3 ms·

This signifies that each vertical dotted line is 20ns apart, so the ripple you see has a frequency of something like 50MHz. Unless you have a 50MHz buck conver

This signifies that each vertical dotted line is 20ns apart, so the ripple you see has a frequency of something like 50MHz. Unless you have a 50MHz buck converter (which would be very exotic --- the fastest common ones are around 1/10th that), that looks more like something may be inadvertently oscillating and/or you're picking up strong RF noise from possibly something in... https://en.wikipedia.org/wiki/6-meter_band#Radio_control_hobby_use https://en.wikipedia.org/wiki/6-meter_band#Radio_control_hob... And "leared" -- the (unintentional?) pun made me click.

codedokode 6mo ago
Cannot it be a noise from imperfect switching? The switching occurs at lower frequency, and the noise is high frequency.
- deleted 6mo ago
  [deleted]
JCTheDenthog 6mo ago
>And "leared" -- the (unintentional?) pun made me click. I assume it's a reference to the "Quality Learing Center" in Minnesota, one of the questionable daycares at the center of the alleged Somali daycare fraud scandal. Ever since some of the expose videos about it came out it's become a meme to say "lear" instead of "learn".
- nielsbot 6mo ago
  > questionable daycares If they don't find fraud, is it "questionable"?
  - peterfirefly 6mo ago
    If they choose not to look, yes.
  - bavell 6mo ago
    Didn't the guy flee the country after posting bail? Doesn't exactly scream "innocent".
    - nielsbot 6mo ago
      I didn’t see that. Is there a source? I saw Minnesota authorities investigated the business and didn’t find evidence of fraud. I did read there was some amount of fraud in state sponsored care programs but nothing extensive.
elch 6mo ago
I guess he also believes that 50 MHz or so signals can be measured reliably on a 40 MHz (on paper at least) scope.
- PunchyHamster 6mo ago
  Most digital scopes have around 5-10 times faster sampling than bandwidth. The one on pic is 250Msps. That's more than good enough for the purpose of checking interference
  - elch 6mo ago
    But he tries to quantify this interference. Anyway Animats's comment is the one that points IMHO to the most likely cause of the observed waveforms. https://news.ycombinator.com/item?id=47931024 https://news.ycombinator.com/item?id=47931024 PS Now that I’ve taken a closer look, this is even sillier than I first thought. He’s hunting for 50 MHz ghost signals by connecting his PCB to a breadboard using (crappy) wires that are at least 10 cm long. And he’s connecting the scope probe to the breadboard (or those breadboard wires). And if I’m not mistaken, he doesn’t even bother to connect the ground lead of the probe.
Animats 6mo ago
It's not oscillating at 50MHz. Look at the waveform, with the big spike in the middle. That's a spike at some lower frequency, wider than the screen, followed by ringing. Need to zoom out the time base some more to see the period of the big spikes. It's no higher than 4 MHZ (the screen is 12 units wide) and possibly much lower. (Assuming that M:20ns on the display means 20ns/grid division. The manual is a bit hazy on that part of the UI.)[1] The power regulator IC mentioned is normally run at 500KHz. There's a reasonable chance that this is the power regulator spike not being damped out. Easy enough to check with a scope handy. [1] https://fotronic.asset.akeneo.cloud/pdfs/media/owon_hds242s_manual.pdf https://fotronic.asset.akeneo.cloud/pdfs/media/owon_hds242s_...

codedokode 6mo ago

Cannot it be a noise from imperfect switching? The switching occurs at lower frequency, and the noise is high frequency.

deleted 6mo ago
[deleted]

JCTheDenthog 6mo ago

>And "leared" -- the (unintentional?) pun made me click. I assume it's a reference to the "Quality Learing Center" in Minnesota, one of the questionable daycares at the center of the alleged Somali daycare fraud scandal. Ever since some of the expose videos about it came out it's become a meme to say "lear" instead of "learn".

nielsbot 6mo ago
> questionable daycares If they don't find fraud, is it "questionable"?
- peterfirefly 6mo ago
  If they choose not to look, yes.
- bavell 6mo ago
  Didn't the guy flee the country after posting bail? Doesn't exactly scream "innocent".
  - nielsbot 6mo ago
    I didn’t see that. Is there a source? I saw Minnesota authorities investigated the business and didn’t find evidence of fraud. I did read there was some amount of fraud in state sponsored care programs but nothing extensive.

elch 6mo ago

I guess he also believes that 50 MHz or so signals can be measured reliably on a 40 MHz (on paper at least) scope.

PunchyHamster 6mo ago
Most digital scopes have around 5-10 times faster sampling than bandwidth. The one on pic is 250Msps. That's more than good enough for the purpose of checking interference
- elch 6mo ago
  But he tries to quantify this interference. Anyway Animats's comment is the one that points IMHO to the most likely cause of the observed waveforms. https://news.ycombinator.com/item?id=47931024 https://news.ycombinator.com/item?id=47931024 PS Now that I’ve taken a closer look, this is even sillier than I first thought. He’s hunting for 50 MHz ghost signals by connecting his PCB to a breadboard using (crappy) wires that are at least 10 cm long. And he’s connecting the scope probe to the breadboard (or those breadboard wires). And if I’m not mistaken, he doesn’t even bother to connect the ground lead of the probe.

Animats 6mo ago

It's not oscillating at 50MHz. Look at the waveform, with the big spike in the middle. That's a spike at some lower frequency, wider than the screen, followed by ringing. Need to zoom out the time base some more to see the period of the big spikes. It's no higher than 4 MHZ (the screen is 12 units wide) and possibly much lower. (Assuming that M:20ns on the display means 20ns/grid division. The manual is a bit hazy on that part of the UI.)[1] The power regulator IC mentioned is normally run at 500KHz. There's a reasonable chance that this is the power regulator spike not being damped out. Easy enough to check with a scope handy. [1] https://fotronic.asset.akeneo.cloud/pdfs/media/owon_hds242s_manual.pdf https://fotronic.asset.akeneo.cloud/pdfs/media/owon_hds242s_...