MightyOhm

I’ve been making some changes and additions to the MightyOhm Wiki over the past few days.

To complement the awesome list of surplus electronics shops, I started creating wiki pages for the various projects I have previously documented on the blog.

Last night I added a list of cheap PID controllers to the wiki page for my DIY PID-controlled Soldering Hotplate.  (Backstory: the PID controller on my hotplate quit working this week and I’ve been shopping for a replacement!)

I have also  been adding more information to the PCB resources page, including where to order cheap solder paste stencils and resources for making test fixtures.

More to come…

Laen of DorkbotPDX has been running a PCB proto service for some time now, and I finally got a chance to try it out this month.

The pricing is simple.  For 2-layer boards, it’s $5 per square inch for three (3) PCBs, with no setup charge, and shipping is free.

The tunaround time is typically 9 days + first class mail shipping, which ends up being just under two weeks total fom PCB release to delivery in Austin.  This is pretty good for a group order, and signficantly faster than BatchPCB (based on my experience).

The only downsides that I am aware of are:

• PCB orders only go out once a month, unless there is enough demand to justify a 2nd run.
• If you wait too long, the panels can fill up.  Again, if there is enough demand, sometimes a 2nd panel can be added, but don’t count on it.
• The soldermask and silkscreen can be any color (and you don’t get to choose!)  BatchPCB at least guarantees the standard white/green.

4-layer boards are available as well, but at a higher cost ($10/square inch) and less frequent intervals.

Entries for the next PCB order are due on October 25th.  The more orders Laen gets, the more likely he is to continue the service, so if you have some designs you’ve been thinking about but have been put off by expensive PCB costs, finish them up and get some boards made!

This week I sold the last AVR HV Rescue Shield kit in stock! This is a significant milestone as it means I have finally sold off all of the kits from the original PCB fab run. At the time I wasn’t sure if anyone would actually buy such a thing, so pulling the trigger on what seemed like a huge number of boards was a leap of faith!

I want to thank everyone who bought kits and PCBs. Thank you for supporting me and the site!

Rather than reorder new boards of the existing design, I am taking this opportunity to re-evaluate my approach to a couple things, with the goal of reducing the BOM cost and lowering the overall cost of the kit.

The bad news is that this means there won’t be any more kits in stock in the short term. I’m planning to release a new PCB design within the next couple weeks, which means kits would be in stock within about a month. Because this is a busy time for me, I can’t promise specific dates, but I will do my best to keep the process moving because I know there are people waiting for the new kits.

If you need a kit right now, I believe Solarbotics still has some in stock.

Otherwise, stay tuned for updates.

And again, if you bought a kit, or even if you built the DIY version with spare parts and helped spread the word, thank you!

- Jeff

If The Art of Electronics is the bible of electronic circuit design, then the Printed Circuits Handbook is almost certainly the bible of printed circuit board (PCB) technology.

I say this because even if you disregard the volumes of useful information inside (much of which I have never seen elsewhere online or in print), this book deserves to win ‘bible’ status thanks to its 1000 pages and phonebook-quality heft!

All joking aside, this book is a great resource for anyone is serious about making good PCBs.  I have worked with PCBs as a design engineer for several years now, and I learned something about printed circuit boards within minutes of opening the cover.  Hours later, I was still flipping pages.

How could I walk away from a book that contains in depth discussions of topics like the difference between water soluble and no-clean flux and how to clean the leftover residue from each?  Ever wondered what the myriad of surface finish options your PCB vendor offers you really mean?  This book will explain the difference between HASL and ENIG, and why you shouldn’t blindly check the box that says “lead-free” without considering the consequences on your assembly process.

This is the kind of stuff they don’t teach you in school, and as a design engineer I have received only glimpses of in the industry.

Some of the highlights of this book for me are:

• The most thorough discussion of PCB manufacturing that I have ever seen (almost 300 pages!).  Want to know how the PCB you just got was made?  One layer or sixteen layers, it’s all in here.
• Lots of information about custom laminates, high density interconnect techniques, microvias, blind/buried vias, plating and surface finishes, solder masks, conformal coating, etc.
• Several charts of current handling ability of PCB traces, planes, and vias.
• A chapter on thermal design of PCBs.
• Lots of information about soldering techniques.  Ever wondered how soldering works and what flux really does?  It’s in here too.
• Seven (!) chapters on design, manufacturing, and test of flex circuits.

Be forewarned that the technical level of this book is fairly high.  It is clearly targeted towards people working in the PCB industry, but most engineers and even serious hobbyists would probably get something out of it.  That said, this is definitely not a book for beginners!

(And to the other design engineers out there: Want to one-up the manufacturing and reliability guys in the break room?  Read this book!  )

Printed Circuits Handbook (McGraw Hill Handbooks)

This all started last year, when I was playing with an ATmega168 microcontroller and did something silly.  I programmed the RSTDISBL fuse bit, which effectively makes it impossible to reflash the chip using an ordinary (serial) programmer.

Instead of giving up and throwing out the “dead” chip,  I decided to try to revive it using an obscure high voltage parallel programming mode that isn’t supported by most AVR programmers.  Armed with my Arduino and the ATmega168 datasheet, I quickly designed and constructed a programmer using parts I already had on my workbench.

A few hours later, I tested my new programmer and it worked!  I revived my “dead” AVR by using spare parts and a few lines of Arduino code.  That week I published the schematics and Arduino sketch to the site and called it my Arduino-based AVR High Voltage Programmer.

The response was overwhelming.  Since I first posted the design, many people have built their own and used it to fix their “dead” AVR microcontrollers by restoring the fuse bits to sane values.  I even received several requests for a PCB and/or kit based on the design, which got me thinking…

Today I’m proud to introduce:

The AVR HV Rescue Shield

The AVR HV Rescue Shield is a high voltage parallel mode fuse programmer for Atmel AVR microcontrollers.

It currently supports the ATmega48/88/168/328 series and the ATtiny2313.  The Rescue Shield does everything my original AVR High Voltage Programmer does, and a lot more.  I think the new features make this a really useful tool for anyone working with AVR microcontrollers.

New features include:

• Custom 2-layer PCB with silkscreen and soldermask.  No more hacking and modifying perfboards to fit Arduino’s nonstandard pin spacing!
• Onboard 12V DC-DC boost converter eliminates the need for an external 12V power supply
• Support for two of the most common families of AVR microcontrollers, the ATmega48/88/168 and ATtiny2313
• Support for programming the extended fuse (EFUSE) byte.
• A new interactive mode, where desired fuses can be entered using the Arduino’s serial port.
• Separate Ready and Burn indicators
• Protection resistors on every single data, control, and supply line to the target AVR, meaning that your Arduino and AVR should survive any mishaps during programming, including inserting the AVR backwards or off by 1 pin.

I spent considerable time testing each new feature and documenting the Arduino sketch.  I hope that you’ll find that the finished product was worth the wait!

Ordering instructions:

To purchase bare PCBs and kits, head over to the AVR HV Rescue Shield product page.