Electronics > Projects, Designs, and Technical Stuff
EMF pickup from amplifier in I2C line causing glitches. (Now with scope trace!)
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Starlord:

--- Quote from: T3sl4co1l on July 05, 2016, 03:10:06 am ---If the answer is no, then as the movie said: "the best decision is not to play".

--- End quote ---

Imagine if Steve Wozniak had taken your advice when he was building the first Apple in his garage.  No Apple.  No personal computer revolution.  No "How about a nice game of chess?" 

https://en.wikipedia.org/wiki/Ribbon_cable


--- Quote ---Around 1980, the U.S. Federal Communications Commission (FCC) discovered that ribbon cables were highly efficient antennas, broadcasting essentially random signals across a wide band of the electromagnetic spectrum.[citation needed] These unintended signals could interfere with domestic TV reception, putting "snow" on the screen. The FCC issued edicts and injunctions to the personal-computer industry, restricting the use of ribbon cables to connect devices together.[citation needed] "Naked" ribbon cable could be used inside the case of a computer or peripheral device, but any ribbon cable connecting two boxes together had to be grounded. This rule led to solutions such as ribbon cables covered by a copper-braid shield, which made it impossible to see or separate the individual connectors.

--- End quote ---
T3sl4co1l:
I don't see your point.  Essentially no commercial systems from that era exist that aren't covered with heavy metal shields!  Early prototypes, perhaps, but how many of those were sold?  Were they recalled?  Disposed of?  Repaired?  At whose expense?  Such less-than-proud history is unlikely to be found in a company's public history file.

If anything, I'd say the FCC ably performed the job they're charged with.  Though it's not clear how long it took them to crack down.

(Also, that's a nice paragraph, but the [citation needed]s are kind of a shame.  I'd love to see some articles about that.  That'd probably require digging through a lot of old, non-internet-accessible records, though..)

By the way -- you're sort of implying that it's okay* to break federal rules.  Which, against a different part of the federal code, is no different from suggesting that, say, drug lords are just as entrepreneurial as Woz.

Which, under some cases, may be no less true (though, much less publicized!).  In fact, I don't doubt at all that there are some quite skillful players in that market.  But that makes it no less illegal of an act.

And suggesting to others, that such action is worthwhile, is often just as criminal.  (I kind of doubt that the FCC has "conspiracy to transmit illegal emanations" in the criminal books, but it would certainly be irresponsible of anyone else to follow such advice.)

*Financially, legally, or otherwise.  This is a legal argument only.  I'm not getting morals involved here, whether the act itself is moral, nor whether the laws are.

Tim
Someone:

--- Quote from: T3sl4co1l on July 05, 2016, 06:08:21 am ---I don't see your point.  Essentially no commercial systems from that era exist that aren't covered with heavy metal shields!
--- End quote ---
To be fair Apple did sell a disk drive connected with a rainbow ribbon cable:
http://ca.meron.cc/post/disk-ii/
'78 copyright '79 date codes
But they changed to round shielded cables in future external interfaces.
dmills:
Here https://e2e.ti.com/support/power_management/simple_switcher/w/simple_switcher_wiki/2243.understanding-measuring-and-reducing-output-voltage-ripple is a decent discussion of measuring high frequency stuff in switching power circuits. Note in particular the improvement when using a very short spring clip rather then the hopeless three inch wire with croc clip (The things are ok for strictly audio band measurements, but forget it for anything with RF involved).

Switch mode power devices like the one TI show above have much in common with class D power amps.

As to why the high speed stuff breaks the low speed I2C bus, it is down to the noise coupled into the I2C lines close to the transition threshold causing the slowly rising I2C signal to cross the threshold multiple times, the fact that I2C is only specified to 400kHz does NOT mean it is immune to energy a decade or so faster then that.

What is your board stackup, and is it the same as the TI eval board for the power amp? IME such things need to be on at least 4 layer boards to work well because you need a solid ground plane to stand any real chance at all.

Regards, Dan.
Starlord:

--- Quote from: T3sl4co1l on July 05, 2016, 06:08:21 am ---I don't see your point.  Essentially no commercial systems from that era exist that aren't covered with heavy metal shields!  Early prototypes, perhaps, but how many of those were sold?  Were they recalled?  Disposed of?  Repaired?  At whose expense?  Such less-than-proud history is unlikely to be found in a company's public history file.

--- End quote ---

As Someone pointed out, they did indeed sell drives with exposed ribbon cables commercially.


--- Quote ---If anything, I'd say the FCC ably performed the job they're charged with.  Though it's not clear how long it took them to crack down.

--- End quote ---

Well going by the copyright date Someone listed, and the date the Wikipedia article states they took action, then it sounds like they got away with it for 2-3 years, assuming they weren't forced to immediately change their design.


--- Quote ---By the way -- you're sort of implying that it's okay* to break federal rules.  Which, against a different part of the federal code, is no different from suggesting that, say, drug lords are just as entrepreneurial as Woz.

Which, under some cases, may be no less true (though, much less publicized!).  In fact, I don't doubt at all that there are some quite skillful players in that market.  But that makes it no less illegal of an act.

--- End quote ---

Well, I have plenty of arguments to make regarding that:

Consider Uber, AirBNB, and Paypal.  And all those handling bitcoin.  All businesses which were/are outright illegal under current codes, or whose legality was in an extreme grey area.  These companies exist and are worth billions because the people running them didn't let a few pesky laws deter them.  They got big first, and then forced the law to change, or changed their businesses after the fact to become compliant.  And the early bird gets the worm, so even though some big retailers decided they wanted to get in on running their own electronic payment systems, it's now too late.  And it's too late for anyone else that wants to run their own ride sharing or crowdsourced bed and breakfast service.

Now add Segway and all those electric scooter/skateboard/hoverboard companies.  All selling products whose use, under the law as written, are illegal.  Could they be held liable for selling devices which count as motor vehicles which they know can only be used illegally, and to kids no less? Perhaps. Of course the flip side of this argument is hoverboards, which due to no care being taken at all in their design caused a lot of fires and bad press, and while I wouldn't advocate putting out an unsafe product, those companies did make a lot of money by rushing a product to market when that fad was at its peak.  Money they wouldn't have made if they'd waited around to make sure their products were perfect.  And to be fair, the problem wasn't so much with the design being rushed, but rather using recycled or out of spec lithium cells.   

And speaking of electric vehicles, let's add drones to the mix. The FAA would love to make them all illegal, and we might have seen a similar fight with them, if it were not for companies rushing millions of them onto the market faster than regulators could react.  The FAA is trying to get people to license the things, but we all know they're only going to succeed in getting the professionals to do so.  Joe Q. Public who got a drone for Christmas can't be bothered registering his new toy. 

Want to add drugs into the mix?  Okay, let's talk about alcohol and pot.  Both outlawed.  Both made legal (or in the process of it) only because people rebelled for years and used them anyway.  And if they hadn't, the government would have had no reason to change the law, and the public pressure wouldn't have been there to make them. 

So how does any of this apply to meeting FCC / CE regulations? 

Well, if the US / UK wants to remain a competitive player in a global market, in a world were more and more people, like me are able to design and sell electronics online, people who, like me, can't afford to spend over $14K on testing alone (https://www.quora.com/What-is-the-average-cost-to-get-FCC-and-CE-certification-for-a-very-simple-electronic-gadget), and where competition from China and Hong Kong (and soon India), aren't bound by such pithy things as regulations, and who have their shipping costs subsidized by the government on top of that, then regulations are going to have to change.  If the FCC wants products to be tested, then the government, not the small business owner, should bear the brunt of those costs.  And regulations, which are clearly too strict, because even with all those billions of untested products coming in from China the world has not devolved into chaos, need to be relaxed.

Do you think Adafruit and Sparkfun got big by rigorously testing every device they sold?  Of course not.  And why should they, when their parts are just going to be stuck in people's art projects or whatever with wires going everywhere and no attempt at shielding being made?  Now, legally, they might be in the clear because those items are classified as electronic kits, but speaking from an ethics standpoint, is what they're doing really any different from releasing a finished product that you know is going to emit EMF?  I would say not really.  The end result is the same, whether someone has to solder the battery holder and neopixels onto their blinky shoe thing or not. 

The long and the short of it is that in today's economy one needs to be willing to take risks and bend/break the rules if they want to be successful.  Even Oculus took a huge risk when they launched that Kickstarter campaign, because even with billions of dollars from Facebook they're still having trouble delivering such a complicated device.  I have no doubts that Palmer Luckey would now be branded a failure and a fraud if his campaign had only just met its funding goal and/or someone with deeper pockets hadn't come along to help out.  But if he hadn't taken that risk, he wouldn't be worth $700 million dollars today, would he?
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