fiddled filter design

e.g. Apple Computer didn't get off the ground initially because Woz over-engineered the Apple II's floppy drive, it was stripped-down.

Numerical optimization can be good, absent getting trapped in a local maximum, but you need an idea to start with, and you have to be careful that the sim han't missed a far-away, better solution.

Once you have a good idea, there are various ways to optimize it.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

That half-bridge config can have an interesting effect driving inductive loads: it can take current from one supply and pump it into the other. The victim rail can be pumped to a very high voltage.

We're using the TPA3251, which is a full-bridge class D amp. It's under the heat sink, left side. It seems very well behaved.

Yes, that is a custom transformer. Sometimes you have to do that.

The little Talema ISDN transformer couples the voltage across a shunt into the uP ADC, so we can compute and report the RMS output current.

Air enters the bottom of the box and gets exhaused from the top part with a small fan. The notch in the board directs that air flow over the amp.

We're seeing some 600 KHz ripple in the output, so we may hack in a parallel LC trap or something.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Exactly. 30 watts, 250 Hz to 5 KHz, is enough for anybody.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Parts are cheap, but we try to minimize the number of different parts on a BOM to make pick-and-place setup easier, minimize the number of reels that have to be mounted on the machine. That becomes a game, and it's a little dangerous to use r-packs whose value can't be changed.

Yes, I trust the Spice simulation of a 10 KHz lowpass filter, so the risk there is basically zero. Other things can't be trusted, so we need to leave hooks for tweaking, or breadboard, or something.

I started with a 3-pole, 2-opamp filter, using values from TI's old Filterpro program. (The new version is terrible.) Then I eliminated the first opamp by scaling the resistors, and split the first resistor to add one pole, and tweaked all that in LT Spice.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

John Larkin wrote

Nice board, maybe better put the heatsink on the back?

Note the link I have to my old audio amp TDA7294, is an analog amp, was discussed here long time ago, it seems there is a follow up 'A'? version that is not so stable. Anyways after years of abuse, driving big transformers, capacitive loads (piezo), all sort of speakers, it is just my choice if I need some power to test something. You say your amp broke down, I have the same experience with the TDA7492 class D 2 x 50 W amplifier from ebay:

It died within a few days, do not even remember what I did with it, tiny inductors it has.

And the ripple indeed, not something you want.

Of course class D is more efficient, but then if you need a new amp every few weeks it is not :-)

Lemme see:

Still, if you use a Raspberry Pi, and WiFi, somebody (not me, I cannot write Android apps) could write an app to control it... seems these days everybody wants that, sales argument, and not class D with all that RF.. And then you could have it play 'star spanked? banner' or what was it? Or connect a monitor and play packman on it. That sells.

Sorry, late here, need sleep. :-)

That's a problem with class-D switchers; not a problem with linear amps. But linears can have huge power dissipations driving inductive loads, which puts them into funny quadrants.

The TI class D part has its power pad on the top side. That heat sink arches over the chip and contacts it on top. We don't have room below the board for the heat sink.

The Gone Guy used

MONOLITHIC POWER MP7782DF-LF

which blew up any time it was in the mood, which was always.

I got the TI eval board and abused it some. Never blew it up. It seems solid.

Our aerospace customers wouldn't like an RF link. They are paranoid about any possibility of transporting any data out of a secure area. If our products have any nonvolatile memory, there has to be a switch to disable it so they can use it in secured areas.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

I recently found a nice ADC that's $1100. And some FPGAs around $70,000 each. We might pass on those.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

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That's not what it says at all. The simplest idea that fits all the facts i s always the preferred idea, but one single non-conforming fact can force y ou to look for new ideas.

John Larkin designs things which he thinks are original, and they work well enough to satisfy his customers.

Being critical of "new" ideas is an essential part of science. A lot of the ideas that John Larkin floats aren't original, and have long since been sh ot down.

Whether or not an idea is "boring" has nothing to do with whether it is rig ht. Nothing could be more boring than the fact that sun rises in east, but that's no justification for being hostile to the idea that it's going to do it again tomorrow.

We do understand how some single cell bacteria work, and we've even made a simplified one that still works

ynthetic-life-1.19633

Human "consciousness" needs to be better defined before we can hope to unde rstand it, though there's a argument that the idea of human consciousness i s essentially a defect in the language we use to describe it.

If we were forced to express the idea in one of those program definition la nguages (like Z) which can let you formally prove the correctness of the pr ogram whose function has been defined in that language, you might find that "consciousness" was a undefinable delusion.

None of this is any kind of denial that amazing things remain to be discove red.

The kind of rubbish that John Larkin will believe in - climate change denia l comes to mind - doesn't suggest that John Larkin is a good guide to the n ew and credible. He looks more like a gullible twit.

--
Bill Sloman, Sydney

We get that now with the debate ofer genetic modification done to humans, and with eugenics and various pogroms and massacres.

No, it'a logical method.

And that's unrelated.

The simple explanation is sufficient until it is shown to be insufficient. We still teach Newton's laws of motion knowing them to be wrong, and most architectural projects assume the world is flat.

I don't see how that follows, can you explain?

--
  When I tried casting out nines I made a hash of it.

Only to an absurdist.

why? Can you give an example? What science would not get done?

Is this merely a claim of adequacy, or do you intend ths as evidence of something, if so what?

a new idea that does the exact same ting as the old idea but is more complicated is useful only for entertainment.

--
  When I tried casting out nines I made a hash of it.

Quantum mechanics. It's so much more complex than classical physics.

That ideas that are correct aren't automatically the simplest ones. That Occam's Razor is not correct by recursion.

Not if it's right.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Umm, speak for yourself on that one.

Michael Behe is a biochemist. He wrote an interesting book

in which he makes a pretty good case that there are biological, specifically biochemical, mechanisms that could not have evolved in any way that we can explain.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

If it's not right, it doesn't meet Occam's requirements. Occam's Razor just suggests that given two answers, the one with the fewest assumptions is probably the right one. Occam's razor is just a suggestion not a natural law.

Bear in mind that most standard filter design approaches don't treat the impedance of middle nodes as variable. I.e. you can have a stage that filters but transforms up or down to a chosen impedance point (other than what is normally used for that topology), as long as something later transforms back down to the target impedance. It seems that creates a few new variables over which to optimise, compared to the standard approach, and can be used to match standard part values.

Isn't an absorptive filter just a diplexer with one port terminated? That is, two conjugate filters whose paralleled input impedance is flat?

Clifford Heath.

You believe this, yet you have precisely zero evidence for it. Do you believe in unicorns too? Why not? There's no more evidence for one over the other.

There will always be things we don't understand. That doesn't matter. What matters is that we believe only things for which we have evidence, and we investigate things we observe which don't fit the theory.

Nonsense. If there is no evidence that the simplest possible solution is wrong, then to imagine a more complex solution means to believe in the existence of something that *has not been observed*. That is, to simply make shit up sight unseen, like religionists do.

Scientists are always happy to investigate unexplained phenomena, but not inscrutable causes.

You really don't know the first thing about me then, do you?

Of course they do. Quite enough to be getting on with in fact, without having to invent unobservable things.

Clifford Heath.

John Larkin wrote

Yes I did not mean that sort of parts, unless it cannot be avoided.

More like protection ciruits and control loops. Just added an other fuse and diode to my lnb_reference, just in case somebody plugs in external power and uses POE at the same time.

John Larkin wrote

sigh, wiring is actually also ... So PICs are out? I assume you mean SDcards and other user writable stuff, even to configure an FPGA you need FLASH. Everybody already knows everything these days, they use ESP, advanced neural nets that read what is playing in your brain.

Take that Boeing that went down last week or so, from what I did read first thought was: HOW can a plane fall out of the sky? Stall! Must be air speed sensor again....

You did not?, no you did not. I mean save on spare parts, backup systems, I mean essential ones, gimme a break.

A 10$ GPS would have given them true speed to ground. And so much for autonomous ...

Occam's Razor is not a formal mathematical logic principle, but an economic one. It's not 'that you can imagine', it's the simplest hypothesis that FITS THE OBSERVED BEHAVIOR that is of interest.

After all, one can explain a wonky risetime by a succession of miracles occuring near the edge... but we can also explain it by known capacitive effects. Which is simpler, because it doesn't introduce new principles, but relies on the old established ones. Following Occam's Razor keeps you from following up on the pixies-did-it theory, and that's good advice.

It's odd, that you could even imagine that science can be stopped in its tracks by good advice.