Recent Posts

1

Test Equipment / Re: Hacking the Rigol DHO800/900 Scope

« Last post by shapirus on Today at 06:54:10 am »

Damn that's great. It will be a crime not to share

BTW, it's better to keep decompiled sources in git rather than an assembled .apk -- for the very purpose of VCS, that is, to keep history, to be able to see diffs, to be able to cooperate with others via forks and pull requests.

Please consider this.

2

Projects, Designs, and Technical Stuff / Re: Heated Ferrite == Useless Ferrite

« Last post by Berni on Today at 06:53:25 am »

Airgaps are very important in ferrite transformers.

The ferrite saturates much faster than classical iron lamination while having a high permeability. So airgaps have a larger effect on the behavior of a transformer.

Transformers designed for forwards converters or gate drive and similar typically have no air gap as they are not meant to store energy, just pass it on instantly. So for these transformers it is important to assemble them as tightly as possible to avoid creating an unnecessary airgap, otherwise the transformer might not reach the designed inductance.

Transformers designed for flyback converters and similar do tend to have a precisely designed intentional airgap. They are designed for storing energy between switching cycles, but ferrite is fairly bad at this, so they introduce an airgap to provide a place to store the energy. While this does reduce the inductance, it also increases the saturation current by a lot. The size of this airgap is carefully designed to make a good compromise of both. If you remove the carefully designed in air gap then the transformer might just saturate when used in a flyback topology.

3

Test Equipment / Re: Choosing between entry-level 12-bit DSOs

« Last post by Fungus on Today at 06:47:13 am »

Since we are so far off topic, I guess it's okay for me to ask an incidental question. While all this conversation is quite interesting and instructive, I'm curious how many people actually use or need bandwidth or sampling beyond 100 MHz and 312.5 S/s?

This is a very good question.

Even at 100Mhz the probing method and all those little cables on your breadboard will dominate any measurement and you need knowledge/experience to interpret what's on the screen.

Presumably, anyone working in comms, but who else? My thought process when buying the DHO800 was that even with 4 channels operating, I still have enough sampling to adequately cover the 100 MHz capability of the scope with the 150 MHz probes being well clear of having any attenuation effect at 100 MHz.

You have to be slightly careful here because the measured bandwidth of the Rigols is much higher than what the label says.

In reality the "70Mhz" model has 125Mhz bandwidth and the "100Mhz" model has 200Mhz bandwidth.

The probes have also been tested and are good for both.

My $0.02:

You could easily argue that "125Mhz" is the optimum configuration for a DHO800 and that it's as much as a hobbyist needs.

I wouldn't disagree.

As noted above: Probing dominates, even at these "low" frequencies.

eg. The difference between "probes" and "springs" is huge and I hardly ever use the springs (they're a pain in the ass).

I admit I usually have my DHO804 set to "200Mhz" because ... well ... I'm not sure. It's a head thing, I don't believe there's a practical difference for me in my "Arduino" work. The difference on screen is tiny and mostly swamped by probing (see above).

I'm not saying that nobody needs the extra 75MHz but you have to be into coax cables and 50 Ohm terminators to take advantage of it. If that's your case then fine. People who poke handheld probes at circuits? Not so much.

(I also think "200Mhz" is a very arbitrary number - why does no Siglent owner ever need 300Mhz?)

4

Projects, Designs, and Technical Stuff / Re: Heated Ferrite == Useless Ferrite

« Last post by Kleinstein on Today at 06:15:57 am »

Soft ferrites are not permanently effected by heat (unless you go to the extremes near 1000 C). They however have a relatively low curie temperature and thus don't work as long as they are hot (e.g. > 150 C). This effect is however reversible. The air gap can be a big issue - there would have been a spacer that is not much different from the glue.

In therory there could be flybacl transformers with a permanent magnet premagnetization, that could be effected by heat. However I have not seen such a thing, except for linearity correction with CRTs. So I doubt one would find it in more normal PC supply - though they would do all kind of tricks to save a few cents.

5

Beginners / Re: Why are thermal jumpers so expensive?

« Last post by dietert1 on Today at 06:14:23 am »

Somewhat similar and a possible replacement could be a high resistance SMD resistor, like this: https://www.digikey.de/de/products/detail/vishay-beyschlag-draloric-bc-components/MCA1206MD1005BP100/11196602.
Price is similar, too: 33 cents in 1000s.

Regards, Dieter

6

Projects, Designs, and Technical Stuff / Re: more modern version of tl494?

« Last post by 2strokeforever on Today at 05:28:47 am »

My applications will always be DC input, could be ac or dc out, usually a buck converter.

I could see it being extra complicated to make a multi KW converter cheap, compact, accurate, and efficient.

But for a one off where none of that is a concern had some extremely crude designs work well enough by simply oversizing the fets.

7

Manufacturing & Assembly / Re: Source for small "potting boxes"??.....

« Last post by Smokey on Today at 05:06:01 am »

Why not order from a reputable vendor like DigiKey? “Box, potting” is a type of box you can filter for in the Boxes product subcategory.

 https://www.digikey.com/short/8ttbh7jt

I would actually very much prefer to order from a "reputable distributor".  That is always my first choose. While I appreciate the link to a digikey category, if you had gone to that link you would see that the box configuration I need isn't available.  And while there are a bunch of pages of products, once you get past the first pages the boxes cost like $10+ each.  If I wanted to spend that much money I'd have something custom injection moulded.
This is compared to a random Chinese seller, but with the thing I actually need and a cost of $0.12.

Lose the bad attitude, dude. Newsflash, I’m not clairvoyant. I have no idea what configuration you need — you posted a screenshot with 38 different sizes.

Meanwhile, your original post made it clear you hadn’t even looked at regular sources, since you didn’t even seem to know if the boxes existed as a standard product, something a cursory google search would have shown.

Hah.  All good.  I can't be in a bad mood in a world where I finally know where to buy "Negative Ion Generator Modules".

8

Projects, Designs, and Technical Stuff / Re: How is a motor run capacitor sized?

« Last post by bdunham7 on Today at 05:05:08 am »

I assume these motors run only very intermittently and only for a minute.  Do you know how much current they draw?  These might work OK.

https://www.ebay.com/itm/115457681769

OTOH, if you can get the exact replacement for $30, that might be the way to go.

9

RF, Microwave, Ham Radio / Re: High bandwidth FM signal generation

« Last post by coppercone2 on Today at 05:03:59 am »

guy with 6 posts asking about high power amplifiers and broadband jamming signals what can go wrong?

i like how the first post is basic ass questions made by someone that never used a amplifier before going at 100W, and the next one is about broad band random noise. "heating" in quote marks. I love that one lol. Perhaps its not really heating. What can it be doing? how did someone get into 5g research when something is "heating". does he think we are using double speak or something ? "heating" is such a point of contention with ratings of components in electronics study... it sounds like someone that has no idea WTF their doing. I commonly see components maximum ratings described as being dependent on something thats not related to heat so I will put "heating" like its some abstract complex we came up 

Must be someone from the CB radio community? but those guys would not have a problem understanding heating, after all you just drop the amp in a bucket of water to cool it down.

what a strange uncomfortable user


and before someone smarter then him thinks its a good idea, FM signals are FROWNED upon because it EATS bandwidth. I feel like a spy would like this technology if they think someone is snooping on them

10

Projects, Designs, and Technical Stuff / Re: Heated Ferrite == Useless Ferrite

« Last post by amyk on Today at 04:38:53 am »

Even that link you mentioned shows that ferrites are not affected by the sort of temperatures you're using. My guess is that you are not reassembling them correctly. Even a tiny air gap will have a huge effect.