Recent Posts

1

Beginners / Re: Bulk input caps and impedance

« Last post by T3sl4co1l on Today at 05:39:36 pm »

Now I want to try what an inductor does.

10uH torroid ... not what I expected.
470uH - more what I expected, although it appears to only delay the steep portion of the rise.
4.7mH and it's much better.... longer / smoother / lower gradient.

What's the catch?

An apparent delay is a likely result of saturation: as current goes up, incremental inductance decreases, so dI/dt accelerates, and peak current moves from a gentler to more aggressive trajectory.

This can be exacerbated by ceramic capacitors, which saturate in an analogous way (ferromagnetic and ferroelectric materials have many similarities), with the difference that, since capacitance is reducing, the peak voltage Vpk ~ sqrt(L/C) * Ipk can be many times higher.  (Which, since for an LC resonant circuit, normally this applies for the initial step, and you'd expect Ipk = Vin / sqrt(L/C), and Vpk = 2Vin.)

Wiring itself has inductance, within a geometric factor of the permeability of free space, 1.257 uH/m.  Usually the geometric factor is less than 1, say 0.3-0.6.  So 0.5 to 1uH per meter of cable length.  Typical cabling is fractional to a couple uH, so you get time constants with ~10s uF in the low us range.

Damping is best introduced with capacitor ESR, and a good way to provide it is to put excess capacitance in parallel with the existing capacitor, and put the ESR there.  Electrolytics are a good source of this.

Tim

2

General Technical Chat / Re: $20,000 dollars of software or licences on a thumbdrive ?

« Last post by tooki on Today at 05:38:11 pm »

This is why non-FOSS licensing sucks.

Well that statement just means you don’t feel software is worth paying for. But there do exist non-FOSS licensing models that don’t suck. I remember when you could just - gasp! - buy software in a box and it asked, at the most, for a license key to be entered from a card in the box.

3

General Technical Chat / Cable Management

« Last post by dcbrown73 on Today at 05:37:20 pm »

Hey all,

No, I don't mean cable management from wires connecting devices, but test cable management!

So, I've seen pictures and how a lot of people manage their test leads / cables.   Many hang them like they are on towel racks and stuff, and I'm just want to ask about any innovative ways that maybe you guys have come up with to manage the mass of cables you collect and use often.

I am an IT guy by trade, a ham radio operator, and an electronics tinkerer and my cable collection has run amuck between all of them.   I normally just use drawers and keep the most used ones on top of the devices I use them with, but I'm always switching them out and don't feel the drawers help protect them so well as I'm always digging around in them for the cable I need.

Anyhow, I just wanted to reach out and see how you guys handle yours and how I may learn from the community a better way.

Thanks,
Dave

4

Beginners / Re: Checking for noise in resistors

« Last post by TimFox on Today at 05:36:57 pm »

I agree about metal oxide to replace old carbon composition resistors.
In this context, you are looking for “excess” (aka 1/f or pink) noise, which is added to the unavoidable thermal noise of a resistor when current flows through it (i.e. with voltage applied across it), due to fluctuations in the path taken by the current.
Any fixture to measure it requires a quiet voltage source, and the resulting noise is at low frequency (1/f dependence);  you need to compare low-frequency noise without and with bias voltage, and to avoid confusion from noise in the bias source.
Compare against a premium resistor known to have low excess noise (ideally wirewound, but good metal film is usable).
You could carefully measure the noise voltage at the junction of your tested part and a comparable value premium resistor, with a polypropylene capacitor coupling the noise voltage to a high impedance noise meter.

5

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

« Last post by Mechatrommer on Today at 05:35:55 pm »

All 4 channels on.

this is what i meant... perfect sine reconstruction.. i tuned my sim files to this setup, 220MHz sampled at 500MSps (Sr / 2.28), here is what i come up with. so it seems Rigol and VisaDSO got broken implementation.

6

Test Equipment / Re: Siglent SDS800X HD 12 bit DSO's

« Last post by BillyO on Today at 05:33:26 pm »

Me too...

7

Projects, Designs, and Technical Stuff / Re: PC74hct4046ap Replacement

« Last post by dj_holmes on Today at 05:32:56 pm »

I'm going to send an image of the current waveform across. Any suggestions on what to change would be great. The idea of a drop in replacement IC really appeals to me 

8

Repair / DAEAN DMPS3434 manual

« Last post by TobiasG on Today at 05:32:45 pm »

Hello all,

Could you help me to finde the manual or datasheet of DAEAN DMPS3434 power supply?

9

General Technical Chat / Re: Russia and China to Build a Nuclear Plant on the Moon.

« Last post by dcbrown73 on Today at 05:29:20 pm »

probably reactor will melt if sun shines effectively onto such IR radiator

A heat shield would fix that.  The James Webb Telescope has a heat shield.  It's -452F (-269C) in the shade and 752F (400C) on the hot side that faces the Sun.

10

Computers / Re: Linux Mint 21.02 - Clone & Replace 1TB NVMe with a 2TB NVMe

« Last post by bjorn_helgaas on Today at 05:28:40 pm »

IIUC, you had this issue with the new Samsung 980 PRO 2 TB PCIe 4.0 NVMe SSD:

Code: [Select]

Aug 20 16:02:18 Laptop kernel: [56893.050368] nvme 0000:07:00.0: PCIe Bus Error: severity=Corrected, type=Physical Layer, (Receiver ID)
Aug 20 16:02:18 Laptop kernel: [56893.050369] nvme 0000:07:00.0:   device [144d:a80a] error status/mask=00000001/0000e000
Aug 20 16:02:18 Laptop kernel: [56893.050371] nvme 0000:07:00.0:    [ 0] RxErr                 

and "pci=noaer" made no real difference.

And you resolved the issue by switching from the Samsung NVMe to a WD NVMe, and no kernel parameters like "pci=noaer", "pcie_aspm=off", etc are needed.

We have a report of a similar issue with that Samsung device (https://bugzilla.kernel.org/show_bug.cgi?id=215027), but I suspect it may be related to ASPM configuration.

I would really like to debug this PCIe Correctable Error issue.  If you're interested in helping, you could reinstall the Samsung 980 Pro2, reproduce the issue, and open a bug report at https://bugzilla.kernel.org/, product Drivers/PCI.  Mention the hardware platform, and attach:

• complete dmesg log (I assume this will include some Correctable Errors)
• output of "sudo lspci -vv"

Try booting with the "pcie_aspm=off" kernel parameter to see if it makes any difference. If it does, please also attach similar dmesg and lspci output for this boot.

This seems similar to https://bugzilla.kernel.org/show_bug.cgi?id=215027, which we originally thought was related to Intel VMD and/or the Samsung NVMe device you have, but I now suspect we might have an ASPM configuration problem.