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!

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.

The pool features over 400 pictures of printed circuit boards, many of them CC licensed.  There’s a little bit of everything, from homebrew board fab to PCB jewelry and even miniatature cityscapes.

If you have some cool PCB images of your own, add them to the pool!

One of my favorites: Car Park or Printed Circuit Board?

This is actually the second spin of the PCB but the first to bear the ‘Rescue Shield’ name.  The first spin was a one-off prototype to check a couple things out, mostly related to the 5V to 12V step up converter.  That design allowed me to fix a couple bugs before doing a production run with the improved design, show below.

So far all I can say is that the step up converter works perfectly.  (Yipee!)

More details to come!

Here’s a really cool Instructable about using a flexible copper-clad material called Pyralux to make flexible printed circuit boards.  You could make some really cool business cards with this stuff.

DIY Flexible Printed Circuits

(via makezine)

Ladyada has a PCB Cost Comparison Calculator that shows the significant differences in price between various low volume PCB vendors, but what’s missing from the chart is the answer to: What vendors are people actually using?

If the cheapest fab house is also the best, obviously the more expensive vendors wouldn’t be around, would they?  Unfortunately, it’s usually not that simple, cheap usually means slow, or low quality, or both.

I know that some visitors to this site make prototype PCBs at home and others send them out to be fabricated.  How do you get your prototype boards made?  Vote below.

The right tool for this job is a stereo microscope.  Stereo microscopes use two separate optical paths to provide you with depth perception, very helpful for working with 3-dimensional objects like printed circuit boards.  Even better is a stereo zoom microscope, where the magnification factor can be changed by turning a knob instead of swapping out lenses.

Until now I assumed that a stereo zoom microscope would be way out of my price range, at least several hundred or a thousand dollars for a very basic setup.  However, some searching on eBay showed that good deals can be had, and a used microscope with a boom stand suitable for surface mount work can be found for as little as $200-$300.  New microscopes are available for $400-$500, although there is some debate regarding the quality of low-cost imported microscopes.  Caveat emptor.

For surface mount soldering, 7-30x magnification is reasonable (that’s 10x eyepieces * a 0.7-3x objective), and a 4″ or greater working distance makes using tools under the microscope a lot easier.

I ended up buying an American Optical (AO) model 569 with an illuminator and boom stand, shown below.  Total cost was just over $200 with shipping.

Combined with the PID controlled hotplate I just put together this is a very powerful setup for doing rework of very tiny components – I could probably work with 0402′s, maybe even 0201′s if I was careful.  Using this setup, 0805′s are easy. (and they look huge!)

The scope is very old, it was made in the late 1970s, but it has survived in extremely good condition.  Upon receiving it, I tightened some setscrews and regreased the slides and it’s as good as new, despite being over 30 years old!

There are a few more photos of the microscope setup on flickr.

The image quality is excellent.  Here are a couple pictures of my SYBA USB-Audio Adapter taken with the microscope and my Sony DSC-V1 digital camera.  I held the camera up to one eyepiece, set it into macro mode, and snapped the shutter – these images are straight off the camera with no retouching.

Click to enlarge.

Enter gerbv, a free, open source gerber viewer that is available for many platforms, including Debian and OS X (via fink).

I recently upgraded to version 2.0 (I was using the really outdated version 1.0 on Macports) and I am really impressed by the improvements in the GUI and overall usability.

gerbv is a part of the gEDA suite, which also includes layout and schematic capture tools that are slowly becoming more popular vs. more established non-free tools like Eagle.

Update: I missed an interesting update to a post over on My 2uf, not everyone seems to like the rest of the gEDA suite.

gerbv screenshot

AVR HV Programmer Shield PCB Layout

What’s this???

In response to the continued demand for a PCB version of my Arduino-based AVR High Voltage Programmer, I just released a first cut to BatchPCB and should have a prototype within 3-4 weeks.

This design is an improvement upon the original HV programmer shield in the following areas:

• Onboard 12V 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
• 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 hope to have kits for sale in early February.  Sorry for the delay in getting these made, but I wanted to make the best possible shield I could!

The symbol and pin definitions are usually pretty easy – just copy the datasheet.  The hard part is the land pattern: the collection of copper traces, soldermask openings, silkscreen, and other features that define the part on the PCB.

To come up with a land pattern, you usually have a few options:

1. Someone else may have done you a big favor by creating a part definition and uploading it to the Eagle library directory.  Caveat: Use it at your own risk.  Surface mount parts tend to be particularly hard to use right out of the box – often someone else’s land pattern won’t even pass your DRC.  Whose process were they using, anyway??
2. Look through the datasheet for the part to try and find a recommended land pattern. (Good luck!  Increasingly these are not included, but may be somewhere else on the manufacturer’s website.  Google is your friend!)
3. Take a guess based on the geometry of the part, assuming you have a mechanical drawing or a physical sample somewhere.
4. Skip 1-3 and use an IPC-7351 land pattern generator.

IPC-7351 is a standard for printed circuit board land pattern designs.  The standard attempts to, well, standardize land patterns to try to discourage every PCB designer from having his or her own custom library of land patterns.  IPC takes known good land patterns and combines them with accepted manufacturing tolerances to produce a land pattern that will work for most people most of the time.  Increasingly you will see references to IPC-7351 in datasheets instead of a land pattern drawing, so access to the standard is becoming more important over time.

Cool, right?  Well, the bad news is that while you can browse through the table of contents/introducton for free, downloading the standard costs big bucks.

Fortunately, PCB Matrix has a free IPC-7351 Land Pattern Calculator (direct download link here) that you can use to generate land patterns based on the standard.  You don’t need to own a copy of the standard to benefit from it.

The calculator is somewhat tricky to use but if you click the right buttons you can get something like what is shown below (click to enlarge).

PCB Matrix IPC-7351 Land Pattern Calculator Screenshot

X and Y are the dimensions of the recommended pads for an 8-lead Thin SOT-23, which happens to be the package for the LT3464.

With this information, you can return to Eagle and create a land pattern for your device.  PCB Matrix will also sell you premade Eagle libraries, but from their site it was not clear how much they cost.  Based on their other products, my guess is several hundred dollars and a yearly maintenance contract – I’ll draw my own, thanks.

Unfortunately, the calculator is Windows only, so Mac guys like me need to use VMware Fusion or similar to use it.  Can someone create a web version, please?

I am using this tiny USB-audio adapter as part of my Wifi Radio project.  It’s a ridiculously cheap $8 at Newegg.com and contains a C-Media CM119 chip targeted at VoIP applications.  I have no idea why they chose to use a VoIP chip for this application because it contains a lot of bells and whistles that are not being used in this device, such as support for a matrix keypad!

Unfortunately, I have not been able to locate a datasheet for the CM119 so for now I will be using it only for it’s intended application – adding an audio output to a wireless router with USB.  Come to think of it, that is probably not it’s intended application, but it’s close enough.  Hooray for embedded Linux!