Makelab Charleston, a place for hobbyists and professionals

Makelab Charleston is a hackerspace for hobbyist and professionals who share common interests in technology, computers, science, or digital/electronics art. It provides an environment for people to create anything they can imagine: from electronics, 3D printing, and construction, to networking, and programming.

Location 3955 Christopher St, North Charleston, SC 29405
Members 24

Treasurer David Vandermolen will tell us something more about Makelab Charleston.

MakeLabCharleston

Tell us about your meeting space!

We started in a 500 sq. ft. garage, but took a step up and are currently renting a 900+ sq. ft. home that’s been renovated.  We now have the space for a electronic/soldering room that also has our 3-D printer. One other room is dedicated to power-type tools and our CNC machine that is still being built by our members.  The other spaces in the house are used for classes and member activities such as LAN parties.

What tools do you have in your space? (Soldering stations? Oscilloscopes? 3-D printers?)

Soldering stations, oscilloscopes, 3-D printer, power tools, large table-top CNC machine (in progress), and a rack server for the IT minded to play with.

Are there any tools your group really wants or needs?

A laser CNC, nice tables, and chairs .

Does your group work with embedded tech (Arduino, Raspberry Pi, embedded security, MCU-based designs, etc.)?

We have members that dabble in multiple areas so we try to provide classes on the technology people want to learn about and explore.

Can you tell us about some of your group’s recent tech projects?

Our most recent tech project has been a overhaul of our server system. Other projects include the CNC currently in progress. That’s been an ongoing project for about a year.

What’s the craziest project your group or group members have completed?

Probably the wackiest project we completed was actually, something not tech related at all, building a bed for Charleston Bed Races. We put together a Lego bed (not real Legos) complete with Lego man and all.

Do you have any events or initiatives you’d like to tell us about? Where can we learn more about it?

We list any events or classes we are doing or plan on doing on our Website. Just click on classes and events on the main page or go to the calendar tab.

What would you like to say to fellow hackers out there?

Makelab Charleston is about opening the world to information and sharing that information with the people in our community. The best way to do that is through teaching.

Show us your hackerspace! Tell us about your group! Where does your group design, hack, create, program, debug, and innovate? Do you work in a 20′ × 20′ space in an old warehouse? Do you share a small space in a university lab? Do you meet a local coffee shop or bar? What sort of electronics projects do you work on? Submit your hackerspace and we might feature you on our website!

A Shed Packed with Projects and EMF Test Equipment

David Bellerose, a retired electronic equipment repairman for the New York State Thruway, has had a variety of careers that have honed the DIY skills he employs in his Lady Lake, FL, workspace.

Bellerose has been a US Navy aviation electronics technician and a computer repairman. “I also ran my own computer/electronic and steel/metal welding fabrication businesses, so I have many talents under my belt,” he says.

Bellerose’s Protostation, purchased on eBay, is on top shelf (left). He designed the setup on the right, which includes a voltmeter, a power supply, and transistor-transistor logic (TTL) oscillators. A second protoboard unit is on the middle shelf (left). On the right are various Intersil ICM7216D frequency-counter units and DDS-based signal generator units from eBay. The bottom shelf is used for protoboard storage.

Bellerose’s Protostation, purchased on eBay, is on top shelf (left). He designed the setup on the right, which includes a voltmeter, a power supply, and transistor-transistor logic (TTL) oscillators. A second protoboard unit is on the middle shelf (left). On the right are various Intersil ICM7216D frequency-counter units and DDS-based signal generator units from eBay. The bottom shelf is used for protoboard storage.

Bellerose’s project interests include model rockets, video security, solar panels, and computer systems. “My present project involves Intersil ICM7216D-based frequency counter modules to companion with various frequency generator modules, which I am also designing for a frequency range of 1 Hz to 12 GHz,” he says.

His workspace is an 8′-by-15′ shed lined with shelves and foldable tables. He describes how he tries to make the best use of the space available:

“My main bench is a 4′-by-6’ table with a 2’-by-6’ table to hold my storage drawers. A center rack holds my prototype units—one bought on eBay and two others I designed and built myself. My Tektronix 200-MHz oscilloscope bought on eBay sits on the main rack on the left, along with a video monitor. On the right is my laptop, a Heathkit oscilloscope from eBay, a 2.4-GHz frequency counter and more storage units. All the units are labeled.

“I try to keep all projects on paper and computer with plenty of storage space. My network-attached storage (NAS) totals about 23 terabytes of space.

“I get almost all of my test equipment from eBay along with parts that I can’t get from my distributors, such as the ICM7216D chips, which are obsolete. I try to cover the full EMF spectrum with my test equipment, so I have photometers, EMF testers, lasers, etc.”

The main workbench has a 4′-by-6′ center rack and parts storage units on the left and right. The main bench includes an OWON 25-MHz oscilloscope, storage drawers for lithium-ion (Li-on) batteries (center), voltage converter modules, various project modules on right, a Dremel drill press, and a PC monitor.

The main workbench has a 4′-by-6′ center rack and parts storage units on the left and right. The main bench includes an OWON 25-MHz oscilloscope, storage drawers for lithium-ion (Li-on) batteries (center), voltage converter modules, various project modules on the right, a Dremel drill press, and a PC monitor.

Photo 3: This full-room view shows the main bench (center), storage racks (left), and an auxiliary folding bench to work on large repairs. The area on right includes network-attached storage (NAS) storage and two PCs with a range extender and 24-port network switch.

Photo 3: This full-room view shows the main bench (center), storage racks (left), and an auxiliary folding bench to work on large repairs. The area on right includes network-attached storage (NAS) and two PCs with a range extender and 24-port network switch.

Photo 4: Various versions of Bellerose’s present project are shown. The plug-in units are for eight-digit displays. They are based on the 28-pin Intersil ICM 7216D chip with a 10-MHz time base oscillator, a 74HC132 input buffer, and a 74HC390 prescaler to bring the range to 60 MHz. The units’ eight-digit displays vary from  1″ to 0.56″ and 0.36″.

Various versions of Bellerose’s present project are shown. The plug-in units are for eight-digit displays. They are based on the 28-pin Intersil ICM 7216D chip with a 10-MHz time base oscillator, a 74HC132 input buffer, and a 74HC390 prescaler to bring the range to 60 MHz. The units’ eight-digit displays vary from 1″ to 0.56″ and 0.36″.

Photo 5: This is a smaller version of Bellerose’s project with a 0.36″ display mounted over an ICM chip with 74hc132 and 74hc390 chips and 5-V regulators. Bellerose is still working on the final PCB layout. “With regulators, I can use a 9-V adapter,” he says.  “Otherwise, I use 5 V for increased sensitivity. I use monolithic microwave (MMIC) amplifiers (MSA-0486) for input.”

This is a smaller version of Bellerose’s project with a 0.36″ display mounted over an ICM chip with 74HC132 and 74HC390 chips and 5-V regulators. Bellerose is still working on the final PCB layout. “With regulators, I can use a 9-V adapter,” he says. “Otherwise, I use 5 V for increased sensitivity. I use monolithic microwave (MMIC) amplifiers (MSA-0486) for input.”

 

 

Stand-Alone, 8-Channel Event, State, and Count Data Logger

DATAQThe DI-160 is a stand-alone event, state, and count data logger that features four programmable measurement modes. The data logger enables you to determine when events occur, the total number of events, and the period of time in between events. It can count parts by monitoring a proximity sensor’s pulse output, or determine a machine’s downtime by monitoring AC power.

The DI-160 includes eight channels. Four ±300-VDC/peak AC isolated channels can accommodate high-level DC voltage signals, pulse inputs up 2 kHz, or AC line voltage. Four ±30-VDC/peak AC non-isolated channels (pulled high) enable you to monitor lower-level DC voltages, TTL-level, signals, or switch closures.

You can use DATAQ’s Event Recorder set-up software, which is included with the data logger, to enable/disable channels, select measurement modes on a channel-by-channel basis, and choose one of 21 sample intervals, ranging from 1 s to 24 h. Data is stored to a removable SD memory card in CSV format, enabling up to 500 days of continuous recording and easy viewing in Microsoft Excel.

The DI-160’s AC channels provide channel-to-channel and input-to-output isolation up to 500 VDC (±250-V peak AC) and have a 4-V trigger threshold. The low-voltage channels are protected up to ±30 VDC/peak AC and trigger at 2.5 V.

A built-in rechargeable battery acts as a “bridge” when disconnecting the data logger from a PC and connecting it to the USB power supply. Three LEDs indicate when the DI-160 is actively acquiring data, when the unit is connected via USB to a PC (or the included AC power supply), and the battery’s charge state. A push button enables you to start and stop recording to the SD memory card.

The DI-160’s four selectable measurement modes. State mode determines an event’s duration. Event mode detects a single change of state (within a sample interval). High-Speed (HS) Counter mode yields the total number of state changes within a sample interval. AC Counter mode counts the number of times AC power turns on/off within a sample interval.

The DI-160 costs $299 and includes a mini screwdriver a 2-GB SD memory card, an AC power supply, and a mini-USB cable. The DATAQ Event Recorder software is available for free download.

DATAQ Instruments, Inc.
www.dataq.com

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.

Q&A: Embedded Systems Consultant

Elecia White is an embedded systems engineer, consultant, author, and innovator. She has worked on a variety of projects: DNA scanners, health-care monitors, learning toys, and fingerprint recognition.—Nan Price, Associate Editor

 

NAN: Tell us about your company Logical Elegance. When and why did you start the company? What types of services do you provide?

ELECIA: Logical Elegance is a small San Jose, CA-based consulting firm specializing in embedded systems. We do system analysis, architecture, and software implementation for a variety of devices.

Elecia White

Elecia White

I started the company in 2004, after leaving a job I liked for a job that turned out to be horrible. Afterward, I wasn’t ready to commit to another full-time job; I wanted to dip my toe in before becoming permanent again.

I did eventually take another full-time job at ShotSpotter, where I made a gunshot location system. Logical Elegance continued when my husband, Chris, took it over. After ShotSpotter, I returned to join him. While we have incorporated and may take on a summer intern, for the most part Logical Elegance is only my husband and me.

I like consulting, it lets me balance my life better with my career. It also gives me time to work on my own projects: writing a book and articles, playing with new devices, learning new technologies. On the other hand, I could not have started consulting without spending some time at traditional companies. Almost all of our work comes from people we’ve worked with in the past, either people we met at companies where we worked full time or people who worked for past clients.

Here is Elecia’s home lab bench. She conveniently provided notes.

Here is Elecia’s home lab bench. She conveniently provided notes.

NAN: Logical Elegance has a diverse portfolio. Your clients have ranged from Cisco Systems to LeapFrog Enterprises. Tell us about some of your more interesting projects.

ELECIA: We are incredibly fortunate that embedded systems are diverse, yet based on similar bedrock. Once you can work with control loops and signal processing, the applications are endless. Understanding methodologies for concepts such as state machines, interrupts, circular buffers, and working with peripherals allows us to put the building blocks together a different way to suit a particular product’s need.

For example, for a while there, it seemed like some of my early work learning how to optimize systems to make big algorithms work on little processors would fall to the depths of unnecessary knowledge. Processors kept getting more and more powerful. However, as I work on wearables, with their need to optimize cycles to extend their battery life, it all is relevant again.

We’ve had many interesting projects. Chris is an expert in optical coherence tomography (OCT). Imagine a camera that can go on the end of a catheter to help a doctor remove plaque from a clogged artery or to aid in eye surgery. Chris is also the networking expert. He works on networking protocols such as Locator/ID Separation Protocol (LISP) and multicast.

I’m currently working for a tiny company that hopes to build an exoskeleton to help stroke patients relearn how to walk. I am incredibly enthusiastic about both the application and the technology.

That has been a theme in my career, which is how I’ve got this list of awesome things I’ve worked on: DNA scanners, race cars and airplanes, children’s toys, and a gunshot location system. The things I leave off the list are more difficult to describe but no less interesting to have worked on: a chemical database that used hydrophobicity to model uptake rates, a medical device for the operating room and ICU, and methods for deterring fraud using fingerprint recognition on a credit card.

Elecia says one of the great things about the explosion of boards and kits available is being able to quickly build a system. However, she explains, once the components work together, it is time to spin a board. (This system may be past that point.)

Elecia says one of the great things about the explosion of boards and kits available is being able to quickly build a system. However, she explains, once the components work together, it is time to spin a board. (This system may be past that point.)

In the last few years, Chris and I have both worked for Fitbit on different projects. If you have a One pedometer, you have some of my bits in your pocket.

The feeling of people using my code is wonderful. I get a big kick seeing my products on store shelves. I enjoyed working with Fitbit. When I started, it was a small company expanding its market; definitely the underdog. Now it is a success story for the entire microelectromechanical systems (MEMS) industry.

Not everything is rosy all the time though. For one start-up, the algorithms were neat, the people were great, and the technology was a little clunky but still interesting. However, the client failed and didn’t pay me (and a bunch of other people).

When I started consulting, I asked a more experienced friend about the most important part. I expected to hear that I’d have to make myself more extroverted, that I’d have to be able to find more contracts and do marketing, and that I’d be involved in the drudgery of accounting. The answer I got was the truth: the most important part of consulting is accounts receivable. Working for myself—especially with small companies—is great fun, but there is a risk.

NAN: How did you get from “Point A” to Logical Elegance?

ELECIA: ”Point A” was Harvey Mudd College in Claremont, CA. While there, I worked as a UNIX system administrator, then later worked with a chemistry professor on his computational software. After graduation, I went to Hewlett Packard (HP), doing standard software, then a little management. I was lured to another division to do embedded software (though we called it firmware).

Next, a start-up let me learn how to be a tech lead and architect in the standard start-up sink-or-swim methodology. A mid-size company gave me exposure to consumer products and a taste for seeing my devices on retailer’s shelves.

From there, I tried out consulting, learned to run a small business, and wrote a Circuit Cellar Ink article “Open Source Code Guide” (Issue 175, 2005). I joined another tiny start-up where I did embedded software, architecture, management, and even directorship before burning out. Now, I’m happy to be an embedded software consultant, author, and podcast host.

NAN: You wrote Making Embedded Systems: Design Patterns for Great Software (O’Reilly Media, 2011). What can readers expect to learn from the book?

ELECIA: While having some industry experience in hardware or software will make my book easier to understand, it is also suitable for a computer science or electrical engineering college student.

It is a technical book for software engineers who want to get closer to the hardware or electrical engineers who want to write good software. It covers many types of embedded information: hardware, software design patterns, interview questions, and a lot of real-world wisdom about shipping products.

Elecia White's BookMaking Embedded Systems is intended for engineers who are in transition: the hardware engineer who ends up writing software or the software engineer who suddenly needs to understand how the embedded world is different from pure software.

Unfortunately, most college degrees are either computer science or electrical engineering. Neither truly prepares for the half-and-half world of an embedded software engineer. Computer science teaches algorithms and software design methodology. Electrical engineering misses both of those topics but provides a practical tool kit for doing low-level development on small processors. Whichever collegiate (or early career) path, an embedded software engineer needs to have familiarity with both.

I did a non-traditional major that was a combination of computer science and engineering systems. I was prepared for all sorts of math (e.g., control systems and signal processing) and plenty of programming. All in all, I learned about half of the skills I needed to do firmware. I was never quite sure what was correct and what I was making up as I went along.

As a manager, I found most everyone was in the same boat: solid foundations on one side and shaky stilts on the other. The goal of the book is to take whichever foundation you have and cantilever a good groundwork to the other half. It shouldn’t be 100% new information. In addition to the information presented, I’m hoping most people walk away with more confidence about what they know (and what they don’t know).

Elecia was a judge at the MEMS Elevator Pitch Session at the 2013 MEMS Executive Congress in Napa, CA.

Elecia was a judge at the MEMS Elevator Pitch Session at the 2013 MEMS Executive Congress in Napa, CA.

NAN: How long have you been designing embedded systems? When did you become interested?

ELECIA: I was a software engineer at the NetServer division at HP. I kept doing lower-level software, drivers mostly, but for big OSes: WinNT, OS/2, Novell NetWare, and SCO UNIX (a list that dates my time there).

HP kept trying to put me in management but I wasn’t ready for that path, so I went to HP Labs’s newly spun-out HP BioScience to make DNA scanners, figuring the application would be more interesting. I had no idea.

I lit a board on fire on my very first day as an embedded software engineer. Soon after, a motor moved because my code told it to. I was hooked. That edge of software, where the software touches the physical, captured my imagination and I’ve never looked back.

NAN: Tell us about the first embedded system you designed. Where were you at the time? What did you learn from the project?

ELECIA: Wow, this one is hard. The first embedded system I designed depends on your definition of “designed.” Going from designing subsystems to the whole system to the whole product was a very gradual shift, coinciding with going to smaller and smaller companies until suddenly I was part of the team not only choosing processors but choosing users as well.

After I left the cushy world of HP Labs with a team of firmware engineers, several electrical engineers, and a large team of software engineers who were willing to help design and debug, I went to a start-up with fewer than 50 people. There was no electrical engineer (except for the EE who followed from HP). There was a brilliant algorithms guy but his software skills were more MATLAB-based than embedded C. I was the only software/firmware engineer. This was the sort of company that didn’t have source version control (until after my first day). It was terrifying being on my own and working without a net.

I recently did a podcast about how to deal with code problems that feel insurmountable. While the examples were all from recent work, the memories of how to push through when there is no one else who can help came from this job.

Elecia is shown recording a Making Embedded Systems episode with the founders of electronics educational start-up Light Up. From left to right: Elecia’s husband and producer Christopher White, host Elecia White, and guests Josh Chan and Tarun Pondicherry.

Elecia is shown recording a Making Embedded Systems episode with the founders of electronics educational start-up Light Up. From left to right: Elecia’s husband and producer Christopher White, host Elecia White, and guests Josh Chan and Tarun Pondicherry.

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

ELECIA: I have a few personal projects I’m working on: a T-shirt that monitors my posture and a stuffed animal that sends me a “check on Lois” text if an elderly neighbor doesn’t pat it every day. These don’t get nearly enough of my attention these days as I’ve been very focused on my podcast: Making Embedded Systems on iTunes, Instacast, Stitcher, or direct from http://embedded.fm.

The podcast started as a way to learn something new. I was going to do a half-dozen shows so I could understand how recording worked. It was a replacement for my normal community center classes on stained glass, soldering, clay, hula hooping, laser cutting, woodshop, bookbinding, and so forth.

However, we’re way beyond six shows and I find I quite enjoy it. I like engineering and building things. I want other people to come and play in this lovely sandbox. I do the show because people continue to share their passion, enthusiasm, amusement, happiness, spark of ingenuity, whatever it is, with me.

To sum up why I do a podcast, in order of importance: to talk to people who love their jobs, to share my passion for engineering, to promote the visibility of women in engineering, and to advertise for Logical Elegance (this reason is just in case our accountant reads this since we keep writing off expenses).

NAN: What are your go-to embedded platforms? Do you have favorites, or do you use a variety of different products?

ELECIA: I suppose I do have favorites but I have a lot of favorites. At any given time, my current favorite is the one that is sitting on my desk. (Hint!)

I love Arduino although I don’t use it much except to get other people excited. I appreciate that at the heart of this beginner’s board (and development system) is a wonderful, useful processor that I’m happy to work on.

I like having a few Arduino boards around, figuring that I can always get rid of the bootloader and use the Atmel ATmega328 on its own. In the meantime, I can give them to people who have an idea they want to try out.

For beginners, I think mbed’s boards are the next step after Arduino. I like them but they still have training wheels: nice, whizzy training wheels but still training wheels. I have a few of those around for when friends’ projects grow out of Arduinos. While I’ve used them for my own projects, their price precludes the small-scale production I usually want to do.

Professionally, I spend a lot of time with Cortex-M3s, especially those from STMicroelectronics and NXP Semiconductors. They seem ubiquitous right now. These are processors that are definitely big enough to run an RTOS but small enough that you don’t have to. I keep hearing that Cortex-M0s are coming but the price-to-performance-to-power ratio means my clients keep going to the M3s.

Finally, I suppose I’ll always have a soft spot for Texas Instruments’s C2000 line, which is currently in the Piccolo and Delfino incarnations. The 16-bit byte is horrible (especially if you need to port code to another processor), but somehow everything else about the DSP does just what I want. Although, it may not be about the processor itself: if I’m using a DSP, I must be doing something mathy and I like math.

NAN: Do you have any predictions for upcoming “hot topics?”

ELECIA: I’m most excited about health monitoring. I’m surprised that Star Trek and other science fiction sources got tricorders right but missed the constant health monitoring we are heading toward with the rise of wearables and the interest in quantified self.
I’m most concerned about connectivity. The Internet of Things (IoT) is definitely coming, but many of these devices seem to be more about applying technology to any device that can stand the price hit, whether it makes sense or not.

Worse, the methods for getting devices connected keeps fracturing as the drive toward low-cost and high functionality leads the industry in different directions. And even worse, the ongoing battle between security and ease of use manages to give us things that are neither usable nor secure. There isn’t a good solution (yet). To make progress we need to consider the application, the user, and what they need instead of applying what we have and hoping for the best.

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

Gigabit Ethernet Designs

WurthWurth Electronics Midcom and Lantiq recently announced The Evaluation Kit, a jointly developed demonstration kit. The kit enables users to easily add Ethernet hardware to an application or device and provides all necessary information to understand the demands of an Ethernet hardware design.

The Evaluation Kit includes an easy-to-use 1-Gbps demonstration board. The (54-mm × 92-mm) credit card-sized demonstration board is powered by USB. The board plugs into PCs and provides up to 1-Gbps bidirectional data rates.

The Evaluation Kit costs approximately $175.

Wurth Electronics Midcom, Inc.
www.we-online.com

Lantiq
www.lantiq.com

16-Bit Digitizer

SpectrumThe M2i.4960 and the M2i.4961 mid-speed 16-bit digitizers are available for PCI/PCI-X and PCIe. The devices offer two or four synchronous channels with a 60 megasamples-per-second (MSPS) speed and a 30-MHz bandwidth.

The channels can be individually switched between single-ended and true differential input mode, therefore single-ended and differential signals can be simultaneously acquired with one digitizer. Each input channel includes an on-board calibration. The channels can be software programmed for proper termination, user offset, and input range.

The devices’ acquisition modes include segmented acquisition, gated acquisition, or streaming mode. The devices also feature a versatile clock and trigger section, making them suitable for a variety of different applications. Multiple cards can be internally synchronized to obtain more synchronous channels or to directly synchronize to arbitrary and digital waveform generators or digital waveform capture cards.

A digital input option enables up to 32 synchronous digital input channels to be acquired by multiplexing them into the analog data in different ways. Each of the 16 digital inputs can completely replace one analog channel or each of the 2/4 digital inputs can be stored together with the A/D sample by reducing its resolution.

Contact Spectrum for pricing.

Spectrum GmbH
www.spectrum-instrumentation.com

The Future of Monolithically Integrated LED Arrays

LEDs are ubiquitous in our electronic lives. They are widely used in notification lighting, flash photography, and light bulbs, to name a few. For displays, LEDs have been commercialized as backlights in televisions and projectors. However, their use in image formation has been limited.

A prototype emissive LED display chip is shown. The chip includes an emissive compass pattern ready to embed into new applications.

A prototype emissive LED display chip is shown. The chip includes an emissive compass pattern ready to embed into new applications.

The developing arena of monolithically integrated LED arrays, which involves fabricating millions of LEDs with corresponding transistors on a single chip, provides many new applications not possible with current technologies, as the LEDs can simultaneously act as the backlight and the image source.

The common method of creating images is to first generate light (using LEDs) and then filter that light using a spatial light modulator. The filter could be an LCD, liquid crystal on silicon (LCoS), or a digital micromirror device (DMD) such as a Digital Light Processing (DLP) projector. The filtering processes cause significant loss of light in these systems, despite the brightness available from LEDs. For example, a typical LCD uses only 1% to 5% of the light generated.

Two pieces are essential to a display: a light source and a light controller. In most display technologies, the light source and light control functionalities are served by two separate components (e.g., an LED backlight and an LCD). However, in emissive displays, both functionalities are combined into a single component, enabling light to be directly controlled without the inherent inefficiencies and losses associated with filtering. Because each light-emitting pixel is individually controlled, light can be generated and emitted exactly where and when needed.

Emissive displays have been developed in all sizes. Very-large-format “Times Square” and stadium displays are powered by large arrays of individual conventional LEDs, while new organic LED (OLED) materials are found in televisions, mobile phones, and other micro-size applications. However, there is still a void. Emissive “Times Square” displays cannot be scaled to small sizes and emissive OLEDs do not have the brightness available for outdoor environments and newer envisioned applications. An emissive display with high brightness but in a micro format is required for applications such as embedded cell phone projectors or displays on see-through glasses.

We know that optimization by the entire LED industry has made LEDs the brightest controllable light source available. We also know that a display requires a light source and a method of controlling the light. So, why not make an array of LEDs and control individual LEDs with a matching array of transistors?

The marrying of LED materials (light source) to transistors (light control) has long been researched. There are three approaches to this problem: fabricate the LEDs and transistors separately, then bond them together; fabricate transistors first, then integrate LEDs on top; and fabricate LEDs first, then integrate transistors on top. The first method is not monolithic. Two fabricated chips are electrically and mechanically bonded, limiting integration density and thus final display resolutions. The second method, starting with transistors and then growing LEDs, offers some advantages in monolithic (single-wafer) processing, but growth of high-quality, high-efficiency LEDs on transistors has proven difficult.

My start-up company, Lumiode (www.lumiode.com), is developing the third method, starting with optimized LEDs and then fabricating silicon transistors on top. This leverages existing LED materials for efficient light output. It also requires careful fabrication of the integrated transistor layer as to not damage the underlying LED structures. The core technology uses a laser method to provide extremely local high temperatures to the silicon while preventing thermal damage to the LED. This overcomes typical process incompatibilities, which have previously held back development of monolithically integrated LED arrays. In the end, there is an array of LEDs (light source) and corresponding transistors to control each individual LED (light control), which can reach the brightness and density requirements of future microdisplays.

Regardless of the specific integration method employed, a monolithically integrated LED and transistor structure creates a new range of applications requiring higher efficiency and brightness. The brightness available from integrated LED arrays can enable projection on truly see-through glass, even in outdoor daylight environments. The efficiency of an emissive display enables extended battery lifetimes and device portability. Perhaps we can soon achieve the types of displays dreamed up in movies.

Ultra-Compact Ultrasonic Sensor Series

MaxbotixThe UCXL-MaxSonar-WR series of sensors are flexible, OEM-customizable products that can be integrated into a system with MaxBotix’s horns or flush-mounted into an existing housing. Mounting design recommendations are provided through MaxBotix’s 3-D CAD models (available in multiple formats) to facilitate your design process. The sensor layout offers four conveniently placed mounting holes for design flexibility.

The rugged, high performance sensors are individually calibrated and feature a 1-cm resolution, an operational temperature range from –40˚C to 70˚C, real-time automatic calibration (voltage, humidity, and ambient noise), 200,000+ h mean time between failures (MTBF), and an operational 3-to-5.5-V voltage range with a low 3.4-mA average current requirement.

Contact MaxBotix for pricing.

MaxBotix, Inc.
www.maxbotix.com

Op-Amp Versus Comparator (EE Tip #128)

Practically every lecture course or textbook on electronics describes how to use an operational amplifier as a comparator. Here we look at the possibility in more detail, and see how it can often be a very poor idea.

The idea behind the comparator configuration is simple. An op-amp has a very high open-loop DC gain which means that even a tiny differential input voltage will drive the output to one extreme or the other. If the voltage at the non-inverting (“+”) input is greater than that at the inverting (“–“) input the output goes high; otherwise the output goes low. In other words the two voltages are compared and the output is a binary indication of which of the two is the greater.

Figure 1: SPICE simulation results: an LT1028 op-amp pressed into service as a comparator versus a real comparator type LT1720.

Figure 1: SPICE simulation results: an LT1028 op-amp pressed into service as a comparator versus a real comparator type LT1720.

So the op-amp looks like the perfect device to use as a comparator. But why then do there exist special-purpose comparator devices? Looked at from the outside, op-amps and comparators appear indistinguishable. Besides power connections, they both have “+” and “–” inputs and a single output. Taking a look at the internal circuit diagram, again the two devices appear broadly very similar (although a comparator device with an open-collector or open-drain output does look more obviously different from an op-amp). The big difference, which is not apparent without looking at the circuit more closely, is that the output stages of operational amplifiers are designed for linear operation, with the general aim of amplifying the input signal with as little distortion as possible (assuming that some negative feedback is provided), but in the case of a comparator the output circuit is designed to operate in saturation, that is, to switch between the upper and lower output voltage limits without the provision of external feedback. Comparators often also offer a ground connection in addition to the usual power connections, and provide digital logic levels at their outputs while accepting symmetrical analogue input signals.

What do these differences mean in practice? Comparators can react very quickly to changes in their input voltages with short propagation delays and output rise- and fall-times all specified by the manufacturer.

In contrast, because op-amps are not expected to be used in this mode, manufacturers tend not to give explicit specifications for propagation delay and rise- and fall-times (although they do normally specify slew rate), and these characteristics can be considerably poorer for op-amps than for comparators. To take an extreme example, a low-power op-amp might have a propagation delay measured in milliseconds, whereas a comparator might react in nanoseconds: a million times faster.

There is a further problem with op-amps. Many devices exhibit significantly increased power consumption when the output is in saturation, the resulting power dissipation on occasion being enough to destroy the device. Also, many op-amps (those not advertised as having “rail-to-rail outputs”) are not capable of driving their outputs close to the supply rails, for example having a maximum output voltage of 3 V with a 5-V supply. There can also be restrictions on the inputs. Some op-amps are equipped with antiparallel diodes across their input terminals, which prevent differential input voltages of more than about 0.6 V, whereas comparators’ inputs are often allowed to vary over the whole supply range.

Of course, there are many noncritical applications where an op-amp will work perfectly acceptably as a comparator, but it is not a practice to be recommended. The skeptic should lash up a quick test with a comparator and an op-amp side-by-side, each fed with a squarewave signal with rapid edges. Some of the potential pitfalls are shown up more easily in simulation, such as the possibility of an op-amp being so slow that it entirely misses a narrow pulse. It is hard to guarantee circuit performance, current consumption, and even the survival of the device.

The illustrations show a SPICE simulation of a relatively nimble op-amp (an LT1028 with a minimum slew rate of 11 V/µs) and a type LT1720 comparator. It is clear that the comparator responds sooner and with a much shorter rise-time. Its output swings all the way to +5 V rather than the 3 V managed by the op-amp. The situation is similar when the output swings low: the op-amp is much slower and only reaches an output voltage of –3 V rather than –5 V. The original squarewave is hardly recognizable at the op-amp’s output. Although the LT1028 cannot achieve its maximum specified gain with a –5-V supply, it is still a factor of at least 20 faster than an LM324 (with a slew rate of 0.5 V/µs); what the latter would make of our squarewave would not be a pretty sight. The op-amp fails to cope at all with shorter pulses, which are then effectively “swallowed,” while the comparator continues to handle them without difficulty.

Worthwhile further reading on this subject is Texas Instruments application note SLOA067 by Bruce Carter entitled “Op Amps and Comparators—Don’t Confuse Them!.”— Michael Holzl, Elektor January 2011

CircuitCellar.com is an Elektor International Media publication.

A Timely Look at RFID Technology

Most of us have had that annoying experience of setting off an alarm as we leave a store because one item in our bags has a still-active radio-frequency identification (RFID) tag. So it’s back to the cashier for some deactivation (or to security for some questioning).

Retailers love RFID, for obvious reasons. So do other industries and governments dealing with limiting building access; tracking goods, livestock and people; collecting highway tolls and public transit fares; checking passports; finding airport baggage; managing hospital drug inventory… The list goes on and on.

RFIDRFID is a big business, and it is anticipated to grow despite concerns about privacy issues. Market researcher IDTechEx recently estimated that the RFID market—including tags, readers, and software and services for RFID labels, fobs, cards, and other form factors—will hit $9.2 billion in 2014 and increase to $30.24 billion in 2024.

So it’s good timing for columnist Jeff Bachiochi’s series about passive RFID tagging. Part 1 appears in Circuit Cellar’s May issue and focuses on read-only tags and transponder circuitry. It also hints at Bachiochi’s unfolding RFID project.

Other May issue highlights include DIY project articles describing an MCU-based trapdoor lift system, a customizable approach to an ASCII interface for sending commands to a sensor tool and receiving data, and a solar-powered home automation controller that enables household-device management and cloud connectivity to log temperature, energy use, and other data.

In addition, our columnists explore low-power wireless data receivers, testing and analyzing old and new batteries in a personal collection, and designing data centers to participate in smart-grid power management.

If you are a female engineer in search of some inspiration, read our interview with embedded systems expert Elecia White. Also, find out why new technology means a bright future for LEDs in emissive microdisplays.

Low-Power Remote-Control Transceivers

LinxThe TT Series remote-control transceiver is designed for bidirectional, long-range, remote-control applications. The module includes an optimized frequency-hopping spread spectrum (FHSS) RF transceiver and an integrated remote-control transcoder.

The FHSS is capable of reaching more than 2 miles in typical line-of-sight environments with 0-dB gain antennas. An amplified version increases the output power from 12.5 to 23.5 dBm, boosting the range to more than 8 miles in line-of-sight environments with 0-dB antennas.

The TT Series transceiver features best-in-class receive sensitivity (up to −111 dBm) and low power consumption (only 19.2 mA in receive mode and 36 mA in transmit mode at 12.5 dBm). The initial version operates in the 902-to-928-Hz frequency band for North and South America.

The transceiver is housed in a compact reflow-compatible surface-mount technology (SMT) package. It doesn’t require any external RF components except an antenna, which simplifies integration and reduces assembly costs.

Programming is not required for basic operation. The transceiver’s primary settings are hardware-selectable, which eliminates the need for an external microcontroller or other digital interface. Eight status lines can be set up in any combination of inputs and outputs to transfer button or contact states. A selectable acknowledgement indicates that the transmission was successfully received. For advanced features, a UART interface provides optional software configuration.

A simple pairing operation configures two modules to operate together. A single button press on each side causes the modules to automatically swap their 32-bit addresses and store them in nonvolatile memory. It can be configured to automatically send an acknowledgement to the transmitting unit either after receiving a command or with external circuitry when an action has taken place. An optional external processor can send two data bytes with the acknowledgement.

The TT Series transceiver module is available as part of Linx Technologies’s master development system that comes with two development boards for benchmarking and prototyping. Each board is populated with a transceiver, two remote-control development boards, and programming boards. The system also includes antennas, a daughterboard with a USB interface, demonstration software, extra modules, and connectors.

Contact Linx Technologies for pricing.

Linx Technologies
www.linxtechnologies.com

Electronics Workspace: Pure Function, Minimal Form

Engineering consultant Steve Hendrix of Sagamore Hills, OH, says the “corporate headquarters” of Hx Engineering, LLC, pictured below, “is pure function, minimal form, and barely fits.”

This basement workspace reflects Steven's diverse projects and clients.

This basement workspace reflects Steve’s diverse projects and clients.

It’s a home basement workspace that reflects a variety of projects and clients. “I do a range of design work, from transistor-level hardware design through microcontrollers and FPGAs, as well as the embedded firmware and PC-side software to run the products,” Hendrix says. “Most of my clients are small to medium businesses in northeast Ohio, although I’ve done designs for companies as far west as New Mexico, as far south as Florida, and as far east as Cypress.”

Hendrix describes a workspace layout that stresses utility and a certain attention to thriftiness:

As I look through my equipment, probably the central theme is cost-effective solid equipment, without necessarily being the ‘first kid on the block.’ I learned long ago to be the second kid on the block with the newest toy… er… TOOL. The early bird gets the worm, but the second mouse gets the cheese.

He provides the following detailed description of his equipment and desk, which is a very large, solid-core door purchased cheaply from a lumberyard because it had been damaged:

Being natural wood and not plastic, it makes an inherently anti-static workstation. I used a router to round the front edge to be a bit friendlier to elbows, and carefully trimmed it and wedged it between the wall on the right and the utility room wall on the left, supported by vertical plywood against the walls. My PCs are in the adjacent utility room so I don’t have to listen to fans all day and they’re up on custom brackets on the wall so I don’t have to shinny under the desk to get to them. All the wires pass through plumbing fittings in the wall. The main work computer runs the lower dual monitors. The next-older work computer is still used for some specialized hardware, via the monitor above and an extra mouse. Under the left monitor is an all-band receiver that I sometimes use to monitor equipment under development, but also listen to broadcast music.

My late father-in-law was always extremely thrifty, and salvaged the flatbed scanner at the top left from a dumpster. It’s turned out to be the best scanner I’ve seen, and I used it to scan their family pictures. There’s also an HP Photosmart scanner that’s excellent on slides and negatives.

The middle stack has a parts cabinet that I really should retire, holding mainly SN74 series dual in-line packages (DIPs) that I very rarely use these days. Below that is an Ethernet-enabled power switch that controls various equipment. Next down is my trusty old Tektronix TDS-220 oscilloscope

I was pleased to note that past contributors to [Circuit Cellar’s Workspace feature] also use that same scope. It was the first digital scope I ever encountered that wouldn’t fib to me about aliasing, and it’s still a real workhorse. The ability to do screen captures with the free PC software helps a lot in documenting a finished product and in discussing problems remotely. Below that is a very solid bench multimeter. If it just had a capacitance function, I could abandon my Fluke 12! Then there’s a basic analog function generator, and some manual switches for AC.

Over on the far right are some more parts cabinets, several power supplies (including the ±5V/±12V supply my dad helped me build during my very first excursions into the then-new SN74 series of logic), an RF signal generator, and a good old boat-anchor Hewlett-Packard (HP) spectrum analyzer. I got that one off eBay, and spent as much again to get it repaired and calibrated. It’s in many ways better than the newer instruments. If it had a synthesized local oscillator and a computer interface, it would do it all. Actually, I have on occasion faked a computer interface by connecting the video outputs on its front panel to my TDS-220, and then capturing the resulting waveform.

In front of that is my solder station and stereo zoom microscope. Sitting on its stage is a backup prototype identical to the one currently controlling 4,800 W of my total 6,800 W of installed solar capacity. I routinely do prototypes using 0603 parts and recently more 0402 parts, with occasional 0201 parts. Don’t sneeze around those! The cabinets on the right wall are mainly connectors and surface-mount parts.

I needed some more bench space for a project, so I added a “temporary” shelf between the right end of my bench and the bookshelves on the wall to the right. As you can imagine, the “temporary” part of that wasn’t. So now it holds a voltage standard, on which sits my solder station and a ham radio. The latter is powered directly by 12-V solar power. At the extreme right are an inverter connected to the same solar batteries and the side of a breaker panel that allows me to safely connect to those same batteries when I need a heavy-duty 12-V power supply.

The whole office is lighted by strips of white LEDs run directly by 12-V solar power. The self-adhesive strips are just stuck to the drop-ceiling rails on each side of the standard florescent fixture. The standard fixture is still present and functional as a backup, but the solar lights are actually brighter and don’t flicker like a florescent. The 12-V solar is also wired to the rear jacks of the HP multimeter, so I can get an instant reading on the battery charge state. I have future plans to move some or all of my office circuits to the 120 VAC solar power that runs a portion of our home.

To the right and out of the picture is a solid wall of bookshelves that I built to hold databooks when I first set up this office over 20 years ago. The Internet and PDFs have pretty much made that obsolete, so those shelves now hold various supplies, projects in various states of completion, and some archival data. Behind me as I take this picture is a long table, made of another big door sitting atop filing cabinets. My original intent was for the desk to be for software/firmware, and the long table to be for hardware. Indeed, there are still a couple of RS-232 lines up through the ceiling and down to the table. However, now it serves as an assembly area when I have contractors doing assembly, as well as for storage and general workspace. But there’s Ethernet available on both the desk and the bench, for connecting Ethernet-enabled prototypes.

The biggest drawback to this office comes on a clear, cold, sunny day. The upstairs has lots of glass, so it absorbs lots of free solar heat. However, that means the furnace doesn’t run at all (even near zero outside), so the office and the rest of the basement get really cold. But since the furnace blower is on solar power, which is abundant under those conditions, I just force the blower on to share some of that heat!

If you’re interested in learning more about Hendrix’s work, check out our member profile posted last year. Also, be sure to pick up Circuit Cellar‘s upcoming July and August issues, which will include Hendrix’s two-part series on his personal solar-power setup.

These solar panels are mounted on Steve's east-facing roof.

These solar panels are mounted on Steve’s east-facing roof.

 

“No Opto” Synchronous Forward Controller

LinearThe LT3752/LT3752-1 is a high-input voltage-capable synchronous forward controller with an active clamp transformer reset. A controlled VOUT start-up and shut-down is maintained with an integrated housekeeping controller to bias the primary and secondary ICs. The internal bias generation also reduces the main power transformer’s complexity and size by avoiding the need for extra windings to create bias supplies.

The LT3752 operates over a 6.5-to-100-V input voltage range. The LT3752-1 is well suited for hybrid vehicle (HV) and hybrid electric vehicle (HEV) applications. For up to 400-V inputs and greater, it enables RC start-up from the input voltage with the maximum voltage limited only by the choice of external components.

A ±5% output voltage regulation can be attained without using an optocoupler. An optocoupler can be used to obtain ±1.5% output voltage regulation. The LT3752/-1 uses a pulse transformer to send a control signal to a secondary-side MOSFET driver for the synchronous rectification timing. It can also be used in self-driven applications the power transformer pulses control the secondary-side MOSFETs. With the LT3752/-1, secondary-side ICs no longer require start-up circuitry to operate when the output voltage is 0 V, which enables a controlled VOUT start-up.

The LT3752/-1 has a programmable 100-to-500-kHz operating switching frequency. It can be synchronized to an external clock, so a range of output inductor values and transformer sizes can be used.

The LT3752/-1 is available in a TSSOP-38 package with several pins removed for high-voltage spacing. The LT3752/-1 E- and I-grade versions function from a –40°C-to-125°C junction temperature. The LT3752/-1 H-grade functions from a –40°C-to-150°C operating junction temperature. The LT3752/-1 MP-grade functions from –55°C-to-150°C operating junction temperature.

The LT3752/LT3752-1 costs $3.39 in 1,000-piece quantities.

Linear Technology Corp.
www.linear.com