did not know that was something I’d want to change later.

My teacher, who is now one of my colleagues, was quite amused with my development and he gave me an A+. I learned a lot about microcontrollers, serial communications, Assembly language, monitor programs, and EEPROM programming algorithms. And, I learned it was not fun to design PCBs with system buses on only one copper layer. …

NAN: You designed a system to simulate strokes on a keypad to trigger modes on an alarm system (“Reverse-Engineered ECP Bus,” Circuit Cellar 201, 2007). Why did you design it and how have you used it?

MIGUEL: A local company wanted to give new life to old Ademco alarm units. These boards could only be programmed by a serial port socket once a certain service code was typed at the keyboard. I was asked whether an add-on board could be created to make these old boards Internet-enabled so they could be remotely managed and reconfigured over the ’Net.

The first thing I needed to do was to figure out how to simulate the required keystrokes. But I couldn’t find any information about the way that bus worked, so I figured that out myself. Later, I thought both the information itself and the way I figured it out might be useful to others, so I approached Circuit Cellar editors with a proposal to write an article.

That project ended up as a Rabbit-core powered board that connected the alarm board and the remote access to its serial port. Combined with a virtual serial port on the PC, it fooled the original management software into thinking the PC was directly connected to the alarm board, although it was all happening over the Internet. But the project never made it to the market for reasons unknown.

NAN: In “Three-Axis Stepper Controller” (Circuit Cellar 234, 2010), you describe how you built an Arduino-based, platform-independent driver board. Tell us about the design.

MIGUEL: When I discovered the Arduino platform, I was surprised by a few things. First, this development system was not designed by a chip vendor. Second, it was not intended for engineers but for artists! Third, I was shocked because it was multiplatform (which was possible because it was based on Java and GCC) and because none of the other development systems I was aware of were so easy to use. The price was low too, which was a plus for hobbyists and students.

The aim of that project was to show all that to the readers. The idea was also not only to show how to build a stepper controller and to explain the difference between the drive modes and the bipolar and unipolar designs, but to demonstrate how easy it was to work with Arduino.

In his 2010 article, “Three-Axis Stepper Controller,” Sanchez provided this controller circuit schematic to interface Arduino I/O headers with stepper motors. (Source: M. Sanchez, Circuit Cellar 234)

NAN: Your most recent Circuit Cellar article, “Image Processing System Development: Use an MCU to Unleash the Power of Depth Cameras” (263, 2012), describes how you used Microsoft’s Kinect motion-sensing device for an interactive art project. Tell us about the project and how you came to be involved.

MIGUEL: My university offers a master’s degree in fine arts. I met a professor from the drawing department who had seen a video of my vertical plotter on YouTube and was interested in contacting me, as we worked on the same campus. We became friends and he asked me to help him out with an idea for an installation.

The first approach used an RGB camera, but then Kinect was launched. From what I read on the ’Net, I was convinced it would be a better mousetrap. So, I bought one unit and started learning how to use it, thanks to the hack that had been made available.

The project required gathering visitors’ silhouettes and later drawing them on a big wall. The drawing was performed with a properly scaled-up version of my vertical plotter, which, by the way, was controlled by an Arduino board.

I have found working with artists is a lot of fun too, as they usually have a totally different vision than engineers.

The full article appears in the September issue.

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>@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.

Issue 265: Design with End Users in Mind

Whether you’re building or programming microcontroller-based systems, you should always keep your end users and their needs in mind. That means restraining any urges to stuff a project with superfluous functionality and parts. In “What Were They Thinking?” (Circuit Cellar 165), Steve Ciarica argues that over-engineered electronics products are typically more annoying than impressive. Ciarcia writes:

I’ve mentioned this before, but the original BMW iDrive on my 2002 745iL was a prime example of overzealous design. Back then, somebody had the bright idea of condensing nearly all the switches and knobs formerly found on typical car dashboards down to a large knob, called iDrive, on the center console. Combined with a fancy graphics LCD, the joystick provided the driver with 3-D motion control for selecting specific subsystems and individual functions within that subsystem. The bad news was that zooming into and backing out of various control functions was so complicated it was a real driving hazard.

I’m guessing the iDrive designers got caught up in the process of creating a slick design and completely forgot about the basic reason you’re in the car in the first place—to drive, not to run a computer! Let’s face it, when you’re driving, it’s more expedient to reach for a single-function control you can locate out of the corner of your eye. The world was not ready to deal with a 3-D joystick, a complex decision tree on an LCD, and a dozen hand motions to tell a computer to accomplish the same thing. With the original iDrive, you either left the same Sirius station on forever with the hot air blowing in your face or learned to use the voice-response system to at least jump over some of the “slick” functionality and get directly to the heater or radio LCD screens.

It took until I got my 2010 X5 for them to get it right. (My three BMWs in between had iterative improvements.) The solution? They put most of the buttons back! Yeah, like most other cars these days, it still has a joystick knob and an LCD that controls individual settings, but a “real” button takes you directly to the right subsystem.

Circuit Cellar Project Editor Dave Tweed related another example to me while I was talking to him about this editorial idea. He told me about the Kawasaki intelligent proximity activation start system (KIPASS), which is an ignition system for some of Kawasaki’s high-end motorcycles that’s based on a “proximity fob” (RFID). If the physical key is in the ignition and you bring the fob within a few feet of the bike, you can start it (by turning and pushing the key). Sounds nice, right?

You can leave the key in the ignition all the time. When you walk away with the fob in your pocket, the key is captured by an electric latch so it can’t be stolen. All’s well and good. But it seems that most riders are in the habit of stopping the engine by using the “kill switch” instead of turning off the key. That’s fine until you realize that the headlight is only controlled by the ignition key—the light stays on until you turn the key to the “off” position. On a normal bike, you would do this anyway in order to pocket the key before walking away. But with the KIPASS fob, you don’t need the key and lots of bikers simply stop the engine and walk away—leaving the headlight on and killing the battery.

Here’s where it gets fun. With a dead battery, you can’t start the bike except by jumping it using another vehicle. The Allen wrench you need to open the panel you have to remove to get at the battery is in the tool kit under the seat, which is locked by the ignition key. In a real Catch-22, the ignition key is still “captured” by KIPASS even without power, and you can’t remove it to unlock the seat! The only solution is to find a friend or a tow truck with both jumper cables and the correct Allen wrench.

Home theater equipment is another irritation. Forgiving for now that most functions can be accessed only from the remote control, you’d think the few buttons they do have would work correctly. For some reason, I’m finding the built-in buttons are a lot less responsive than the remote. I suspect the interrupt handling software for the IR receiver has a much higher priority than the hardwired switches. My Blu-ray player, in particular, virtually never responds to the physical change disc button on the front, and I almost always have to use the button on the remote. Even powering up the unit takes two to three firm panel button presses but only one click on the remote. My HDTV is similar. There’s a manual button to change the input selection, and it always takes two to three presses before it actually starts to switch inputs. On the IR remote, it is instant. Grrrr.

The point is, when designing a new piece of equipment, don’t get caught up demonstrating as much technology as possible to the exclusion of all other considerations. How hard can it be to design a piece of equipment to respond equally to a few hardwired buttons as well as the IR? Similarly, just because you have the computing power and software expertise, sometimes it’s counterproductive to put all functional control only in the remote control or to put every function into one multi-option/multitasking joystick. As a designer, you have a responsibility to reduce hardware costs by eliminating excess manual controls, but you should always take the time to put yourself in the place of the end user who has to deal with your choices. More importantly, think about what happens after the dog eats the remote.

Circuit Cellar August 2012 is now available.

Design West Update: Intel’s Computer-Controlled Orchestra

It wasn’t the Blue Man Group making music by shooting small rubber balls at pipes, xylophones, vibraphones, cymbals, and various other sound-making instruments at Design West in San Jose, CA, this week. It was Intel and its collaborator Sisu Devices.

Intel's "Industrial Controller in Concert" at Design West, San Jose

The innovative Industrial Controller in Concert system on display featured seven Atom processors, four operating systems, 36 paint ball hoppers, and 2300 rubber balls, a video camera for motion sensing, a digital synthesizer, a multi-touch display, and more. PVC tubes connect the various instruments.

Intel's "Industrial Controller in Concert" features seven Atom processors 2300

Once running, the $160,000 system played a 2,372-note song and captivated the Design West audience. The nearby photo shows the system on the conference floor.

Click here learn more and watch a video of the computer-controlled orchestra in action.