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General Chat / Re: Painting that shred itself
« Last post by ebastler on Today at 05:06:40 pm »
At 0:16, they really know how to do these videos.

Ouch... Where's the smoke?
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Test Equipment / Re: Digilent Analog Discovery 2
« Last post by 2N3055 on Today at 05:06:34 pm »
Is there a built in functions for trend plotting...say power energy voltage, frequency, pulse width, AC voltage etc....say for example you want to monitor over a much longer time period?
Logger window is standard.
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That beast looks like it would be a blast to fly.  I wouldn't want to have to feed that PT-6, though!   :o  Turbines are rather thirsty buggers unless you get up really high with them.

-Pat
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General Chat / Re: No more free shipping from China to USA?
« Last post by ebastler on Today at 05:00:30 pm »
The subsidized chinese postage only applies to certain products and sellers, the average person on the street in china still has to pay the full normal postage costs.

I don't think you got this right. The trick is that the "full postage costs", i.e. the cost to the Chinese mail service for sending something to Western countries, are very low, because they are subsidized. The Chinese mail service only has to handle the transport to the destination country or region (via low-cost bulk shipments). The mail services in the destination countries handle the much more expensive distribution to the individual recipients. But the compensatory payments the Western mail services receive from China do not even cover their costs.

Looking at all the small operators who sell direct via ebay etc. at very low (or free) shipping cost, apparently the attractive shipping rates are generally available to Chinese senders.

Quote
For international courier services, this is much the same as we pay in the west.

That may be the case, but I believe these courier services are not covered by the UPU treaty.
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General Chat / Re: Painting that shred itself
« Last post by Siwastaja on Today at 05:00:03 pm »
Banksy posted a new Video with a lot more details about the shredder

At 0:16, they really know how to do these videos.

Some pro multi-level trolling going on.
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What is easier to implement, the analog filters I have an ideal on how to make them, but it is a bit complicated because of the narrow band (or high Q factor).
On the other hand, the demodulator seems easy but I am not knowledgeable in that field
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Years ago, when I was a kid, old radios that were thrown out were tube type with power transformers and there was a rating tag on the back so you knew how many watts the transformer was good for. Almost all these radios had tubes with 6.3 volt filaments except for the rectifiers which were generally 5.0 volt filaments. (The really old TVs had much larger transformers as did some industrial test equipment.) If I took all the ‘E’s and ‘I’s out of the transformers then unwound the low voltage secondary filament windings and counted the turns I could calculate the turns per volt needed when I rewound my windings on the existing primary.  The high voltage windings could be unwound without counting because I already had the turns per volts from the low voltage windings I removed so I didn’t need to count a few hundred more turns of wire.

I would leave the insulating stiff paper on top of the primary winding and also save any other insulating paper to reuse. I would anchor the start of my new winding with sturdy fabric tape and evenly wind the required number of turns for my new secondary, generally putting insulating paper between layers, just in case. The wire size I needed could be calculated from knowing how much total current the tube filaments used and that could be found from looking up all the tubes used in a tube manual. Using a wire gauge I could measure the wire size and look up the circular mils for that wire size in a wire table then calculate the number of circular mils per amp. With this information I could use the wire table to calculate the wire size I would need for my winding. Knowing the wattage of the transformer from the rating tag on the radio would tell me if the transformer was large enough for my needs. For instance, if the tag said 50 watts and I wound my secondary carefully I should be able to wind a 25 volt 2 amp winding on the existing primary. 

There was a 16 volume set of ‘Popular Mechanics Do-It-Yourself Encyclopedia’ from the 1960s or 1980s I had that went into detail on winding transformers that I used back then. There is one reference I found on line that probably goes into more detail than you need at:
 
https://www.electronicdesign.com/power/build-your-own-transformer

but is pretty good. As to the rust on the ‘E’s and ‘I’s you had, I would have just brushed the loose flakes off because as others have mentioned, polishing them could increase eddy currents and heating. Generally the better transformers alternate the ‘E’s and ‘I’s rather than put them in clumps. Some transformers do put all the ‘E’s in one side then lay the ‘I’s across the top and weld where they join but I believe that makes for a higher watts-loss design even though it is cheaper to assemble that way.   
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That is NOT a solid block of gold, its just a thin layer of gold that was electrochemicaly plated on. Such a big chunk of gold would cost a fortune and there is no point in it being solid. Nor is gold the best conductor of electricity. The most conductive metal is silver flowed really closely by copper(hence why we use copper for wires). Gold is the 3rd most conductive element (About 50% worse then copper) and is just slightly more conductive than aluminum.

Aluminum is easily machined into shape, is cheap and light so it ends up the material of choice for solid shielding blocks. While on a circuit board copper is the metal of choice because of its excellent conductivity and the ability to be easily soldered.

So why is it gold then? One reason, oxidation resistance.
Gold unlike most other metals really really does not want to oxidize even in very aggressive conditions. If you plate a thin layer of gold onto a metal object means you use very little of the expensive gold while it makes the metal object immune to oxidation. This is very helpful in anything that has to make a good electrical contact (oxides are not electrical conductive). Additionally gold loves being soldered as much as copper does so gold plated parts solder really well (Even more so due to no oxides). The oxidation resistance also makes gold easy to cold weld, just smoosh two objects of gold together hard enough under the right conditions and they spontanusly stick together without any heat required(This is why chip bond wires are gold)

So why not platinum? It has even better oxidation resistance and can also be soldered to copper. Well.. the electrical resistance of platinum is 6 times higher than copper and it costs a lot more than gold. So you would be paying a lot more for a coating that's just as good as gold or possibly even worse than gold.
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General Chat / Re: Painting that shred itself
« Last post by Urs42 on Today at 04:53:37 pm »
Banksy posted a new Video with a lot more details about the shredder

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Projects, Designs, and Technical Stuff / Re: OLED Noise on Power Rails
« Last post by Siwastaja on Today at 04:51:53 pm »
Am I reading your scope trace correctly? It seems the 3V3 line is browning out between over 3V3 and basically 0V? How can anything work at all?

Given such ridiculously low frequency, and massive amplitude, it's clearly something not typically called "noise", and any sane amount of filtering won't work. Sounds like something is taking too much current (the display shorting out?) and the supply regulator is hitting the current limit and shutting down?? Or you have a loose wire / contact issue with tens/hundreds of ohms of resistance somewhere, so that the normal, slow load changes that can't be supplied by the bypass caps cause massive voltage drops?
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