Recent Posts

1

General Technical Chat / Re: Why does the US provide all critical electronic design knowledge to the world?

« Last post by wilfred on Today at 02:49:11 pm »

Yes you are! You are seeking to impose your will - to get the thread closed - on the rest of us.  It's a clear case of "I don't like it so I'm going to spoil it for everyone." If that isn't selfish and arrogant, I don't know what is.

There is no logical reason for you to ask for it to be closed, because you can be entirely free of this thread BY NOT CLICKING ON IT.

The fact that you seem unwilling to behave reasonably, and just stay away, raises all sorts of questions about your integrity and your real reason for being here.

I don't spend as much time on the forum as I did a few years ago but before you delude yourself that you speak for "the rest of us" be assured you don't speak for me.
This was a more common style of thread 4 or 5 years ago and I took a closer look at the threads back then and found the top 10 posters within would take up over 50% of the threadspace. Sometimes well over. They were hardly representative of a majority of members since the vast majority stayed well clear.

I thought then, and still do, that they are best avoided on the forum entirely.

One thing stands out as different is Dave isn't so active yet in this thread.

2

Test Equipment / Re: Rigol's New DHO800 Oscilloscope unbox & teardown

« Last post by Fungus on Today at 02:43:24 pm »

I'm running on 1.02.02 (I guess), and they're reverted 1.03 as far as I know. But thanks for the warning.

Yes, 1.03 was pulled because of this bug.

The next 1.03 should be a good one...

3

Beginners / Re: Supercapacitors and ESR

« Last post by jwet on Today at 02:42:06 pm »

just4...

The .6 ohms is a magic number, Vbe is .6/.7 or .6 ohm x 1 amp.  When you sense with the upstream 1k, you turn off the PNP.

The pulldown trick won't work as well in real life.  Falstad is a pretty simple simulator and assumes beta is constant- its highly variable and inconsistent and even depends a bit on temp. 

Get out of simulation mode and go burn your fingers.  Its a classic circuit but you'll learn a lot playing with it.  Transistors are very odd beasts.  You'll learn if you dig in deep enough that beta is a lousy parameter- bipolars are transconductive devices- they're Ic is controlled by Vbe in a logarithmic way.  Look up Ebers-Moll equation and get ready to forget what you think you knew about transistors.

This general application is called "inrush" current  limiting and its pretty common- hundreds of ways to solve it.  Another simple way is to use a Positive Tempco Power Thermistor- "PTC".  These have low resistance nominally but their R increases rapidly when they heat up- like when the cap tries to charge like a short- you can get stuff sized to do something similar- they cool off and return to normal after a bit.  They're often used in switching power supply so the lights don't dim when you plug them in, etc.

The LM-317 and MOSFET's both have the problem of large drop out and equivalent of high Vbe (1.2V for 317 and ~4v for big fet).

Many ways to skin this cat...

4

Test Equipment / Re: Portable Oscilloscopes List (cheap)

« Last post by Fungus on Today at 02:40:19 pm »

I'm thinking to start with less capable and cheaper portable scope first.
Ideally around 150 USD.

Nah, simply not worth it. Not only are they much worse, they have no resale value.

The bugs aren't as bad as you hear. A recent Rigol update fixed basically all of them.

(it also introduced one really bad one but they're working on that right now. The next firmware will be here by the time you get one...)

Am I right to guess that these ones are still better than used old analogue scope at the same price range ?

At least 100x better.

And they won't break down or be a constant "work in progress".

5

General Technical Chat / Re: What do you WANT to buy?

« Last post by themadhippy on Today at 02:39:11 pm »

a simple analog thermostat that is silver instead of white.

tin of chrome paint? or if moneys no object you can chrome plate plastic.

6

General Technical Chat / Re: Possible to trigger at battery explosions in pagers ?

« Last post by tszaboo on Today at 02:37:55 pm »

That's why it's good to ask questions. I knew they were a completely separate network, I did not know that don't talk back at all.
Apparently some networks do transmit time. I do not know if this is one did. (pages are from before my time)

The radio plane is an interesting possibility, I do know modern phased-array radars are capable of EW, but can they also generate these signals.

In the end it's about facts. And those are difficult on this subject.

As I said, I'm not targeting you with that remark, don't take it personally.
I could say the same for the "experts" and "journalists" in general.
They ask the expert if it's possible to blow up a battery, they answer "Yes, but not with this much power and without modifications in a pager such as this." Next day headlines: Battery explosion possible in pagers. Also then they go ahead and publish causality figures coming from known terrorists organizations on face value. And now we started seeing news articles where the source is "Anonymous users on reddit claimed" 

The radio plane is an interesting possibility, I do know modern phased-array radars are capable of EW, but can they also generate these signals.
In the end it's about facts. And those are difficult on this subject.

The EW part on the plane is speculation from my part. I've read some technical report years ago, that some of these newer AWACS type planes didn't have dedicated radio, it was all part of the radar installation with phase arrays, and it makes sense. These planes are going to be able to transmit and receive with any communication protocol on any radio band, and the true capabilities are going to be closely guarded secrets.

7

RF, Microwave, Ham Radio / Re: Unexpected Smith chart behavior

« Last post by TimFox on Today at 02:37:44 pm »

For LCR meters, it is mandatory to compensate the connections using the calibration procedure in the manual.
I do it at the start of any measurement set, after connecting the test fixture or cables.

8

General Technical Chat / Re: What do you WANT to buy?

« Last post by ftg on Today at 02:34:59 pm »

...
I've also been wanting to buy something that checks the charge of batteries (one that can hold AA and AAA preferably, as I have a mixture of these in a drawer). Been trying to scout for that for months on Amazon but no luck...
...

ANENG BT168 Pro
https://www.aliexpress.com/item/1005003385787090.html

The non-Pro one has an analog dial and is only good for 1.5V batteries.
https://www.aliexpress.com/item/1005005492915965.html

Might also be worth it to resist temptation and buy only one.

9

Beginners / Re: High-side N-channel FET Switch (100% duty cycle ?).

« Last post by Dannyx on Today at 02:31:23 pm »

I figured the easiest thing to do is to move that connection before the "diode" at the top, represented by Q4.

10

Beginners / Re: Kits/Projects for advancing beginners???

« Last post by Doctorandus_P on Today at 02:27:57 pm »

I really like the Elliot Sound Products website. They sell kits and have lots of background information freely available for the products they sell, and they sell them at very reasonable prices.
They very clearly have a goal of education too besides just selling kits.

https://sound-au.com/schools.htm