Traveling With a “Portable Workspace”

As a freelance engineer, Raul Alvarez spends a lot of time on the go. He says the last four or five years he has been traveling due to work and family reasons, therefore he never stays in one place long enough to set up a proper workspace. “Whenever I need to move again, I just pack whatever I can: boards, modules, components, cables, and so forth, and then I’m good to go,” he explains.

Raul_Alvarez_Workspace _Photo_1

Alvarez sits at his “current” workstation.

He continued by saying:

In my case, there’s not much of a workspace to show because my workspace is whichever desk I have at hand in a given location. My tools are all the tools that I can fit into my traveling backpack, along with my software tools that are installed in my laptop.

Because in my personal projects I mostly work with microcontroller boards, modular components, and firmware, until now I think it didn’t bother me not having more fancy (and useful) tools such as a bench oscilloscope, a logic analyzer, or a spectrum analyzer. I just try to work with whatever I have at hand because, well, I don’t have much choice.

Given my circumstances, probably the most useful tools I have for debugging embedded hardware and firmware are a good-old UART port, a multimeter, and a bunch of LEDs. For the UART interface I use a Future Technology Devices International FT232-based UART-to-USB interface board and Tera Term serial terminal software.

Currently, I’m working mostly with Microchip Technology PIC and ARM microcontrollers. So for my PIC projects my tiny Microchip Technology PICkit 3 Programmer/Debugger usually saves the day.

Regarding ARM, I generally use some of the new low-cost ARM development boards that include programming/debugging interfaces. I carry an LPC1769 LPCXpresso board, an mbed board, three STMicroelectronics Discovery boards (Cortex-M0, Cortex-M3, and Cortex-M4), my STMicroelectronics STM32 Primer2, three Texas Instruments LaunchPads (the MSP430, the Piccolo, and the Stellaris), and the following Linux boards: two BeagleBoard.org BeagleBones (the gray one and a BeagleBone Black), a Cubieboard, an Odroid-X2, and a Raspberry Pi Model B.

Additionally, I always carry an Arduino UNO, a Digilent chipKIT Max 32 Arduino-compatible board (which I mostly use with MPLAB X IDE and “regular” C language), and a self-made Parallax Propeller microcontroller board. I also have a Wi-Fi 3G TP-LINK TL-WR703N mini router flashed   with OpenWRT that enables me to experiment with Wi-Fi and Ethernet and to tinker with their embedded Linux environment. It also provides me Internet access with the use of a 3G modem.

Raul_Alvarez_Workspace _Photo_2

Not a bad set up for someone on the go. Alvarez’s “portable workstation” includes ICs, resistors, and capacitors, among other things. He says his most useful tools are a UART port, a multimeter, and some LEDs.

In three or four small boxes I carry a lot of sensors, modules, ICs, resistors, capacitors, crystals, jumper cables, breadboard strips, and some DC-DC converter/regulator boards for supplying power to my circuits. I also carry a small video camera for shooting my video tutorials, which I publish from time to time at my website (www.raulalvarez.net). I have installed in my laptop TechSmith’s Camtasia for screen capture and Sony Vegas for editing the final video and audio.

Some IDEs that I have currently installed in my laptop are: LPCXpresso, Texas Instruments’s Code Composer Studio, IAR EW for Renesas RL78 and 8051, Ride7, Keil uVision for ARM, MPLAB X, and the Arduino IDE, among others. For PC coding I have installed Eclipse, MS Visual Studio, GNAT Programming Studio (I like to tinker with Ada from time to time), QT Creator, Python IDLE, MATLAB, and Octave. For schematics and PCB design I mostly use CadSoft’s EAGLE, ExpressPCB, DesignSpark PCB, and sometimes KiCad.

Traveling with my portable rig isn’t particularly pleasant for me. I always get delayed at security and customs checkpoints in airports. I get questioned a lot especially about my circuit boards and prototypes and I almost always have to buy a new set of screwdrivers after arriving at my destination. Luckily for me, my nomad lifestyle is about to come to an end soon and finally I will be able to settle down in my hometown in Cochabamba, Bolivia. The first two things I’m planning to do are to buy a really big workbench and a decent digital oscilloscope.

Alvarez’s article “The Home Energy Gateway: Remotely Control and Monitor Household Devices” appeared in Circuit Cellar’s February issue. For more information about Alvarez, visit his website or follow him on Twitter @RaulAlvarezT.

Experimenting with Dielectric Absorption

Dielectric absorption occurs when a capacitor that has been charged for a long time briefly retains a small amount of voltage after a discharge.

“The capacitor will have this small amount of voltage even if an attempt was made to fully discharge it,” according to the website wiseGEEK. “This effect usually lasts a few seconds to a few minutes.”

While it’s certainly best for capacitors to have zero voltage after discharge, they often retain a small amount through dielectric absorption—a phenomenon caused by polarization of the capacitor’s insulating material, according to the website. This voltage (also called soakage) is totally independent of capacity.

At the very least, soakage can impair the function of a circuit. In large capacitor systems, it can be a serious safety hazard.

But soakage has been around a long time, at least since the invention of the first simple capacitor, the Leyden jar, in 1775. So columnist Robert Lacoste decided to have some “fun” with it in Circuit Cellar’s February issue, where he writes about several of his experiments in detecting and measuring dielectric absorption.

Curious? Then consider following his instructions for a basic experiment:

Go down to your cellar, or your electronic playing area, and find the following: one large electrolytic capacitor (e.g., 2,200 µF or anything close, the less expensive the better), one low-value discharge resistor (100 Ω or so), one DC power supply (around 10 V, but this is not critical), one basic oscilloscope, two switches, and a couple of wires. If you don’t have an oscilloscope on hand, don’t panic, you could also use a hand-held digital multimeter with a pencil and paper, since the phenomenon I am showing is quite slow. The only requirement is that your multimeter must have a high-input impedance (1 MΩ would be minimum, 10 MΩ is better).

Figure 1: The setup for experimenting with dielectric absorption doesn’t require more than a capacitor, a resistor, some wires and switches, and a voltage measuring instrument.

Figure 1: The setup for experimenting with dielectric absorption doesn’t require more than a capacitor, a resistor, some wires and switches, and a voltage measuring instrument.

Figure 1 shows the setup. Connect the oscilloscope (or multimeter) to the capacitor. Connect the power supply to the capacitor through the first switch (S1) and then connect the discharge resistor to the capacitor through the second switch (S2). Both switches should be initially open. Photo 1 shows you my simple test configuration.

Now turn on S1. The voltage across the capacitor quickly reaches the power supply voltage. There is nothing fancy here. Start the oscilloscope’s voltage recording using a slow time base of 10 s or so. If you are using a multimeter, use a pen and paper to note the measured voltage. Then, after 10 s, disconnect the power supply by opening S1. The voltage across the capacitor should stay roughly constant as the capacitor is loaded and the losses are reasonably low.

Photo 1: My test bench includes an Agilent Technologies DSO-X-3024A oscilloscope, which is oversized for such an experiment.

Photo 1: My test bench includes an Agilent Technologies DSO-X-3024A oscilloscope, which is oversized for such an experiment.

Now switch on S2 long enough to fully discharge the capacitor through the 100-Ω resistor. As a result of the discharge, the voltage across the capacitor’s terminals will quickly become very low. The required duration for a full discharge is a function of the capacitor and resistor values, but with the proposed values of 2,200 µF and 100 Ω, the calculation shows that it will be lower than 1 mV after 2 s. If you leave S2 closed for 10 s, you will ensure the capacitor is fully discharged, right?

Now the fun part. After those 10 s, switch off S2, open your eyes, and wait. The capacitor is now open circuited, at least if the voltmeter or oscilloscope input current can be neglected, so the capacitor voltage should stay close to zero. But you will soon discover that this voltage slowly increases over time with an exponential shape.

Photo 2 shows the plot I got using my Agilent Technologies DSO-X 3024A digital oscilloscope. With the capacitor I used, the voltage went up to about 120 mV in 2 min, as if the capacitor was reloaded through another voltage source. What is going on here? There aren’t any aliens involved. You have just discovered a phenomenon called dielectric absorption!

Photo 2: I used a 2,200-µF capacitor, a 100-Ω discharge resistor, and a 10-s discharge duration to obtain this oscilloscope plot. After 2 min the voltage reached 119 mV due to the dielectric absorption effect.

Photo 2: I used a 2,200-µF capacitor, a 100-Ω discharge resistor, and a 10-s discharge duration to obtain this oscilloscope plot. After 2 min the voltage reached 119 mV due to the dielectric absorption effect.

Nothing in Lacoste’s column about experimenting with dielectric absorption is shocking (and that’s a good thing when you’re dealing with “hidden” voltage). But the column is certainly informative.

To learn more about dielectric absorption, what causes it, how to detect it, and its potential effects on electrical systems, check out Lacoste’s column in the February issue. The issue is now available for download by members or single-issue purchase.

Lacoste highly recommends another resource for readers interested in the topic.

“Bob Pease’s Electronic Design article ‘What’s All This Soakage Stuff Anyhow?’ provides a complete analysis of this phenomenon,” Lacoste says. “In particular, Pease reminds us that the model for a capacitor with dielectric absorption effect is a big capacitor in parallel with several small capacitors in series with various large resistors.”

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.

 

 

 

Member Profile: Scott Weber

Scott Weber

Scott Weber

LOCATION:
Arlington, Texas, USA

MEMBER STATUS:
Scott said he started his Circuit Cellar subscription late in the last century. He chose the magazine because it had the right mix of MCU programming and electronics.

TECH INTERESTS:
He has always enjoyed mixing discrete electronic projects with MCUs. In the early 1980s, he built a MCU board based on an RCA CDP1802 with wirewrap and programmed it with eight switches and a load button.

Back in the 1990s, Scott purchased a Microchip Technology PICStart Plus. “I was thrilled at how powerful and comprehensive the chip and tools were compared to the i8085 and CDP1802 devices I tinkered with years before,” he said.

RECENT EMBEDDED TECH ACQUISITION:
Scott said he recently treated himself to a brand-new Fluke 77-IV multimeter.

CURRENT PROJECTS:
Scott is building devices that can communicate through USB to MS Windows programs. “I don’t have in mind any specific system to control, it is something to learn and have fun with,” he said. “This means learning not only an embedded USB software framework, but also Microsoft Windows device drivers.”

THOUGHTS ON THE FUTURE OF EMBEDDED TECH:
“Embedded devices are popping up everywhere—in places most people don’t even realize they are being used. It’s fun discovering where they are being applied. It is so much easier to change the microcode of an MCU or FPGA as the unit is coming off the assembly line than it is to rewire a complex circuit design,” Scott said.

“I also like Member Profile Joe Pfeiffer’s final comment in Circuit Cellar 276: Surface-mount and ASIC devices are making a ‘barrier to entry’ for the hobbyist. You can’t breadboard those things! I gotta learn a good way to make my own PCBs!”

Dual-Display Digital Multimeter

The DM3058E digital multimeter (DMM) is designed with 5.5-digit resolution and dual display. The DMM can enable system integration and is suitable for high-precision, multifunction, and automatic measurement applications.

The DM3058E is capable of measuring up to 123 readings per second. It can quickly save or recall up to 10 preset configurations, including built-in cold terminal compensation for thermocouples.

The DMM provides a convenient and flexible platform with an easy-to-use design and a built-in help system for information acquisition. In addition, it supports 10 different measurement types including DC voltage (200 mV to approximately 1,000 V), AC voltage (200 mV to approximately 750 V), DC current (200 µA to approximately
10 A), AC current (20 mA to approximately 10 A), frequency measurement (20 Hz to approximately 1 MHz), 2-Wire and 4-Wire resistance (200 O to approximately 100 MO), and diode, continuity, and capacitance.

The DM3058 is ideal for research and development labs and educational applications, as well as low-end detection, maintenance, and quality tests where automation combined with capability and value are needed.

The DM3058E digital multimeter costs $449.

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www.rigolna.com