About Circuit Cellar Staff

Circuit Cellar's editorial team comprises professional engineers, technical editors, and digital media specialists. You can reach the Editorial Department at editorial@circuitcellar.com, @circuitcellar, and facebook.com/circuitcellar

Use Watchdog Timers (EE Tip #143)

Watchdog timers are essential to many complete electronic system designs.  As Bob Japenga explains, following a few guidelines will help make your designs more effective.

No longer used in just the realm of fault-tolerant systems, independent watchdog timers are put on systems because we know something can go wrong and prevent it from being fully functional. Sometimes the dogs reset the processor and sometimes they just safe the device and notify a user. However they work, they are an essential part of any system design. Here are the main guidelines we use:

  • Make it independent of the processor. The last thing you want is for the processor to lock up and the watchdog to lock up too.
  • Do not tickle the watchdog during an interrupt. (The interrupt can keep going while a critical thread is locked up.)
  • Do not tickle the watchdog until you are sure that all of your threads are running and stable.
  • Provide a way for your debugger to have break points without tripping the watchdog.
  • If the watchdog can be disabled, provide a mechanism for this to be detected.

I provide many more guidelines for watchdog design in a white paper that’s posted on our website.—Bob Japenga, CC25, 2013

Workspace for Precision Design

Brad Boegler is a do-it-yourselfer’s DIYer. His West Bloomfield, MI-based workspace is something to admire. It features a sturdy 8’ × 5’ workbench, a well-built machining bench, and dozens of handy tools that enable him to work on projects ranging from constructing a temperature-monitoring network to milling custom heatsinks. Simply put, it’s an appealing space for any innovator interested in DIY electronics and machining projects.

Photo 1: One of Boegler’s Altera CPLD breakout boards is on the bench. He said he was “experimenting with some video generators in VHDL” when he took this picture. (Source: B. Boegler)

As I reviewed Boegler’s space, the same word kept popping into my mind: precision. Why? Let’s see.

Building a bench (or benches) for a workspace like Boegler’s takes a lot of precision measuring, cutting, fitting, and constructing. Check out the workbench in Photo 1. That’s no “Ikea hack.” The 8’ × 5’ bench fits a dual monitor setup, plenty of test/measurement equipment, a solder station, and more.

Boegler—who works as Linux sysadmin—described some of the equipment on this bench via email:

The left side of the bench is mostly RF equipment: there are two HP RF frequency generators, a VNA, and spectrum analyzer. The analog scope is a Tek 2246 and is one of my favorite scopes. Next to that is an HP 16500B logic analysis system and then a HP 54112D digital scope … The bench was custom made. I was not able to find any benches to my liking so I ended up building my own. It is 8′ wide by 5′ deep and constructed out of mostly 4×4s. It weighs a ton, but it has to be sturdy as a lot of this equipment is very heavy. I like very deep benches as I can push the equipment back far enough on it and still provide enough working space.

And don’t forget the power!

Those are various adjustable voltage current limiting power supplies, when working on projects needing various voltages you can never have too many supplies.

I’m sure everyone agrees that access to power supplies is key.

Photo 2: Boegler’s workspace for machining (Source: B. Boegler)

On a separate bench (Photo 2) are Boegler’s milling machine and drill press, which are two tools intended for precision designing and machining. Boegler wrote:

The drill press is used almost daily, one of the best tools ever. I use the milling machine for custom shielded aluminum cases for RF boards, making special sized heatsinks, and it comes in handy for any special brackets I can make to hold boards or components.

I’m sure you’d agree that machining board cases and heatsinks requires a bit of exactitude.

Much like the bench in Photo 1, building the actual machine bench required precise measurements and cuts. Just look at its clean edges and sturdy frame. And don’t you like the shelf underneath? It’s a simple yet effective place for stowing frequently used tools.

On the topic of storage, check out Boegler’s wheeled shelf system. I like it and will consider something similar for my garage. (We all take wheels for granted until we’re in a pinch and need to move a heavy object. For instance, try moving a wheel-less six-shelf system full of parts in order to track down a screw that fell on the floor. Actually, don’t try that. It’s an accident waiting to happen.)

A wheeled shelf system for microcontrollers, op-amps, and parts of all sorts (Source: B. Boegler)

Lastly, check out the neatly labeled parts boxes. I see labels such as “Microcontrollers/DSP,” “Op-Amps,” “Serial Cables,” and more. Nice!

Share your space! Circuit Cellar is interested in finding as many workspaces as possible and sharing them with the world. Click here to submit photos and information about your workspace. Write “workspace” in the subject line of the email, and include info such as where you’re located (city, country), the projects you build in your space, your tech interests, your occupation, and more. If you have an interesting space, we might feature it on CircuitCellar.com!

Electronica Munich 2014: Can You “Make” It?

EL-Munich-2014Visiting Elektor International Media’s booth at the Electronica 2014 in Munich (November 11–14,2014) will have its perks. Attendees can stop at the space to relax, recharge their electronics, have coffee, and chat with like-minded electrical engineers and electronics “makers.” The Elektor.Labs team and Circuit Cellar staffers will also be there.

Attendees will also have the opportunity to get some work done. EIM’s booth (#380) will feature the following: desk space for engineering, test and measurement equipment, a 3-D printer, free Wi-Fi, and more.

Download Elektor’s Electronica 2014 info sheet to learn more about what the EIM team has in store for the conference.

Learn more about Electronica Munich: www.electronica.de

 

 

Cabinet-Based DIY Electronics Workspace

Micrcontrollers and electrical engineering probably don’t come to mind when you flip through an IKEA product catalog. But when you think about it, IKEA has plenty of easy-to-assemble tables, cabinets, and storage containers that could be handy for outfitting a electronics workspace or “circuit cellar.”

(Source: Patrik Thalin)

(Source: Patrik Thalin)

Sweden-based Patrik Thalin built a workspace within an IKEA Husar cabinet. The setup is compact, orderly, and well-planned. He noted:

It has a pull-out keyboard shelf that I use it as an extension of the workspace when the doors are open. My inspiration came from a friend that had built his lab in a two door closet. The main idea is to have a workspace that can be closed when not used and to be able to resume my work later. I have used this lab for nearly ten years and I am still happy with it!

In the upper part of the cabinet I keep commonly used tools and instruments. On the top shelf are two PSUs, a signal generator, assortment boxes with components, the SMD component kit and shelf trays with cables and small tools. On the lower shelves are things like multimeter, callipers and a power drill. At the bottom is the work space with a soldering station. On the left wall are screwdrivers,wrenches and pliers. To the left are cables hanging on hooks.The thing hanging under the shelf is an old radio scanner. You can also see a small vise hanging on the front of the workspace.

The lower part of the cabinet is for additional storage, he noted.

(Source: Patrik Thalin)

(Source: Patrik Thalin)

The information and images were submitted by Patrik Thalin. For more information about his space and work, visit his blog.

100-V Forward Voltage Controller

Linear Technology recently announced the LT8310, which is a resonant-reset forward converter controller that drives an external low side N-channel MOSFET from an internally regulated 10-V supply. The LT8310 features duty mode control to generate a stable, regulated, isolated output using a single power transformer. With the addition of output voltage feedback, via optocoupler (isolated) or directly wired (nonisolated), current mode regulation is activated, improving output accuracy and load response. A choice of transformer turns ratio makes high step-down or step-up ratios possible without operating at duty cycle extremes.

Source: Linear Technology

Source: Linear Technology

The switching frequency is programmable from 100 kHz to 500 kHz to optimize efficiency, performance or external component size. A synchronous output is available for controlling secondary side synchronous rectification to improve efficiency. User programmable protection features include monitors on input voltage (UVLO and OVLO) and switch current (overcurrent limit). A soft-start feature helps prevent transformer flux saturation.

The LT8310 main features include:

  • Input voltage range: 6 V to 100 V
  • Duty mode control regulates an isolated output without an opto
  • High efficiency synchronous control
  • Short-circuit (Hiccup mode) overcurrent protection
  • Programmable OVLO and UVLO with hysteresis
  • Programmable frequency (100 kHz to 500 kHz)
  • Synchronizable to an external clock
  • Positive or negative polarity output voltage feedback with a single FBX pin
  • Programmable soft-start
  • Shutdown current < 1 μA

The LT8310 is available in an FE20 TSSOP with high voltage pin spacing

Source: Elektor