Recent Posts

1

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

« Last post by nctnico on Today at 08:02:41 pm »

With a better, higher order reconstruction filter you can achieve much better results compared to sin x/x at the expense of computational power (I did some experiments with this a long time ago).

i bet your higher order reconstruction filter is one of sin x/x derivative:
https://en.wikipedia.org/wiki/Reconstruction_filter
https://en.wikipedia.org/wiki/Whittaker%E2%80%93Shannon_interpolation_formula

about "anti-aliasing filters which prevent violating Nyquist", we went through that rigol is not properly BW limited at 4CH turned on, and Sinc reconstruction implementation is a bit broken. but your earlier post is too general, so i'm agitated to reply... such as this...

The real problem is that you can only use Fourier series to construct continuous functions. You can't use Fourier series to construct functions with a step in them like a square wave. However, when sampling a square wave like signal (which in the real world can never be a step function) it can turn into a step function in the digital world due to insufficient samples to follow the edges. And as a result you'll get Gibb's ears when applying the sin x / x filter to the sampled signal

some part of it imho is misleading, esp the bolded line. a properly bw limited scope and correct implementation of Sinc derivative filter will not produce gibbs ear, thats not me saying, thats from theory saying (at least what i understand). ymmv.

That is true and I'm not denying that in any way. Actually, I wrote that earlier on. But in the real world DSO manufacturers push the bandwidth up high so you can get as close to Nyquist as possible and still get a decent sine wave. At the cost of some signals getting artefacts (like a square wave getting Gibbs ears). And as I wrote a few posts earlier, if you don't want Gibbs ears, then you need to turn the bandwidth limit on. But this will reduce bandwidth. IOW: the DSO manufacturers leave it up to the user whether they want the most bandwidth or the best signal representation. Given the fixed, maximum samplerate you have to choose between one or the other. And again, sin x / x reconstruction is rather crude so that doesn't help.

2

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

« Last post by tautech on Today at 08:02:32 pm »

3 & 5 - One of the responses rightly points out that appropriate defaults can offset these issues. On the other hand, I have experienced the overwhelming frustration (with other sorts of instruments) of somehow changing one of those settings, and since I don't know enough to even know the setting is there - up to now the default has conveniently hidden it - I spend hours trying to figure what I'm doing wrong.

This is why most DSOs have a "Default" button that completely (almost, anyway) restores the scope to an original configuration.  I use it routinely when I can't remember what I was using the scope for last and just want to start over.  This prevents me missing something like having turned up the holdoff time that won't immediately be obvious but might cause some issues.

The user definable Default is even more useful so with the press of just one button to have the DSO set up just as you like it.
Further, some DSO's allow internal and/or external saving of a Setup file where you might have the scope configured for specific tasks.

3

Projects, Designs, and Technical Stuff / Re: What is Popular smaller than 0.1 inch pin header and jumper cable

« Last post by mariush on Today at 08:01:26 pm »

Lots of 2 mm options

AdamTech 2SH, 2BHR : https://www.digikey.com/short/8p5rjm02

Harwin M22

Hirose DF3 : https://www.digikey.com/short/mdfhmwqf

Hirose DF11 : https://www.digikey.com/short/zzq4mf23

JST PA, PAD, PH , PHD , PUD  : https://www.digikey.com/short/nbzqq79d

TE HPI : https://www.digikey.com/short/v0hhtvmt

Molex Milli-Grid, Micro-Clasp, Micro-Latch , Micro-One etc

4

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

« Last post by Wallace Gasiewicz on Today at 08:01:25 pm »

OK, back to the original point, which I think indicates that large clusters of animals are a health risk.   

I think so.   Here is one example.

The current hypothesis of the likely origin of the 1918 really bad influenza is this:   

The flu started because stockyards in Kansas were in the flight path of Geese. Lots of pigs. The goose droppings contained the virus and the virus was passed to the animals and then to humans.    As we have said, Flu mutates rapidly and the hypothesis is that it mutated in this process of going from geese to farm animals to humans,   
As close as they can find, the first outbreak was at an nearby Army Camp. I like this article:   
 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC340389/

Now this is not really absolutely provable, but a lot of folks believe it is the best rational explanation of all sorts of incomplete data that we can hobble together.  I think this hypothesis is rational.
Notice I said "Hypothesis" not even "Theory".     

(There are a lot of other ideas about where the virus started.)     

Currently we believe the Flu virus strain starts in poultry.  We believe that the Flu that passes through swine is most dangerous.    So, I do believe that large concentration of animals are a health risk.

Now. I do not know what exactly should be done about it. Some poultry farming is done in isolated buildings with pretty strict hygiene. I think this is a good idea.
 

5

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

« Last post by tggzzz on Today at 08:00:15 pm »

at one of my previous employers we used a very simple question to weed out those that understood it from those that thought they understood it.

Is that why it's a previous employer? 😉😉

Nah!

I left them because after >10 years I was in a fur-lined rut, and because the new CEO struck me as someone I didn't believe would be good for the company.

Both judgements turned out to be prescient

6

Microcontrollers / Re: Starting with STM32 (NUCLEO-L412KB)

« Last post by Picuino on Today at 08:00:13 pm »

I did not know them. Thank you very much.

7

Projects, Designs, and Technical Stuff / Re: Using a current output DAC to control laser diode brightness: which IC to use?

« Last post by phennessey on Today at 07:59:13 pm »

1. I need to EITHER modulate the BRIGHTNESS of a laser diode from zero (no light) to an arbitrary brightness (not sure what that is yet)
OR I need to modulate the FREQUENCY of a laser diode (OR modulate the emitted light) between either 525–550nm or between 375–400nm
2. The diode wavelength must be in the range of 375—550nm (525nm is preferred if the brightness method is used)
3. I need to modulate it accurately and reliably at a rate of around 2MHz
4. I need to modulate it with 256 levels of brightness/wavelength (8-bits)
5. I need to be able to try a different power diode in case the max brightness isn't bright enough

These are the non-negotiable design specs. I'm hesitant to say more than that because this is a potential product idea that could become commercialized. If someone wants to sign an NDA and contact me privately, I would be more than happy to discuss!

I realize I'm in over my head. I've decided that will not stop me, but I know full well that I will have to rely on the expertise of others. If you're not able or willing to help with these restrictions, there is no need to reply. Keep in mind that I have every intention of learning as much as I need to in order to accomplish my goal. I'm not giving up.

8

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

« Last post by Picuino on Today at 07:57:57 pm »

The MCP6G02 is not really a good choice for an input amplifier. The noise is quite high - so if at all only for later stages.  In addition it only is for a 5 V supply and thus has a limited dynamic range.

The amplifier part for the input would be similar for an analog an digital solution.

Ok. I have ordered an AD8422 amplifier that can be used with 5V single supply. I am going to use it along with a microcontroller to make a milliohm meter as a starter project.

https://www.analog.com/media/en/technical-documentation/data-sheets/ad8422.pdf

9

Repair / Re: Tektronix calibration set (TM503, PG506A, TG501A, SG503) repair

« Last post by Pinörkel on Today at 07:57:11 pm »

Just an update to my issue with the high amplitude mode. I de-soldered the CR810 diode, only to find that it measured OK and was not shorted. Also the asymmetric resistance measurement at the output disappeared, which means that this behavior is most likely normal. The reduced amplitude went away after putting the diode in again and retouching a suspicious looking solder joint at Q758.

As a side note: The solder mask does not seem to be very resistant to either heat or flux and gets damaged really quick, even at 280°C. I think, it is mostly a heat issue, since I could observe damaged solder mask around other factory soldered components like the cam switch contacts.

10

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

« Last post by tggzzz on Today at 07:55:11 pm »

Have you been paying attention to all the discussions in this thread about the theory and practice of sampling?

In general there are many significant erroneous beliefs about sampling, held by far too many people - beginners and professionals alike.

Sampling is not an easy topic to understand; at one of my previous employers we used a very simple question to weed out those that understood it from those that thought they understood it.

I am happy to report that I do not misunderstand it. I simply don't understand it at all! But I'm learning ...

Excellent

That is an ideal beginning to a never-ending quest for deep understanding.

Fortunately that quest never ends; there are always new and interesting topics. Hence, in a real sense, I will continue to be a beginner - and love it