Screaming Circuits: General interest


Loopy Ground Loops

A while back, I posed a question about using flood fill (AKA copper pours). I've been reading a lot about ground loops lately which brought me back to that original question.

LED scroll ground plane Some people suggest segmenting your ground plane between analog and digital sections. Some people suggest segmenting the ground plane for individual critical ground return paths. The follow on to my original question is: On non-exotic designs does segmenting ground planes really help? There's actually two questions, with the second being: At what clock speed does it make sense to start worrying about issues caused by ground return paths / ground loops? There are probably more questions. Those are just the two rattling around in my head at the moment.

Interestingly, though, when I wrote the original post, there didn't seem to be a clear "most common" between pour and no pour PCBs. Today, I'd have to say that the majority of designs we see here at Screaming Circuits do use flood-fill ground planes, either internal or external.

Duane Benson
You can solve ground and noise problems by just not hooking up power

Bouncing BGAs

I dropped my cell phone on the pavement the other day. That's bad enough, but in my instinctive attempt to catch it, I actually hit it and increased it's downward velocity. Luckily, everything still works. The odd thing is that I just assumed that it would still work. No real questions or doubts on that thought.

That realization got me thinking. (it happens now and then) What other devices do I have that I automatically expect to survive a drop onto concrete? I have a carpenter's hammer. I expect that to survive a drop intact. I would not expect my camera to survive such a drop intact, and have empirically verified that fact. A little car GPS? Probably not. Laptop; uh... no.

I'm sure there are some other devices that would easily survive. I just can't think of any off the top of my head. I suspect that there are a lot of factors that go into making cell phones survivable. The case, the overall mass, the quality of solder joints.

Along those lines, some folks use an underfill glueish type substance to hold their BGAs more securely. Some designers use pick and placeable solid underfil. Some just rely on extra good soldering and some leave it to luck. Of course, not all BGA installations require much shock resistance. How do you secure your parts when shock or vibration are serious concerns?

Duane Benson
Quick, where's Henry? I need an inductor.

Hi Ho. Hi Ho. It's off to Scone I go

I found this video over on the adafruit blog. Asimo, by Honda, is cool. Mars rovers, by JPL, are cool. Packbots, by iRobot, are cool. But, for robots to really take off, they need to be able to run down to McDonald's and buy some Big Macs or saunter on down to the Latte shop and pick me up a 16 oz non-fat Latte while I stay at my desk and keep working. Maybe hop out of the car and get one while I drive around because I can't find a parking spot. Donuts would be good too.

Now, that is a real robot. The only problem with the bot in this picture is that it needs a place to put the drink. Scones can be pretty good, but they tend to be kind of dry for my tastes without a drink to go with them.

Duane Benson
Watson - come here! Find Juan Valdez and ask him where I can get some coffee.
Five

Twitter, What is it Good For? Absolutely 555contest

I follow a few people on Twitter. A few people follow me on Twitter.

A number of web sites have engaged their readers in debates about the usefulness of Twitter (and other social media) to engineers. In general, these debates are talking about hardware engineers. A lot of software engineers pretty much live on the Internet and will embrace or invent any new thing.

The overwhelming majority of the responses that I've read put Twitter in the class of "a waste of time." Not everyone feels that way, but there's quite a few who do.  I'm still in study mode. I can see how it can take up a lot of time if you don't exercise some self control and it has a weird partial-voyeur aspect.

If I'm following, person A and person B, I'll see any conversation they are having. Most discussions are undertaken with that in mind, but some start to lean toward the personal side. Now, if person C gets in the conversation with one or both of A and B, and I'm not following C, I end up 723px-NE555_Bloc_Diagram.svg seeing part of the conversation. It's a bit like listening to someone talk on the phone and hearing only their side. It's odd.

It can lead to interesting activity though. Recently, one tweeter, Jeri (twitter.com/jeriellsworth) suggested a design contest centered around the old stalwart 555 timer. Chris (twitter.com/Chris_Gammell) picked up the ball with her and In about three days, just over Twitter, they organized it, other tweeters chimed in, sponsors offered prize money and they've set up a website for it. Fascinating.

If you're on Twitter, search for "555contest" to see the conversation in action. In any case, if you're a fan of the now 368 year old 555 timer, you might want to dig into the recesses of your brain for entry ideas. You can also follow Screaming Circuits on Twitter at "twitter.com/pcbassembly" and see for yourself if it's useful or too loaded with mindless drivel.

Duane Benson
Huh! Yeah!

0 or 1?

I've been running around telling people "Happy New Decade." Generally, such has been received with a blank stare or some comment related to me being sarcastic.

Back when we turned from 1999 to 2000 and again from 2000 to 2001, I heard a lot of controversy related to which year actually started the new century. Oddly, I haven't heard any of that this transition, even though the question is just as relevant.

I can certainly understand the two schools of thought on this. 01, 02 ... 09 all don't have a leading digit so they sound and look much different from something that does have a leading digit, e.g., 11, 12, 13... But, look closer at my first list. You don't see "00" in there. Certainly we did have a year "2000", but did we actually have a year "0000"? I've heard of the year one BC and the year 1 AD, but never zero BC or zero AD.

According to Wikipedia, which is never wrong, the Gregorian and Julian calendars do not have a year zero. Astronomical year numbering apparently designates 1 BC as the year zero. But "astronomical year numbering" sounds like a science thing and how many of the average population actually like to deal with "science things"?

If you're a digital person, maybe. Most arrays start with 0. Although some languages do start their arrays with 1.

But here's where I have decided to sit. I was one once. No one has ever said I was zero. I was also ten once and ten equals a decade. Although, decade counters do count from zero to 9. Again, in a purist digital world, 10 would start the new decade. However, for the most part, while machines operate in a digital world, people do not. On the other hand, as soon as I turned one, I had been on this earth for one year, so had the calendar been in existence for one year when year one started? If so, we would have had a year zero. People actually do have a year zero. Extra young folks are called one week old, one month old, etc. In that there is an implied zero and one month old. That is not the case with the calendar. Therefore, in my mind, 2001 - 2010 is the first decade of this millennium and 2011 is the start of the new decade.

So, happy new decade!

Duane Benson
Let's count it in binary next time

Open Source Mea Culpa or back pedaling? You decide

Last week I wrote about "Ten electronics things to be thankful for in 2010." If you're reading this now, you probably don't need the link because you probably read that article then too. But that's not really relevant. What is relevant is that in my #6, about open source hardware. I wrote, in part, that in some ways open source seems a bit exploitative of the designers. pt wrote in the comments for the blog article asking if I could give an example of how open source is exploitative.

I got to thinking about my choice of words and came to the conclusion that "exploitive" doesn't quite cover what I was trying to say. Although, in some cases, I think it does. It's possible that there are some aspects of the open source movement that I just don't get. Or it's possible that I have the capacity to pick a black cloud out of anything. If that's the case, I like to think that I can also pick a silver lining out of anything as well. That combination becomes a problem with recursion.

I'm a capitalist so I believe that (a) it's important to have profit as an ultimate goal of any commercial endeavor. I still have a bit of idealism left so I also believe that (b) when making that profit, we should be like the Boy Scouts and leave the planet a little better off than we found it. I get sick to my stomach when I read about executives making massive millions of dollars when their employees struggle to adequately feed and clothe their kids. (Is this post turning into one of those "I believe..." manifestos?) Following up that last point, I believe that (c) if someone does good work, they should get something in return for it. It's a trade. You give me something valuable and I'll give you something valuable in return. Not always money, but something of value.

That's where the mushiness comes in for me. Here's the good side. Ti is a big company that, with the Beagleboard, is giving something of great value to the electronics design community. As far as I know, the people at Ti working on the project are paid. My guess is that the ultimate motivation of Ti is it to help sell chips, but the project has given a whole lot of people access to a level of performance whom would not have had access it otherwise. That endeavor meets my abc conditions. Companies like Adafruit, Sparkfun and DIYdrones have built successful small (and growing) businesses with the help of open source hardware and software. People are making a living (I assume) from those organizations. Both companies give a lot back to the community and both companies make it very clear that they benefit from and really appreciate the efforts of open source designers. They give the folks recognition and support. They and companies like them meet my abc.

The other side of open source, and where I smell the exploitation, is when big companies use open source, make large profits and don't return anything. I mean, sure, the licence allows them to and I suppose that by reducing their costs, they can be more competitive and stay in business, keeping their employees employed. But when a software company buys the remains of another company or two that allegedly "own" some opensource code and then tries to make a business of suing people that use that open source software; I consider that to pretty exploitive of all of the people that voluntarily gave their time to the project.

When a large muti-national company that sells server farms uses an open source OS and doesn't return anything to the designers, I find that also to be exploitive. I don't know what the answer is. I mean it's cool that Linux, for example, is used in so many places. The fact that big corporations put so much weight on it certainly validates the legitimacy of it. But I can't help but envision open source developers out there, that could really use a bit more money in the bank, looking at those big corporations that are profiting off of their backs, feeling a little used.

So, am I missing something? Do I not get it?

By the way, this piece has a lot of personal opinion in it, but I do believe that my company works hard to meets my abc so I don't have a problem posting this on my work blog. The two times in my career that I did work for companies not meeting my abc, both ended badly for me. Fortunately, I believe in this one.

So, help me out here. If I'm not getting a part of this, feel free to chime in.

Duane "Does idealism hold up in the face of reality?" Benson

Need a Reference for the Reference

Not long ago, I wrote a short post about non-standard use of reference designators. After doing that, I've been looking at some of my own microcontroller and motor driver boards with an eye for how close to standards I am.

All of the R's, C's, D's and U's are okay, but there are some differences. For example, the Eagle library I've been using calls crystals "X" instead of the more standard "Y." I have seen crystals designated as "X", "Y" and "Q." LEDs seem to go by "LED" instead of "D" as indicated in the Wikipedia list. Headers go by "J", "JP", or "H." Wikipedia says "J" is for a female jack connector, "JP" is for jumper, and it doesn't list a "H." My board has break away two-row male headers and keyed single-row male headers. Wikipedia does note that its list is a set of commonly used designators. Not necessarily standard.

We probably do have the specific standards document laying around here someplace, and if I were doing real work on a professional basis, I'd hunt it down and make sure I followed the actual standards. But I'm not doing real work with my controllers and drivers, so I just do the best I can. I wonder how often that happens everywhere. The standards books are "somewhere" but no one really knows where.

Duane Benson
Somwhere over the reflow...

Spam, Spam, Eggs and Spam

I normally expend most of my writing words on challenges our customers and other engineers might face in their day to day design and layout activities. But not today. Today, it's about a specific challenge faced by your typical blogger. Off and on for the last couple of weeks, I've come into work in the morning, opened up the blog and found three spammy comments. Here's today's three"

"Compare to the majority of the other blogs, your site tend to be so fantastic. Therefore nice to examining the post. If I've a probability, I would like to research along with you because I think that my potential haven't yet achieved the excellent amount."

"You may remember the three proverbs: Laugh, and the world laughs with you; Weep, and you weep lone. Life is measured by thought and action not by time. Long absent, soon forgotten."

"You may remenber [sic] the three proverbs: Laugh, and the world laughs with you; Weep, and you weep lone. Life is measured by thought and action not by time. Long absent, soon forgotten."

Now, it is a bit flattering to hear that my site tend to be so fantastic. Not just "fantastic", but "so fantastic"! But perhaps the subject matter could be a bit more on topic. The author noted that if he have probability, he would like to research along with me. I could always use some extra help, but I don't have any probability to pass on. Perhaps a call to Zaphod would be in order.

I'm not sure I agree completely with the second supposition. I'd bet that a lot of unemployed or underemployed folks are weeping right now. Probably enough that they could be considered to have a world weeping with them. I know I would. I'm also not sure what the deal is with the third one. That author just copied from the one above it. How rude.

All is not always as it seems though. After reading these this morning, I did as I always do and fed the three comments into my netlist confabulator. It turns out that the text in these three comments is actually a turbo-encoded form of the design of the Constellation spacecraft. If I had checked the IP address prior to marking the comments as spam, I wonder if I would have found that this is a desperate rocket scientist tying to smuggle his decade of work home before the lights go out and the servers get recycled.

Duane Benson
Have you got anything without spam?

Reference Designators

Not a subject I give much thought to.

For one, we here at Screaming Circuits don't really care too much what convention you use for your components. We want them to match and be properly formatted when in your BOM, of course. But because we program our SMT machines electronically, we don't really care if you mix things up. i.e. O for resistor instead of R or F for capacitor. It's not a good idea to do that, but we can still build it.

But, if we can build it, shouldn't anybody be able to build it? And, if anyone can build it, why should it matter? Well, in theory, it shouldn't matter at all. In practice though, people tend to be human and humans tend to be error prone. That's why we have standards, conventions and test procedures - to reduce the chances for errors. We also have conventions for the purpose of distributing bad, overpriced food and educational sessions, but that's probably a different convention.

It would be kind of like if you drove into a small town and there was a sign at the city limits indicating that in this town, red means go and green means stop. You would have all of the information needed safely traverse the town, but you would still be very prone to go with the green light.

I just recently saw a design where the connectors were labeled U1, U2... Again, we can build this and we did. But, if it comes time to do any rework, or if you want to make some design mods in-house, of if someone else needs to work with the board, they'll see "U something" and think you're talking about an IC instead of some sort of connector.

There are some specific industry standard documents covering the reference designator conventions, but I bet it's one of those things that most people just sort of know, but don't have the official document to go with it. Wikipedia has a list and a lot of companies probably have their own conventions.

It is easy enough to find these lists of conventions, but it does leave me wondering how some of them came to be. I get "R" for resistor and "C" for capacitor. "Q" for transistor even makes sense, although it's derived from a property of the device instead of the name as are R and C. But, why "U" for integrated circuit? It used to be "IC", but that's fallen out of favor now. Really weird is the inductor. It starts with "I", it's inductance value is measured in "henries" and henries are indicated by "L." Go figure.

Duane Benson
U take the high road and L take the low road

 

Easy Reading for a Long Weekend

The holiday is upon us and most folks here in the US will have a three day weekend. Of course, when you're an engineer on deadline, all too often holidays don't really mean that much. Here's a little food for thought for those that will be working over the weekend.

  • If you're trying to finish off that layout and need some advice on a pesky QFN or DFN, read these few bits about laying out for a quality reflow: here, here and here.
  • If you're trying to decide what finish to order on your PCB, read this, this and this.
  • If you just want to confuse yourself a bit, try this, this and this.

Now you can get back to some real problems - like finding that last little bit of clock jitter or figuring out how to keep the back-EMF from mucking with your MOSFETs.

Duane Benson
No shorts allowed under that BGA, 'cause shorts cause tan lines