One Professor and Two Orderly Labs

Professor Wolfgang Matthes has taught microcontroller design, computer architecture, and electronics (both digital and analog) at the University of Applied Sciences in Dortmund, Germany, since 1992. He has developed peripheral subsystems for mainframe computers and conducted research related to special-purpose and universal computer architectures for the past 25 years.

When asked to share a description and images of his workspace with Circuit Cellar, he stressed that there are two labs to consider: the one at the University of Applied Sciences and Arts and the other in his home basement.

Here is what he had to say about the two labs and their equipment:

In both labs, rather conventional equipment is used. My regular duties are essentially concerned  with basic student education and hands-on training. Obviously, one does not need top-notch equipment for such comparatively humble purposes.

Student workplaces in the Dortmund lab are equipped for basic training in analog electronics.

Student workplaces in the Dortmund lab are equipped for basic training in analog electronics.

In adjacent rooms at the Dortmund lab, students pursue their own projects, working with soldering irons, screwdrivers, drills,  and other tools. Hence, these rooms are  occasionally called the blacksmith’s shop. Here two such workplaces are shown.

In adjacent rooms at the Dortmund lab, students pursue their own projects, working with soldering irons, screwdrivers, drills, and other tools. Hence, these rooms are occasionally called “the blacksmith’s shop.” Two such workstations are shown.

Oscilloscopes, function generators, multimeters, and power supplies are of an intermediate price range. I am fond of analog scopes, because they don’t lie. I wonder why neither well-established suppliers nor entrepreneurs see a business opportunity in offering quality analog scopes, something that could be likened to Rolex watches or Leica analog cameras.

The orderly lab at home is shown here.

The orderly lab in Matthes’s home is shown here.

Matthes prefers to build his  projects so that they are mechanically sturdy. So his lab is equipped appropriately.

Matthes prefers to build mechanically sturdy projects. So his lab is appropriately equipped.

Matthes, whose research interests include advanced computer architecture and embedded systems design, pursues a variety of projects in his workspace. He describes some of what goes on in his lab:

The projects comprise microcontroller hardware and software, analog and digital circuitry, and personal computers.

Personal computer projects are concerned with embedded systems, hardware add-ons, interfaces, and equipment for troubleshooting. For writing software, I prefer PowerBASIC. Those compilers generate executables, which run efficiently and show a small footprint. Besides, they allow for directly accessing the Windows API and switching to Assembler coding, if necessary.

Microcontroller software is done in Assembler and, if required, in C or BASIC (BASCOM). As the programming language of the toughest of the tough, Assembler comes second after wire [i.e., the soldering iron].

My research interests are directed at computer architecture, instruction sets, hardware, and interfaces between hardware and software. To pursue appropriate projects, programming at the machine level is mandatory. In student education, introductory courses begin with the basics of computer architecture and machine-level programming. However, Assembler programming is only taught at a level that is deemed necessary to understand the inner workings of the machine and to write small time-critical routines. The more sophisticated application programming is usually done in C.

Real work is shown here at the digital analog computer—bring-up and debugging of the master controller board. Each of the six microcontrollers is connected to a general-purpose human-interface module.

A digital analog computer in Matthes’s home lab works on master controller board bring-up and debugging. Each of the six microcontrollers is connected to a general-purpose human-interface module.

Additional photos of Matthes’s workspace and his embedded electronics and micrcontroller projects are available at his new website.

 

 

 

New 40-nm Microcontrollers for Motor Control

Renesas Electronics Corp. recently announced the RH850/C1x series of 32-bit microcontrollers (MCUs), which it said are designed for motor control in hybrid electric vehicles (HEVs) and electric vehicles (EVs). Based on Renesas’s 40-nm process, the RH850/C1x series features the RH850/C1H and RH850/C1M MCUs, which enable embedded designers to enhance efficiency, reduce system costs, and achieve higher safety levels for HEV/EV motor control systems.

Source: Renesas Electronics Corp.

Source: Renesas Electronics Corp.

The new RH850/C1x devices can be used with the RAA270000KFT RH850 family power supply management IC (PMIC), which is currently available in sample quantities. The power management IC integrates into one device all the power supply systems required for MCU operation, two external sensor power supply tracks, and a full complement of monitoring and diagnostic functions, significantly reducing the user burden associated with power supply system design.

The RH850/C1H and RH850/C1M MCUs incorporate large memory capacities achieved through 40 nm MONOS process technology. The RH850/C1x series is based on Renesas’s metal oxide nitride oxide silicon (MONOS) embedded flash, which has an extensive track record in mass production. The MONOS characteristics include fast readout, low power consumption, and large storage capacity. The RH850/C1M and RH850/C1H devices offer memory capacities of 2 MB and 4 MB, respectively. In addition, 32-KB data flash memory, with essentially the same functionality as EEPROM, is included for data storage.

The microcontrollers also feature an extensive set of peripheral functions for HEV/EV motor control. The RH850/C1x MCUs can implement three types of motor control in hardware: sine wave PWM, over modulation, and square wave.

Samples of the RH850/C1H and RH850/C1M MCUs are scheduled to be available from the beginning of 2015 and will cost $45 and $50 per unit, respectively. Mass production is scheduled for May 2016 and is expected to reach a scale of 100,000 units per month.

Source: Renesas Electronics Corp.

DIY Arduino-Based ECG System

Cornell University students Sean Hubber and Crystal Lu built an Arduino-based electrocardiography (ECG) system that enables them to view a heart’s waveform on a mini TV. The basic idea is straightforward: an Arduino Due converts a heartbeat waveform to an NTSC signal.

Here you can see the system in action. The top line (green) has a 1-s time base. The bottom line (yellow) has a 5-s time base. (Source: Hubber & Lu)

Here you can see the system in action. The top line (green) has a 1-s time base. The bottom line (yellow) has a 5-s
time base. (Source: Hubber & Lu)

In their article, “Hands-On Electrocardiography,” Hubber and Lu write:

We used the Arduino Due to convert the heartbeat waveform to an NTSC signal that could be used by a mini-TV. The Arduino Due continuously sampled the input provided by the voltage limiter at 240 sps. Similar to MATLAB, the vectorized signal was shifted left to make room at the end for the most recent sample. This provided a continuous real-time display of the incoming signal. Each frame outputted to the mini-TV contains two waveforms. One has a 1-s screen width and the other has a 5-s screen width. This enables the user to see a standard version (5 s) and a more zoomed in version (1 s). Each frame also contains an integer representing the program’s elapsed time. This code was produced by Cornell University professor Bruce Land.

As you can see in the nearby block diagram, Hubber and Lu’s ECG system comprises a circuit, an Arduino board, a TV display, MATLAB programming language, and a voltage limiter.

The system's block diagram (Circuit Cellar 289, 2014)

The system’s block diagram (Circuit Cellar 289, 2014)

The system’s main circuit is “separated into several stages to ensure that retrieving the signal would be user-safe and that sufficient amplification could be made to produce a readable ECG signal,” Hubber and Lu noted.

The first stage is the conditioning stage, which ensures user safety through DC isolation by initially connecting the dry electrode signals directly to capacitors and resistors. The capacitors help with DC isolation and provide a DC offset correction while the resistors limit the current passing through. This input-conditioning stage is followed by amplification and filtering that yields an output with a high signal-to-noise ratio (SNR). After the circuit block, the signal is used by MATLAB and voltage limiter blocks. Directly after DC isolation, the signal is sent into a Texas Instruments INA116 differential amplifier and, with a 1-kΩ RG value, an initial gain of 51 is obtained. The INA116 has a low bias current, which permits the high-impedance signal source. The differential amplifier also utilizes a feedback loop, which prevents it from saturating.

Following the differentiation stage, the signal is passed through multiple filters and receives additional amplification. The first is a low-pass filter with an approximately 16-Hz cutoff frequency. This filter is primarily used to eliminate 60-Hz noise. The second filter is a high-pass filter with an approximately 0.5-Hz cutoff frequency. This filter is mostly used to eliminate DC offset. The total amplification at this stage is 10. Since the noise was significantly reduced and the SNR was large, this amplification produced a very strong and clear signal. With these stages done, the signal was then strong enough to be digitally analyzed. The signal could then travel to both the MATLAB and voltage limiter blocks.

Hubber and Lu’s article was published in Circuit Cellar 289, 2014. Get it now!

New DSP “Lab-in-a-Box” for ARM-Based Audio Systems

Cambridge, UK-based, ARM and its partners will start shipping a DSP “Lab-in-a-Box” (LiB) to universities worldwide to help boost practical skills development and the creation of new ARM-based audio systems. This will include products such as high-definition home media and voice-controlled home automation systems. The LiB kits contain ARM Cortex-M4-based microcontroller boards by STMicroelectronics and audio cards from Wolfson Microelectronics and Farnell element14.ARMDSPLiBWeb

As the centerpiece of the ARM University Program, LiB packages offer ARM-based technology and high-quality teaching and training materials that support electronics and computer engineering courses. DSP courses have traditionally used software simulation packages, or hands-on labs using relatively expensive development kits costing around $300 per student. By comparison, this new DSP LiB will cost around $50 and will allow students to practice theory with advanced hardware sourced from widely-available products.

“Our Lab-in-a-Box offerings are proving hugely popular in universities because of the low-cost access to state-of-the-art technology,” said Khaled Benkrid, manager of the Worldwide University Program, ARM. “The DSP kits, powered by ARM Cortex-M4-based processors, enable high performance yet energy-efficient digital signal processing at a very affordable price. We expect to see them being used by students to create commercially-viable audio applications and it’s another great example of our partnership supporting engineers in training and beyond.”

The DSP LiB will begin shipping to universities in July 2014. It is the latest in a series of initiatives led by ARM which span multiple academic topics including embedded systems design, programming and SoC design. The DSP kits will also be offered to developers outside academia at a later date.

[via audioXpress.com]

Specs & Code Matter (EE Tip #136)

No matter how many engineering hours you’ve logged over the years, it’s always a good idea to keep in mind that properly focusing on specs and code can make or break a project. In 2013, Aubrey Kagan—an experienced engineer and long-time Circuit Cellar author—explained this quite well in CC25:

There was a set of BCD thumbwheel switches that I was reading into a micro. In order to reduce the number of input lines required, each 4 bits of a digit was multiplexed with the other digits and selection was made by a transistor enabling the common line of each switch in turn. This was standard industry practice. The problem was that in order to economize, I had used the spare transistors in a Darlington driver IC. Everything worked fine in the lab, but on very hot days the unit would fail in the field with very strange results.

Long story short, the saturation voltage on the Darlington transistor would increase with temperature to above the digital input threshold and the micro would read undefined switch settings and then jump to non-existing code. I learned three things: read and understand all the specifications on a datasheet, things get a lot hotter in a cabinet in the sun than the lab, and you should make sure your code can handle conditions that are not supposed to occur.—Aubrey Kagan, CC25 (2o13)

Want to share an EE tip of your own? Email our editors to share your tips and tricks.

July Issue Offers Data-Gathering Designs and More

The concept of the wireless body-area network (WBAN), a network of wireless wearable computing devices, holds great promise in health-care applications.

Such a network could integrate implanted or wearable sensors that provide continuous mobile health (mHealth) monitoring of a person’s most important “vitals”—from calorie intake to step count, insulin to oxygen levels, and heart rate to blood pressure. It could also provide real-time updates to medical records through the Internet and alert rescue or health-care workers to emergencies such as heart failures or seizures.

Data Gathering DesignsConceivably, the WBAN would need some sort of controller, a wearable computational “hub” that would track the data being collected by all the sensors, limit and authorize access to that information, and securely transmit it to other devices or medical providers.

Circuit Cellar’s July issue (now available online for membership download or single-issue purchase)  features an essay by Clemson University researcher Vivian Genaro Motti, who discusses her participation in the federally funded Amulet project.

Amulet’s Clemson and Dartmouth College research team is prototyping pieces of “computational jewelry” that can serve as a body-area network’s mHealth hub while being discreetly worn as a bracelet or pendant. Motti’s essay elaborates on Amulet’s hardware and software architecture.

Motti isn’t the only one aware of the keen interest in WBANs and mHealth. In an interview in the July issue, Shiyan Hu, a professor whose expertise includes very-large-scale integration (VLSI), says that many of his students are exploring “portable or wearable electronics targeting health-care applications.”

This bracelet-style Amulet developer prototype has an easily accessible board.

This bracelet-style Amulet developer prototype has an easily accessible board.

Today’s mHealth market is evident in the variety of health and fitness apps available for your smartphone. But the most sophisticated mHealth technologies are not yet accessible to embedded electronics enthusiasts. (However, Amulet has created a developer prototype with an easily accessible board for tests.)

But market demand tends to increase access to new technologies. A BCC Research report predicts the mHealth market, which hit $1.5 billion in 2012, will increase to $21.5 billion by 2018. Evolving smartphones, better wireless coverage, and demands for remote patient monitoring are fueling the growth. So you can anticipate more designers and developers will be exploring this area of wearable electronics.

AND THAT’S NOT ALL…
In addition to giving you a glimpse of technology on the horizon, the July issue provides our staple of interesting projects and DIY tips you can adapt at your own workbench. For example, this issue includes articles about microcontroller-based strobe photography; a thermal monitoring system using ANT+ wireless technology; a home solar-power setup; and reconfiguring and serial backpacking to enhance LCD user interfaces.

We’re also improving on an “old” idea. Some readers may recall contributor Tom Struzik’s 2010 article about his design for a Bluetooth audio adapter for his car (“Wireless Data Exchange: Build a 2,700-lb. Bluetooth Headset,” Circuit Cellar 240).

In the July issue, Struzik writes about how he solved one problem with his design: how to implement a power supply to keep the phone and the Bluetooth adapter charged.

“To run both, I needed a clean, quiet, 5-V USB-compatible power supply,” Struzik says. “It needed to be capable of providing almost 2 A of peak current, most of which would be used for the smartphone. In addition, having an in-car, high-current USB power supply would be good for charging other devices (e.g., an iPhone or iPad).”

Struzik’s July article describes how he built a 5-V/2-A automotive isolated switching power supply. The first step was using a SPICE program to model the power supply before constructing and testing an actual circuit. Struzik provides something extra with his article: a video tutorial explaining how to use Linear Technology’s LTspice simulator program for switching design. It may help you design your own circuit.

This is Tom Struzik's initial test circuit board, post hacking. A Zener diode is shown in the upper right, a multi-turn trimmer for feedback resistor is in the center, a snubber capacitor and “stacked” surface-mount design (SMD) resistors are on the center left, USB D+/D– voltage adjust trimmers are on top center, and a “test point” is shown in the far lower left. If you’re looking for the 5-V low dropout (LDO) regulator, it’s on the underside of the board in this design.

This is Tom Struzik’s initial test circuit board, post hacking. A Zener diode is shown in the upper right, a multi-turn trimmer for feedback resistor is in the center, a snubber capacitor and “stacked” surface-mount design (SMD) resistors are on the center left, USB D+/D– voltage adjust trimmers are on top center, and a “test point” is shown in the far lower left. If you’re looking for the 5-V low dropout (LDO) regulator, it’s on the underside of the board in this design.

 

Engineering Consultant and Roboticist

Eric Forkosh starting building his first robot when he was a teenager and has been designing ever since. This NYC-based electrical engineer’s projects include everything from dancing robots to remote monitoring devices to cellular module boards to analog signals—Nan Price, Associate Editor


NAN: Tell us about your start-up company, Narobo.

forkosh

Eric Forkosh

ERIC: Narobo is essentially the company through which I do all my consulting work. I’ve built everything from dancing robots to cellular field equipment. Most recently I’ve been working with some farmers in the Midwest on remote monitoring. We monitor a lot of different things remotely, and I’ve helped develop an online portal and an app. The most interesting feature of our system is that we have a custom tablet rig that can interface directly to the electronics over just the USB connection. We use Google’s Android software development kit to pull that off.

ERIC: The DroneCell was my second official product released, the first being the Roboduino. The Roboduino was relatively simple; it was just a modified Arduino that made building robots easy. We used to sell it online at CuriousInventor.com for a little while, and there was always a trickle of sales, but it was never a huge success. I still get a kick out of seeing Roboduino in projects online, it’s always nice to see people appreciating my work.

dronecell3

The DroneCell is a cellular module board that communicates with devices with TTL UARTs.

The DroneCell is the other product of mine, and my personal favorite. It’s a cellular module board geared toward the hobbyist. A few years ago, if you wanted to add cellular functionality to your system you had to do a custom PCB for it. You had to deal with really low voltage levels, very high peak power draws, and hard-to-read pins. DroneCell solved the problem and made it very easy to interface to hobbyist systems such as the Arduino. Putting on proper power regulation was easy, but my biggest design challenge was how to handle the very low voltage levels. In the end, I put together a very clever voltage shifter that worked with 3V3 and 5 V, with some calculated diodes and resistors.

NAN: Tell us about your first project. Where were you at the time and what did you learn from the experience?

butlerrobot

Eric’s Butler robot was his first electronics project. He started building it when he was still in high school.

ERIC: The Butler robot was my first real electronics project. I started building it in ninth grade, and for a really stupid reason. I just wanted to build a personal robot, like on TV. My first version of the Butler robot was cobbled together using an old laptop, a USB-to-I/O converter called Phidgets, and old wheelchair motors I bought on eBay.

I didn’t use anything fancy for this robot, all the software was written in Visual Basic and ran on Windows XP. For motor controllers, I used some old DPDT automotive relays I had lying around. They did the job but obviously I wasn’t able to PWM them for speed control.

My second version came about two years later, and was built with the intention of winning the Instructables Robot contest. I didn’t win first place, but my tutorial “How to Build a Butler Robot” placed in the top 10 and was mentioned in The Instructables Book in print. This version was a cleaner version of everything I had done before. I built a sleek black robot body (at least it was sleek back then!) and fabricated an upside-down bowl-shaped head that housed the webcam. The electronics were basically the same. The main new features were a basic robot arm that poured you a drink (two servos and a large DC motor) and a built-in mini fridge. I also got voice command to work really well by hooking up my Visual Basic software with Dragon’s speech-to-text converter.

The Butler robot was a great project and I learned a lot about electronics and software from doing it. If I were to build a Butler robot right now, I’d do it completely differently. But I think it was an important to my engineering career and it taught me that anything is possible with some hacking and hard work.

At the same time as I was doing my Butler robot (probably around 2008), I lucked out and was hired by an entertainer in Hong Kong. He saw my Butler robot online and hired me to build him a dancing robot that was synced to music. We solved the issue of syncing to music by putting dual-tone multi-frequency (DTMF) tones on the left channel audio and music on the right channel. The right channel went to speakers and the left channel went to a decoder that translated DTMF tone sequences to robot movement. This was good because all the data and dance moves were part of the same audio file. All we had to do was prepare special audio files and the robot would work with any music player (e.g., iPod, laptop, CD, etc.). The robot is used in shows to this day, and my performer client even hired a professional cartoon voice actor to give the robot a personality.

NAN: You were an adjunct professor at the Cooper Union for the Advancement of Science and Art in New York City. What types of courses did you teach and what did you enjoy most about teaching?

ERIC: I will be entering my senior year at Cooper Union in the Fall 2014. Two years ago, I took a year off from school to pursue my work. This past year I completed my junior year. I taught a semester of “Microcontroller Projects” at Cooper Union during my year off from being a student. We built a lot of really great projects using Arduino. One final project that really impressed me was a small robot car that parallel parked itself. Another project was a family of spider robots that were remotely controlled and could shrink up into a ball.

Cooper Union is filled with really bright students and teaching exposed me to the different thought processes people have when trying to build a solution. I think teaching helped me grow as a person and helped me understand that in engineering—and possibly in life—there is no one right answer. There are different paths to the same destination. I really enjoyed teaching because it made me evaluate my understanding about electronics, software, and robotics. It forced me to make sure I really understood what was going on in intricate detail.

NAN: You have competed in robotics competitions including RoboCup in Austria. Tell us about these experiences—what types of robots did you build for the competitions?

robocup

Eric worked with his high school’s robotics team to design this robot for a RoboCup competition.

ERIC: In high school I was the robotics team captain and we built a line-following robot and a soccer robot to compete in RoboCup Junior in the US. We won first place in the RoboCup Junior Northeast Regional and were invited to compete in Austria for the International RoboCup Junior games. So we traveled as a team to Austria to compete and we got to see a lot of interesting projects and many other soccer teams compete. I remember the Iranian RoboCup Junior team had a crazy robot that competed against us; it was built out of steel and looked like a miniature tank.

My best memory from Austria was when our robot broke and I had to fix it. Our robot was omnidirectional with four omni wheels in each corner that let it drive at any angle or orientation it wanted. It could zigzag across the field without a problem. At our first match, I put the robot down on the little soccer field to compete… and it wouldn’t move. During transportation, one of the motors broke. Disappointed, we had to forfeit that match. But I didn’t give up. I removed one of the wheels and rewrote the code to operate with only three motors functional. Again we tried to compete, and again another motor appeared to be broken. I removed yet another wheel and stuck a bottle cap as a caster wheel on the back. I rewrote the code, which was running on a little Microchip Technology PIC microcontroller, and programmed the robot to operate with only two wheels working. The crippled robot put up a good fight, but unfortunately it wasn’t enough. I think we scored one goal total, and that was when the robot had just two wheels working.

After the competition, during an interview with the judges, we had a laugh comparing our disabled robot to the videos we took back home with the robot scoring goal after goal. I learned from that incident to always be prepared for the worst, do your best, and sometimes stuff just happens. I’m happy I tried and did my best to fix it, I have no regrets. I have a some of the gears from that robot at home on display as a reminder to always prepare for emergencies and to always try my best.

NAN: What was the last electronics-design related product you purchased and what type of project did you use it with?

ERIC: The last product would be an op-amp I bought, probably the 411 chip. For a current project, I had to generate a –5-to-5-V analog signal from a microcontroller. My temporary solution was to RC filter the PWM output from the op-amp and then use an amplifier with a
gain of 2 and a 2.5-V “virtual ground.” The result is that 2.5 V is the new “zero” voltage. You can achieve –5 V by giving the op-amp 0 V, a –2.5-V difference that is amplified by 2 to yield 5 V. Similarly, 5 V is a 2.5-V difference from the virtual ground, amplified by 2 it provides a 5-V output.

NAN: What do you consider to be the “next big thing” in the industry?

ERIC: I think the next big thing will be personalized health care via smartphones. There are already some insulin pumps and heart monitors that communicate with special smartphone apps via Bluetooth. I think that’s excellent. We have all this computing power in our pockets, we should put it to good use. It would be nice to see these apps educating smartphone users—the patients themselves— about their current health condition. It might inspire patients/users to live healthier lifestyles and take care of themselves. I don’t think the FDA is completely there yet, but I’m excited to see what the future will bring. Remember, the future is what you build it to be.

Bit Banging

Shlomo Engelberg, an associate professor in the electronics department of the Jerusalem College of Technology, is well-versed in signal processing. As an instructor and the author of several books, including Digital Signal Processing: An Experimental Approach (Springer, 2008), he is a skilled guide to how to use the UART “protocol” to implement systems that transmit and receive data without a built-in peripheral.

Implementing serial communications using software rather than hardware is called bit-banging, the topic of his article in Circuit Cellar’s June issue.

“There is no better way to understand a protocol than to implement it yourself from scratch,” Engelberg says. “If you write code similar to what I describe in this article, you’ll have a good understanding of how signals are transmitted and received by a UART. Additionally, sometimes relatively powerful microprocessors do not have a built-in UART, and knowing how to implement one in software can save you from needing to add an external UART to your system. It can also reduce your parts count.”

In the excerpt below, he explains some UART fundamentals:

WHAT DOES “UART” MEAN?
UART stands for universal asynchronous receiver/transmitter. The last three words in the acronym are easy enough to understand. “Asynchronous” means that the transmitter and the receiver run on their own clocks. There is no need to run a wire between the transmitter and the receiver to enable them to “share” a clock (as required by certain other protocols). The receiver/transmitter part of the acronym means just what it says: the protocol tells you what signals you need to send from the transmitter and what signals you should expect to acquire at the receiver.

The first term of the acronym, “universal,” is a bit more puzzling. According to Wikipedia, the term “universal” refers to the fact that the data format and the speed of transmission are variable. My feeling has always been that the term “universal” is basically hype; someone probably figured a “universal asynchronous receiver/transmitter” would sell better than a simple “asynchronous receiver/transmitter.”

Figure 1: The waveform output by a microprocessor’s UART is shown. While “at rest,” the UART’s output is in the high state. The transmission begins with a start bit in which the UART’s output is low. The start bit is followed by eight data bits. Finally, there is a stop bit in which the UART’s output is high.

Figure 1: The waveform output by a microprocessor’s UART is shown. While “at rest,” the UART’s output is in the high state. The transmission begins with a start bit in which the UART’s output is low. The start bit is followed by eight data bits. Finally, there is a stop bit in which the UART’s output is high.

TEAMWORK NEEDED
Before you can use a UART to transfer information from device to device, the transmitter and receiver have to agree on a few things. First, they must agree on a transmission speed. They must agree that each transmitted bit will have a certain (fixed) duration, denoted TBIT. A 1/9,600-s duration is a typical choice, related to a commonly used crystal’s clock speed, but there are many other possibilities. Additionally, the transmitter and receiver have to agree about the number of data bits to be transmitted each time, the number of stop bits to be used, and the flow control (if any).

When I speak of the transmitter and receiver “agreeing” about these points, I mean that the people programming the transmitting and receiving systems must agree to use a certain data rate, for example. There is no “chicken and egg” problem here. You do not need to have an operational UART before you can use your UART; you only need a bit of teamwork.

UART TRANSMISSION
Using a UART is considered the simplest way of transmitting information. Figure 1 shows the form the transmissions must always make. The line along which the signal is transmitted is initially “high.” The transmissions begin with a single start bit during which the line is pulled low (as all UART transmissions must). They have eight data bits (neither more nor less) and a single stop bit (and not one and a half or two stop bits) during which the line is once again held high. (Flow control is not used throughout this article.)

Why must this protocol include start and stop bits? The transmitter and the receiver do not share a common clock, so how does the receiver know when a transmission has begun? It knows by realizing that the wire connecting them is held high while a transmission is not taking place, “watching” the wire connecting them, and waiting for the voltage level to transition from high to low, which it does by watching and waiting for a start bit. When the wire leaves its “rest state” and goes low, the receiver knows that a transmission has begun. The stop bit guarantees that the line returns to its “high” level at the end of each transmission.

Transmissions have a start and a stop bit, so the UART knows how to read the two words even if one transmits that data word 11111111 and follows it with 11111111. Because of the start and stop bits, when the UART is “looking at” a line on which a transmission is beginning, it sees an initial low level (the start bit), the high level repeated eight times, a ninth high level (the stop bit), and then the pattern repeats. The start bit’s presence enables the UART to determine what’s happening. If the data word being transmitted were 00000000 followed by 00000000, then the stop bit would save the day.

The type of UART connection I describe in this article only requires three wires. One wire is for transmission, one is for reception, and one connects the two systems’ grounds.

The receiver and transmitter both know that each bit in the transmission takes TBIT seconds. After seeing a voltage drop on the line, the receiver waits for TBIT/2 s and re-examines the line. If it is still low, the receiver assumes it is in the middle of the start bit. It waits TBIT seconds and resamples the line. The value it sees is then used to determine data bit 0’s value. The receiver then samples every TBIT seconds until it has sampled all the data bits and the stop bit.

Engelberg’s full article, which you can find in Circuit Cellar’s June issue, goes on to explain UART connections and how he implemented a simple transmitter and receiver. For the projects outlined in his article, he used the evaluation kit for Analog Devices’s ADuC841.

“The transmitter and the receiver are both fairly simple to write. I enjoyed writing them,” Engelberg says in wrapping up his article. “If you like playing with microprocessors and understanding the protocols with which they work, you will probably enjoy writing a transmitter and receiver too. If you do not have time to write the code yourself but you’d like to examine it, feel free to e-mail me at shlomoe@jct.ac.il. I’ll be happy to e-mail the code to you.”

Build an Automated Vehicle Locator

Several things inspired Electrical and Computer Engineering Professor Chris Coulston and his team at Penn State Erie, The Behrend College, to create an online vehicle-tracking system. Mainly, the team wanted to increase ridership on a shuttle bus the local transit authority provided to serve the expanding campus. Not enough students were “on board,” in part because it was difficult to know when the bus would be arriving at each stop.

So Coulston’s team created a system in which a mobile GPS tracker on the bus communicates its location over a radio link to a base station. Students, professors, or anyone else carrying a smartphone can call up the bus tracker web page, find out the bus’ current location, and receive reliable estimates of the bus’ arrival time at each of its stops. Coulston, computer engineering student Daniel Hankewycz, and computer science student Austin Kelleher wrote an article about the system, which appears in our June issue.

Circuit Cellar recently asked Coulston if the system, implemented in the fall 2013 semester, had accomplished its goals and might be expanded.

“The bus tracker team is tracking usage of the web site using Google Analytics,” Coulston said. “The data reveals that we get on average 100 hits a day during cold weather and fewer on warmer days. Ridership has increased during this past year, helping assure the long-term presence of the shuttle on our campus.”

“Over winter break, shuttle service was increased to a distant location on campus,” he added. “In order to better track the location of the shuttle, a second base station was added. The additional base station required a significant rework of the software architecture. The result is that the software is more modular and can accept an arbitrary number of base stations. There are no plans at present to add a second bus—a good thing, because this change would require another significant rework of the software architecture.”

Initially, Coulston looked to other real-time vehicle trackers for inspiration: “There are a variety of live bus trackers that motivated my early ideas, including the University of Utah’s Live Tracker  and the Chicago Transit Authority’s CTA Bus Tracker. Given our single bus route on campus, I was motivated to keep the interface simple and clean to minimize the amount of time needed to figure out where the bus is and how long it’s going to take to get to my stop.”

The system, as it was originally implemented in August 2013, is fully described in the June issue, now available for single-issue purchase or membership download. The following article excerpt provides a broad overview and a description of the team’s hardware choices.

THE BIG PICTURE
Figure 1 shows the bus tracker’s hardware, which consists of three components: the user’s smartphone, the base station placed at a fixed location on campus, and the mobile tracker that rides around on the bus.

The bus tracking system includes a Digi International XTend radio, a Microchip Technology PIC18F26K22 microcontroller, and a Raspberry Pi single-board computer.

Figure 1: The bus tracking system includes a Digi International XTend radio, a Microchip Technology PIC18F26K22 microcontroller, and a Raspberry Pi single-board computer.

Early on, we decided against a cellular-based solution (think cell phone) as the mobile tracker. While this concept would have benefited from wide-ranging cellular coverage, it would have incurred monthly cellar network access fees. Figure 1 shows the final concept, which utilizes a 900-MHz radio link between the mobile tracker and the base station.

Figure 2 shows the software architecture running on the hardware from Figure 1. When the user’s smartphone loads the bus tracker webpage, the JavaScript on the page instructs the user’s web browser to use the Google Maps JavaScript API to load the campus map. The smartphone also makes an XMLHttpRequests request for a file on the server (stamp.txt) containing the bus’ current location and breadcrumb index.

Figure 2: The bus tracker’s software architecture includes a GPS, the mobile tracker, a smartphone, and the base station.

Figure 2: The bus tracker’s software architecture includes a GPS, the mobile tracker, a smartphone, and the base station.

This information along with data about the bus stops is used to position the bus icon on the map, determine the bus’ next stop, and predict the bus’ arrival time at each of the seven bus stops. The bus’ location contained in stamp.txt is generated by a GPS receiver (EM-408) in the form of an NMEA string. This string is sent to a microcontroller and then parsed. When the microcontroller receives a request for the bus’ location, it formats a message and sends it over the 900-MHz radio link. The base station compares the bus position against a canonical tour of campus (breadcrumb) and writes the best match to stamp.txt.

Early in the project development, we decided to collect the bus’ position and heading information at 2-s intervals during the bus’ campus tour. This collection of strings is called “breadcrumbs” because, like the breadcrumbs dropped by Hansel and Gretel in the eponymously named story, we hope they will help us find our way around campus. Figure 3 shows a set of breadcrumbs (b1 through b10), which were collected as the bus traveled out and back along the same road.

Figure 3: Breadcrumbs (b1 through b10) containing the bus’ position and orientation information were taken every 2 s during a test-run campus tour.

Figure 3: Breadcrumbs (b1 through b10) containing the bus’ position and orientation information were taken every 2 s during a test-run campus tour.

The decision to collect breadcrumbs proved fortuitous as they serve an important role in each of the three hardware components shown in Figure 1.

MOBILE TRACKER
The bus houses the mobile tracker (see Photo 1). Figure 4 shows the schematic, which is deceptively simple. What you see is the third iteration of the mobile tracker hardware.

Figure 4: The mobile tracker includes a Microchip Technology PIC18F26K22 microcontroller, a Micrel MIC5205 regulator, a Digi International XTend RF module, and a Texas Instruments TXS0102 bidirectional translator

Figure 4: The mobile tracker includes a Microchip Technology PIC18F26K22 microcontroller, a Micrel MIC5205 regulator, a Digi International XTend RF module, and a Texas Instruments TXS0102 bidirectional translator

An important starting point in the design was how to step down the bus’ 12-V supply to the 5-V required by our circuit. In terms of hardware, the best decision we made was to abandon the idea of trying to integrate a 12-to-5-V converter onto the mobile tracker PCB. Instead we purchased a $40 CUI VYB15W-T DC-DC converter and fed the mobile tracker 5-V inputs…

We used Micrel’s MIC5205 regulator to step down the 5 V for the 3.3-V GPS receiver, which easily supplied its peak 80 mA. Since we ran a Digi International XTend radio at 5 V for the best range, we ended up with mixed voltage signals. We used a Texas Instruments TXS0102 bidirectional voltage-level translator, which handles voltage-interfacing duties between the 5-V radio and the 3.3-V microcontroller.

The mobile tracker unit

Photo 1: The mobile tracker unit

We selected Microchip Technology’s PIC18F26K22 because it has two hardware serial ports, enabling it to simultaneously communicate with the GPS module and the radio modem when the bus is traveling around campus. We placed two switches in front of the serial ports. One switch toggles between the GPS module and the Microchip Technology PICkit 3 programming pins, which are necessary to program the microcontroller. The second switch toggles between the radio and a header connected to a PC serial port (via a Future Technology Devices FT232 USB-to-serial bridge). This is useful when debugging at your desk. An RGB LED in a compact PLCC4 package provides state information about the mobile tracker.

The XTend RF modules are the big brothers to Digi International’s popular XBee series. These radios come with an impressive 1 W of transmitting power over a 900-MHz frequency, enabling ranges up to a mile in our heavily wooded campus environment. The radios use a standard serial interface requiring three connections: TX, RX, and ground. They are simple to set up. You just drop them into the Command mode, set the module’s source and destination addresses, store this configuration in flash memory, and exit. You never have to deal with them again. Any character sent to the radio appears on the destination modem’s RX line.

The GPS receiver utilizes the CSR SiRFstarIII chipset, which is configured to output a recommended minimum specific (RMC) string every 2 s…

The mobile tracker’s firmware listens for commands over the serial port and generates appropriate replies. Commands are issued by the developer or by the base station…

Burning breadcrumbs into the mobile tracker’s flash memory proved to be a good design decision. With this capability, the mobile tracker can generate a simulated tour of campus while sitting on the lab bench.

BASE STATION
The base station consists of an XTend RF module connected to a Raspberry Pi’s serial port (see Photo 2). The software running on the Raspberry Pi does everything from running an Nginx open-source web server to making requests for data from the mobile tracker.

From Figure 1, the only additional hardware associated with the base station is the 900-MHz XTend radio connected to the Raspberry Pi over a dedicated serial port on pins 8 (TX) and 10 (RX) of the Raspberry Pi’s GPIO header.

The only code that runs on the base station is the Python program, which periodically queries the mobile tracker to get the bus’ position and heading. The program starts by configuring the serial port in the common 9600,8,N,1 mode. Next, the program is put into an infinite loop to query the mobile tracker’s position every 2 s.

Photo 2: The base station includes an interface board, a Raspberry Pi, and a radio modem.

Photo 2: The base station includes an interface board, a Raspberry Pi, and a radio modem.

Q&A: Raspberry Pi Innovation

Orlando, FL-based web app developer and blogger Shea Silverman recently received Kickstarter funding for the latest version of PiPlay, his Raspberry Pi-based OS. Shea and I discussed his ongoing projects, his Raspberry Pi book, and what’s next for PiPlay.—Nan Price, Associate Editor

 

silverman

Shea Silverman

NAN: What is your current occupation?

SHEA: Web applications developer with the Center for Distributed Learning at the University of Central Florida (UCF).

NAN: Why and when did you decide to start your blog?

SHEA: I’ve been blogging on and off for years, but I could never keep to a schedule or really commit myself to writing. After I started working on side projects, I realized I needed a place to store tips and tricks I had figured out. I installed WordPress, posted some PhoneGap tips, and within a day got a comment from someone who had the same issue, and my tips helped them out. I have been blogging ever since. I make sure to post every Friday night.

NAN: Tell us about PiPlay, the Raspberry Pi OS. Why did you start the OS? What new developments, if any, are you working on?

piplay-case

Shea’s PiPlay Raspberry Pi OS recently reached 400% funding on Kickstarter.

SHEA: PiPlay is a gaming and emulation distribution for the Raspberry Pi single-board computer. It is built on top of the Raspbian OS, and tries to make it as easy as possible to play games on your Raspberry Pi. My blog got really popular after I started posting binaries and tutorials on how to compile different emulators to the Raspberry Pi, but I kept getting asked the same questions and saw users struggling with the same consistent issues.

I decided I would release a disk image with everything preconfigured and ready to be loaded onto an SD card. I’ve been adding new emulators, games, and tools to it ever since.

I just recently completed a Kickstarter that is funding the next release, which includes a much nicer front end, a web GUI, and a better controller configuration system.

NAN: You wrote Instant Raspberry Pi Gaming. Do you consider this book introductory or is it written for the more experienced engineer?

SHEA: Instant Raspberry Pi Gaming is written like a cookbook with recipes for doing various tasks. Some of them are very simple, and they build up to some more advanced recipes. One of the easier tasks is creating your user account on the Pi Store, while the more advanced recipes have you working with Python and using an API to interact with Minecraft.

Readers will learn how to setup a Raspberry Pi, install and use various emulators and games, a bit about the Minecraft API, and common troubleshooting tips.

pitroller

The Pitroller is a joystick and buttons hooked up to the GPIO pins of a Raspberry Pi, which can act as a controller or keyboard for various emulators.

NAN: You are a member of FamiLAB, an Orlando, FL-based community lab/hackerspace. What types of projects have you worked on at the lab?

miniarcade

Disney director Rich Moore poses with Shea’s miniature arcade machine. The machine was based on Fix It Felix Jr. from Disney’s Wreck It Ralph.

SHEA: I spend a lot of time at the lab using the laser cutter. Creating a 2-D vector in Inkscape, and then watching it be cut out on a piece of wood or acrylic is really inspiring. My favorite project was making a little arcade machine featuring Fix It Felix Jr. from Wreck It Ralph. A marketing person from Disney was able to get it into the hands of the director Rich Moore. He sent me a bunch of pictures of himself holding my little arcade machine next to the full size version.

NAN: Give us a little background information. How did you become interested in technology?

SHEA: My mom always likes to remind me that I’ve been using computers since I was 2. My parents were very interested in technology and encouraged my curiosity when it came to computers. I always liked to take something apart and see how it worked, and then try to put it back together. As the years went on, I’ve devoted more and more time to making technology a major part of my life.

NAN: Tell us about the first embedded system you designed.

SHEA: I have a lot of designs, but I don’t think I’ve ever finished one. I’ll be halfway into a project, learn about something new, then cannibalize what I was working on and repurpose it for my new idea. One of the first embedded projects I worked on was a paintball board made out of a PICAXE microcontroller. I never got it small enough to fit inside the paintball marker, but it was really cool to see everything in action. The best part was when I finally had that “ah-ha!” moment, and everything I was learning finally clicked.

NAN: What was the last electronics-design related product you purchased and what type of project did you use it with?

SHEA: At UCF, one of our teams utilizes a ticket system for dealing with requests. Our department does a hack day each semester, so my coworker and I decided to rig up a system that changes the color of the lights in the office depending on the urgency of requests in the box. We coded up an API and had a Raspberry Pi ping the API every few minutes for updates. We then hooked up two Arduinos to the Raspberry Pi and color-changing LED strips to the Arduinos. We set it up and it’s been working for the past year and a half, alerting the team with different colors when there is work to do.

NAN: Are you currently working on or planning any projects?

SHEA: My Kickstarter for PiPlay just finished at 400% funding. So right now I’m busy working on fulfilling the rewards, and writing the latest version of PiPlay.

NAN: What do you consider to be the “next big thing” in the industry?

SHEA: Wearable computing. Google Glass, the Pebble smart watch, Galaxy Gear—I think these are all great indicators of where our technology is heading. We currently have very powerful computers in our pockets with all kinds of sensors and gadgets built in, but very limited ways to physically interact with them (via the screen, or a keypad). If we can make the input devices modular, be it your watch, a heads-up display, or something else, I think that is going to spark a new revolution in user experiences.

Execute Open-Source Arduino Code in a PIC Microcontroller Using the MPLAB IDE

The Arduino single-board computer is a de facto standard tool for developing microcomputer applications within the hobbyist and educational communities. It provides an open-source hardware (OSH) environment based on a simple microcontroller board, as well as an open-source (OS) development environment for writing software for the board.

Here’s an approach that enables Arduino code to be configured for execution with the Microchip Technology PIC32MX250F128B small-outline 32-bit microcontroller. It uses the Microchip Technology MPLAB X IDE and MPLAB XC32 C Compiler and the Microchip Technology Microstick II programmer/debugger.

Your own reasons for using this approach will depend on your personal needs and background. Perhaps as a long-term Arduino user, you want to explore a new processor performance option with your existing Arduino code base. Or, you want to take advantage of or gain experience with the Microchip advanced IDE development tools and debug with your existing Arduino code. All of these goals are easily achieved using the approach and the beta library covered in this article.

Several fundamental open-source Arduino code examples are described using the beta core library of Arduino functions I developed. The beta version is available, for evaluation purposes only, as a free download from the “Arduino Library Code for PIC32” link on my KibaCorp company website, kibacorp.com. From there, you can also download a short description of the Microstick II hardware configuration used for the library.

To illustrate the capabilities in their simplest form, here is a simple Blink LED example from my book Beginner’s Guide to Programming the PIC32. The example shows how this custom library makes it easy to convert Arduino code to a PIC32 binary file.

ARDUINO BLINK EXAMPLE 1
The Arduino code example is as follows: Wire an LED through a 1-K resistor to pin 13 (D7) of the Arduino. An output pin is configured to drive an LED using pinMode () function under setup (). Then under loop () this output is set high and then low using digitalWrite () and delay () functions to blink the LED. The community open-source Arduino code is:

Listing 1forwebPIC32 EXAMPLE 1 CODE MODIFICATIONS
The open-source example uses D13 or physical pin 13 on the Arduino. In relation to the PIC32MX, the D13 is physical pin 25. Pin 25 will be used in prototyping wiring.

Now, let’s review and understand the PIC32 project template and its associated “wrapping functions.”  The Arduino uses two principal functions: setup () to initialize the system and loop () to run a continuous execution loop. There is no Main function. Using the Microchip Technololgy XC32 C compiler, we are constrained to having a Main function. The Arduino setup () and loop () functions can be accommodated, but only as part of an overall template Main “wrapping” function. So within our PIC32 template, we accommodate this as follows:

Listing 2

This piece of code is a small but essential part of the template. Note that in this critical wrapping function, setup () is called once as in Arduino and loop () is configured to be called continuously (simulating the loop () function in Arduino) through the use of a while loop in Main.

The second critical wrapping function for our template is the use of C header files at the beginning of the code. The XC32 C compiler uses the C compiler directive #include reference files within the Main code. Arduino uses import, which is a similar construct that is used in higher-level languages such as Java and Python, which cannot be used by the MPLAB XC32 C.

The two include files necessary for our first example are as follows:

Listing 3

System.h references all the critical Microchip library functions supporting the PIC32MX250F128B. The Ardunio.h provides the Arduino specific library function set. Given these two key “wrapper” aspects, where does the Arduino code go? This is best illustrated with a side-by-side comparison between Arduino code and its Microchip equivalent. The Arduino code is essentially positioned between the wrapper codes as part of the Main function.

Blink side-by-side comparison

Blink side-by-side comparison

This approach enables Arduino code to execute on a Microchip PIC32 within an MPLAB X environment. Note that the Arduino code void setup () now appears as void setup (void), and void loop () appears as void loop (void). This is a minor inconvenience but again necessary for our C environment syntax for C prototype function definitions. Once the code is successfully compiled, the environment enables you to have access to the entire built-in tool suite of the MPLAB X and its debugger tool suite.

RUNNING EXAMPLE 1 CODE
Configure the Microstick II prototype as in the following schematic. Both the schematic and prototype are shown below:

Exercise 1 schematic

Exercise 1 schematic

Exercise 1 prototype

Exercise 1 prototype

BETA LIBRARY
Table 1 compares Arduino core functionality to what is contained in the Microchip PIC32 expanded beta library. In the beta version, I added additional C header files to accomplish the necessary library functionality. Table 2 compares variable types between Arduino and PIC32 variable types. Both Table 1 and Table 2 show the current beta version has a high degree of Arduino core library functionality. Current limitations are the use of only one serial port, interrupt with INT0 only, and no stream capability. In addition, with C the “!” operator is used for conditional test only and not as a complement function, as in Arduino. To use the complement function in C, the “~” operator is used. The library is easily adapted to other PIC32 devices or board types.

Table 1

Table 1: Arduino vs Microchip Technology PIC32 core library function comparison

Talble 2

Table 2: Arduino vs Microchip Technology PIC32 core library variable types

INTERRUPTS
If you use interrupts, you must identify to C the name of your interrupt service routine as used in your Arduino script. See below:

Interrupt support

Interrupt support

For more information on the beta release or to send comments and constructive criticism, or to report any detected problems, please contact me here.

LIBRARY TEST EXAMPLES
Four test case examples demonstrating additional core library functions are shown below as illustrations.

Serial communications

Serial communications

Serial find string test case

Serial find string test case

Serial parse INT

Serial parse INT

Interrupt

Interrupt

Editor’s Note: Portions of this post first appeared in Tom Kibalo’s book Beginner’s Guide to Programming the PIC32 (Electronics Products, 2013). They are reprinted with permission from Chuck Hellebuyck, Electronic Products. If you are interested in reading more articles by Kibalo, check out his two-part Circuit Cellar “robot boot camp” series posted in 2012 : “Autonomous Mobile Robot (Part 1): Overview & Hardware” and “Autonomous Mobile Robot (Part 2): Software & Operation.”

 

Tom Kibalo

Tom Kibalo

ABOUT THE AUTHOR
Tom Kibalo is principal engineer at a large defense firm and president of KibaCorp, a company dedicated to DIY hobbyist, student, and engineering education. Tom, who is also an Engineering Department adjunct faculty member at Anne Arundel Community College in Arnold, MD, is keenly interested in microcontroller applications and embedded designs. To find out more about Tom, read his 2013 Circuit Cellar member profile.

DIY IoT: Build a ‘Net-Connected System Today

It’s time to join the Internet of Things (IoT) revolution. Try building a ‘Net-enabled design with WIZnet’s W5500 “smart” Ethernet chip. It’s easier than you think.

In a thorough introduction to the technology, Tom Cantrell presented a garage door monitoring design. He explained:

The W5500 (see Figure 1) starts with a standard 10/100 Ethernet interface (i.e., MAC and PHY) but then goes further with large RAM buffers (16-KB transmit and 16-KB receive) and hardware TCP/IP protocol processing. I discovered WIZnet’s first chip, the  W3100, way back in 2001. Of course by now, as with all things  silicon, the new W5500 is better, faster, and  lower cost. But the concept is still exactly  the same: “Internet enable” applications by  handling the network chores in hardware so  the application microcontroller doesn’t have to do it in software.

Cantrell - WIZ550io

Figure 1: The WIZnet W5500 is an Ethernet chip with a difference—large RAM buffers and hardware TCP/IP processing that make it easy for any microcontroller to go online.

The large RAM buffers help decouple the  microcontroller from network activity. In a  recent project (see my article, “Weatherize  Your Embedded App,” Circuit Cellar 273,  2013), I used the RAM to receive an entire  10-KB+ webpage, completely eliminating the  need for the microcontroller to juggle data at  network speed. And any of the 32-KB on-chip  RAM that isn’t needed for network buffering  is free for general-purpose use, a big plus for  typically RAM-constrained microcontrollers. The other major WIZnet hardware assist  is TCP/IP processing using IP addresses, sockets, and familiar commands including OPEN, CONNECT, SEND, RECEIVE, DISCONNECT.  The high-level interface to the network frees  up microcontroller cycles and code space that  would otherwise be needed for a software TCP/IP stack.

Cantrell goes on to present his design for a ‘Net-connected garage door monitoring system.

For prototyping, check out the WIZnet  ioShield (see Photo 1), which is a baseboard  for the WIZ550io that includes an SD card  socket. There are ioShields for different  platforms (e.g., Arduino, LaunchPad,  mbed, etc.), and with 0.1” headers they are  breadboard friendly.

Photo 1: If you want a fancy server with lots of eye candy, a microSD card is the way to go. The WIZnet ioShields include the card socket and are available for various platforms. The Arduino version is shown here.

Photo 1: If you want a fancy server with lots of eye candy, a microSD card is the way to go. The WIZnet ioShields include the card socket and are available for various platforms. The Arduino version is shown here.

Cantrell prototyped a client version of what he calls his “garage  door ‘Thing’ using an Arduino  and a WIZ550io connected to Exosite (see Photo 2).

A prototype of the client version of my garage “Thing” is shown.

Photo 2: A prototype of the client version of my garage “Thing”

Wondering how to get two clients (e.g., ) to interact with each other? Cantrell used Exosite.

Over on the Exosite website, after signing up for a  free “Developer” account, it was a quick and easy mainly point-and-click exercise to configure my “Device,” “Data,”  “Events,” and “Alerts” (see Photo 3).  As a client, there’s no need to keep the “Thing’s”  Ethernet link powered all the time. Data only needs to  be sent when the garage door opens or closes, but I also  recommend sending a periodic heartbeat just in case. My  garage door monitor will only generate a minute or two  of network activity (i.e., door state changes and hourly  heartbeats) per day, so there’s opportunity for significant  energy savings compared to a 24/7 server.

It only takes a few minutes to set up a simple Exosite dashboard including an e-mail alert. I can “see“ my  garage door without getting off the couch and now, via Exosite, from the farthest reaches of the web.

It only takes a few minutes to set up a simple Exosite dashboard including an e-mail alert. I can “see“ my garage door without getting off the couch and now, via Exosite, from the farthest reaches of the web.

You can download the entire article,  “Connect the Magic: An Introduction to the WIZnet W550,” for free to learn about Cantrell’s garage door control system built with a WIZnet and an Arduino Uno.

Editor’s note: If you have an idea for an innovative, ’Net-enabled electronics system, this is your opportunity to share your original design with the world. Enter the WIZnet Connect the Magic 2014 Design Challenge for a chance to win a share of $15,000 in prizes and gain recognition by Elektor International Media and Circuit Cellar. WIZnet is the sponsor. Eligible entries will be judged on their technical merit, originality, usefulness, cost-effectiveness, and design optimization. The Entry submission deadline is 12:00 PM EST August 3, 2014. How to enter: Implement WIZnet’s WIZ550io Ethernet module, or W5500 chip, in an innovative design; document your project; and then submit your entry. The complete rules and regulations are available on the Challenge webpage.

 

A Coding Interface for an Evaluation Tool

John Peck, a test engineer at Knowles Electronics in Itasca, IL, has used ASCII interfaces to test equipment since he was a graduate student.

“I love test equipment with open, well-documented, ASCII command sets,” he says. “The plain text commands give a complicated instrument a familiar interface and an easy way to automate measurements.”

So when Peck needed to automate the process of reading his ultrasonic range finder’s voltage output, he wanted an ASCII interface to a voltmeter. He also wanted the meter to convert volts into distance, so he added an Atmel AVR Butterfly microcontroller into the mix (see Photo 1). “I thought it would be easy to give it a plain text interface to a PC,” he says.

Atmel AVR Butterfly

Atmel AVR Butterfly

The project became a bit more complex than he expected. But ultimately, Peck says, he came up came up with “a simple command interface that’s easy to customize and extend. It’s not at the level of a commercial instrument, but it works well for sending a few commands and getting some data back.”

If you would like to learn more about how to send commands from a PC to the AVR Butterfly and the basics of using the credit card-sized, single-board microcontroller to recognize, parse, and execute remote commands, read Peck’s article about his project in Circuit Cellar’s May issue.

In the italicized excerpts below, he describes his hardware connections to the board and the process of receiving remote characters (the first step in receiving remote commands). Other topics you’ll find in the full article include setting up a logging system to understand how commands are being processed, configuring the logger (which is the gatekeeper for messages from other subsystems), recognizing and adding commands to extend the system, and sending calibration values.

Peck programmed his system so that it has room to grow and can accommodate his future plans:

“I built the code with AVR-GCC, using the -Os optimization level. The output of avr-gcc –version is avr-gcc (Gentoo 4.6.3 p1.3, pie-0.5.1) 4.6.3.

“The resulting memory map file shows a 306-byte .data size, a 49-byte .bss size, and a 7.8-KB .text size. I used roughly half of the AVR Butterfly’s flash memory and about a third of its RAM. So there’s at least some space left to do more than just recognizing commands and calibrating voltages.”

“I’d like to work on extending the system to handle more types of arguments (e.g., signed integers and floats). And I’d like to port the system to a different part, one with more than one USART. Then I could have a dedicated logging port and log messages wouldn’t get in the way of other communication. Making well-documented interfaces to my designs would help me with my long-term goal of making them more modular.”

These are the connections needed for Atmel’s AVR Butterfly. Atmel’s AVRISP mkII user’s guide stresses that the programmer must be connected to the PC before the target (AVR Butterfly board).

Figure 1: These are the connections needed for Atmel’s AVR Butterfly. Atmel’s AVRISP mkII user’s guide stresses that the programmer must be connected to the PC before the target (AVR Butterfly board).

WORKING WITH THE AVR BUTTERFLY
The AVR Butterfly board includes an Atmel ATmega169 microcontroller and some peripherals. Figure 1 shows the connections I made to it. I only used three wires from the DB9 connector for serial communication with the PC. There isn’t any hardware handshaking. While I could also use this serial channel for programming, I find that using a dedicated programmer makes iterating my code much faster.

A six-pin header soldered to the J403 position enabled me to use Atmel’s AVRISP mkII programmer. Finally, powering the board with an external supply at J401 meant I wouldn’t have to think about the AVR Butterfly’s button cell battery. However, I did need to worry about the minimum power-on reset slope rate. The microcontroller won’t reset at power-on unless the power supply can ramp from about 1 to 3 V at more than 0.1 V/ms. I had to reduce a filter capacitor in my power supply circuit to increase its power-on ramp rate. With that settled, the microcontroller started executing code when I turned on the power supply.

After the hardware was connected, I used the AVR downloader uploader (AVRDUDE) and GNU Make to automate building the code and programming the AVR Butterfly’s flash memory. I modified a makefile template from the WinAVR project to specify my part, programmer, and source files. The template file’s comments helped me understand how to customize the template and comprehend the general build process. Finally, I used Gentoo, Linux’s cross-development package, to install the AVR GNU Compiler Collection (AVR-GCC) and other cross-compilation tools. I could have added these last pieces “by hand,” but Gentoo conveniently updates the toolchain as new versions are released.

Figure2

Figure 2: This is the program flow for processing characters received over the Atmel AVR Butterfly’s USART. Sending a command terminator (carriage return) will always result in an empty Receive buffer. This is a good way to ensure there’s no garbage in the buffer before writing to it.

HANDLING INCOMING CHARACTERS
To receive remote commands, you begin by receiving characters, which are sent to the AVR Butterfly via the USART connector shown in Figure 1. Reception of these characters triggers an interrupt service routine (ISR), which handles them according to the flow shown in Figure 2. The first step in this flow is loading the characters into the Receive buffer.

Figure 3: The received character buffer and pointers used to fill it are shown. There is no limit to the size of commands and their arguments, as long as the entire combined string and terminator fit inside the RECEIVE_BUFFER_SIZE.

Figure 3: The received character buffer and pointers used to fill it are shown. There is no limit to the size of commands and their arguments, as long as the entire combined string and terminator fit inside the RECEIVE_BUFFER_SIZE.

Figure 3 illustrates the Receive buffer loaded with a combined string. The buffer is accessed with a pointer to its beginning and another pointer to the next index to be written. These pointers are members of the recv_cmd_state_t-type variable recv_cmd_state.

This is just style. I like to try to organize a flow’s variables by making them members of their own structure. Naming conventions aside, it’s important to notice that no limitations are imposed on the command or argument size in this first step, provided the total character count stays below the RECEIVE_BUFFER_SIZE limit.

When a combined string in the Receive buffer is finished with a carriage return, the string is copied over to a second buffer. I call this the “Parse buffer,” since this is where the string will be searched for recognized commands and arguments. This buffer is locked until its contents can be processed to keep it from being overwhelmed by new combined strings.

Sending commands faster than they can be processed will generate an error and combined strings sent to a locked parse buffer will be dropped. The maximum command processing frequency will depend on the system clock and other system tasks. Not having larger parse or receive buffers is a limitation that places this project at the hobby level. Extending these buffers to hold more than just one command would make the system more robust.

Editor’s Note: If you are interested in other projects utilizing the AVR Butterfly, check out the Talk Zombie, which won “Distinctive Excellence” in the AVR Design Contest 2006 sponsored by ATMEL and administered by Circuit Cellar. The ATmega169-based multilingual talking device relates ambient temperature and current time in the form of speech (English, Dutch, or French). 

Remote-Control Powered Trapdoor Lift

William Wachsmann, a retired electronic technologist from Canada, has more than 35 years of experience working with minicomputers, microcomputers, embedded systems, and programming in industries ranging from nuclear and aerospace to voicemail and transportation systems.

But despite the complexity of the work he has done over the years, when it came to building a remote-controlled, powered trapdoor lift system for his home, he had two priorities: simplicity and price.

“Although it can be fulfilling to design your own hardware, why reinvent the wheel if you don’t have to? Many reasonably priced modules can be wired together,” Wachsmann says in his article about the project, which appears in Circuit Cellar’s May issue. “Add some software to express the functionality required and you can quickly and inexpensively put together a project. Not only is this method useful for a homebuilt one-of-a-kind application, but it can also be used for proof-of-concept prototyping. It leaves you free to concentrate on solving the problems pertinent to your application.”

Wachsmann’s project relies on off-the-shelf modules for the electrical functions of a trapdoor lift system that provides access to his basement.

“Lifting the trapdoor was hard on my wife’s back,” he says. “If her arms were full when she came upstairs and the door was open, she had to twist her body to release the mechanical latching mechanism while simultaneously stopping the door from falling on her head.”

The multidisciplinary project includes mechanical, electronic, and software components. For the full details—including programming of the project’s Freescale Semiconductor FRDM-KL25Z microprocessor using the mbed online IDE—check out the May issue now available for membership download and single-issue purchase.

(And if you’re interested in other articles about remote-control projects, check out Raul Alvarez’s Home Energy Gateway system, which enables users to remotely monitor home energy consumption and monitor household devices. Alvarez’s project won second place in the 2012 DesignSpark chipKIT challenge administered by Circuit Cellar.)

Excerpts from Wachsmann’s article below describe his system’s mechanical and hardware elements.

INS AND OUTS
I used a screw lift from an old treadmill. It has a 48-VDC motor that draws about 1 A under a 100-lb load. The screw mechanism has a 6” travel distance. Built-in limit switches shut off the motor when the screw reaches the end of its travel in each direction. The screw’s length is nominally 30” when closed and 36” when open. The length can be adjusted slightly by rotating the screw by hand, but the overall travel distance is still 6”.

A simple switch would have sufficed to control the screw lift’s DC motor, but I wanted it to be remotely controlled so the trapdoor could be raised and lowered from anywhere upstairs and from the basement. When someone is in the basement with the trapdoor closed there is no visible way for them to know if the door is obstructed. Initially, I was going to install a warning beeper that the door was opening, but that wouldn’t help if an inanimate object (e.g., a bag of groceries) was on top of the door. I needed to incorporate some form of sensing mechanism into the design.

Figure 1: This diagram represents the trapdoor mechanics. The arm’s down position is shown in red; the up position is shown in blue. Vertical red arrows are labeled with the downward force in pounds

Figure 1: This diagram represents the trapdoor mechanics. The arm’s down position is shown in red; the up position is shown in blue. Vertical red arrows are labeled with the downward force in pounds

THE MECHANICS
I needed a levered system design that used a pivoted bar and the motorized screw lift. The lift also had to enable the door to be manually opened in case of a power failure.
I used IMSI/Design’s TurboCAD program for the mechanical design. By using CAD software, I could experiment with the pivot position, moment arms, and torque requirements to meet the mechanical constraints imposed by the screw lift and the trapdoor’s size and weight.

Photo 1: The screw lift and pivot arm mechanism with a spring assist are shown.

Photo 1: The screw lift and pivot arm mechanism with a spring assist are shown.

Figure 1 shows a diagram of the trapdoor, which is hinged on the left. The opposite side of the door exerts a 15.2-lb downward force. This means the torque (force × distance) required to open the door is 509.2 in-lbs. The pivot arm in red is the position when the door is closed. The blue pivot arm shows the position when the door is open to an 80° angle.

To keep within the 6” lift constraint, I used a 4.25” moment arm to pull down on the pivot arm. This left me with the force required to initially lift the door at 119.5 lb. Also this did not include the added torque due to the pivot arm’s weight.

After mulling this over for a couple of days (and nights) I had an idea. I realized that 119.5 lb is only needed when the door is completely closed. As the door opens, the torque requirement lessens. I incorporated a heavy spring (see Photo 1). When the door is closed the spring extension provides an additional downward force of about 35 lb. This is enough to lessen the load on the screw lift and to compensate for the pivot arm’s additional 2.2 lb. Using a screw lift meant the arm would not spring up if the door was manually opened.

I used an angle iron for the pivot arm. It is 28” long because it had to push up on the door to the right of the door’s center of gravity at 16.75” without adding too much additional torque. The roller is the type used as feet on beds. I used an arbor and 0.75”-diameter bolt through the floor joist for the pivot (see Photo 2).

An arbor is used as a bearing with a 0.75” bolt through the floor joist. The lift mechanism pivots at this point.

Photo 2: An arbor is used as a bearing with a 0.75” bolt through the floor joist. The lift mechanism pivots at this point.

THE HARDWARE
I had set an arbitrary $100 limit for the rest of the system and I quickly realized I would easily come in under budget. I used a $24.25 two-channel RF wireless garage door remote-control receiver, which I purchased from eBay (see Photo 3). This controller can be used in a latched or an unlatched mode. The latched mode requires a momentary push of one of the buttons to cause one of the relays to switch and stay in the On position. When the controller is in unlatched mode, you must hold the button down to keep the relay switched.

Photo 3: The two-channel wireless remote control is shown with the cover removed from the receiver. It came with two keychain-style remotes, which I marked with Up and Down arrows.

Photo 3: The two-channel wireless remote control is shown with the cover removed from the receiver. It came with two keychain-style remotes, which I marked with Up and Down arrows.

Unfortunately, this remote control and any similar ones only come with single-pole double-throw (SPDT) relays. What I really wanted were double-pole double-throw (DPDT) relays to switch both sides of the motor to enable current reversal through the motor.
A remote control system with two remotes seemed ideal and was possible to design with SPDT, so I purchased the relays. Figure 2 shows the circuit using two bridge rectifier DC power supplies. It turns out there were problems with this approach.

SW1 and SW2 represent the Up and Down relays. In latched mode, the door would open when SW1 was energized using the A button on a remote. Pressing the A button again would stop the motor while the door was opening. So would pressing the B button, but then to continue opening the door you needed to press the B button again. Pressing the A  button in this state would cause the door to close because SW2 was still energized. Added to this confusion was the necessity of pressing the A button again when the door was fully opened and stopped due to the internal limit switches. If you didn’t do this, then pressing the B button to close the door wouldn’t work because SW1 was still energized.

Figure 2: It would be theoretically possible to use dual-power supplies and single-pole double-throw (SPDT) switches to control a motor in two directions. When SW1 (b,c) is connected, current flows through D2. When SW2 (b,c) is connected, current flows through D1 in the opposite direction.

Figure 2: It would be theoretically possible to use dual-power supplies and single-pole double-throw (SPDT) switches to control a motor in two directions. When SW1 (b,c) is connected, current flows through D2. When SW2 (b,c) is connected, current flows through D1 in the opposite direction.

I decided to just use the door in unlatched mode and continuously hold down the A button until the door was fully open. What was the problem with this? Noise! Interference from the motor was getting back into the control and causing the relay to frequently switch on and off. This is not good for mechanical relays that have a finite contact life.

After playing around for a while with both operation modes, I noticed that even in the latched mode the motor would sometimes stop and it would occasionally even reverse itself. This was really bad and it became worse.

If both SW1 and SW2 happened to switch at the same time and if the current was at a maximum and there was arcing at the terminal, there could conceivably be a momentary short through a diode in each of the bridge rectifiers that would burn them out. Arc suppression devices wouldn’t help because when active at high voltages, they would almost look like a short between the switch’s terminals A,C. I needed to step back and rethink this.

I found an $8.84 two-channel DPDT relay switch board module on eBay. The module enabled me to use a single-power supply and isolated the motor current from the remote-control board. These relays boards have TTL inputs, so it is tricky to use relays on the remote control board to control the relays on the second relay board. You have to contend with contact bounce. Even if I incorporated debounce circuits, I still didn’t have a way stop the door from opening if it was obstructed.

It was time to get with the 21st century. I needed to use a microcontroller and handle all the debounce and logic functions in firmware.

I bought a $12.95 Freescale Semiconductor FRDM-KL25Z development board, which uses the Kinetis L series of microcontrollers. The FRDM-KL25Z is built on the ARM Cortex-M0+ core. This board comes with multiple I/O pins, most of which can be programmed as required. It also has two micro-USB ports, one of which is used for downloading your program onto the microcontroller and for debugging (see Figure 3).

Figure 3: This is the system’s complete wiring diagram. On the left is a 48-V AC supply and an unregulated 12-V DC motor. A 2.7-Ω, 5-W resistor, which is used for current sensing, is in series with the motor.

Figure 3: This is the system’s complete wiring diagram. On the left is a 48-V AC supply and an unregulated 12-V DC motor. A 2.7-Ω, 5-W resistor, which is used for current sensing, is in series with the motor.

Active ESD Protection for Microcontrollers (EE Tip #129)

Microcontrollers need to be protected from of electrostatic discharge (ESD). You can use the circuit described in this post when you have an application requires a greater degree of ESD protection than what you get from an IC on its I/O pins. Although there are many ESD clamping devices out there, they don’t typically enable you to precisely limit voltage overshoots and undershoots.

Normally, when dealing with a microcontroller or other digital circuit the connections on the device are protected against electrostatic dis­charge. Nevertheless engineers are 4ever taking special precautions when handling such devices to avoid the risks of ESD: the lab will have an anti-static covering on the floor, and nylon clothes and shoes with soles made of insulating material are avoided. And, in case that is not enough, it is normal to wear an anti-static wrist band when moving devices from their anti-static bags to the anti-static bench surface. But what exactly do we mean when we talk about ESD?

HUMAN BODY MODEL

The first model for static discharge, mentioned as early as the 19thcentury, was the “human body model” (HBM). This takes as its starting point a voltage of up to 40 kV, a body capaci­tance of a few hundred picofarads, and a (skin) resistance of 1.5 kΩ. We find that even with a static voltage of only 10 kV, as might easily be acquired by walking across an artificial fiber car­pet in shoes with synthetic soles, it is possible to discharge through a fingertip at peak cur­rents of up to 20 A! The discharge also hap­pens in a very short period, perhaps measured in nanoseconds.

The HBM was adopted in the electronics industry in the 1970s with the introduction of sensitive JFET devices in space applications. The compo­nents were tested using a simple RC circuit like the one shown in Figure 1. The discharge cur­rent depends only on the resistance in the cir­cuit, and the damped discharge curve is largely free of oscillation and is accurately reproducible.

Figure 1—Standard test circuit and current waveform for the human body model

Figure 1—Standard test circuit and current waveform for the human body model

There are also other models that deal with dis­charge through a sensitive component, for exam­ple when a low-resistance electrical connection is made between two devices (the “machine model,” or MM), or when a static charge present on the device itself is discharged (the “charged device model,” or CDM)…

ESD CLAMP CIRCUITS

Figure 2 shows the typical protection circuitry provided on a microcontroller’s I/O port. This example is from an Atmel ATmega. Other microcontrol­lers and logic devices use similar arrangements. Two bipolar protection diodes conduct discharge currents that could cause undershoots or overshoots to one of the supply rails, either VCC or ground. However, the diodes take about 6 ns before they conduct fully.

Figure 2—Typical ESD protection circuit, as found in an Atmel microcontroller

Figure 2—Typical ESD protection circuit, as found in an Atmel microcontroller

Since ESD transients can sometimes be considerably shorter than this, it is possible that the CMOS circuit structures will be damaged long before the diodes spring into action. The parasitic capacitance of the pin is around 6 pF, and this is quickly charged up by the energy in the electrostatic discharge. Unfortunately, we cannot increase this capacitance with­out increasing the impedance of the pin, which is not desirable.

Standard ESD protection circuits like this one are designed to meet the particular requirements set by the ESD Association. However, it is becoming apparent that the traditional models are not appropriate for modern applications. Recent efforts have been directed toward developing a new “system level model” (SLM), which takes into account the different aspects of the older models. This model employs two stored charges that are discharged in different ways, creating a high-amplitude current pulse that decays very quickly plus a low-amplitude pulse that dies away more slowly. The energy transferred in a dis­charge under the SLM can be very much higher than that in the traditional models (Figure 3).

Figure 3—Current waveform under the system-level model

Figure 3—Current waveform under the system-level model

It is readily apparent that the conventional I/O pin circuitry on the IC is not sufficient to provide ESD protection under this model. Also, the con­tinuing industry pressure to make smaller and more complex structures makes it very difficult for design engineers even to maintain current levels of ESD protection, let alone improve on them. In other words: the silicon area needed to provide ESD protection in accordance with the SLM is simply not available! For this reason, external ESD clamp circuits are becoming more rele­vant. If a component provides only a low level of ESD protection (or even none at all) it is possible to add such a circuit at the points most at risk. The clamp circuits usually use so-called transient suppression diodes (transils or tranzorbs) which, like Zener diodes, start to conduct at a specified threshold voltage. However, unlike Zener diodes, they react quickly and can withstand much higher current transients. There are many variations on the circuit design, but none has exceptional performance and none offers precise clamping of voltage undershoots and overshoots.

STATE-OF-THE-ART ESD CLAMPING

If we are in the lucky position of not having to worry about the last cent of materials cost or the last square millimeter of board area, we can easily cre­ate a state-of-the-art active ESD protection circuit from discrete components (Figure 4).

Figure 4—This protection circuit clamps voltage transients outside defined upper and lower thresholds

Figure 4—This protection circuit clamps voltage transients outside defined upper and lower thresholds

The transistor circuit forms a kind of regulated voltage divider. The current through the two resistors R2 and R3 is such that the voltages across them are just enough that transistors T1 and T4 start to conduct and T2 and T3 are just short of saturation. So we have one base-emitter voltage (about 600 mV) across each of these two resistors, which means in turn that the emitters of T2 and T3 are 600 mV below VCC and above ground respectively. The circuit as shown is suitable for a 5 V supply; R1 can be changed to suit supplies of 3.3 V or 2.7 V if needed.

What is the point of this complexity? If the I/O pin is high (at +5 V) the upper 1N4148 switching diode will conduct fully as its cathode is at only 4.4 V. If a positive voltage transient should occur it will be conducted by the 1N4148, without switching delay, to the positive rail by 1N5817 Schottky diode D2, which acts quickly and has a low forward voltage. The same thing happens with polarities reversed when a negative voltage transient (below ground) occurs. Hence the digital inputs and outputs are protected against voltage excursions outside the range of the supply rails. In addition, voltage peaks are limited by the use of suppression inductors. The Murata BLM series inductor presents a relatively high impedance to signals in the 100 MHz range and so can significantly reduce the level of transients.

Although the approach we have described works well with digital levels, it is not suitable for use with signals destined for the analog-to-digital converter (ADC) on a microcontroller. In this case a reverse-biased diode between the signal and each supply rail is required to clamp overshoots and undershoots, with a pair of 10 kΩ series resistors to limit the transient current.

The series-connected capacitors C2 and C3 present a low-impedance path for transients between VCC and ground, and hence spikes on the supply rails will also be conducted away.—P. Kruger, “Active ESD Protection,” Elektor January/February 2014

Editor’s note: This article originally appeared in Elektor January/February 2014. It was shortened and updated for publication on CircuitCellar.com, which is an Elektor International Media Publication.

 

RESOURCES

www.teseq.de/de/de/service_support/technical_information/01_Transient_ immunity_testing_e.pdf

www.ti.com/lit/sg/sszb130b/sszb130b.pdf

www.semtech.com/circuit-protection/esd-protection/

www.murata.com/products/emc/basic/feature/bl_intro.html