Recent Posts

1

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

« Last post by Picuino on Today at 01:17:11 pm »

I want start measuring several experiments:
 * Milliohms in pcb traces
 * Coupling between different twisted pairs of cables.
 * Voice with a laser in a crystal. (Microphone)

2

Mechanical & Automation Engineering / Paint Bubbles On Snowblower

« Last post by bostonman on Today at 01:16:30 pm »

Since this is a mechanical question, I figured this would be the best place to post my question.

I have an Ariens snowblower that's maybe eight-years-old and I always maintain it along with cleaning the body before storing it for the summer. This year I noticed the paint is bubbling in many areas.

My parents also have an Ariens that's well over twenty-years-old, and, with the exception of paint chips, the paint is immaculate.

They don't live far from me, so we get equal salt poured from the plow trucks, and we both store them the say way in all seasons.

The bubbles can be seen in the attached picture. Most places that are bubbling have a black color that doesn't come off easy.

My question: since both snowblowers are the same company (different vintages though), they see the same type of snow/salt, etc... Does anyone know what is happening with the paint on mine?

My assumption is that it's a factory issue and the paint didn't adhere to the metal, but I'm not a paint person.

3

Projects, Designs, and Technical Stuff / Re: (Yet Another) DIY Multislope ADC

« Last post by NNNI on Today at 01:07:32 pm »

iMo, I got a chance to talk to Eben Upton at Maker Faire Hannover 2023. He mentioned that the instruction memory for PIO was closely coupled to the architecture, so more memory is apparently not the easiest to implement. He did hint at using out exec to overcome this limitation, but that comes with its own challenges.

I was looking at suitable crystals, and apparently a 48MHz version of the crystal [1] Jaromir used in the ADC for his NVM project [2] exists. I was not able to find jitter specs in the datasheet. But as Kleinstein says, a 'regular' oscillator will probably suffice, since a latch like the '273 will add its own jitter. The 48MHz version [3] of the temperature compensated crystal series PCB.Wiz recommended is available at a reasonable price in single quantities from Mouser.

Once I have the issues with the code sorted out, I think it would make for an interesting comparison to see how well the latched version performs.

[1]: https://www.mouser.com/datasheet/2/137/SG5032CAN_en-961596.pdf
[2]: https://github.com/jaromir-sukuba/nvm/blob/main/hardware/Schematics_pdf/HOMER/rnvm_homer.pdf
[3]: https://www.mouser.com/datasheet/2/122/ECS_3225MVQ-1825332.pdf

4

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

« Last post by KL27x on Today at 01:01:31 pm »

Thanks!

That's was one of my first questions that was never answered. How to get boards made using my original soldermask layer? Why did this happen and how do I avoid this from happening again? Did I do something wrong?

Even though they're remaking them, they never answered this. They just told me to not worry, it will never occur, again. So I'll be sure to look these preferred extensions up.

I don't expect any given tech to know all the words that might be used for a paste/cream/stencil layer in 100 different languages. You'd think "soldermask" is more univeral, if they actually read the layer names. Maybe they don't always or ever do that.

5

Power/Renewable Energy/EV's / Re: DIY Battery Bank from Recycled 18650

« Last post by BrokenYugo on Today at 01:00:55 pm »

Hundreds of crappy solder joints on something you're supposed to spot weld.

No insulation.

Mixed mystery cells.

No BMS/protection.

That's just what I see not knowing anything about the details of lithium bank assembly. I just report and move on in this sort of situation, all you can really do.

6

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

« Last post by Mechatrommer on Today at 12:57:55 pm »

No, it does not have to be periodic. "Perfect reconstruction" only requires that the original signal sampled by the ADC sampled was bandwidth-limited.

Nope. The signal in this image is bandwidth limited (5Hz signal, 11Hz sample rate) but sin(x)/x won't reconstruct it unless the filter is infinitely wide and the signal is periodic (which can't happen in practice).

man what are you smoking? please focus on gf's word here "realizable real-world reconstruction/interpolation filter"... true Sinc by theory cant be implemented in real world, so professors have to find a way to make it "realizable" or "practical", similar to Fourier Transform, without DFT or FFT, real Fourier Transform will not be "realizable" because real FT is infinitely long. go read some literatures on how to make those "realizable", i cant comprehend them myself but at least i got some idea. the FFT you keep bragging about, is one crippled version of FT that brings some complications with it, ymmv.

7

Microcontrollers / Re: STM32F407 - CMSIS DSP - IFFT not working with audio input/output

« Last post by newbrain on Today at 12:57:33 pm »

I don't have a direct answer, but rather some questions, that might guide you to a solution:

• Are you getting the input data from one of the STM32F407 SAI interfaces?
• What's the format of the audio stream?
• If using SAI, what's the purpose of manipulating the byte order?
  SAI data will come correctly aligned for the CPU to handle (Little Endian), and if the "LSb/MSb first" bit in SAI configuration is wrong, well, changing byte order won't help.
• What are the types of the used buffers?
  The int -> float and float -> int conversions both look really fishy: the sign is not kept in the first one, and the second one is not even possible, since floats cannot be shifted; moreover, you are shifting by 16 position instead of 8...

8

Beginners / Re: Convert US standard 115V to International 230V

« Last post by Haenk on Today at 12:55:50 pm »

I assume the Meanwell PSUs are easily good enough to handle 50Hz&60Hz, and likely the filtering does not need to be super critical, otherwise one would likely find a very-highly-priced US PSU in there.

However, I'm not so sure the medical certification will still be valid when used at a different voltage - as the supply voltage is probably one of the stated test parameters (unless they do state something like "90-270V 45-65Hz supply voltage" in their certification sheet)

9

Test Equipment / Re: UTG932 testing by multiple instruments with a lot of screenshots

« Last post by bb1 on Today at 12:54:17 pm »

Here is very short Python code to send ARB waveform to UTG. As is it defines 10 sin periods in the waveform, but you can change the formula for "signal" to define any other ARB shape.  To send modulation waveform just replace "CARRier" by "MODulate". Of course, you need free Python and numpy and pyvisa packages.


import numpy as np
import pyvisa

rm = pyvisa.ResourceManager()
uniGen=rm.open_resource('USB0::yourUTGaddress::0::INSTR')

t=np.arange(0,4000,dtype=np.float64)/4000

# define waveform , here N=10 sin periods:
N=10
signal= 32767*np.array(np.sin(2*np.pi*N*t))
signal=signal.astype(np.int16)
# send to UTG
h1=b'[HEAD]:115\r\nVPP:1.000000\r\nOFFSET:0.000000\r\nCHANNEL:1\r\nRATEPOS:0.000031\r\nRATENEG:0.000031\r\nMAX:32767.000000\r\nMIN:-32767.000000\r\n[DATA]:4000\r\n'
showName='t1'   
uniGen.write(':WARB1:CARRier '+showName+' ')
uniGen.write_raw(h1+signal.tobytes())

10

Test Equipment / Re: Magnova oscilloscope

« Last post by nctnico on Today at 12:51:21 pm »

Yokogawa has / had a whole bunch of scopes which have the input & controls under the screen. So the casing is narrow & high.

Since the Magnova is basically a tablet with 4 encoders and 2 push-buttons, allowing to use a rotated screen (0 - 90 - 180 degrees) is only a matter of supporting this in software. From the description is sounds like there is a fan inside so use in a rotated position shouldn't pose a problem cooling wise.