Recent Posts

1

PCB/EDA/CAD / Re: JLCPCB alters soldermask without any notice

« Last post by KL27x on Today at 02:20:34 pm »

After uselessly poking around the website, I finally found it using Google. Thanks.
https://jlcpcb.com/help/article/592-gerber-files-preparation

They don't even have an extension for what I idiosyncratically call my paste layer. I don't think I've ever ordered a stencil from JLC, come to think of it. It's just in my default gerber CAM job for the occasion I need it.

2

Beginners / Re: LC filtering for combined Vref/VDD of ADC

« Last post by T3sl4co1l on Today at 02:20:15 pm »

I think it's switching noise from a DC-DC converter mainly. No idea what frequency the switcher is running at. I should probably try and analyse it in more detail than I've done so far: that is, poke it briefly with the 'scope and go "ew, that's dirtier than I was expecting".

Yeah, do that.  Then figure how much LC is needed, and if an LDO is still needed to cover the bottom end / save space.

I wouldn't know how to pick an LDO regulator with good PSRR, though. It seems difficult to make comparisons because the manufacturers all give specs according to different conditions. Some give it at 1kHz, some at 100kHz, etc. I'm not even sure what magnitude of PSRR is good. Is 50 dB good or poor? 70 dB? 90 dB?

Oh well they usually give it at DC.  So you get numbers in the table like 60, 80, 100dB that are meaningless.  But you pop over to the PSRR vs. freq plot (if they give it, and if not, keep shopping!) and see what it's like.  Note that it usually falls near zero at high frequencies (control loop GBW, i.e. feedback gain drops below 1 around that point -- it literally can't respond anymore), at which point bypass caps take over, there might be peaks or valleys, it goes back up at HF... this all depends on the fixture used (which they never tell you about), things like stray L in the layout, ESL of the caps, how many caps are used and in what combination (parallel (ceramic) caps have resonance between them), but in any case you can do the same, your LC filter will take over above cutoff (and preferably somewhat below, as needed).

But note that PSRR vs. F is usually done at some large-ish drop, maybe 1V or more.  If they give a series of curves with Vdrop as parameter, that's great.  Assume it gets worse as Vdrop goes down.

Doing statistics, will be sensitive to AC readings, and you'll want a stable reading to tell more from less.  If it's unstable to begin with, at least seeing the variance increase would be a thing, but you can't tell if it's in/out of phase with the system noise floor (which isn't noise at all but coherent: peaks in the frequency spectrum), and any time those correlate, you end up with (constructive/destructive) interference, and you could see the variance decrease instead, which would just be strange, but is perfectly reasonable when things line up just right.

Note that, so far, you've implied these signals are independent, or can be assumed as such.  You might know better.  If the other supplies are derived from the first, then that ripple carries through according to the transfer functions of everything between, and the statistics will be stable.  If they're separate switching circuits, likely not, but there could still be weird ratios and mixing tones that result in fluctuating readings.  Gathering statistics over a long enough period, reduces those fluctuations to only when beat frequencies are on the order of that collection period, making such error much rarer, and if the frequencies themselves aren't that stable in the first place (e.g. COT controllers, spread spectrum), the error can also be made small.

Tim

3

RF, Microwave, Ham Radio / Re: fake MPF102s from AliExpress

« Last post by radiolistener on Today at 02:20:03 pm »

I would speculate that they are still fakes, but probably of the better side of the spectrum. I'm almost tempted to get some (mosfets, I think, as they're the easiest to test for basic parameters) and see how far the fake inductry has progressed .

I think yes, when there is "original" word, it is usually fake. You can find not fake items on aliexpress, they can be marked as "genuine", but usually their price is about 30-50% higher than you can buy it from EU sellers. This is because the seller needs to pay additional import tax which is pretty high for electronics components in China.

4

General Technical Chat / Re: H5N1 bird flu and how we're risking another global pandemic

« Last post by themadhippy on Today at 02:16:20 pm »

it will be something else later. It adds to the many other health problems related to factory farming as justification to phase it out and replace it with sustainable farming.

And then mother nature will find another novel way of trying to keep the population of the most destructive  species on the planet under control

5

General Technical Chat / piano switch

« Last post by vivi-d on Today at 02:16:04 pm »

Hi, I found this neat looking switch on digikey. I read the datasheet, but it is unclear whether this is a momentary switch or not.

How can I tell? Does anyone know?

It's part number CKN10346-ND on digikey.

https://www.digikey.com/en/products/detail/c-k/BPA01B/2641381

6

General Technical Chat / Re: H5N1 bird flu and how we're risking another global pandemic

« Last post by ConKbot on Today at 02:12:34 pm »

Oh no, even chickens bad now, the only solution to save humanity is to switch to industrially produced protein supplement brick meals! Totally not because it's very very profitable for us to turn any garbage protein, fat, and carb source into kibble for humans.

7

Projects, Designs, and Technical Stuff / Re: Homebrew Lock-In Amplifier

« Last post by shabaz on Today at 02:10:30 pm »

This won't meet the OP's needs, but it might be of slight interest to beginners: I created an educational project. I was hoping people could create new experiments with it to improve on my simple ones, but there's no traction (at least, I'm not aware of anyone trying it out).

The project is called Wave Miner (Github link) and has 10 starter experiments so far.

It uses a DSP board from AliExpress and a simple breakout board to BNC connectors (the photo shows it attached to a Raspberry Pi for programming the DSP; the Pi can be detached afterward).

The Gerber files for that breakout board are at that Github link. From the 10 starter experiments, experiment #9 is a very crude lock-in amplifier.

Here is a video demo of the LIA  (before I constructed the breakout board).


The experiments are very basic and for fun/learning rather than serious use, and the DSP used is extremely limited, but on the plus side, very little construction is needed (the breakout board is entirely through-hole construction for simplicity).

8

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

« Last post by mawyatt on Today at 02:10:18 pm »

We have both the Siglent SDS800 and the Rigol DHO800, well the Rigol is a clients that has run into financial difficulty, so likely to remain at "The Labs" for awhile.

We acquired the Rigol for said client and the plan was to teach them the DSO use for a specific application, so spent some time and became familiar with such.

Simply put, Rigol hit a Home Run with the DHO800 introduction, with the custom 12 bit Chip Sets, small form factor, nice screen (altho a bit dim), solid build, excellent UI, VESA, HDMI, nice probes and so on at a price point most could afford. As one popular Rigol Fanboy put it, "Game Changer"!! Which was true, this little Rigol DSO was quite remarkable in every respect, especially considering the price point!!

Needless to say we were impressed with this Rigol DSO, and this was our 1st direct "hands on" with any Rigol product, similar to our experience with our 1st "hands on" with our Siglent SDS2000X+ a few years back, both these folks have really done a superb job   

When the SDS800 was available we decided to spend our own nickel, well the Rigol so far has ended up on our nickel as well

Simply put, Rigol hit a Home Run with the DHO800 introduction, then Siglent hit a Grand Slam with the SDS800 introduction 

As good as the Rigol DHO800 is, and it's good, really good is every aspect, the Siglent SDS800 is just overall better IMO.

We have no brand preference, just have a preference for the best instrument for the task (know thy instrument so to speak), and when one factors in cost, the best value instrument for the task!!

Bottom line is you can't go WRONG with either the Rigol or Siglent, but as 2N3055 mentioned the Siglent is the more "Pro Like" Instrument, and more in-line with making quality/trustworthy measurement/observations rather than just playing around and tinkering, which is fun BTW    

So when we reach for a DSO, now we reach for the SDS800, usually with the Rigol probes tho (these are really good, better than the Siglent IMO) 

Anyway, how either one of these can be offered at this price point is remarkable and a tribute to both Rigol and Siglent, but honestly from a well seasoned old Pro who's used every piece of TE imaginable, one would expect the Siglent to cost ~10X......yes it's that good!! Heck one would expect the Rigol to cost ~3X also!!!

BTW we are NOT open for doing direct comparisons, we'll let that reside in the hands of others!!

Of course, as always, YMMV!

Best,

 

9

Repair / Re: Rigol DP712 Output Shorted; Fuse? / I Screwed Up

« Last post by Harry_22 on Today at 02:08:03 pm »

You are absolutely right, the SCR should short the output if the voltage exceeds a set threshold for any reason. This is confirmed by the cooling radiator designed for long-term operation. To discharge the energy stored in 470 uF capacitor a radiator is not needed.
Topic starter sent us the PS settings that he installed. We see that the OVP was 13 volts and the battery was 11.5 volts. In this case, the OVP should not have worked. Only the current through the shunt could exceed the OCP set value. But it flowed in the opposite direction and I'm not sure that the reverse current is measured here.

10

Projects, Designs, and Technical Stuff / Re: Accurate sine wave in terms of amplitude

« Last post by Majorassburn on Today at 02:05:21 pm »

What could be a proved single opamp for a wien oscillator?

Anything with sufficient frequency response, and output voltage swing, and drive capability.

Since you still haven't bothered to tell us those parameters, how do you expect us to help you?

In addition, ponder the second paragraph here.

More thread-choking negativity and useless crap from tggzzz. 
He's a real thread-killer if I ever saw one!

Your question about op amps?  I use T.I. OP07's with excellent results in my low frequency sine wave oscillators.
Data Sheet link: https://www.ti.com/lit/ds/symlink/op07c.pdf?ts=1714331934514&ref_url=https%253A%252F%252Fwww.google.com%252F

Also, check out the numerous TI App Notes for oscillator designs with sample circuitry you might use as starting points. Best Regards.

The context is these threads from MajorAssBurn:
https://www.eevblog.com/forum/buysellwanted/fs-affordable-dmm-checkers-ac-reference-dc-reference-ohms-reference-etc/msg5463700/#msg5463700
https://www.eevblog.com/forum/metrology/affordable-useful-ac-dc-references/msg5438690/#msg5438690
Anybody with too much time on their hands can read those. They will, no doubt, notice that many people have made negative comments about MajorAssBurn's claims in those threads.

BTW, it isn't good practice to read the first couple of posts in a thread and then jump to conclusions without reading the rest of the thread.

I have this mental image of tggzzz sitting in his week-old undies and moth-eaten robe, in the corner of his tiny, gloomy, cold-water flat, in a poverty-stricken slum section of Birmingham, pecking away at his twenty-year-old Pentium computer while desperately searching forums and threads for topics wherein he can spew out his unwelcome drivel and negativity and display his legendary (in his own mind) philosophical and technical superiority as compared to the woefully ignorant and uninformed commoners who participate in these threads looking for useful suggestions from fellow members, as he, the self-ordained master of thread imposition, reflects within himself how utterly failed as a human being he is, as he seeks out these thread-killing opportunities so as to feel somewhat compensated for his lifelong worthlessness and complete failure to achieve anything noteworthy or meaningful.

Now, with those facts in mind, I will ignore all further written diarrhea that tggzzz dumps in various discussions from now on.