IR reflow oven for your prototype PCBs

When you use solder paste to assemble your prototype PCB (printed circuit board) you need a stencil or hypodermic needle to apply the paste to the pads on the board. Then you use an IR (infra-red) reflow oven to melt the solder. Scott Fritz, an Atmel IC designer on the third floor, found this neat home-made controller that turns a cheap toaster oven into an IR reflow oven. I assume the name Reflowster is a combination of the words “reflow” and “toaster.”

The Reflowster will do closed-loop control of a cheap toaster over so you can do IR reflow soldering on your prototype circuit boards.

The Reflowster is an Arduino-based controller that that gives you predicable and repeatable heating and cooling profiles to melt the solder paste and connect up all the components on your board. They got their start on Kickstarter, and have actually shipped, so all the Kickstarter people are rewarded. Now the Reflowster folks are starting to offer the product to the general public.

The Reflow controller V3 PRO from PCB POOL in Europe is another product meant to work with a toaster oven.

I have mentioned a similar reflow controller made by the fine people at PCB-POOL in Europe. That article also described how my buddy Wayne Yamaguchi was using a toaster oven a decade ago to make his PCBs. Wayne did not use a controller. He just did a whole bunch of tests until he was satisfied he was getting good whetting and solder fillets on his circuit boards.

The great thing about the Reflowster is that it is a closed-loop controller. It is actually measures the temperature of the oven, and then controls the power to it so that the heating and cooling match the profiles recommended by component makers like Atmel (pdf).

Precise temperature control is needed to do quality lead-free soldering.

While I love, admire, and respect my buddy Wayne Yamaguch’s “theory of experiments” approach, you might really need the Reflowster. If you want to use different ovens, or have changing wall voltage, or the boards you are soldering are different sizes or have a different set of components on them, you want a closed-loop controller. If the chips have a big pad on the bottom, the die-attach-paddle, you need reflow. The other big factor is lead-free solder. Many of the crazy analog engineers I hang out with still use tin-lead solder for prototypes. It looks better, it feels better, and lead solder is more reliable. We also pull the solder off the reel by biting it gently and tugging, so we don’t have to set the soldering iron down. Lead poisoning might explain why we are all crazy. But if you are sane and insist on using lead-free solder, the preciseness of reflow control is important.

Solder paste application is like silkscreening T-shirts. Instead of silk the stencil is stainless steel. Instead of ink you use solder paste. Instead of T-shirts you do printed circuit boards.

Solder paste has its own hassles. You should refrigerate open containers so the little solder balls do not oxidize and change the reflow parameters. I am not sure the same caveat applies to when you use a big hypodermic to apply the solder paste. There the hassle is you have to do it one pad a time. A solder stencil is a thin stainless steel sheet where the PCB fab house has etched through all the areas where there is supposed to be solder. Sometimes called the “cream layer” Its not exactly the solder mask art, but it is pretty close, depending on your particular design. I know you can set up OrCAD 9.2 to do it, and I am sure other CAD packages can make it, or the PCB fab house can create one from your solder mask layer art.

Here is a typical solder stencil from Stencils Unlimited. With one swipe of a squeegee you apply solder paste to the pads for your chips and passive components.

The fine folks at Sunstone used to offer a free stencil, now it looks like they charge a little. Most fab houses can supply one. Assembly houses like Screaming Circuits or Advanced Assembly have the relationships with board houses to they can make your stencil when they assemble your boards. If you are really masochistic, and have a high-powered CO2 laser cutter handy, you can make your own stencils. You can also live in a cave and use flint tools, but I prefer to operate a little higher on the food chain. The LPKF laser mill can make your stencils as well.

This solder stencil from Proto-Advantage lets you apply solder paste for a QFN-32 chip.

There are also hybrid approaches. You can buy cheap solder stencils just for high-pin-count chips on your board. You squeegee the solder paste onto the board for each of those parts, Then you can use a hypodermic for the passive components or hand-solder them after you reflow the big chips.

If you are a big-time engineer on a big-budget project then just contact Screaming Circuits or Advanced Assembly or you local board assembly house (not PCB fab, but board assembly). I know Screaming Circuits can do it all since they have teamed up with Sunstone and Digi-Key. Just send Screaming Circuits the fab Gerber and fab files which they send to Sunstone, the assembly drawing and insert file which they use themselves, and the BOM (bill of material) they order the parts with from Digi-Key. They can do quick-turn and they can ship anywhere in the world.

So the prototyping ecosystem is like this:

• If you are a hobbyist use DIP (dual-inline plastic) chips with 0.1 inch lead spacing and through-hole passive components. You might use surface mount chips on DIP breakout boards.
• If you are a pro-hobbyist or low-budget engineer buy a temperature-controlled Weller soldering iron or a Metcal and a good stereo microscope. Now you can hand-solder surface mount boards. For chips with bottom pads you have to either heat the whole chip with a big soldering iron, use a heat gun, or try to wick the solder in from vias you design in on the backside of the board.
• If you are a hobbyist doing low-volume manufacturing or a medium-budget engineer, go to solder stencils and reflow ovens.
• If you are a hobbyist that hit it big or a big-budget engineer, use the board house to order the parts, get the PCB fab, and assemble and maybe even test your board.

TQM Solutions knows that total quality management means you not only have a mountain of documentation, but that you organize that mountain.

Note that last item. See, as an engineer, your real job is to make a set of documentation so the design can get manufactured by non-engineers and non-technicians and non-hobbyists. Its nice you are a hands-on person. Heck, its critical you are a hands-on person to be a good engineer. But your real responsibility is making sure the CAD files are correct. it might speed things up if you make a first-spin board yourself, and its neat if you make the board on an LPKF mill and you can get parts from the factory floor or Radio Shack or a salvage yard.

I used to design products with parts I found cheap at places like Weird Stuff Warehouse in Silicon Valley. Then one of my designs went to production but Weird Stuff had sold off all the parts I had used. Now I select parts from distributors.

The great thing about using Screaming Circuits and Sunstone and a distributor like Mouser or Arrow or Newark or DigiKey is that you are proving out your documentation. You make it clear to Screaming Circuits that if your pick-and-place insert file has mistakes they tell you, you fix them and they use that file. This way, when they see that the part origin for a DPAK is at the pad and not the part center, they know the vacuum picker cannot pick it up, so you catch that AND FIX IT. If your Gerbers have problems you make sure Sunstone tells you, or you use the free DFM (Design for manufacturing) check offered by Advanced Circuits. Then you FIX THE FILES. Same deal for any BOM mistakes. Make sure somebody tells you so you can FIX THE FILE, and not the text file, you fix the CAD file in OrCAD or Altium or whatever, so it spits out a perfect BOM.

Now when you send the CAD files to China to get assembled on the cheap, you know the files are correct. Anything less and you are not an engineer, you are an amateur. Proto Express even works with a Chinese partner to ensure you can get cheap-high volume boards that work as well at the Proto-Express boards made right here in Silicon Valley.

The oqo Model 2 used a Via processor. The third model with an Intel Atom never got built since they ran out of money (courtesy Engadget).

This level of diligence and exactness is critical. I worked at oqo, a San Francisco start-up that made the first palm-top computer that ran real Windows OS. The first model was based on the Transmeta “emulated” x86 processor. The second model used a Via chip. Lesson there is never base a business plan on being smarter than Intel. The third prototype never went into production. I had left the company for National Semiconductor, but pals there told me they used an Intel Atom processor and it was a real product that could really work good. But they were running out of money. So I assume in a big rush, they sent the design to the Chinese contract manufacturer. A pal familiar with the company told me oqo had to fly out an engineer to China and there were 1000 ECOs (engineering change orders) to get the design ready for high-volume manufacturing. One thousand mistakes. Now it probably didn’t matter, but its nice to think that if they had scrubbed the CAD files, the fab, the assembly, and the rework documentation through a US quick-turn prototype manufacturer, and fixed most of those mistakes, then maybe they could have gotten that product to market and saved the company.

This is a perfect example of the asymmetric respect problem in engineering. The Chinese manufacturing engineers respected those high-tone former Apple designers at oqo. But the oqo engineers may have thought manufacturing was some triviality and beneath them. Perhaps they thought any idiot should be able to do it. Sorry. Wrong. Dead wrong. Dead just like oqo is today. You need to be every bit as smart, clever, and creative to do manufacturing and test as to do design work. When you take a product all the way to production, you will learn to respect everybody involved. Respect the planners, the clerks, the assemblers, and ALL the engineers. So be a good and respectful design engineer and make sure your CAD files are a good as they can be before you send them out for production. That is your responsibility, not a Flextronics responsibility.

The cover of my mentor Bob Pease’s book Troubleshooting Analog Circuits has one of his “airball” prototypes on the cover. Application engineers like Bob can do proof-of-concept, but don’t try sending this out for high-volume manufacturing.

So like all things, prototyping has an analog continuum to it, There is a place for quick-and dirty hacks. There is place for super-diligence. And there is a whole spectrum of tradeoffs for an appropriate design effort in between those poles. Just don’t do some rush-job today that you just know will bite you a few months later.

[Update] I showed this post to Wayne Yamaguchi and he had this great comment:

“One of the major drawbacks to solder paste is the shelf life.  No matter how you buy it, the container and contents will go bad in about 6 months time, even in the refrigerator.  It’s the flux that ages and slowly solidifies making the reflow consistency different over time.  It’s just a real pain to dispense the paste with a tiny-tip syringe when it it’s fresh, and even worse when it has aged a bit. If I recall correctly, the smallest syringe runs about $50.00.  You can solder a lot with that but if you only make one proto this is an expensive proposition.

“Mine tends to absorb water over time and this makes it pop when reflowing, blowing off chunks of solderpaste in all directions. I can hand-solder 0402 and DFN parts with the soldering iron.  I only need the hot-air station for pads that are not exposed, like power pads and some SMT inductors. I would recommend a really good soldering iron or two, and a general-purpose hot air station if you want to hand-solder small runs of boards. You will need one with a 0.2mm tip or smaller for the leadless and 0402 parts.

“I prefer to still use leaded solder.  It solders at a lower temp and the chemicals are less caustic, unlike the solder flux used for leadless solder.  Unless I have to, I try to use “no clean” flux and occasionally will use Kester 331 (IIRC) for gold-plated pads.

“Good stencils are cut non-vertical.  The edges are beveled so the bottomside is slightly larger than the top, making the solderpaste less resistant to sticking to the stencil.  Hopefully, when you lift the stencil the solderpaste adheres to the PCB and not the stencil.  I’ve never actually seen the process, but, I always imagined  that the paste would not all tranfer.  I guess it works.  Just doesn’t work in my mind.  The bevel is only 5-10 degrees.  Hardly noticeable by the eye, but, I guess it makes a difference.

“Another gotcha will come when you doing rework.  You remove the part in question and/or use solderwick to clean the pads.  If you try and apply solderpaste right away the residual heat will outflow the flux from the syringe tip which is most frustrating as now the tip is full of paste with no flux.  When this occurs it is like concrete and won’t flow.  It is possible to drain more than the tip into the larger part of the syringe tube rendering the whole syringe load bad.  You can unscrew the tip and plunge out the bad material, but, who knows if you now have the right ratio of flux to solder anymore?  If this is the tube from the vendor you can kiss $50.00 down the drain.  If you transferred solderpaste to a smaller syringe the loss is less than $50.00.”

I guess all those years at HP and Agilent, and then being in business for himself gave Wayne a valuable perspective on prototyping. Many thanks to him, and add you own comments below.

The home lab of Bo Lojek

I was touring Atmel’s fab in Colorado Springs, so I made a point of contacting Bo Lojek, the author of the great book, the History of Semiconductor Engineering. Although Bo is now a professor at University of Colorado, he worked at Atmel for 15 years. I was honored that he asked me to his home in Colorado Springs. Well, I have a pretty good home lab, but Bo’s lab just blew me away. Bo said he wanted to be an engineer from the time he was 7 years old. It runs in the family, his dad was an engineer too.

So Bo told me that he built his house in Colorado Springs. If one of my Silicon Valley buddies says this he means that he had a custom floor plan home built by a homebuilder. For Bo, it means he had an engineer design the house to his specs, using metal studs, and Bo himself constructed the house, driving all 37,000 self-tapping drywall screws. I think he said it was 3600 square feet. Yes, it’s an engineer’s paradise.

This is what meets you at the foyer just inside the front door of Bo’s house. Bo said if I came back at daytime I could check out his collection of Dumont scopes in the garage.

Every engineer worth his salt needs a Data General Eclipse computer in the hallway, just for data processing emergencies. Bo has arranged for all his stuff to go to the University of Colorado when he dies. It will be great to keep this museum together. It will also be a great excuse to visit Colorado Springs, other than to meet the space aliens that the Stargate people have inside the NORAD mountain.

Bo has some early computer boards nicely framed on the wall.

Lojek has a huge collection of voltmeters, including this Cubic model V-46A. It uses telephone stepper relays and a handful of transistors to measure voltage. Pretty cool for 1960.

On Bo Lojek’s bookshelf are propped up some vacuum tube modules from a very early computer.

And let’s enjoy Bo checking out the whole bookshelf. His house is not only engineer paradise, its college professor paradise.

While Bo does not have the disorganization of dear departed Bob Pease, he does have a few things littering the floor. I used to use the same Data IO programmers to program the microcontrollers I designed into my consulting work.

It does not disturb me that Lojek has a stack of early Tektronix mainframe scopes. What bothers me is I have several friends that have the same sort of stack.

How about these early 2N1302 transistors from honored competitor Texas Instruments?

Lojek has drawer after drawer full of electronic components, including these vacuum tube computer boards.

Bo told me that when Bob Pease visited his house, he could not tear him away from these two analog computers. I should mention that I knew of Bo because Pease told me what a cool guy he was. Bob knew Bo because Bob edited Bo’s book. Since English is Bo’s second language that was a lot of work, but Pease was happy to do it since it was such an important contribution from such a cool guy.

Here is a close-up of the analog computer that so entranced Bob Pease.

All this cool stuff above is just stacked like cordwood all over the house. This is where we finally got to Bo Lojek’s lab bench.  Bo told me he likes to write or read for a while, but then he has to go to the bench to do some experimentation. It reminds me so much of my mentor Bob Pease, who had an equal love for working with his hands a soldering iron.

Every surface in Bo Lojek’s house is a treasure trove of memorabilia and electronic equipment.

Here is a very early computer board that used “air gap” integrated circuits. Analog Devices’ Barrie Gilbert told me that he got into electronics because surplus WWII magnetrons were so beautiful to look at he had to learn how they worked.

And how about this, a Bob Widlar business card? I love the title “ROAD AGENT”. Widlar had style.

And when your engineer friend tells you he has a walk-in closet— this is what he means.

Lojek has an artistic streak. Amongst the pretty glass are a handful over very early galvanometers, some from the 1800s.

More cool galvos and such. I wonder if the founder of Digi-Key has that same telegraph key? Ronald Stordahl started out Digi-Key by selling electronic telegraph key kits to Ham radio operators.

Here Bo Lojek admires a framed set of Minuteman missile circuit boards. Jim Williams had an interconnected set on his living room. Check the Minuteman missile PCBs and Jim Williams out in this video.

OK, so I lied. That picture earlier, the one I called Bo Lojek’s lab bench. That was just the emergency downstairs lab bench useful of quick jobs. Here is the real lab bench. Next time I get to his house, I will fire up that big soldering iron and put it down right before the picture, so there will be a wisp of smoke coming off of it, like a Cowboy’s 6-shooter.

That main bench above has a side bench on another wall.

And books, boy do college professors love books.

It was a real treat to see Bo. He said he is going to try and make it to the next Analog Aficionados party, so I will remind him so he can be among like-minded souls out here in Silicon Valley. The party will be Feb 8 2014, the Saturday before the IEEE ISSCC conference.

Automotive circuit design headaches

I wrote an article for Electronic Design magazine about Bob Pease and his solenoid driver circuit. Former National Semiconductor employee Myles H. Kitchen was nice enough to drop me an encouraging note.

“Thanks for your great article on Bob Pease and the solenoid drivers. Having worked with Bob in the late 1970s and early 1980s at National Semiconductor, I came to appreciate his wisdom and simplicity for addressing issues that seemed simple, but were really quite involved. As someone who’s worked on automotive electronics my entire career, an issue such as a solenoid driver is critical. I recall when testing early automotive product designs at one company, we would put the module under test in a car, and then turn on the 4-way flashers to see if operation was affected, or if it stopped working completely. The combination of multiple inductive and high-current resistive loads operating on and off at several hertz would play havoc with the power supply, and immediately point out design deficiencies in module power supplies, regulation, protection, and noise immunity…. some of which could be traced to poor relay or solenoid driver circuits.  Surviving the 4-way flasher test was only a quick way to see how robust the new design might be, but it was a quick indicator if we had things right up to that point. I miss Bob and his ramblings in ED, but hope to see more of your work in the future.  Loved it.”

Well, having been an automotive engineer at both GM and Ford before moving out to Silicon Valley, Myles’s note sparked a flood of memories. His four-way flasher story was prophetic. When I was in college at GMI (General Motors Institute) one of my pals worked at Delco. They were just coming out with the integrated electronic voltage regulator in the back of the alternator, circa 1973. So all the executives were standing around at a demo and after they ohhhh and ahhhh, and congratulate themselves, my buddy gets in the car, and knowing what Myles knows, he cycles the air conditioning switch a few times. The “Charge” light promptly came on.

I asked my fellow student if he was in trouble or if they hated him for causing the failure, and to GM’s credit, he told me “No, they were actually glad I found it before it went into production.” It must have been some serious egg on some faces, though. After that, survival after repeated AC clutch cycling became part of the spec for the voltage regulator. I bet four-way flashers are included as well.

I later worked on anti-lock brakes for GMC heavy duty trucks. This was way before anti-lock brakes on cars, about 1975. We dutifully shielded all the wires to the sensors with expensive braided cable. When we pulled the truck out on the road, the brakes started modulating, with the truck just sitting there. We realized that the entire 24V power system was a pretty nice antenna and that noise can get into a module from the power side as easy as from the sensors. We begged the government to give us more time, and they did. Indeed, I don’t know if they ever put in antilock brakes on heavy trucks. Let me check, yeah, wow, it’s still called MVSS 121 (motor vehicle safely standard) and it finally went into effect in 1997. That was at least a 20-year delay in getting it working.

I told Bob Reay over at Linear Tech that automotive design was the toughest, because you had a military temperature and vibration, but consumer cost. He added another factor, the chips for automotive have to yield well, since you need to ship millions. What a crazy challenge.

When I thanked Myles Kitchen for his kind words and told him the above stories, he responded with a great story about load dump. The phenomena called load dump is usually caused by a mechanic who is troubleshooting the battery and charging system of a car. You get the car running, rev it up a bit, and yank off the battery cable. If the car keeps running, that means the alternator and regulator are OK, it is just a bad battery. Thing is, the alternator is often putting full output into this bad battery. And when you yank the cable off the battery, the voltage regulator controlling the alternator cannot react instantly. So there is this huge overvoltage spike as all the stored energy in the alternators magnetic field has to dissipate into whatever loads are still connected, like your radio. A load dump can put over 100 volts on electrical system. And it is not a fast spike; it can last for hundreds of milliseconds. Smart mechanics just leave the battery cable on and hook up a voltmeter to see if the alternator is putting 13.75 to 14.2 volts on the battery. So Myles recounts:

“Thanks for your email.  Yes, sounds like we’ve run up against many of the common automotive issues in our time.  I’ll add one brief anecdote here.  When I worked at Motorola’s automotive division, I certainly learned all about what a load dump is, but I’d never really heard of anyone experiencing one first-hand and what it could do.  One day, our admin complained that her 70’s vintage Plymouth Duster wasn’t running right, and that her headlamps and radio quit working.  She had been driving it the night before when something went wrong.  We brought it into the garage at Motorola, and found that she had a very discharged battery with very loose battery connections. You could just lift them off with your hand.  As a result, her battery was discharged, and when she hit a Chicago pothole it all went bad.  The resulting load dump had blown out every light bulb filament in the car, along with the radio.  Only the alternator/regulator had survived.  The ignition was still a points and condenser system, or that would have probably died as well.  A new battery, tight connections, and a bunch of replacement bulbs got her back on the road again.  And, I’ve never doubted the need for a load-dump-tolerant design since!”

Those are wise words from someone who has been there and seen it first-hand. And I wonder if the voltage regular in that old Duster was a mechanical points type. In the early days we automotive engineers would try to protect each individual component for load dump. The radio would have a Zener diode clamp, so would the cruise control module. Then manufactures put a big Zener clamp right in the voltage regulator that clamps the voltage on the whole car. Maybe that was too low an impedance to clamp, because now I see there are a lot of smaller distributed TVS (transient voltage suppressor) clamps that you use to protect the circuitry of your module.

There are two other approaches. One, you can just disconnect your circuit with a high-voltage FET when the load dump happens:

I used this circuit to keep automotive overvoltage from destroying an LT1513 chip I used as a battery charger. When the DC Bus voltage exceeds the 24V Zener plus the base-emitter drop of Q10, it turns Q10 on and that turns Q12 off and protects downstream circuitry from overvoltage.

Alternative two, you can put a high-voltage regulator in front of your circuit that will maintain power to your circuit through the load dump, at the risk that the pass transistor will overheat since it is dropping a lot of voltage while passing current during the load dump. Linear Tech makes such a part.

There is one more tip for every engineer regarding automotive electronics. Remember that there are laws that make auto manufacturers offer service parts for 10 or 15 years. So no matter what your application, you might consider using an automotive part like Atmel’s line of MCUs, memory, CAN/LIN bus, and RF remote controls. We state that we will be making many of these parts for over a decade. If you design them into your industrial, medical or scientific application (ISM) you can have some assurance you can still get the part for years, or at least a pin-for-pin compatible part. That means no board spins. On top of that assurance, most of the parts have extended temperature range, which might help in your application as well. Since we make the parts for high-volume automotive customers, they are usually priced very reasonably.

Bob Pease says: “My favorite programming language is solder”

The famous analog engineer and writer Bob Pease mentored me over at National Semiconductor. I was deeply saddened by his tragic death and I miss him every day. So you can imagine my delight when Lenore over at Evil Mad Scientist told me a pal had made a fun little tribute circuit board in honor of Pease.

Saar Drimer at boldport.com made up this cute PCB in honor of Bob Pease.

One of Pease’s exasperations was engineers that would rely solely on computer simulations. Bad enough they didn’t rely on real hardware, but when the real hardware did not agree with the simulation, these engineers would blame the hardware, not the computer. I touched on this tendency of engineers to rely on pretty simulations in a recent article in Electronic Design.

So when engineers would as Bob Pease what his favorite Spice or his favorite programming language, Bob would loudly pronounce “My favorite programming language is solder!” I really get his point. When I was a consultant, clients wanted to see working hardware, not computer print-outs. So my doing minimal Spice, I got prototype hardware in their hands sooner, and then we could use Spice to optimize component values, or for what it is really good for—doing Monte-Carlo simulations with your discrete component tolerances so you could see the corner cases of performance of your design.

To kid Bob Pease about his saying “My favorite programming language is solder,” I bought him this hefty 200W unit at the Silicon Valley Flea Market.

Saar Drimer was hoping that I could send one of his Pease PCBs to Bob’s widow Nancy. I will do that tonight, and I am sure she will be delighted as I was.

The backside of the Pease tribute PCB has a nice silkscreen that emulates Bob’s classic handwritten schematics.

So thanks to Saar over at Boldport, for keeping the Pease flame alive, just the way Bob would want— in some hardware.

Mathis, Proffitt, and Evans on FCC and CE testing

After reading my article about Bob Pease’s solenoid drivers, Howard Evans wrote me a letter explaining how he drives solenoids with an H-bridge. Its great stuff and we are working on a follow-up article. Evans mentioned some FCC approval things and that got an email thread started between my consultant pal Dave Mathis, who has already weighed in on FCC requirements here and here. Then Howard asked his pal Scott Proffitt to chip in. Scott runs an EMC approval lab and was kind enough to clear the air.

The first lesson is that I have been too cavalier in my terminology. Saying “FCC certification” is different than saying “FCC approval”. Dave Mathis kept calling me on this, because we were talking orthogonally. Dave was thinking about radios and I was thinking about computer equipment. Understand that a radio is an “intentional radiator” and it gets its own section in the hundreds of pages of rules. A computer without a wireless system is an “unintentional radiator”.

Dave would get exasperated with me when I would say something “…needs to get FCC approval”. To him that sounded like I wanted to get a TV station or some other licensed use where you need FCC permission to operate. As Dave keep reminding me, Zigbee and Wi-fi are unlicensed. That means the end user does not need to ask the FCC for approval to use the device. It does not mean there are no rules and you can just build anything you want and sell anything you want. Dave does note that you are allowed to build 5 units for personal use, but prototypes for a salable product are not personal use, so you need to worry about the FCC right from the start. Dave reminded me of the $10,000 per device penalty if you exceed the FCC limits on your Gizmo.

So let’s get Scott Proffitt to clear the air about what FCC things you need with what gizmos:

“It all depends on the type product and category it falls under.”

“FCC ‘Certification’ is intended for all radio transmitters (Intentional radiators) per FCC 47 CFR, Part 15, Subpart C, Section 15.201.  Certification is also required for Scanning Receivers, Radar Detectors and Access BPL and is an option for TV interface devices, personal computers, computer peripherals, personal computer mother boards and supplies and all other receivers except TV and radio broadcast receivers per FCC 47 CFR Part 15, Subpart B, Section 15.101.

“FCC ‘DoC’ [Declaration of Conformity] is required for Cable System Terminal Devices and a personal computer employing certified components.  A “DoC” is an option for a TV interface device, personal computer, PC peripheral and all receivers except a scanning receiver and broadcast receivers.

“FCC Verification is for everything else, that is not captured above, to include broadcast receivers and all other digital devices.

“The above categories have two classes.  Class B is intended for residential environments… including apartments, nursing homes, etc… any living situation.  Class A devices are anything that is not Class B.  Class A would be office environments, commercial, retail, public areas that are not residential areas.

“Now, given all that… there are some exceptions and exemptions, laboratory equipment for example, as long as it’s not a radio transmitter.  These are too many and too complex to list.  So at this point we ask what the device is and what it does and see if any of the exemptions apply.”

Now in the context of the solenoid circuits Howard Evans and I were talking about, I asked if you would need FCC anything if you used an Atmel chip and did not bring the oscillator out to any pin. I thought I was being clever and beating the FCC requirement that you have to test and self-certify (using Scott’s lab or equivalent) anything with a clock that runs faster than 9kHz. This is a big deal, the fact that anything with a clock frequency over 9kHz falls into the perview of the FCC rules. Dave parsed the FCC rules and told me that even a clock internal to the IC will still require testing. But Scott Proffitt chimed in with the reminder that testing is only needed for end user equipment:

“Your last point of discussion regarding your and Dave’s pondering on the chip… I think if I understand it correctly, this chip is a component not to be defined as an electronic device requiring FCC approval.  The end user device that the chip will be integrated within, will be subject to FCC rules, but not the chip itself.  The end user device is where all compliance requirements should be applied.  (There is the exception for modular components of a system, such as components for a PC per Part 15, Section 15.101 where those components require authorization.)“

“If the intent of the question may have been regarding what sources should be considered in determining the maximum Radiated Emissions measurement frequency, then you are correct, it is above the threshold and the end device the chip is integrated in, would fall under the FCC requirements for testing and approval.”

So this means that the certainly the chip itself is not tested, but if you make a solenoid driver board that is for sale to companies that integrate into their equipment, then you don’t have to test it either. But both Proffitt and Mathis agree that just because the 32kHz in internal to the chip and does not appear on any pin, if you do sell it as part of an end-use device, you still have to test it. Howard Evans had some advice as well, and note how he too got confused when I used the term “FCC approval” instead of FCC verification”:

“Well as long as you are not an intentional radiator of RF you do not need FCC approval.  By law you are still required to meet FCC limits for emissions, but you can test this yourself or go to a compliance lab.  If it is later found your emissions are too high, the government could force you to pull your product from the market.  In practice, you can get away with radiating too much as long as it doesn’t interfere with enough people to garner the FCC’s attention.   That said, you should be a good citizen and not pollute the RF spectrum.  Your IC will radiate some, but it is usually the traces from a bad PCB layout and the cables that radiate the most.  If you keep your edge rates no faster than necessary and keep your signals well coupled to their return paths (i.e. follow good EMC design practices), you will be well on your way.”

Making your devices FCC compliant is being a good citizen. I note that the engineers who seem to care most about this are also ham radio operators who want to keep the radio spectrum clean of unwanted junk.

This graphic points out mis-designed CE logos. More serious is when a wireless system just forges an FCC number for their product.

And although I have been talking about FCC compliance, getting world-wide approvals under CE (Conformité Européenne) is similar. Howard Evans notes those are even tougher:

“I am by no means a certifications expert and being that my background is in industrial equipment, I can only speak to how we deal with the FCC in relation to our class of equipment which is to say we do not deal with the FCC at all. So I was incorrect in saying that as long as the device is not an intentional radiator, it does not need certification.  That is only true for my situation.  It is safe to say that unless your device falls into an exempted category, it does indeed need FCC certification for sale in the US.  Sorry for the misinformation.”

“We perform emissions testing to CE levels which are stricter than the FCC’s, so we give no mind to passing FCC limits.  Yes, when doing emissions, we must operate the device in its intended worst case scenario (highest expected emissions state for standard use).  So the cycle rate and duty cycle that you operate the solenoid will have a dramatic effect on your average and quasi-peak readings.

“We test at only one distance, usually 3 or 10meters depending on the size of the test facility’s semi-anechoic chamber or OATS [Open Air Test Site].  I believe the standard for the class of equipment we test to (CISPR 11) allows us a choice of distance as long as you adjust the limits accordingly.  I don’t have the standard in front of me so I may be incorrect and that it is a device class standard that allows us to do that.  CISPR 11 is a generic standard that applies to industrial equipment in general but there are device class specific standards that override parts of the generic one.  You should consult with a competent EMC engineer to determine which standards apply to your product.”

I noted that some engineers dither the clock frequency to spread out the interference. This does not really lower the interference, it just looks lower since the spectrum analyzer is sweeping a narrow bandwidth as it tests so the dithering just gives a lower reading, it doesn’t really make the interference go away. Evans, agreed, pointing out,

“Dithering is certainly frowned upon by most engineers I know because, like you suggest, it doesn’t really lower your emissions.  It just spreads them out and takes advantage of the fact that testing limits pertain to average and quasi-peak measurements, not peak measurements.  It might lower interference if the victim equipment is susceptible to only a narrow band within the dithering band.  Without dithering, the polluting equipment could be radiating continuously in that band causing continuous interference while only some of the time with dithering, but is interfering some of the time really acceptable?  It really depends on how well the victim handles the interference, but practically I’d rather just lower the total emissions than play games with the test method.  But that said, it is a tool which you can use if needed.”

“With PWM circuits like this and assuming the PCB layout is solid, it really comes down to containing the edge rates on the signals leaving the board.  It is hardly the switching frequency that bites me, but the edge rate of all the signals.  I always use gate resistors on my MOSFETs to slow the turn-on and turn-off which has worked well for me in the past.  It does increase the switching losses some but not too much if the resistance is reasonable.  I also usually add some capacitors between the outputs and the rail to divert the high frequencies back in to the driver.   “I also often add a common-mode choke (either ferrite or wound) for the common-mode noise which radiates very well from your cables given the miniscule currents involved.  Cable design is critical.  I always use shielded twisted pair with the shield bonded (360 degree is best) to the metal enclosure of the driver.  The shield limits E-field radiation while the twisting helps lower the H-field in the far field.  It helps too if the coil is in an enclosure with a decent RF ground.

“Finally, I would encourage you to keep the cable distance as short as possible.  There can be some very high voltages (3X the bus voltage or more) that can develop along the cable that can surpass the insulation rating of the cable and/or the magnet wire of the coil.  This has been well written about with regard to variable frequency motor drives.  This is probably not an issue for you unless you run the bus from rectified line.”

Howard Evan’s comments about cable length reminded me of a problem I had with CE immunity when I was a consultant. Many engineers are finding it is tougher to pass immunity than emissions. Immunity testing is when you bombard your machine and its cables with RF and verify that it does not malfunction. I will tell that story in a future blog post, since Evans also points out: “I’ll comment on immunity in a future email.  I just went through a somewhat difficult issue with that.”

The 1955 Heathkit 500V PS-3 power supply

New York engineer Reginald Neale recently sent pictures of his antique and unusual electronic collection. So I figured it would be a great idea to feature one of his interesting gizmos for our #ThrowbackThursday blog.

Here is Reginald’s Heathkit PS-3 500-Volt power supply. Neale notes, “Heathkit. The Big Name in build-it-yourself electronics. I built this one in the late 1950’s.” After getting this image from Reg, I found a scan of the spec page on the internet, and used the fantastic ABBYY FineReader OCR (optical character recognition) to change it into text:

                  SPECIFICATIONS
Output............................Continuously variable from 0-500 volts, 
                                   no load
Regulation, Line Voltage 117 volts AC: Linear 0-10 MA at 450 volts output < 0.5%
                                              0-20 MA at 400
                                              0-40 MA at 350
                                              0-70 MA at 300
                                             0-100 MA at 250
                                             0-130 MA at 200
Line Variation 105-120 volts..........Output variation less than ±2.0%
Meter.................................4 1/2" streamlined case
      Sensitivity.....................1 MA full scale
      Range...........................0-500 volts DC, 0-200 MA DC
Tubes.................................1 - 5V4G Rectifier
                                      1 - 6X5GT Rectifier
                                      2 - OA2 Regulator tubes
                                      2 - 1619 Control tubes
                                      1 - 6SJ7 Control Amplifier
Power Requirements....................105-125 volts 50/60 cycles AC 90 watts
Dimensions............................8 1/2" high x 13" wide x 7" deep
Shipping Weight.......................17 lbs.

Neale points out: “Heathkit was famous for their easy-to-follow manuals and large, detailed pictorial instructions.”

There was a nice schematic on the Sal’s Antique Radios site. Note how the unit makes 6.3V to power the filaments of any tubes you have in your circuit, as well as the high-voltage output.

The Old Tube Radio Archives had this nice interior shot.

The same site had this shot of under the chassis.

The RadioMuseum site has a page on the PS-3 as well. It a heck of supply, putting out 500 Volts, enough to bias up tube circuits. Be sure to read up on how my mentor Bob Pease made a low-noise 300V supply. Both Reginald and Bob go back to the day when your lab supply could kill you.

Here is an ad from 1955 that Reginald scanned for your enjoyment (1.2MB pdf). Heathkit-ad_1955