Recent Posts

1

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

« Last post by nctnico on Today at 05:29:12 pm »

It's not (only) a bandwidth issue. It's the failure to interpolate the sample data points correctly.

EDIT: Rephrased the question.

@shapirus, assume that you probe an almost ideal square wave and a scope would show you either figure7 or figure8.
Which one would you prefer subjectively? [ I'll explain the difference later in order to get an unbiased vote. ]

Neither pictures are correct. They both show Gibbs ears which do not exist in the real world. If you want to prevent seeing Gibbs ears, you need to use extra bandwidth limiting so the sin x/x   reconstruction does not add the Gibbs ears. IOW, for the best view of a square wave you need to bandwidth limit it in respect to the oscilloscope's bandwidth.

Nobody said they are "correct". Yes, both are imperfect (similarly imperfect as the 3rd screenshot here).
My question was just "which one [of the two imperfect ones] would you prefer subjectively".

You need to keep in mind that sin x /x interpolation on the Rigol is broken resulting seriously distorted results. So there is little use in selecting either imperfect one.

The difference between my two plots is in fact the interpolation filter. Figure7 was calculated with a sharper filter (Siglent-like, about 0.4*fs...0.6*fs), and figure8 uses a filter with a softer transition band (Rigol-like, about 0.3*fs...0.7*fs). The sharper interpolator does not help here. Contrary, I find figure8 a little bit more pleasing. Both suffer severely from aliasing of course.

The problem isn't in the interpolation filter at all. Rigol implemented the sin x/x wrong. That's it.

The real problem is that you can only use Fourier series to construct continuous signals. You can't use Fourier series to construct signals 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. And as a result you'll get Gibb's ears when applying the sin x / x filter to the sampled signal.

2

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

« Last post by eugene on Today at 05:28:32 pm »

The STM32 MOOCs are a pretty good place to start. Have you seen them?

https://www.st.com/content/st_com/en/support/learning/stm32-education/stm32-moocs.html

3

Metrology / Re: HP3458A ref BD, potential fake? Ebay (photos): 03458-66509 DCV Reference

« Last post by Vertamps on Today at 05:26:49 pm »

Im wondering if it came a destroyed meter,it seems a bit dirty. There is a recycling place in Pontiac,MI i visit that scraps nice stuff just for the gold covered cpu's and scrap the pcbs. Not everything makes it to resale.

Iv just noticed the outline markings from the missing plastic cover over the reference, so you are probably right on it being authentic. Well, i will do my diligence to have a test setup for it asap.
I can always return it and start work with Xdevs project LTZ1000 board. I cannot and probably with not be able to test like those folks, not my current goal really.

I do have a spare A/D ref board from an benchtop Fluke 8506A that i may power up in a box, but thats out of the scope of this post.

4

Repair / Anyone have National Semiconductor "HPC" User's Manual?

« Last post by Conventional Wisdom on Today at 05:25:12 pm »

Hi folks,

I'd like to help out a friend who needs to modify a 30-year-old system, the controller for which was a custom design based on the National Semiconductor HPC46003 CPU.  The firmware change should be fairly easy, but the original designer is long gone, along with the documentation and source code (of course).

Now, I'm a heck of a reverse engineer (see my HP548xx post), but I need more info on the CPU.  Thanks to Bitsavers I've got the data sheet, lots of app notes, and an old DOS-based assembler and C compiler, and I've even written most of a disassembler for the HPC, but I'm missing a crucial document that's referenced by all the others:

National Semiconductor Publication Number 424410897-001A July 1987
"HPC16083/HPC16043/HPC16003 User’s Manual."

It used to be available on National's "Dial-a-Helper" BBS (remember those?) but I've searched everywhere on the web and can't find it.  I even emailed Texas Instruments support, since they acquired all those NS CPUs, but they don't have it either.   The User's Manual apparently has a lot more information about the peripherals and instruction set that isn't in the data sheet.

My only hope is that someone will remember that they have a copy of it that's been collecting dust and cobwebs in a box in the attic since 1989.
 
I really don't want to have to replace the controller entirely.  Can anyone point me to this manual?  Thanks for reading!

5

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

« Last post by Gyro on Today at 05:24:17 pm »

...
Did anyone consider the sociological result of lying to the public???  (maybe)
Did Trump actually say to inject yourself with Bleach or Toilet Cleaner???   He did not.  Your comment here is politically based. 

I regret that you have been successfully indoctrinated to believe things that are not truthful at all.
...

However, you can't just look at the technical aspects where it comes to a pandemic. You have to look at the sociological side as well. The general public wants an answer and wants to take some action to protect themselves. This is where the surgical face masks come in. Even though these are intended to limit outgoing particles and do little against incoming, having people wear them makes them feel safe. You should not underestimate the effect of that from a social perspective. It is better than suggesting people to inject themselves with toilet cleaner like Trump did.
...

Just for clarification, the video record of what he actually said... https://www.bbc.co.uk/news/world-us-canada-52407177

6

Test Equipment / Re: Siglent Bench DMMs SDM3065X, SDM3055 and SDM3045X

« Last post by rolfdegen on Today at 05:23:30 pm »

I think I lucked out with my SDM3065X. Stability was awesome pretty quickly.

I have an SDM3055 with modified fan (150 ohm resistance). The values after warming up for 1/2 hour also look good.

7

Other Equipment & Products / Re: PCBite is a brilliant oscilloscope probe holder

« Last post by trp806mo on Today at 05:21:56 pm »

I bought a set of 4 "standard SQ10" and its true that it's useful (must have but really not mandatory :-)) .
BTW I made 2 probe holders; one for testec/lecroyPP23 2.5mm and one for PMK/lecroyPP09  5mm as it was a try and didn't want to buy the dedicated oscilloscope probe.

8

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

« Last post by tggzzz on Today at 05:20:47 pm »

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.

I must admit to being lazy, and occasionally using the "beam find" button 

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

« Last post by tggzzz on Today at 05:18:55 pm »

You need to keep in mind that sin x /x interpolation on the Rigol is broken resulting seriously distorted results. So there is little use in selecting either imperfect one.

At least analogue scopes are repairable 

10

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

« Last post by tggzzz on Today at 05:16:49 pm »

Maybe you overlooked where I stated the obvious, a scope is a scope is a scope.
They all operate the same, exactly the same !
V/div and s/div, really how hard is that ?
Certainly not rocket science.

The modern DSO is no different...

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.