Passing CE immunity testing

When I was working on semiconductor machinery, we used TUV to get CE certification so we could sell the machines in Europe. We got through emissions alright, it’s similar to the FCC testing we already did, but immunity testing was brutal. When we broadcast RF at a machine, the wafer elevators went nuts and started breaking wafers. We had managed to convince the TUV guy that the speckles and snow on the monitor were not technically a failure, since you could still read it. But robots going open-loop? No, nobody could talk that past TUV. Turns out the cabling was the culprit. There was shielded twisted pair to the Banner sensors that located the elevator stops. In fact, I think they even used braid+foil shielded wire. But the semiconductor machinery company connected the cables with those red-brick AMP connectors, the MR series.

MR These MR (miniature rectangular) connectors work great for appliance wiring, but they provide no continuous shielded path for radio frequency interference (RFI).

Now designing cabling is often thought of as a mechanical engineering function. But mechanical engineers often don’t understand the principles of RF shielding. Get this— they cut the cable shielding about 2 inches back, connected the power, ground, and signal to pins, and yeah, they connected the braid to a pin, and sent it into the connector, to mate with another cable that had 2 inches pulled back. The cables were all dressed beautifully and shrink tubing everywhere. But like my buddy says—“4 inches of untwisted unshielded wire is a nice antenna.”

D-sub The D-sub connector was developed for military applications and then picked up by PC makers for serial, parallel and video ports. One reason is its good RF performance. Make sure your cable braid contacts the metal shell.

I switched them to D-subs using 9 pins with a metal shell, and we finally passed. So remember, RF energy is like light—it can leak into the smallest spaces and screw things up. Make sure the EE department revises the detailed design of the cable, or your machine might get held up in certification too.

Crushed avionics from a 737 nose wheel collapse

I have several pals that work on airplane avionics. Talking to one last week, he mentioned that he has a picture of what happens to the high-dollar avionics bay of a 737NG when the nose wheel folds back and collapses on landing.

Ouch. This 737NG avionics bag got pretty well crushed when the nose gear folded up on landing.

Be glad your electronics was not in this mess. I guess this is a case of just taking out the whole rack and putting in a new one. It was nice that the collapsing electronics sort of cushioned the blow, and protected the airframe from a high-g impact.

My pal Jerry Alvarado (RIP) worked as a machinist for United up in San Francisco airport. He told me that they were constantly rebuilding nose gears, as the load when the plane drops onto it is pretty severe. I asked if they pushed him to rush out a job, and he said “No way, I can take as long as I need. Hey, our mothers ride on airplanes too.”

That was certainly comforting in this day of cutting corners and slapping things together.

Wayne Yamaguchi talks home-made PCBs

My buddy Wayne Yamaguchi sent a little update on making printed circuit boards (PCBs) at home. Wayne always was the expert on toner transfer PCBs. This is where you print your Gerber art on a special film. Then you use an iron or a hot roller to transfer the printer toner from the plastic film to the copper-clad PCB material. The printer toner becomes the resist that keeps the acid away from the copper foil. Wayne has also figured out how to use a sponge to rub the ferric chloride on the board, so the copper etches away in seconds, not minutes.

I gave this a brief mention in an article about prototyping years ago. Wayne just keeps on improving this process and I hope to give a complete update soon. Wayne is also the guy that figured out PCB-Pool in Ireland was doing good work, as well as the USA triumvirate, Proto Express in Silicon Valley, Advanced Circuits in Colorado, and Sunstone (PCB123) in Oregon. Lately Wayne has been a fan of OSH Park up in Oregon. They operate like a community, where they take a bunch of PCB orders and panalize them on one substrate, so you can share the cost with a bunch of other people. For Wayne’s small boards, this can be ideal.

Wayne Yamaguchi holding a PCB he had made by OSH Park. Before stage this he makes his prototypes with toner transfer and acid etch.

So here is Wayne’s latest missive:

“Many of you know I still make my own PCBs at home. I think I just tweaked or ironed out a nagging issue. Sometimes I would lose some toner during the process of putting it on the PCB. Using the GBC laminator I’ve had reasonable success and I finally think that putting the board through once is insufficient to apply pressure across the whole board. I put the board in offset 30 degrees and then a second pass with the board turned offset -30 degrees. Putting the board through the laminator at different angles ensures all of the board gets heated and pressed.

“Here’s a board I made a week ago and now it’s aged and somewhat tarnished. You can see the test patterns in the circuit and one test pattern outside of the circuit board. All test patterns came out. The test pattern has an 8 mil trace, 6 mil trace, 4 mil trace and a 2 mil trace. Of course they all get flattened out during the process, but, the 2mil really had little toner and was surprised how well it came out even if it was flattened.

Wayne Yamaguchi gets down to 2-mil traces with home-made PCBs done with toner transfer and ferric chloride acid etch.

“Rough measurements show the 2mil came out around 3mil and the 4 mil squished out to around 5.5mil and the 8 came out around 11 mil. Typically for prototypes I try and stay with 10mil trace widths.

“This particular prototype yielded some good info and with that info I’ve made a few changes and have sent out for real 2 sided PCB at OSHPark. The OSHPark order came out to a total $4.95. The boards were placed on a panel within a day or so and have been sent out to the fab shop. I might get the boards next week some time.

“The process is a slight derivation from Pulsar, who created this process a long time ago.  Frank at Pulsar is the originator and should get all the credit for the process.”

Well thanks Wayne, many of us still like to whip out a single-piece prototype before going to fab and this is a great way to do it. My only warning, gleaned from personal experience, is to not put any vias under surface mount parts. There are no plated-through holes with these home-made PCBs, so you have to solder a little wire into every via.

Istvan Novak on power integrity

A couple years ago my pal Bob Thomas over at Apple told me how Istvan Novak over at Sun Microsystems figured out a clever way to keep RF from radiating out the edge of the board. For years, engineers have put power and ground planes or two ground planes on the top and bottom of the board, so it makes an enclosure, a metal can that keeps the signal traces inside from radiating. Those same engineers noticed that when the edges of the boards were open, RF would leak out of the edges and cause problems with signal integrity, power integrity and EMC (electromagnetic compatibility).

Istvan Novak, here at the DesignCon show in 2014, figured out you should stitch resistors or RCs around the edge of a PCB so the RF would die when it hits it’s characteristic impedance.

So these same engineers would stitch hundreds of vias between the top and bottom ground planes, all around the edge of the PCB (printed circuit board). If they had a top-side power plane instead of two ground planes, they would stitch hundreds of decoupling caps all around the edge of the board.

Istvan figured out a problem with this scheme. See, if you have a via or a decoupling cap at the edge of the board, that looks like a dead short. Remember that RF reflects off a dead short. So what would happen is that the RF radiating out of the signal traces would hit the vias and then bounce back inside the board and wreak even more havoc with signal integrity.

Istvan figured out that you don’t want to just stitch vias, you want to figure out the characteristic impedance of the two planes, which you can think of as a big fat transmission line. Then you stitch resistors all around the edge of the board. When the RF hits the resistors, it dies with no reflections, since it just hit its characteristic impedance. If you have a power and ground plane, you leave the decoupling caps, but add a resistor in series to each cap. That way there is no dc power loss from all the resistors. Istvan patented this at Sun, but he insists he is not the sole person to see this. He mentioned several people that have also worked on this problem.

All this bouncing RF also raises hell with your power integrity. See, Bob Thomas described the RF radiating out of the board edge. When I mentioned Istvan’s trick to Howard Johnson, the famous signal integrity consultant, he said that what was going on is that the power planes were resonating and the resistors were adding damping. OK, but I knew my pal Bob is no slouch, and what he described seemed to be right.

Howard Johnson, shown here in repose at his Signal Hill Ranch in Washington State sees the RC stitching as stopping power plane oscillation.

Bob Thomas, a pal from my HP consulting days back in the 90s, was at Cisco when he told me Istvan’s trick.

Accordingly I arranged to meet with Istvan at the DesignCon show here in Silicon Valley. He was part of a panel discussion run by my old pal Martin Rowe, over at EDN and EETimes. So after the panel I put Istvan on the spot. Who was right, my brilliant pal Bob Thomas, who says it was killing leaking RF, or brilliant consultant Howard Johnson, who said it stopped the planes from oscillating?

Istvan smiled and said “They are both right!” He explained that if RF is pumping out the edge of the board or hitting a dead short and bouncing back inside, well then the planes are oscillating, they are intimately related. I really love this signal integrity stuff, or in this case, power integrity. Istvan also pointed out that these days you need so many power planes, you don’t get one big plane you can stitch all around the edge. For this he says you bring the power and ground planes close together, and close means like a 1-mil (0.001 inch) spacing. That raises the capacitance up and makes the transmission line formed by the plans lossy, which keeps them from oscillating and radiating RF.

Best of all, Istvan was nice enough to write me a follow up note:

“To get the basics about terminating planes, you can specifically look at “Reducing Simultaneous Switching Noise on Power Planes by Dissipative Edge Termination,” EPEP’98, October 25-27, 1998. I just realize that there is no link any more from my webpage to this paper, but you can get from this direct link:

http://www.electrical-integrity.com/Paper_download_files/EPEP98_DET.pdf

“As I mentioned during our brief chat, this paper and the subsequent patents, were not the first on the subject. One earlier paper is referenced in my EPEP98 conference paper as:

“G. Lei, R. Techentin, B. Gilbert, “Power distribution noise suppression using transmission line termination techniques,” Proceedings of the 5th Topical Meeting on the Electrical Performance of Electrical Packaging, October 28-30, 1996, pp. 100-102.”

“If you Google the plane termination subject, you will find other papers and other patents as well. One other thing worth mentioning: like every new solution, these inventions have their optimum time when they are needed and it makes sense to use them.

“The plane termination technique was very useful in the late 90s and early 2000s when many boards had large contiguous power and ground planes, prone to strong resonances. However, as system density continues to grow, we are now forced to chop up the power plane layers into many smaller puddles. Under these circumstances using edge termination becomes less attractive. If resonances are still making problems, a better way of using very thin laminates. See for instance:

http://www.electrical-integrity.com/Paper_download_files/DC02_HP-TF2.pdf

So thanks to Istvan, and Bob Thomas and Howard Johnson for making our power integrity more solid and reliable. I have a video about this as PCB202, and will back link to that as soon as it is posted.

DesignCon 2014, even the badges are cool

So I got to pop into DesignCon 2014, the signal integrity, test, and high-speed schematic and PCB design show here in Silicon Valley. In addition to seeing some great panels and vendor displays, I got to see industry favorites like Dave Bursky, Martin Rowe, and Patrick Mannion. Sure EDN has lots of nice coverage, here, here, here, and here. Most of my analog pals love DesignCon. It’s not just a show with hundreds of exhibitors; it is a conference with keynotes, classes, and panel discussions.

But the thing I love about these UBM shows is that even the badges can teach you something. I noticed the printed part of my badge was paper.

This badge from DesignCon 2014 is printed on paper.

Thing is, when I looked on the backside of the paper there was a thin plastic disk covering up something with a small bump.

In the backside, you can see a small disk in the center. What caught my eye was the small bump at the bottom of the disk.

So what is an analog guy to do but peel back the disk?

Peeling back the plastic cover reveals a spiral antenna and an RFID chip.

The RFID chip spans the end of the loop antenna, while the other side of the circle has the underside connection with 9 vias to complete the loop.

The white cover disk is applied over a clear disk that has a spiral antenna and an RFID chip. The clear disk is printed on both sides so the spiral can form a loop with a back-side connection with 9 vias on each end.

Here you can see that the RFID system is itself printed on a clear disk.

Here is a close-up of the underside trace and the vias on each end. This is all made from conductive ink that is printed on fast and cheap.

A close-up of the chip. It’s made by a competitor to Atmel, so I have covered up the logo or cropped it out from the previous pics. It’s not just a competitor; it is where my boss worked previously.

The RFID chip may not have encryption like Atmel’s RFID chips, not sure if show badges are a secure application. But it still astounds me we can afford to print antennas and chips on paper badges meant to be thrown away after the event.

Here is a side-shot of the RFID chip. It is powered by an RF field you apply to the spiral, and then modulates the energy received to communicate with the transmitter. There is no battery in the badge.

So there you have it. A show so cool even the badges can teach you electronics. The next big UMB Tech show  here in the Valley is EE|Live! which is a super-show that has the Embedded Systems Conference along with some other major attractions. Atmel is a sponsor of the IoT (Internet of Things) track and we are submitting at least one paper. I will be sure to attend as will the hundreds of embedded engineering pals I know in the Valley. And my own Analog Aficionados party is Sunday, February 9^th2014. Steve Taranovich is signed up, as is EDN VP/Brand Director Patrick Mannion.

Video: The Gingerbread Arduino

My pal Andreas over in the microcontroller business group sent me this great video showing the kind of fun non-technical folks can have with Arduino.

He writes:

My cousin who is a math/physics geek wanted to learn embedded  programming and decided to make an fancy gingerbread santa for Christmas using an Arduino. Turns out not only kids but also grownups play with Arduino. ☺

OK, so a math physics guy is not exactly non-technical, but it is safe to say he is not an engineer. That is the great thing about Arduino, it can get you started with some results the same day you start to play with it.

The January 2014 eFlea breakfast

My friends and I still get together for breakfast even when the Silicon Valley electronic flea market is shut down for the winter. The first one of the new year was Jan 11, 2014. We go to Bobbies in Cupertino, and feel free to stop by the second Saturday of the month. We eat outside so dress warm. When the eFlea is running in the summer, we get to Bobbies about 9:30 AM. In the winter, with no Electronic Flea Market we show up at 7:00 and hang out until noon.

The big news this eFlea was that Phil Sittner and Dave Mathis are designing an antenna analyzer using Atmel chips. Phil, who I wrote about before is doing the hardware and Dave is doing the software. They plan on going to Ham shows to sell the product once they perfect it.

Dave Mathis (L) and Phil Sittner are working on an antenna analyzer.

Phil has already hacked up some prototypes to help develop the analog part of the product.

Here is Phil after I prompted him to show off all the cool Atmel hardware he is using.

That’s an XMEGA-A3BU Xplained eval board on the left and an AVR Dragon debugger on the right. I am mad because he paid for the stuff rather than hitting me up for some samples.

Next show-and-tell was from a pal that wants to go un-named despite the statute of limitations being invoked. He found a box in a culvert 20 years ago and assumes it was someone disposing of stolen goods. I assume it was more like the PCBs I found years ago that probably just fell off a truck.

These ceramic Motorola 68030 microprocessors sure are pretty. They make a neat noise when you clank them together.

Google’s Eric Schlaepfer and mechanical engineer Dave Ruigh admire one of the gold-plated beauties.

These mixers work from 1200MHz to 1600MHz. There are two layers of them in the box.

Eric Schlaepfer looks at one of the boards from the mystery culvert box of goodies. The PCB is not Mulitbus or VME, it was some custom job.

John Haggis and his son Xander showed up later in the morning but did not disappoint with an Omron wearable blood pressure health monitor. John is the pal that went all the way through med school and decided he preferred engineering.

Xander and John Haggis made the January 2014 eFlea breakfast and brought a whole batch of goodies.

This Omron wearable blood pressure monitor is just the thing to monitor your health.

John Haggis also brought this waterproof Bluetooth speaker to show us.

John Haggis also has hacked a fone wireless charger into his Samsung Galaxy S4

John also had a neat ANKER battery setup to run the hacked wireless charger.

Here is a link to that ANKER battery setup.

After seeing all the smudges on that ANKER battery, I was quite the hero when I whipped out these Atmel screen cleaners. You peel off the little pad, which is a cleaner on the visible side, and then you can stick it down to the back of your phone. I convinced John to take 4 of them to form little “feet” for his gizmo.

Atmel has this swag giveaway pad. It’s the little one-inch square at the bottom right. You peel if off this card, use the top side to clean the smudges off your screen, and then the bottom side will stick to the underside of your phone or gizmo until you need it the next time.

Here is another screen cleaner pad Atmel gives away at events.

Atmel’s Director of Events Donna Castillo assures me if you come to her Tech on Tour events she will have some of these for you take home.

Lastly, my pal Martin DeLateur, the International Man of Mystery brought an older Sirius radio and dock. He snagged it at an estate sale. Problem is it got hooked up to 12V battery, and has some issues. We scratched our heads and offered some advice. We will see if he got it charged and powered up at the next eFlea breakfast, Feb 8, 2014, which is the day before the 2014 Analog Aficionados party here in Silicon Valley.

This old Sirius radio has some power problems we will try to fix by the next eFlea Breakfast.

A Tesla hacked into a Vanagon

My buddy Otmar Ebenhoech is hacking a wrecked Tesla chassis underneath a VW Vanagon van. And not just any Vanagon, he is doing it to a stretched Vanagon that has two side doors.

Otmar Ebenhoech stretched this Vanagon years ago. When the engine blew out he decided to hack a wrecked Tesla S into the undercarriage.

I met Otmar when he lived in Silicon Valley. I was converting a 1975 Honda Civic to all-electric, and he was the go-to guy for help and advice. He sold his house during the housing craze, and went up and bought a house and a shop up in Corvalis Oregon. If anyone has the can-do spirit to pull this off, it is Otmar. He is the designer of the Zilla dc motor controller used in the White Zombie electric drag car.

Here is a video from the project blog:

Hopefully Burning Man and all Otmar’s other projects won’t keep him from this great adventure. I saw he paid about $38k for the Tesla so its not something you want to just let sit. When I watched the video  above I wrote Otmar and asked if that hoist was his personal shop. He replied:

“Yes, that’s the Garage Mahal you see in the background. I spoiled myself by moving to Oregon where I can afford a shop, and seemingly to buy a wrecked model S though I’m still in a bit of shock over that!”

Arc explosions illustrate the dangers of electricity

I wrote a blog post a while back about the difficulty or having cars with 42V instead of 12V batteries. I also pointed out the difficulties of distributing dc inside your house and to your house. It got picked up by EDN, and the comments were interesting. Someone challenged my assertion that 24V relays switches are less reliable. Sorry, I worked for GMC Truck and Coach as an auto engineer in the electrical group. Heck, just read any switch or relay datasheet and you can see you have to de-rate for dc and de-rate even more for higher-voltage dc. Someone pointed out the phone company uses 48V dc, and I had to explain that the 48V the POTS (plain-old telephone system) sends to your house is also high impedance, 600 ohms, so that make is much less arc-prone and easier to switch.

Others challenged my observation that it is hard to distribute dc in your house due to the fire hazard from the arcs and the same problems with switches and relays. Well, even ac has arcs that are hard to quench. Bigger dc circuit breakers have magnets in them to pull the arc one side and make it longer so it can break. Really big breakers, both ac and dc, have compressed air that blows the arc out just like your kid with a birthday candle.

So here is a nice video of an ac arc flash that should give you some idea of the difficulty of quenching an arc. Palo Verde had a horrible arc flash in 2008 that thankfully had no injuries. And here is a training video of an arc flash form the fine folks at e-Hazard.com

Here is another training video from Westex flameproof clothing:

And if you wondered if there was any glory left in the American worker, check out this high-voltage lineman working from a helicopter.

So that’s the trouble with dc. Since the voltage is not going through zero 120 times a second it is much harder to quench the arc. The operative word is “plasma”. That is what Fran Hoffart from Linear Tech taught me about li-ion batteries. He said that the burning lithium is certainly a problem. But the real mess is that a plasma ball forms, and that shorts out any other battery cells in the vicinity. An arc is plasma, and that is some nasty stuff. I mentioned to Fran that the iron phosphate chemistry lithium cells are supposed to be burn-proof. Fran looked at me with an expression that said “you can’t be that stupid” and replied “they all burn”. It is remarkable the difference you hear when talking to people who are making and selling the battery cells versus the people like Fran, that are making the chips to reliably charge the cells.

I guess that is why that outlaw biker told me that the only thing that he was really scared of was electricity. I asked why and he said “Because it can kill you and you can’t see it.”

Cure RF squegging with a Neutrodyne circuit

Some headlines write themselves, huh? Squegging is when an RF amplifier or MHz-class switching regulator starts cycling on and off. In an audio amp it is called “motorboating” since that is the sound it makes. FET amplifiers are subject to this, like old tube amplifiers. Both have a high-impedance input, the tube grid or the FET gate. A FET gate is capacitive, so any charge that gets put on it will be stored by the gate, moving the bias point of the FET too high, and causing squegging. The Neutrodyne circuit comes from 1920 vacuum tube amplifiers. It is one of the ways you can tame squegging. High Frequency Electronics magazine has a nice article about squegging (pdf). The best way to show it is a figure in the article, who I hope the fine legal team at Summit Technical Media will let me show you.

Squegging is when the input of a FET or vacuum tube floats up momentarily and shuts down oscillations. This make the output cycle on and off, called motorboating (courtesy High Frequency Electronics).

Trust me; you really want to click over to the article since it has the schematics of a FET amplifier that will start to motor boat, as well as several ways to fix it. The whole magazine is pretty good. While you are at it, think of signing up for a print copy of the magazine. You need to be an engineer or tech worker, since the magazine is audited by BPA, so the advertisers know they are reaching tech people and not random idiots.

Remember that these tips apply to high frequency switching converters. And regulators are getting up into RF ranges. I remember seeing an 8-MHz switching regulator from Micrel years ago when I worked at EDN magazine. You might be using one of these fast regulators for some extreme size problems. These high speeds do cause less efficiency, as the gate charge is getting shunted to ground, but the inductor you need with these fast converters is miniscule. That Micrel part still manages 90% max efficiency, but you can use a 0.47µH inductor. That is one tiny inductor.

So I assume the Micrel folks have solved any squegging problems in their part, but it is still a good principle to understand should you run across it. It’s like sub-harmonic oscillations in switchers with a duty cycle greater than 50% (pdf page 10, pdf page 5, pdf page 72. It might befuddle you if you have never heard of it and don’t know the steps you need to take to solve it.