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.”

Next-Generation Wi-Fi Modules

eConaisThe EC19D family is small, easily integrated, low-standby power single chip 802.11b/g/n Wi-Fi System In Package (SiP) modules for the Internet of Things (IoT).

The SiP modules help designers quickly and easily connect their devices to 802.11b/g/n Wi-Fi networks. At 8-mm × 8-mm, the EC19D modules can be embedded in almost any product or application. The EC19D will also include FCC, IC, and EC certifications to further simplify and speed up product design and production for use with Wi-Fi networks.

The EC19D incorporates the newest Wi-Fi 802.11b/g/n standards and features to provide designers with many options for embedding the module in their designs. The EC19D’s features include Wi-Fi Direct, ProbMeTM configuration, full TCP/IP stack, HTTPS/SSL, DHCP Client/Server, WPS, legacy Wi-Fi Client, and SoftAP modes with WPA/WPA2 support, serial to Wi-Fi, and Cloud service support.

Contact eConais for pricing.

eConais Inc.
www.econais.com

RS-422/-485 Serial Interface for PCI Express

SealevelThe 7802e is a PCI Express serial interface adapter that provides eight serial ports individually configurable for RS-422 or RS-485 communications. The adapter is well suited for applications including test and measurement, security systems, and broadcast.

The board’s high-performance 16C950 UART includes 128-byte FIFOs for error-free operation in high-speed serial applications. The 16C950 UART also supports 9-bit framing and is software compatible with legacy UART applications.

A PCI Express link supplies the 7802e’s 62.5-MHz clock. This ultra-high speed clock is divided by a flexible 8-bit clock prescalar. In RS-485 mode, the transmitter is automatically enabled in hardware, eliminating the need for application software control. This enables the 7802e to be used with standard serial applications without the risk of bus contention and data corruption.

All Sealevel PCI Express serial adapters include SeaCOM software for Windows and Linux OSes. The adapters also include WinSSD, a full-featured application for testing and diagnostics including bit error rate testing (BERT), throughput monitoring, loopback tests, and test pattern message transmissions.

The 7802e costs $469.

Sealevel Systems, Inc.
www.sealevel.com

Remote Control and Monitoring of Household Devices

Raul Alvarez, a freelance electronic engineer from Bolivia, has long been interested in wireless device-to-device communication.

“So when the idea of the Internet of Things (IoT) came around, it was like rediscovering the Internet,” he says.

I’m guessing that his dual fascinations with wireless and the IoT inspired his Home Energy Gateway project, which won second place in the 2012 DesignSpark chipKIT challenge administered by Circuit Cellar.

“The system enables users to remotely monitor their home’s power consumption and control household devices (e.g., fans, lights, coffee machines, etc.),” Alvarez says. “The main system consists of an embedded gateway/web server that, aside from its ability to communicate over the Internet, is also capable of local communications over a home area wireless network.”

Alvarez catered to his interests by creating his own wireless communication protocol for the system.

“As a learning exercise, I specifically developed the communication protocol I used in the home area wireless network from scratch,” he says. “I used low-cost RF transceivers to implement the protocol. It is simple and provides just the core functionality necessary for the application.”

Figure1: The Home Energy Gateway includes a Hope Microelectronics RFM12B transceiver, a Digilent chipKIT Max32 board, and a Microchip Technology ENC28J60 Ethernet controller chip.

Figure 1: The Home Energy Gateway includes a Hope Microelectronics RFM12B transceiver, a Digilent chipKIT Max32 board, and a Microchip Technology ENC28J60 Ethernet controller chip.

Alvarez writes about his project in the February issue of Circuit Cellar. His article concentrates on the project’s TCI/IP communications aspects and explains how they interface.

Here is his article’s overview of how the system functions and its primary hardware components:

Figure 1 shows the system’s block diagram and functional configuration. The smart meter collects the entire house’s power consumption information and sends that data every time it is requested by the gateway. In turn, the smart plugs receive commands from the gateway to turn on/off the household devices attached to them. This happens every time the user turns on/off the controls in the web control panel.

Photo 1: These are the three smart node hardware prototypes: upper left,  smart plug;  upper right, a second smart plug in a breadboard; and at bottom,  the smart meter.

Photo 1: These are the three smart node hardware prototypes: upper left, smart plug; upper right, a second smart plug in a breadboard; and at bottom, the smart meter.

I used the simple wireless protocol (SWP) I developed for this project for all of the home area wireless network’s wireless communications. I used low-cost Hope Microelectronics 433-/868-/915-MHz RFM12B transceivers to implement the smart nodes. (see Photo 1)
The wireless network is configured to work in a star topology. The gateway assumes the role of a central coordinator or master node and the smart devices act as end devices or slave nodes that react to requests sent by the master node.

The gateway/server is implemented in hardware around a Digilent chipKIT Max32 board (see Photo 2). It uses an RFM12B transceiver to connect to the home area wireless network and a Microchip Technology ENC28J60 chip module to connect to the LAN using Ethernet.

As the name implies, the gateway makes it possible to access the home area wireless network over the LAN or even remotely over the Internet. So, the smart devices are easily accessible from a PC, tablet, or smartphone using just a web browser. To achieve this, the gateway implements the SWP for wireless communications and simultaneously uses Microchip Technology’s TCP/IP Stack to work as a web server.

Photo 2: The Home Energy Gateway’s hardware includes a Digilent chipKIT Max32 board and a custom shield board.

Photo 2: The Home Energy Gateway’s hardware includes a Digilent chipKIT Max32 board and a custom shield board.

Thus, the Home Energy Gateway generates and serves the control panel web page over HTTP (this page contains the individual controls to turn on/off each smart plug and at the same time shows the power consumption in the house in real-time). It also uses the wireless network to pass control data from the user to the smart plugs and to read power consumption data from the smart meter.

The hardware module includes three main submodules: The chipKIT Max 32 board, the RFM12B wireless transceiver, and the ENC28J60 Ethernet module. The smart meter hardware module has an RFM12B transceiver for wireless communications and uses an 8-bit Microchip Technology PIC16F628A microcontroller as a main processor. The smart plug hardware module shows the smart plugs’ main hardware components and has the same microcontroller and radio transceiver as the smart meter. But the smart plugs also have a Sharp Microelectronics S212S01F solid-state relay to turn on/off the household devices.

On the software side, the gateway firmware is written in C for the Microchip Technology C32 Compiler. The smart meter’s PIC16F628A code is written in C for the Hi-TECH C compiler. The smart plug software is very similar.

Alvarez says DIY home-automation enthusiasts will find his prototype inexpensive and capable. He would like to add several features to the system, including the ability to e-mail notifications and reports to users.

For more details, check out the February issue now available for download by members or single-issue purchase.

Desoldering Components (EE Tip #118)

Every engineer and technician sooner or later faces the challenge of having to desolder a component. Sometimes the component can be a large transformer with 10 pins or a power chip with many connections, and desoldering tools are typically around the $1,000 mark and above.

Chip Quik is a solder-based alloy that stays molten for up to 30 seconds and makes desoldering any component very easy. The only drawback is that the cost of a 2´ length of Chip Quik is around $20. But a little experience can make this go a long way. Having some Chip Quik lying around in the workshop is reassuring for when that urgent job comes in.

Editor’s Note: This EE Tip was written by Fergus Dixon of Sydney, Australia. Dixon, who has written two articles and an essay for Circuit Cellar, runs Electronic System Design, a website set up to promote easy to use and inexpensive development kits. Click here to read his essay “The Future of Open-Source Hardware for Medical Devices.”

MakeHartford Cuts “Ribbon” at Grand Opening of a New Makerspace

A crowd gathers at the MakeHartford Grand Opening.

A crowd gathers at the MakeHartford grand opening.

Right in Circuit Cellar‘s backyard, a group of dedicated makers, technologists, artists, and entrepreneurs has spent the past year planning, building, and equipping a brand new space to serve the Connecticut capital’s maker community. The fruits of their labor, MakeHartford, held its grand opening and ribbon-cutting event  January 25th.

MakeHartford founder and President Steven Yanicke with Mayor Pedro Segarra

MakeHartford founder and President Steven Yanicke with Mayor Pedro Segarra

Steven Yanicke, founder and president of MakeHartford, welcomed a crowd of more than 75 people before turning the microphone over to Hartford Mayor Pedro E. Segarra, a strong supporter of the educational and innovation opportunities that MakeHartford represents. Wielding a ceremonial power saw in true maker fashion, Segarra cut the machine-carved “ribbon,” signifying the official opening of MakeHartford.

 

Throughout the afternoon, MakeHartord members talked with visitors from the community, entrepreneurial development organizations, and schools, showing their projects and discussing their plans for using the space. The event included presentations and demonstrations covering everything from traditional and modern ham radio to Arduino-powered wearable art to tessellation origami.

MH Grand Opening-0026 MH Grand Opening-0068Adults and kids alike listened to the Gus Robotics Team 228 from Meriden, CT, talk about its VEX robots, while members of the West Hartford-based Athena’s Warriors FIRST Robotics Team were on hand to show off their mechanized, computerized creations. A “deconstruction table” gave guests the opportunity to void warranties and open up everyday items—printers, keyboards, routers, motor controllers—to begin to understand that “what’s inside the box still counts.”

MH Grand Opening-0087

Artist and innovator Balam Soto demonstratates one of his Arduino-powered musical sculptures.

MH Grand Opening-0084

A “deconstruction workshop” provided guests the opportunity to see that “what’s inside the box still counts.”

For more information about MakeHartford, contact steve@makehartford.com

 

Embedded SSDs For Long-Life Applications

GreenliantGreenliant Systems’s eMMC NANDrive GLS85VM embedded solid state drive (SSD) product family is available to select customers. The SSDs combine Greenliant’s internally developed NAND controller with NAND flash die, providing a fully integrated SSD in a multi-chip package. The SSDs are available with two bits per cell (MLC) or one bit per cell (SLC) NAND to meet varying customer requirements for lifespan, endurance, and performance.

The 14-mm × 180-mm eMMC NANDrives are offered in a 100 ball grid array (BGA) package with 1-mm ball pitch for increased long-term reliability. The SSDs offer data storage in a small BGA form factor capable of withstanding severe conditions. The NANDrive devices support the JEDEC eMMC 4.4 standard and are backward compatible with the eMMC 4.3 standard.

The eMMC NANDrives feature advanced wear-leveling, bad block management, and error correction code (ECC) capabilities. They also include power interrupt data protection and enhanced security features to safeguard sensitive data.

Contact Greenliant for pricing.

Greenliant Systems, Ltd.
www.greenliant.com

Protocol-Decoding Oscilloscope Software

Agilent2Agilent Technologies has introduced the N8819A USB 3.0 SSIC and N8820A MIPI CSI-3 protocol decoders. The software decodes USB 3.0 SuperSpeed Inter-Chip (SSIC) and MIPI Camera Serial Interface 3 (CSI-3) protocols on oscilloscopes. The protocol decoders provide engineers with a fast, easy way to validate and debug SSIC and CSI-3 interfaces.

The N8819A USB 3.0 SSIC and N8820A MIPI CSI-3 protocol decoders are designed to run on 90000 A-, 90000 X-, and 90000 Q-Series oscilloscopes. They decode protocol packets for the SSIC V1.0 and MIPI CSI-3 V1.0 specifications, respectively. The decoders provide accurate timing measurements associated with the protocols.

The software supports correlated protocol decode information with the analog waveforms; symbol, packet, frame, and payload detail of the protocols; high-speed (HS-BURST) and low-speed PWM (PWM-BURST) transmission modes; cyclical redundancy check (CRC) on the packets; and search capability for various frames, sequences, and errors.

Both protocol decoders can be used on Infiniium 90000 Q-Series oscilloscopes, which deliver real-time bandwidth of up to 33 GHz on four channels. The oscilloscopes feature bandwidth upgradability to 63 GHz and low noise and jitter measurement floor performance.

The Agilent N8819A USB 3.0 SSIC and N8820A MIPI CSI-3 protocol decoders cost $3,500 and $3,000, respectively.

Agilent Technologies, Inc.
www.agilent.com

A Visit to the World Maker Faire in New York

If you missed the World Maker Faire in New York City, you can pick up Circuit Cellar’s February issue for highlights of the innovative projects and hackers represented there.Veteran electronics DIYer and magazine columnist Jeff Bachiochi is the perfect guide.

“The World Maker Faire is part science fair and part country fair,” Bachiochi says. “Makers are DIYers. The maker movement empowers everyone to build, repair, remake, hack, and adapt all things. The Maker Faire shares the experiences of makers who have been involved in this important process… Social media keeps us in constant contact and can educate, but it can’t replace the feeling you can get from hands-on live interaction with people and the things they have created.

Photo 1: This pole-climbing robot is easy to deploy at a moment’s notice. There is no need for a ladder to get emergency communication antennas up high where they can be most effective.

Photo 1: This pole-climbing robot is easy to deploy at a moment’s notice. There is no need for a ladder to get emergency communication antennas up high where they can be most effective.

“It should be noted that not all Maker Faire exhibitors are directly involved with technology. Some non-technological projects on display included the ‘Art Car’ from Pittsburgh, which is an annual revival of an old clunker turned into a drivable art show on wheels. There was also the life-size ‘Mouse Trap’ game, which was quite the contraption and just plain fun, especially if you grew up playing the original game.”

Bachiochi’s article introduces you to a wide variety of innovators, hackers, and hackerspaces.

“The 721st Mechanized Contest Battalion (MCB) is an amateur radio club from Warren County, NJ, that combines amateur (ham) radio with electronics, engineering, mechanics, building, and making,” Bachiochi says. “The club came to the Maker Faire to demonstrate its Emergency Antenna Platform System (E-APS) robot. The robot, which is designed for First Responder Organizations, will turn any parking lot lamppost into an instant antenna tower (see Photo 1).”

The keen and growing interest in 3-D printing as a design tool was evident at the Maker Faire.

“Working by day as an analog/mixed-signal IC design engineer for Cortina Systems in Canada, Andrew Plumb needed a distraction. In the evenings, Plumb uses a MakerBot 3-D printer to create 3-D designs of plastic, like thousands of others experimenting with 3-D printing,” Bachiochi says. “Plumb was not satisfied with simply printing plastic widgets. In fact, he showed me a few of his projects, which include printing plastic onto paper and cloth (see Photo 2).”

Photo 2: Andrew Plumb showed me some unique ideas he was experimenting with using one of his 3-D printers. By printing the structural frame directly on tissue paper, ultra-light parts are practically ready to fly.

Photo 2: Andrew Plumb showed me some unique ideas he was experimenting with using one of his 3-D printers. By printing the structural frame directly on tissue paper, ultra-light parts are practically ready to fly.

Also in the 3-D arena, Bachiochi encountered some innovative new products.

“It was just a matter of time until someone introduced a personal scanner to create digital files of 3-D objects. The MakerBot Digitizer Desktop 3-D Scanner is the first I’ve seen (see Photo 3),” Bachiochi says. “It uses a laser, a turntable, and a CMOS camera to pick off 3-D points and output a STL file. The scanner will create a 3-D image from an object up to 8″ in height and width. There is no third axis scanning, so you must plan your model’s orientation to achieve the best results. Priced less than most 3-D printers, this will be a hot item for 3-D printing enthusiasts.”

Bachiochi’s article includes a lengthy section about “other interesting stuff” and people at the Maker Faire, including the Public Laboratory for Open Technology and Science (Public Lab), a community that uses inexpensive DIY techniques to investigate environmental concerns.

Photo 3: The MakerBot Digitizer Desktop 3-D Scanner is the first production scanner I’ve seen that will directly provide files compatible with the 3-D printing process. This is a long-awaited addition to MakerBot’s line of 3-D printers. (Photo credit: Spencer Higgins)

Photo 3: The MakerBot Digitizer Desktop 3-D Scanner is the first production scanner I’ve seen that will directly provide files compatible with the 3-D printing process.  (Photo credit: Spencer Higgins)

“For instance, the New York chapter featured two spectrometers, a you-fold-it cardboard version and a near-infrared USB camera-based kit,” Bachiochi says. “This community of educators, technologists, scientists, and community organizers believes they can promote action, intervention, and awareness through a participatory research model in which you can play a part.”

At this family-friendly event, Bachiochi met a family that “creates” together.

“Asheville, NC-based Beatty Robotics is not your average robotics company,” Bachiochi says. “The Beatty team is a family that likes to share fun robotic projects with friends, family, and other roboticists around the world. The team consists of Dad (Robert) and daughters Camille ‘Lunamoth’ and Genevieve ‘Julajay.’ The girls have been mentored in electronics, software programming, and workshop machining. They do some unbelievable work (see Photo 4). Everyone has a hand in designing, building, and programming their fleet of robots. The Hall of Science is home to one of their robots, the Mars Rover.”

There is much more in Bachiochi’s five-page look at the Maker Faire, including resources for finding and participating in a hackerspace community. The February issue including Bachiochi’s articles is available for membership download or single-issue purchase.

Photo 4: Beatty Robotics is a family of makers that produces some incredible models. Young Camille Beatty handles the soldering, but is also well-versed in machining and other areas of expertise.

Photo 4: Beatty Robotics is a family of makers that produces some incredible models. Young Camille Beatty handles the soldering, but is also well-versed in machining and other areas of expertise.

Build an Inexpensive Wireless Water Alarm

The best DIY electrical engineering projects are effective, simple, and inexpensive. Devlin Gualtieri’s design of a wireless water alarm, which he describes in Circuit Cellar’s February issue, meets all those requirements.

Like most homeowners, Gualtieri has discovered water leaks in his northern New Jersey home after the damage has already started.

“In all cases, an early warning about water on the floor would have prevented a lot of the resulting damage,” he says.

You can certainly buy water alarm systems that will alert you to everything from a leak in a well-water storage tank to moisture from a cracked boiler. But they typically work with proprietary and expensive home-alarm systems that also charge a monthly “monitoring” fee.

“As an advocate of free and open-source software, it’s not surprising that I object to such schemes,” Gualtieri says.

In February’s Circuit Cellar magazine, now available for membership download or single-issue purchase, Gualtieri describes his battery-operated water alarm. The system, which includes a number of wireless units that signal a single receiver, includes a wireless receiver, audible alarm, and battery monitor to indicate low power.

Photo 1: An interdigital water detection sensor is shown. Alternate rows are lengths of AWG 22 copper wire, which is either bare or has its insulation removed. The sensor is shown mounted to the bottom of the box containing the water alarm circuitry. I attached it with double-stick foam tape, but silicone adhesive should also work.

Photo 1: An interdigital water detection sensor is shown. Alternate rows are lengths of AWG 22 copper wire, which is either bare or has its insulation removed. The sensor is shown mounted to the bottom of the box containing the water alarm circuitry. I attached it with double-stick foam tape, but silicone adhesive should also work.

Because water conducts electricity, Gualtieri sensors are DIY interdigital electrodes that can lie flat on a surface to detect the first presence of water. And their design couldn’t be easier.

“You can simply wind two parallel coils of 22 AWG wire on a perforated board about 2″ by 4”, he says. (See Photo 1.)

He also shares a number of design “tricks,” including one he used to make his low-battery alert work:

“A battery monitor is an important feature of any battery-powered alarm circuit. The Microchip Technology PIC12F675 microcontroller I used in my alarm circuit has 10-bit ADCs that can be optionally assigned to the I/O pins. However, the problem is that the reference voltage for this conversion comes from the battery itself. As the battery drains from 100% downward, so does the voltage reference, so no voltage change would be registered.

Figure 1: This is the portion of the water alarm circuit used for the battery monitor. The series diodes offer a 1.33-V total  drop, which offers a reference voltage so the ADC can see changes in the battery voltage.

Figure 1: This is the portion of the water alarm circuit used for the battery monitor. The series diodes offer a 1.33-V total drop, which offers a reference voltage so the ADC can see changes in the battery voltage.

“I used a simple mathematical trick to enable battery monitoring. Figure 1 shows a portion of the schematic diagram. As you can see, the analog input pin connects to an output pin, which is at the battery voltage when it’s high through a series connection of four small signal diodes (1N4148). The 1-MΩ resistor in series with the diodes limits their current to a few microamps when the output pin is energized. At such low current, the voltage drop across each diode is about 0.35 V. An actual measurement showed the total voltage drop across the four diodes to be 1.33 V.

“This voltage actually presents a new reference value for my analog conversion. The analog conversion now provides the following digital values:

EQ1Table 1 shows the digital values as a function of battery voltage. The nominal voltage of three alkaline cells is 4.75 V. The nominal voltage of three lithium cells is 5.4 V. The PIC12F675 functions from approximately 2 to 6.5 V, but the wireless transmitter needs as much voltage as possible to generate a reliable signal. I arbitrarily coded the battery alarm at 685, or a little above 4 V. That way, there’s still enough power to energize the wireless transmitter at a useful power level.”

Table 1
Battery Voltage ADC Value
5 751
4.75 737
4.5 721
4.24 704
4 683
3.75 661

 

Gaultieri’s wireless transmitter, utilizing lower-frequency bands, is also straightforward.

Photo 2 shows one of the transmitter modules I used in my system,” he says. “The round device is a surface acoustic wave (SAW) resonator. It just takes a few components to transform this into a low-power transmitter operable over a wide supply voltage range, up to 12 V. The companion receiver module is also shown. My alarm has a 916.5-MHz operating frequency, but 433 MHz is a more popular alarm frequency with many similar modules.”

These transmitter and receiver modules are used in the water alarm. The modules operate at 916.5 MHz, but 433 MHz is a more common alarm frequency with similar modules. The scale is inches.

Photo 2: These transmitter and receiver modules are used in the water alarm. The modules operate at 916.5 MHz, but 433 MHz is a more common alarm frequency with similar modules. The scale is inches.

Gualtieri goes on to describe the alarm circuitry (see Photo 3) and receiver circuit (see Photo 4.)

For more details on this easy and affordable early-warning water alarm, check out the February issue.

Photo 3: This is the water alarm’s interior. The transmitter module with its antenna can be seen in the upper right. The battery holder was harvested from a $1 LED flashlight. The box is 2.25“ × 3.5“, excluding the tabs.

Photo 3: This is the water alarm’s interior. The transmitter module with its antenna can be seen in the upper right. The battery holder was harvested from a $1 LED flashlight. The box is 2.25“ × 3.5“, excluding the tabs.

Photo 4: Here is my receiver circuit. One connector was used to monitor the signal strength voltage during development. The other connector feeds an input on a home alarm system. The short antenna reveals its 916.5-MHz operating frequency. Modules with a 433-MHz frequency will have a longer antenna.

Photo 4: Here is my receiver circuit. One connector was used to monitor the signal strength voltage during development. The other connector feeds an input on a home alarm system. The short antenna reveals its 916.5-MHz operating frequency. Modules with a 433-MHz frequency will have a longer antenna.

 

Arduino-Based DIY Voltage Booster (EE Tip #117)

If your project needs a higher voltage rail than is already available in the circuit, you can use an off-the-shelf step-up device. But when you want a variable output voltage, it’s less easy to find a ready-made IC. However, it’s not complicated to build such a circuit yourself, especially if you have a microcontroller board that’s as easy to program as an Arduino. And this also lets you experiment with the circuit so you can get a better understanding of how it works.

Source: Elektor, April 2010

Source: Elektor, April 2010

No surprises in the circuit—a largely conventional boost converter. The MOSFET is driven by a pulse width modulated (PWM) signal from the microcontroller, and the output voltage is measured by one of the microcontroller’s analog inputs. The driver adjusts the PWM signal according to the difference between the output voltage measured and the voltage wanted.

We don’t have enough space here to go into details about how this circuit works, but it’s worth mentioning a few points of special interest.

The small capacitor across the diode improves the efficiency of the circuit. The load is represented by R3. The components used make it possible to supply over 1 A (current limited by the MSS1260T 683MLB inductor from Coilcraft), but maximum efficiency (89%) is at around 95 mA (at an output voltage of 10 V). To avoid damaging the controller’s analog input (≤5 V), the output voltage may not exceed 24 V. For higher voltages, the values of resistors R1 and R2 would need to be changed.

The MOSFET is driven by the microcontroller, which is nothing but a little Arduino board. The Arduino’s default PWM signal frequency is around 500 Hz—too low for this application, which needs a frequency at least 100 times higher. So we can’t use the PWM functions offered by Arduino. But that’s no problem, as the Arduino can also be programmed in assembler, allowing a maximum frequency of 62.5 kHz (the microcontroller runs at 16 MHz). To sample the output voltage, a frequency of 100 Hz is acceptable, which means we can use Arduino’s standard timers and analog functions. The Arduino serial port is very handy: we can use it for sending the output voltage set point (5–24 V) and for collecting certain information about the operation. Thanks to the Arduino environment, it only took about half an hour to program. Software is available. — Clemens Valens (Elektor, April 2010)

Client Profile: Invenscience LC

Invenscience2340 South Heritage Drive, Suite I
Nibley UT, 84321

CONTACT: Collin Lewis, sales@invenscience.com
invenscience.com

EMBEDDED PRODUCTS: Torxis Servos and various servo controllers

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Issue 282: EQ Answers

PROBLEM 1
Construct an electrical circuit to find the values of Xa, Xb, and Xc in this system of equations:

21Xa – 10Xb – 10Xc = 1
–10Xa + 22Xb – 10Xc = –2
–10Xa – 10Xb + 20Xc = 10

Your circuit should include only the following elements:

one 1-Ω resistor
one 2-Ω resistor
three 10-Ω resistors
three ideal constant voltage sources
three ideal ammeters

The circuit should be designed so that each ammeter displays one of the values Xa, Xb, or Xc. Given that the Xa, Xb, and Xc values represent currents, what kind of circuit analysis yields equations in this form?

ANSWER 1
You get equations in this form when you do mesh analysis of a circuit. Each equation represents the sum of the voltages around one loop in the mesh.

PROBLEM 2
What do the coefficients on the left side of the equations represent? What about the constants on the right side?

ANSWER 2
The coefficients on the left side of each equation represent resistances. Resistance multiplied by current (the unknown Xa, Xb, and Xc values) yields voltage.
The “bare” numbers on the right side of each equation represent voltages directly (i.e., independent voltage sources).

PROBLEM 3
What is the numerical solution for the equations?

ANSWER 3
To solve the equations directly, start by solving the third equation for Xc and substituting it into the other two equations:

Xc = 1/2 Xa + 1/2 Xb + 1/2

21Xa – 10Xb – 5Xa – 5Xb – 5 = 1
–10Xa + 22Xb – 5Xa – 5Xb – 5 = –2

16Xa – 15Xb = 6
–15Xa + 17Xb = 3

Solve for Xa by multiplying the first equation by 17 and the second equation by 15 and then adding them:

272Xa – 255Xb = 102
–225Xa + 255Xb = 45

47Xa = 147 → Xa = 147/47

Solve for Xb by multiplying the first equation by 15 and the second equation by 16 and then adding them:

240Xa – 225Xb = 90
–240Xa + 272Xb = 48

47Xb = 138 → Xb = 138/47

Finally, substitute those two results into the equation for Xc:

Xc = 147/94 + 138/94 + 47/94 = 332/94 = 166/47

PROBLEM 4
Finally, what is the actual circuit? Draw a diagram of the circuit and indicate the required value of each voltage source.

ANSWER 4
The circuit is a mesh comprising three loops, each with a voltage source. The common elements of the three loops are the three 10-Ω resistors, connected in a Y configuration (see the figure below).

cc281_eq_fig1The values of the voltage sources in each loop are given directly by the equations, as shown. To verify the numeric solution calculated previously, you can calculate all of the node voltages around the outer loop, plus the voltage at the center of the Y, and ensure they’re self-consistent.

We’ll start by naming Va as ground, or 0 V:

Vb = Va + 2 V = 2 V

Vc = Vb + 2 Ω × Xb = 2V + 2 Ω × 138/47 A = 370/47 V = 7.87234 V

Vd = Vc + 1 Ω × Xa = 370/47 V + 1 Ω × 147/47A = 517/47 V = 11.000 V

Ve = Vd – 1 V = 11.000 V – 1.000 V = 10.000 V

Va = Ve – 10 V = 0 V

which is where we started.

The center node, Vf, should be at the average of the three voltages Va, Vc, and Ve:

0 V + 370/47 V + 10 V/3 = 840/141 V = 5.95745 V

We should also be able to get this value by calculating the voltage drops across each of the three 10-Ω resistors:

Va + (Xc – Xb) × 10 Ω = 0 V + (166 – 138)/47A × 10 Ω = 280/47 V = 5.95745 V

Vc + (Xb – Xa) × 10 Ω = 370/47V + (138-147)/47A × 10 Ω = 280/47 V = 5.95745 V

Ve + (Xa – Xc) × 10 Ω = 10 V + (147-166)/47 A × 10 Ω = 280/47 V = 5.95745 V

Electrical Engineering Crossword (Issue 283)

The answers to Circuit Cellar’s February electronics engineering crossword puzzle are now available.

283-crossword-key

Across

2. LITZWIRE—Separately insulated strands woven together [two words]
4. LINKFIELD—First in a message buffer’s line [two words]
6. PETAFLOPS—Measures a processor’s floating point unit performance
8. ANION—negatively charged atom
9. LISP—Used to manipulate mathematical logic
11. STATCOULOMB—i.e., franklin (Fr)
12. AMBISONICS—Typically requires a soundfield microphone
15. BROUTER—This device can send data between networks and it can forward data to individual systems in a network
16. TRINITRON—This CRT technology was originally introduced the 1960s
17. OXIDE—The “O” in CMOS
18. DETENT—Used to prevent or stop something from spinning

Down

1. ELECTRICSUSCEPTIBILITY—XE [two words]
3. RADECHON—A barrier-grid storage tube
5. COLPITTS—This oscillator uses two-terminal electrical components to create a specific oscillation frequency
7. BEAGLEBOARD—TI’s open-source SBC
10. PICONET—A network that is created using a wireless Bluetooth connection
13. BETATRON—Designed to accelerate electrons
14. TEBIBYTE—More than 1,000,000,000,000 bytes

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