MightyOhm

Psst…  Today is the last day to buy discount Maker Faire tickets.  Buy them by midnight PDT or pay full price!

Make: Online : Maker Faire advance tickets, going, going….

Keith of Keith’s Electronics Blog made a PID-Controlled Soldering Hotplate based on the one I fabricated earlier this year.  He’s already using it to build the stepper controller PCB for the MakerBot CupCake CNC!

He also posted a bunch of teardown photos (like the one shown below) of the CD101 PID Controller from Sure Electronics.  I suspect the CD101 is a cheap knockoff of an RKC PID controller since I can’t find the part number on RKC’s website, even though the front panel clearly says RKC on it.  I guess at $40 you can’t ask too many questions, the price is right…

Copycat PID-Controlled Solder Hotplate « Keith’s Electronics Blog.

Everything You Know About Cooling Electronics Is Wrong!

Working as an electrical engineer, I have often been faced with thermal design problems. They are usually in the form of: “Given a maximum system temperature X, ensure that the maximum temperature of all devices in the design does not exceed Y.”  Temperature X is usually a customer spec, while temperature Y is almost always driven by MTTF constraints on the semiconductors used in the design.  This sounds simple enough until you realize that:

• The system temperature is often not clearly defined.  Is it the ambient air temperature?  The temperature of the printed circuit board the part is mounted on?  The temperature of a baseplate (usually a sizable piece of aluminum) that won’t even exist in the finished design?
• The MTTF spec is usually based on things you can’t measure directly (at least not easily or accurately), like the junction temperature of a transistor that is on a die you can’t even see, inside a package you don’t have a thermal model for.  In addition, MTTF numbers are often wildly inaccurate, don’t account for duty cycle, etc.  Yikes.
• Chances are, the guy who worked on the part before you hasn’t checked the thermal readings in years, so it’s actually running way over the limits, and now you have to fix it.  A small change in the design can drastically affect the numbers

At the end of the day, numbers are scribbled on envelopes or entered into spreadsheets, guesses estimates are made, and everyone resolves to develop a better thermal model next time, which of course never happens.

I stumbled upon this book at the Stanford University Bookstore a few months ago.  Given my experience (frustration) with thermal design, I couldn’t help but pick it up and start reading.

It’s a fairly quick read and thoroughly entertaining.  Kordyban’s style is very informal.  The chapters are in the form of several short stories about fictional characters at a made-up company called TeleLeap.  These characters have to solve a series of design problems, which are used as examples to explain several concepts of thermal design.  There are no lengthy derivations and the technical discussions are pretty understandable, even to someone who never took thermodynamics in college (like me).

In particular, I found Kordyban’s discussions of the errors that can creep into thermocouple measurements, the difficulty of measuring junction temperature directly, and the problem with pin-fin heatsinks very interesting and educational.  I won’t say that I am an expert in thermal design having read this book, but I do have just a little bit more insight into what’s going on (and what to avoid).

Unfortunately, the book is out of print, so you’ll have to find a used copy and pay some big bucks – unless you get lucky like I did and find one that’s still sitting on the shelf.  No, you can’t have mine!

Hot Air Rises and Heat Sinks: Everything You Know About Cooling Electronics Is Wrong

Pete Harrison at Micromouse Online wrote a short tutorial about using Eclipse to program AVRs.   Eclipse is  an open source IDE that is supported on many platforms, including OS X on the Mac.

I have never used Eclipse myself, so I can’t vouch for how well this works, but I would like to upgrade from the command line tools I am using (part of AVRMacPack, which is now called CrossPack).  I could use Apple’s Xcode but last time I checked, the AVR integration in Xcode wasn’t that great.

Is anyone using Eclipse for AVR development? What do you like/dislike about it?

AVR, Eclipse and the Mac | Micromouse Online

The Fat Man and Circuit Girl Cast 9 from Jeri Ellsworth on Vimeo.

I don’t know why it took so long, but recently someone turned me onto The Fat Man and Circuit Girl show, which has been airing on the net for almost six months now.  This is definitely the quirkiest and most entertaining electronics themed webcast I have ever seen.  The episode above includes an awesome segment about making a floppy drive reverb machine and thoughts on brewing coffee with PID, which reminded me of some other projects I have worked on…

The Fat Man and Circuit Girl are:

George Sanger – (fatman.com)

Musician, artist, composer of music for several video games, most notably Maniac Mansion on the NES and Wing Commander.

Jeri Ellsworth – (blog, twitter, flickr, vimeo, youtube)

Self taught electrical engineer.  Designer of the C64 DTV.

I had a chance to meet George and Jeri at NOTACON in Cleveland this month.  They are as entertaining in person as they are on video!  Jeri told me that she will be at the Maker Faire in San Mateo this year, showing off her Easy-Bake Chip Lab.  I am really looking forward to seeing it!

They have a website for the show at fatmanandcircuitgirl.com.  You can also follow @fmandcg on twitter.

Who needs television when you can stream a show like this?