That's what my thought of "adaptive zener" was implying. We don't have timing information, but a large capacitor charged "on-the-fly" to a value of VDD might be made to work. ...Jim Thompson
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Spice is like a sports car...
Performance only as good as the person behind the wheel.
I've had a bunch of management level book but gave them all away. They aren't all that relevant for the technical sector.
Nah, I think the author is wrong. At least when it comes to technical consulting. Companies use us just like people use doctors. They go there only when it hurts and in over 90% of cases the outcome is that it eventually doesn't hurt anymore.
Now when it comes to legal or financial stuff, well, that can be different. I have seen some rather blatant unprofessional behavior in that area. Sometimes to the point where it almost made me sick and I simply took over.
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I don't see any fatal flaws in John's zener-comparator circuit, but also worry about the tight voltage tolerances.
I still prefer the current-sensing approach above. R4 senses the current flowing out of terminal B, which avoids the problems of absolute thresholds, lets A drive B to GND, and truly senses when B is being driven, avoiding latchup.
I simulated a transistorized version of this--the approach works. Capacitive loading on B must be watched, otherwise R4 will sense current when A goes high. If problematic, you could control A's ramp time...if that delay's okay. (We haven't been told how fast this thing has to be.)
Another possibility: dusty old 10KH MECL-TTL translator chips + interface stuff.
Interestingly, the author specifically excludes engineers and other people who actually build stuff, presumably because our stuff works, and whether is works is not generally a matter of opinion.
Turns out, I just learned accidentally, that I2C buffer chips sometimes use a similar scheme, in that their outputs only pull down to, say, 0.4 volts, and they use a comparator at 0.2 to detect a hard low coming in from the other guy.
Then maybe he is doing what many other management book authors do, stating the obvious. People who haven't been born yesterday probably know which professions are full of quacks, and engineering isn't one of them ;-)
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Problem with I2C is, that bus requires such tricks and with an increasing fanciness level there is a rise in hardcore hang-ups. I've seen some when the only thing that helped them snap out of it was a hard power-cycle.
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Yes, and it was the first post that had it: you feed a current source Ibias to node A, connect node A to node B through a zener (for accuracy, probably a TL431 programmed chip), then current-sink exactly Ibias from node B.
So, for any signal that stays below Ibias, node A and node B are going to have a fixed voltage offset, exactly as though they were battery connected. If the source and sink currents are accurately matched, neither node A nor B gets any stray current injected, as long as the nodes are in the compliance range of the source and sink.
One other use for this, is some kinds of chip don't have input offset adjustments; transconductance amplifiers, for instance. You could connect a Wheatstone bridge to the 'virtual battery', with one pair of legs being fixed resistors, the other pair being a potentiometer, and get +/- regulated voltage source that could be connected in series with an arbitrary signal.
Because of the nature of my work I deal with both professions quite a lot. In medicine mostly cardiologists. They sure know their turf well, are very hard workers and lots of people wouldn't be here anymore if it wasn't for them.
Physics folks usually have a Ph.D. and sometimes a bit much of an academic background. Meaning things can take longer than what you and I are used to. Still, all the ones I have ever worked with are very methodical guys and can go to the ground of just about any technological issue. Quite frankly, when a semiconductor or MEMS process goes off kilter I wouldn't want to be without them.
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The quack density is higher in the more (ahem) public-policy related areas, I think. There aren't so many among the experimentalists and gizmo-builders, for the same reason as the engineers. (Though I've had recent experience with some fairly crappy ones, two of whom managed to talk themselves into very senior positions on the basis of no expertise that I could discern--no technical expertise, anyway.)
In their defense, most of the cracked physicists I've met believe their own stuff. There are some real crooks--some in the climate world come to mind, as well as Jan Hendrik Schön at Bell. However, the Dawkinses of this world appear to really believe that they're infallible and that everyone who doesn't do their bidding is a fool or a knave who should be crushed. They're just suffering from some grandiose personality disorder (or as the Greeks would have put it, hubris).
In physics, besides the climate folks, there are the string theorists, who have been theorizing for 20 years or more with zero data to confirm or falsify their calculations, yet still call what they do 'physics'. The moral character of this is unclear, I think--it really depends on what their supporters think that they're buying. If the customer is okay with it, then fine, though personally I wish they'd call it something else.
Then there are the ones who write popular science as though it were SF--using the wildest speculations to sell books, never mind how they confuse the public and damage everyone's confidence in real science. This is often done to try to use their scientific prestige to foist their other opinions on everyone, in areas where they have zero actual expertise. Examples are Shockley's eugenics, 'quantum logic', multiverses, and Hawking's theology.
Physicists are almost all shockingly bad philosophers and theologians, because they're taught to use leaps of intuition supported by very sloppy math and relying on Nature to correct them via experiment. ("Brilliance", it's called.) ;) In philosophy and theology, once the data comes in, it's too late--just ask the Germans and Russians, not to mention numerous examples closer to home. To get anywhere good in philosophy and theology, you have to be very careful, and you have to have deep respect for, and knowledge of, the history of thought.
Of course, being wrong at the top of your lungs is easier and more fun, especially when you don't care much about the consequences. It's also far less work and it pays much better.
Cheers
Phil Hobbs
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Nope, it's not (far). I2C isn't my favorite bus. It's often flaky, needing such hacks. SPI is far more forgiving. Easier to bit-bang or build into an FPGA, too.
Sadly, we have a european customer who uses I2C all over the place. Not just on boards, but between boards, in what is potentially a nasty EMI environment. We're just about to jump, literally, into the middle of the system.
That's scary. We have an I2C bus that goes between boards, too. That 4311 is in there for a reason. :-(
Device manufacturers love to violate the specs, too. Our LCD controller insists on being address 0, even though that address is reserved for broadcast transactions. Yep, our codec listens to broadcasts.
I hope you don't need it, but you easily might. The NXP PCA9540 or PCA9542 I2C Bus Muxes are also a handy critters for interboard I2C kludges.
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