Your inductance needs to allow for the full range of currents with minimum to maximum duty

@Asmyldof I guess the question with regards to duty is "what's the most critical condition for inductance?"

guys can anyone here help me

with block diagrams for discrete systems?

@pingOfDoom just ask your question man

yeah so there it is

im confused by how to create direct i and direct II forms of block diagrams from a given difference equation

@pingOfDoom Can you be more specific?

so im in a signal processing course

and im confused by the flow diagrams

that are created from difference equations

@Shalvenay The granularity of your PWM block dictates how much ripple to expect with a given set-up, the minimum duty + minimum output current dictate minimum inductance, the maximum duty + maximum output current dictate the maximum inductance.

@ThePhoton Thank you for your earlier answers :)

@RoronoaZoro np

:/ Taxes

@Asmyldof I thought Euro-utopia didn't have that. Just let your employer take a big whack out of each check, send in a short form at the end of the year, and done.

@ThePhoton You know that half the time I am my employer?

@Asmyldof Sounds like a lot of extra work.

Or maybe you should domicile your business in Italy

It's not that complex, just takes an evening I could spend complaining about never meeting any hawt grlz while sitting at home tinkering

@ThePhoton funny you say that Europe is a good place regarding taxes. I am Belgian and have heard several American engineers telling that the US is much more interesting for that kind of stuff (depending on which state you live in).

the noise doesn't even appeart when just plotting the curves of the input signal

FYI the noise is gaussian.

@privetDruzia What is the amplitude (or PSD) of the noise?

@privetDruzia I'm mostly thinkiing of what I've been told about Germany (how simple the typical tax form is there).

The US tax system is a horrific mess.

The only positive is that taxes are low. which of course also leads to crap public services and poor infrastructure investment.

the most annoying thing about US taxes is that prices are displayed without

@ThePhoton Ended up taking about an hour this time

Rest of the time I've been cleaning up the Laptop so if it explodes in aussie I haven't lost anything of any importance

@PlasmaHH You have obviously never done income taxes here.

@ThePhoton nor here

Hey, newbie question. Background: My building has a 15-year-old intercom that is failing. I suspect the power supply can't handle the load. Our security guys say "Oh, too old, can't be fixed. You need to buy a whole new system to replace it." I suspect a savvy electrical/electronic engineer could patch it up for a 20th of the cost, and get another 5 years out of it, but I don't know the process of finding one. Is asking how to find an engineer on the street an on-topic question here.

@Oddthinking here as in site, or chat? chat of course, site not so much I guess

though assume some hourly rates of say $150+ and several hours of work...

@PlasmaHH Plus a ticket to wherever it is.

yeah, though "on the street" sound like in walking distance

@PlasmaHH Thanks. Avoided an off-topic question. I'll just stick to asking here then!

@PlasmaHH That is still 1/50th of the cost of a new system!

@Oddthinking just saying to put things into perspective... if you think the PSU is at fault, iit might be sufficient to learn a bit yourself and replace it

@PlasmaHH No, my question is how do I go about finding one? Is there a name for such a "trouble-shooter for hire for quick building jobs" that I can search the White Pages for?

@Oddthinking what country? guess you best ask people living there

@PlasmaHH I have the problem that (a) I am out of my depth, (b) the Owner's Committee don't trust me because they think I am out of my depth, and (c) I haven't the insurance. So I want to hire a professional.

(c) is most likely the most valid reason to do so

find one that doesn't sell those things ;)

@PlasmaHH It is Australia, but I don't know who to ask here. I am having a problem of knowing where to start. Once I do, I will be able to bootstrap.

@PlasmaHH One what? That's my real question!

no idea really, not a native speaker even

@privetDruzia You can try me, but might I suggest StackOverflow?

@Oddthinking -- perhaps an electrician can look at it?

@Shalvenay Just a "regular" electrician? I was expecting someone with more detailed knowledge of circuit boards.

(e.g. someone that can confirm the reason the video vertical hold is bad, is because the input voltage is too low)

sadly, electronics repair techs of that type are an extreme rarity in today's throwaway society

@Shalvenay :-(

maybe try eevblog forum

can you at least get a meter on it and verify it's being overloaded? or is the PSU like integrated into the rest of the intercom system? and yeah, the eevblog forum might be able to help you

the most likely reason is caps gone bad

@PlasmaHH Interesting. I was thinking "I need someone like Dave Jones of eevblog," Where can I find them. (Given he's a friend of a friend, maybe I can get him :-) )

@Shalvenay A meter on the voltage coming to my apartment was 20V where 24 v was expected, but I don't know if that is within tolerance.

The power supplies are locked in closets that I could ask for access, but politically it will be easier with a professional by my side.

nods

@Oddthinking He does skip logical steps and never circles back though

@PlasmaHH yeah, sadly, electrolytic caps are a) ubiquitous and b) guaranteed to fail sooner or later, p. much

@Oddthinking 20V doesn't mean much. Some intercoms work from 7V to 40V

Noise levels are much more important than DC value most likely

@Shalvenay Proper use of proper electrolytics later can be in 30 years

@Asmyldof Interesting. I am following the rabbit hole because I read that voltages lower than tolerances can cause vertical hold symptoms on CRT screens.

Which is the main symptom.

I reiterate: I know I am out of my depth here.

I'll go trawl the eevblog forums. Good suggestions. Thanks, all.

If they designed an intercom with crap wires to work only in the 10% band your best bet is to just use cans and strings from now, because the quality was saddening to begin with

Regardless of what type of screen or amplification is driven how

@Asmyldof Ah, so what I heard from that is decent quality intercoms would tolerate 20 V where 24 V was spec, and that that is probably not the real problem.

@Oddthinking It really shouldn't be a problem yet.

UNLESS there's 3V or ripple on it

@Asmyldof Useful. Thank you.

Easy enough to test though, add 2 penlites for a short test

though that's still not ruling ripple or noise out

@Asmyldof yeah -- that's too much to ask of all the Madman Muntz clones running around this planet though

Gentlemen. Our close-vote review queue have flared-up again. This happens once in a while. If you have the time, could you please do a pass on it? Cheers.

@NickAlexeev aaarrrgggh...just under 250 rep shy of being able to pitch in :/

hello all

does anyone here have any expertise with general system theory?