Recent Posts

91

Beginners / Re: XOR gate problem with GND

« Last post by Ian.M on Today at 03:19:56 pm »

You expect anyone to figure out what you are even trying to do from crappy breadboard photos with half or more of the interconnect wiring going out of frame, unreadable component markings, and no schematic?

 Life's too short for that s--t!  

OTOH if you had provided a clear and conventionally drafted schematic (i.e. most positive power rail at the top, most negative at the bottom, signal flow left to right,  all interconnects drawn, not just net labelled), with part numbers, there are many here who would take an interest and help you figure it out.  You've been asked for schematics before, so *PLEASE* just take it as standard to provide them when ever you are asking a question about circuit theory, operation, and/or troubleshooting!

92

Beginners / Re: Power supply multi-rail noise separation?

« Last post by T3sl4co1l on Today at 03:19:41 pm »

Is that a common-ground (non isolated) module?  I guess being that it says "buck", it is.  This can introduce noise in the common-mode (between grounds) loop between equipment, and tends to be rather pernicious.  The C-mult filter can help, but you might still need a common mode choke and whatnot to keep the noise confined locally.

(Normally a buck module should be common ground, as in identical ground pins, but the fact that they often put connections on opposite ends of the board, and may have a DC offset between them besides (e.g. if low-side current sensing is used), means ground-loop EMI can be picked up, i.e. the ground path crosses the main switching loop.)

As for the filter, you typically want to design it for some cutoff frequency far enough below Fsw to be useful, and Zo a modest fraction of the DC operating conditions.  Notice that a filter only works when both ports are terminated into a resistance (or at least one for suitable prototypes), but we have no resistance in the circuit: the battery is as good as a short, or still reactive (consider stray inductance of the connecting cables), and the supply is negative-resistance if anything (current draw decreases as supply voltage increases).  We can't match to that at all, or, if we did we'd get an oscillator not a supply.

The solution is to use enough ESR (= Zo) in the capacitor(s) to dampen the filter; this necessarily costs HF response (adds zeroes to the transfer function), but stabilizes it by introducing resistance to dampen the system.  Losses can be added anywhere, really, but a deadass shunt resistor at the input or output is obviously out of the question (it would sink way more DC than the load proper!), but we can basically cap-couple it in place, blocking DC while still keeping it effective at the transition frequency (where the filter is most reactive, and therefore in need of damping).

The preferable way is to design the LC filter, and wire additional R+Cs in parallel with capacitor C, with Cs > 2.5 C and R = Zo.  This gives a zero in the transfer function, right in the middle where it's needed (for damping), then the hard-C-to-GND still gives good HF performance.

If electrolytics are used, the ESR likely comes along for free.

Tim

93

Test Equipment / Re: Vevor SDS1104 for first oscilloscope?

« Last post by Aldo22 on Today at 03:17:58 pm »

I keep seeing that for this price (~200 USD), you can get better scopes?

Well, in a nutshell, afaics for max. $200 there is really only the Vevor/Owon/Hanmatek and the Hantek DSO2C10 (benchtop scopes).
If you absolutely want 4 channels, the Vevor etc. is the only one.
The Hantek is better in most other specs and features. Not flawless, but better.

Personally, I see 4 channels as a luxury and wouldn't place much value on it on a small budget.

94

Test Equipment / Re: My poor mans SMU - The Agilent 66311B

« Last post by Veketti on Today at 03:17:40 pm »

Would "GPIB to USB Cable National Instrumens NI GPIB-USB-HS" -cable then be the correct to use with for example pigrew's  (https://github.com/pigrew/HP663xxCtrl) program?
Link to the cable in Ali.

95

Other Equipment & Products / Re: Different bases on Amscope microscope

« Last post by HobGoblyn on Today at 03:16:58 pm »

Many thanks everyone.

I’ve ordered the double boom direct from Amscope as this week they have a 15% off deal, so it’s cost me £242 delivered.

I queried again about which base I would get, they responded with

————————
 
It is confirmed by our product manager: our website is the correct image. The pictures in Amazon must be updated.

Thank you for pointing that out.

Feel free to contact us again any time for further assistance.

————————

Their website has the larger flat  base as shown in the first pic of my OP.  So they must have changed the design, mind you, who wants to place bets that when it arrives, it’s like  the second pic lol.

That’s interesting voltsandjolts, hopefully they have improved things, but I’ve bookmarked it just in case.

96

Beginners / Re: buying a oscilloscoop

« Last post by 5U4GB on Today at 03:16:37 pm »

If you think you need things like Fourier transform to look at the spectrum and rise time measurements, your only reasonable choice is digital.

It's not only the fancy stuff, it's simpler maths too.  While I normally dislike soft-controls, with a digital scope it's really easy to perform operations on waveforms where, for an analog scope, you have to figure out exactly which combination of a faceplate full of controls you need to use to get the effect you want, including things like adding the inverse in lieu of subtracting and other bits of lateral thinking.

97

Other Equipment & Products / Re: Pace ADS200 soldering station

« Last post by bdunham7 on Today at 03:15:41 pm »

I'm being sarcastic. There is a scaled up version of his coin test, where JBC is king of the large copper unscientifically controlled tests.

I think the 2p test and others are OK for comparing the effective power output of a system, but for actually doing large things perhaps a separate tool is appropriate?  None of these stations can compete with American Beauty.

https://www.grainger.com/product/5ZGU9

98

Beginners / Re: Do I understand the terminology of voltage/current?

« Last post by jwet on Today at 03:13:30 pm »

I think that is a very cogent description.

One quibble that might shows some misunderstanding is saying the that the "current at point A..."- voltage applies to a point but current applies to a path.  You might say that "the current along the top conductor..." or the "current through point A...".  Its a small point and anyone would know what you meant as long as you understand.

99

Test Equipment / Re: Vevor SDS1104 for first oscilloscope?

« Last post by Phil1977 on Today at 03:10:54 pm »

If I´d buy my first personal scope today I´d also either take one of the current 12-Bit-models for little over €500 or e.g. an used Rigol 1054 instead of the Vevor.

The Rigol 1054 is anything but new nowadays, but anyhow it´s quite a solid instrument with *lots* of tutorials and experiences available in the internet. It has its flaws but for 99% of hobby scope applications its just good.

I do not know the Vevor personally, but so far all instruments I have seen of this price class had some serious drawbacks like low update rate, only few waveforms/s, no High-Res- or Peak2peak-mode, no good measurement implementation etc. Please correct me if my knowledge is outdated, but so far I didn't find these features for < €350 new. And from my point of view it´s one main reason to personally own a scope to learn using these features.

100

Beginners / Re: Switching a 3KW (240V) immersion heater: Solid state or mechanical relays?

« Last post by 5U4GB on Today at 03:09:10 pm »

ones who provide the necessary SDOC

Curious why the SDOC is required? Is this an Australian thing?

I'm not an electrician so this is at best an approximation: Without an SDOC being available if required for whatever's being installed the electrician can't issue a COC, or possibly the COC will say "except for this bit" for the item without an SDOC.  I don't know what the implications of that are but they're probably not good if, say, there's an electrical fire.

This stuff and other restrictions on what you can and can't do were brought in to deal with people importing masses of dubious through to downright dangerous electrical items from (usually) China.  You can still as an individual buy suicide kits from Aliexpress and bodge them in yourself but it's become a lot harder for vendors and resellers to do.