Recent Posts

1

Projects, Designs, and Technical Stuff / Duty cycle and frequency to drive LED for best energy efficiency

« Last post by Wilson__ on Today at 10:36:24 am »

For battery capacity limited device, what is the 'sweet spot' duty cycle and frequency to drive LED at highest energy efficiency (high brightness using low energy) for human active observer for attention-seeking guide light. 

Instead of ON all the time, human visible persistence mean one can see the light even if it is a short pulse. 

My question is how short (duty cycle) the pulse that huamn can 'feel' good brightness compare with 100% on time.  Extreme example is xeon flash in film photography to freeze motion.  On time is kind of 0.1 to 1ms.  Traditional LED bed side clock is 4 digits driving 25% duty cycle.

Many thanks

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Projects, Designs, and Technical Stuff / Re: Keeping NiCd battery pack charged

« Last post by nctnico on Today at 10:36:24 am »

I have a drill which has two NiCd battery packs and when I go to use them they are always discharged and I am fed up. I end up using other drills which have NiMh or Lion batteries and hold their charge.

What is the best policy? Any ideas?

I have replaced such drills with corded ones from Makita. Plug in and go.

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RF, Microwave, Ham Radio / Re: Problem with Inductor Self Resonant Frequency

« Last post by Solder_Junkie on Today at 10:34:30 am »

I dont need precision, just a tool to find where noise comes from and what changes reduces it.

What is the problem you are trying to solve with a line impedance stabilization network (LISN)?

If you just want to filter any mains borne noise from equipment, this filter has helped many radio amateurs:
https://gm3sek.com/2019/10/11/clean-up-your-shack-2019/

Measurements of capacitors and inductors with a VNA show they have strange behavior compared to a "pure" component. All inductors will have self resonance, the "trick" is to measure the whole assembled circuit, which I guess you have done.

EMC filters tend to use lossy ferrites, such as type 31 as used in the GM3SEK mains filter.

SJ

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Repair / Re: APC Smart-UPS 1500 (SMT1500)

« Last post by RadioNZ on Today at 10:29:28 am »

Your first photos look catastrophic, but most of that is just soot.
The clean-up photos reveal it's not as bad as first thought.
From what I can see, one of the MOV (MV4 - the charred one inside the heatshrink) has taken a hit.
This could be due to a lightning strike or there's been one hell of a surge on the mains.
I would also check the other MOV to see if any of them have gone short as well.
As to whether you can swap out the board from a rack mount unit to this one, well the part numbers appear the same (apart from the revision) so it's possible.
You would be better off leaving the rack mount unit intact and just trying to repair this one.
Given that the unit is throwing up an over-volt indication, it's likely whatever took out that MOV is responsible for this indication and there
may be more failed components than what is initially visible. It may have damaged the line voltage sensing circuitry.
You mentioned that the batteries measured 27 volts together, that's about right - assuming your UPS runs the batteries in series for 24 volt operation. Many do.

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Buy/Sell/Wanted / Re: Canceled Because Thread All Shit Up by "tggzzz"

« Last post by Muttley Snickers on Today at 10:25:40 am »

I have mixed feelings about these types of episodes as nobody really benefits.   

As I see it, the OP had these references listed on ebay so if they didn't live up to expectations or meet specifications then purchasers had an avenue for reimbursement and negative feedback.

Regardless of other peoples views or opinions on the products, the OP was in fact a contributor to the forum which entitles them to post items in this B/S/W section, and if the items weren't fit for purpose then they wouldn't last here very long, that's for damn sure.

I don't know the reason for the ban and perhaps a timeout may have been sufficient but unfortunately the OP nominated to instigate what could be deemed a personal attack against another member by the (offensive?) thread title and that according to the rules won't be tolerated.

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Beginners / Re: Automatic golf ball dispenser

« Last post by Doctorandus_P on Today at 10:24:42 am »

One way to automate it, is to remove the "wooden peg", and/or integrate it in the arm. The Idea is that the weight of the ball keeps the dispensing arm folded out, and as soon as the ball has been removed, it will fetch the next ball.

A disadvantage is that the system is vulnerable. The gulf club is likely to hit the arm occasionally and destroy it. This can be mitigated by making the arm easily replaceable and having some spares, or by building the whole thing on some sort of plateau, with the result that the arm sinks "below ground level".

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

« Last post by watchmaker on Today at 10:24:11 am »

In the fall of 2019, when Covid was starting to appear, my wife and I read Pale Rider.  This was published  BEFORE the outbreak and was an analysis of the 1918 pandemic which was incorrectly termed "Spanish Flu" because the warring powers kept it secret and only Spain acknowledged it.

Anyway, it recorded almost everything we saw and continue to see.  Long Covid, impacts on the young that impacted the draft in WWII, social reactions, etc.  It was all there and.

The author (UK Based science writer Laura Spiney) concluded we never really heard about the 1919 pandemic because people were too embarrassed by their own behavior.  That is how bad it was.  Today bad behavior is seen as a sign of personal courage.  That is basically the only difference.

Here is a construct that has proven useful.  When a person takes a hard position and is proven wrong by the outcomes, they tend to not admit their mistake.  Instead they double down.

Here is my "creation story".  When the world was created, (By whatever deity; but here I think of  Adam and Eve), everything that was to be was provided.  Including common sense.  That has been getting divided into smaller and smaller bits ever since.

The annoying part to me is that all this was known, but not one policy maker looked at the historical record as a guide to their response.  Instead, they acted like kids who think they discovered sex.

This is why old people get cranky, BTW. (that and the loss of libido).

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Buy/Sell/Wanted / Re: Canceled Because Thread All Shit Up by "tggzzz"

« Last post by tatel on Today at 10:18:57 am »

I really don't think so. The sort of people on here know how to make these simple things if they need one, but if they're that way inclined they will buy a cheaper and better looking one from AliBayzon. I mean, he showed that it's just some cheap parts on a perf board - anyone could do it.

What the people on here would be interested in is showing how superior they are by finding the tiniest fault, and loudly noting that you couldn't set a 20-digit meter from one so it must be shit. It's that community attitude that led to his attitude.

He seemed impervious to taking advice, but that's not an indictable offence. Often, one will get contradictory advice so if you follow one you'll be pissing off the supplier of the other, but why should he take any at all? In the end he has considered it all and decided that the way he will go is the way to go, and that should perfectly OK. It would be OK, except to those that think their advice is gold plated and simply must be followed.

In that thread it might be kind of OK to try and make him look a fool by asking about stuff that only applies to high-end super-expensive traceability (although using that as as a weapon surely sucks), but here in buy & sell it's just designed to stiff his sale. If you're actually interested in buying his kit then that sort of question is sensible, but the only ones asking here were those with a grudge intent on screwing any potential sale. I don't think that's on - if someone is happy to buy shit, it should be between them and the vendor.

Well, in fact this thread had been inactive for some days... so nobody compelled him to take any advice, and everyone put up with his bad manners ...and he was free to continue selling his things on eBay.

It should be realized that it was him who suddenly "closed" the thread, deleting his posts and stating he would open another thread -where it would have been free from any critics?

Hell, no. These eBay listings were misleading and we all have a right to criticize that. If he wanted propaganda without criticism, it would have been better for him to pay for some ads somewhere.

I think, should that listing read something like:

"LT1236-10 5ppm 10V Reference."
"Final Trim to 10.0000 VDC @ 78F, 50% Humidity"
"Designed to affordably verify the function of Digital Multimeters up to 4.5 digits".

... there would have been much less critics

But at the end of the day, by making it clear that he does not accept criticism or else (temper tantrum), he was the one who made the ban inevitable

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

« Last post by Picuino on Today at 10:18:32 am »

RoGeorge:

Thanks for the links, I hadn't seen your post with the forum page change.
The idea I have is to experiment with the components and learn. Yes, for more serious experiments it is best to buy a second hand LIA.

The "Shorty" looks like quite a useful device, I didn't know it, thanks.
https://hackaday.io/project/3635-shorty-short-circuit-finder

My idea is to be able to measure the milliohms with a numerical value. I want to use it for printed circuit boards and for screw connections (terminals). It may also be useful in other occasions.
My Agilent 34401A can do those measurements without a problem anyway, so measuring milliohms is not a real need. I want to experiment with the concept of synchronous measurement, which I have never used before.

10

Test Equipment / Re: Hacking the DSO2X1X

« Last post by Freelander on Today at 10:09:09 am »

thanks David.