Recent Posts

1

Repair / Re: Help with bricked APC UPS SMT1500

« Last post by DavidAlfa on Today at 07:34:00 pm »

.enc might be anything.

2

Test Equipment / Re: New Hantek DSO2X1X models?

« Last post by komodo on Today at 07:32:47 pm »

Hi,
Maybe this was already mentioned here, but I didn't find it.

As you can see on the screenshot. why is my scope not showing the frequency of the second channel ?

Is it some known bug or is it some new ?

Thanks

Martin

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Projects, Designs, and Technical Stuff / Re: role of optocoupler for biasing drain of amplifiers

« Last post by xvr on Today at 07:31:28 pm »

Voltage on MOSFET Gate swing from zero (when BJT is open) and to Vdd (when it closed). Voltage drop on R2 considered negligible and can be assumed as zero. Purpose of R2 is reduce current surge when BJT opened, because MOSFET Gate is a capacitor and without R2 its churge current is not limited. R1 used to bring Gate voltage to zero when BJT is closed and to provide path to discharge Gate capacitor.
If MOSFET maximum Gate voltage is lover than Vdd additional TVS should be placed in series with R2 to reduce Gate voltage to allowed limit. R1 in this case used to provide minimal stabilization current to TVS

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Repair / Re: Troubleshooting HV section of a Tektronix 7904 scope --- Help needed

« Last post by BlownUpCapacitor on Today at 07:29:59 pm »

The 7904 is notorious for tantalums being shorted. Check the resistances of the power rails.

https://www.eevblog.com/forum/repair/tektronix-7904-repair/

One of my previous threads has resistance of power rails so use that. Find a rail that has a low resistance. There is likely a bad tantalum on that rail.

5

Microcontrollers / Re: Memory model for Microcontrollers

« Last post by PlainName on Today at 07:28:14 pm »

The stack could move between samples, so it will give you a good idea but risks missing peaks.

6

Beginners / Re: Override Switch for Relay Circuit

« Last post by Ian.M on Today at 07:26:53 pm »

The concept is probably fatally flawed! Do you really want the Arduino to think its turned the pump off, but instead its really on?

How about an alternative:  Take a small SPDT center off switch,   Wire its moving contact to Arduino Ground, and its fixed contacts to the relay driver transistor base, and collector.  When the switch is cantered (off), the Arduino has normal control of the pump.  Flick it one way to ground the base and the pump is forced off.  Flick it the  other way to bypass the transitor, and the pump is forced on.

7

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

« Last post by Zero999 on Today at 07:26:23 pm »

Then there's all the other misinformation exaggerating the efficacy of masks, keeping 2m apart etc. which lacked rigorous evidence to support and the authoritarian policies copied from Communist China. It appears as though the public health authorities did their level best to destroy their reputation.

And what proof is there that distancing does not work?

It isn't. I didn't say that it's proof that masks and keeping 2m apart don't work, just that there's no strong evidence they do. The Cochrane review into masking found it to be inconclusive and as far as I'm aware no studies have been conducted into whether keeping 2m apart does anything to reduce the spread or not. And why 2m? Perhaps 1m would have done? Or maybe we needed to keep 3m or 5m apart? Where's the evidence?

It would be different if we were just advised to wear masks and keep 2m apart. That wouldn't have been ideal, given the lack of evidence, but the fact we were forced to, under pain of a fine, is disgusting. If the authorities are going to punish people for breaking rules, then there needs to be extremely strong evidence to support them in the first place.

Both distancing and masks rely on basic physics! You want a study? go an throw some tennis balls and notice that the further they go the closer to the ground they get. And that if you through them as several layers of nets they will no go nearly as far. What you are asking for in the equivalent to arguing about the distance to the moon because a tape measure was not used.

But actual field studies, conducted in real life have failed to show masking actually works in practice. Fair enough, it doesn't prove a negative, but it certainly doesn't prove positive either.

The Cochrane review even looked at N95/P2 respirators.
https://www.cochrane.org/CD006207/ARI_do-physical-measures-such-hand-washing-or-wearing-masks-stop-or-slow-down-spread-respiratory-viruses

Perhaps mask work, when worn properly? It doesn't matter, the fact not enough people wear them properly in real life to be effective, shows that the mandates lacked evidence.

Many failed medications and interventions have good science behind them.

Given most proposed medical interventions, even those with sound theory, don't work, it's reasonable to believe something doesn't work, until there's solid proof it does.

Do you realise that if you keep taking a vaccine you loose immunity to the disease it is for?

FFS It is exactly the other way around! Vaccines train your immune system against virusses. For mutating virusses, you'll need regular updates to stay current. It is like airplane pilots taking courses in a simulator to learn what to do in an emergency situation for a different airplane.

Repeat infections will do the same.

As I stated in another post, the risk of some adverse events due to the vaccine is higher than the virus for some people, so it makes no sense for them to get vaccinated.

If you've had COVID once and survived, you're much less likely to get really sick if you catch it again. This is also because the virus is mutating to become less deadly, as well as memory T-cells.

There arge instances of immunization not working as intended and causing untoward reactions when the patient gets infected.  Past RSV immunizations are an example.

No one is disputing that a small number of people will have adverse reactions. It does happen. But rather, for the vast majority of the population (i.e.: almost everyone), it has a positive impact overall.

You're wasting your time; in the words of Simon and Garfunkel, "The man hears what he wants to hear and disregards the rest".

This is why I don't participate in these types of thread, they just attract the conspiracy nuts, and others, all of whom have apparently zero understanding of epidemiology, or statisitics and how to interpret them.

Sure, but my aim isn't to change the minds of those who are set in their ways, rather try to educate those who are willing to listen and consider facts from different sources. If we let the conspiracies run wild, there would be nothing other than "vaccines are poison" and "5G activates the nano-robots".

But yes you're right, these types of threads generally have a finite life, after which it just becomes utter chaos.

Except being sceptical of COVID and seasonal influenza boosters is not a fringe position, based on conspiracy theories. I don't appeal to authority so won't post any names, but there are plenty of highly esteemed medical experts who are respiratory virus/mRNA vaccine septics.

The fact I've changed my position on this, shows I'm open to accepting new ideas and evidence.

I supported the first two doses of the vaccine, especially for older, more vulnerable people, when the virus was more deadly and fewer people had natural immunity.

I became sceptical when the boosters started. There simply isn't randomised data to support it.

Not taking natural immunity into account was also a big mistake. When the vaccine was initially rolled-out, no attention to natural immunity was paid. A 60 year old who had had a positive test result a month ago, was still vaccinated before a 50 year old who had not had a known infection.

A lot of misinformation was pushed about antibodies, i.e. that someone who had been infected while ago and their antibodies had dropped below a detectable level, was just as vulnerable to getting really sick, as the first time, if they caught it again, but this is not the case. Memory T-cells are the key to lasting protection against severe disease. They persist in the bone marrow for decades and enable the body to rapidly generate antibodies, when it encounters a similar virus. This will provide some protection against severe disease and death, even if the virus has mutated a bit and isn't exactly the same, due to cross-immunity.

People who were infected with the original SARS still had memory T-cells over a decade later. Although it's not proven, they would be much less likely become just as sick, if they were exposed to the virus again.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7115611/

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Projects, Designs, and Technical Stuff / Re: Connector ID - PLC cable - AL-232cab

« Last post by RitschRatsch on Today at 07:26:22 pm »

I can't think of anything right off the bat, but I always use GoogleLens or AliExpress Photo import for these kinds of questions. What we'd need now are some details, like pitch and contact size.

With kind regards
RitschRatsch

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Mechanical & Automation Engineering / Re: low temperature coolants?

« Last post by Doctorandus_P on Today at 07:26:19 pm »

Liquid nitrogen has a pretty low viscosity.

10

Microcontrollers / Re: Memory model for Microcontrollers

« Last post by nctnico on Today at 07:23:51 pm »

Probably ST wanted to hide the init as part of the HAL or avoid confusion and have everything initialised before calling main. In my own code these two lines do all the required initialisation:

Code: [Select]

memset(_data, 0, _stack_end - __bss_start__-32); //clear memory including stack
if (_edata!=_data) memcpy(_data, _datastart , _edata-_data); //copy initialised variables if present

I make it a point to clear the stack as well. In some rare cases old data on the stack can trigger very rare bugs in combination with (for example) an array / pointer going out of bounds even across resets. Clearing the stack results in consistent behaviour of the fault.

clearing the stack (or setting it to some magic number) can give you an hint on how much is being used by examining the stack area

I do that differently. I sample the stack pointer inside a timer interrupt and update the 'lowest stack address' variable when it is below the previous value. This gives a very quick idea of worst case stack usage without going through a lot memory. I do admit I 'stole' this idea from someone else though. Clearing memory to zero is a very safe thing to do as 0 or NULL is often regarded as the end of something or invalid. Setting the stack memory area to a different value, could cause more problems than is solves. Also, used stack space is likely to be unequal to zero.