Recent Posts

1

General Technical Chat / The strange case of phase angles

« Last post by ballsystemlord on Today at 04:21:58 am »

Hello,
I was doing some practice problems in my textbook and came upon a parallel RLC circuit. I calculated the phase angle using the impedance but my value differed from the answer key.

Puzzled, I tried obtaining it from the amperage and power vectors successfully. I tried reviewing my math, but can't figure out why my impedance vector doesn't yield the same result as the amperage and power ones. Which is correct? I thought I could try and build a circuit to test this, but the fact that this is a textbook circuit makes it unrealistic so I can't make one.

Attached are images of the problem, my calculator with results, and the answer key.

So, what's the correct phase angle? Why do the impedance and amperage/power vectors differ in their angles?

Thanks!

2

Projects, Designs, and Technical Stuff / Heated Ferrite == Useless Ferrite

« Last post by GelatinCapacitor on Today at 04:21:08 am »

Thanks YouTube videos (mainly diodegonewild), I was convinced that modifying a ferrite transformer was easy. Just heat up the core to destroy the glue that holds the core together.

However, I have had many repair attempts where I had to separate the core of small power supplies to modify the windings. All of them have failed. And I always put the blame on something besides the transformer.

Not long ago, I began using a small flyback SMPS with its transformer taken away to test other flyback transformers. A simple idea. And that let me notice that taking apart the transformer killed it every time.

So, after that I performed an experiment. I sacrificed many flyback SMPS to unglue their cores through various methods (boiling, air, iron), and then test them again with to see which of them survive.

None of them survive.

So, simply heating the core until it can be separated, then putting it back together, without modifying anything else, makes the transformer useless. Even with the iron method, in which anything other than the core barely gets hot.
I did my test with small flyback SMPSs, in the range of a tiny 5W USB charger to a 90W CRT TV power supply.

I found a question on StackExchange which declares the same conclusion.
https://electronics.stackexchange.com/questions/497489/temperature-degradation-of-ferrite-cores

I had originally planned to modify an ATX supply to suit my needs by modifying the transformer this way. That's cancelled now.
One of the comments in that StackExchange question says that bigger power transformers don't suffer from this problem, but I'm not willing to test that out.

My iron method consists of making the core make contact with the soldering iron, and over the span of ~20 min., slowly raise the temperature to ~160°C.
The core may be ready to take apart way before that. The signal I take is a certain smell, which I assume is the glue giving up.

After I discovered all of this, I have made many transformer mods without taking the core apart, even though painfully and slowly, and all of them have been successful.


Customizing windings without opening the core

3

Test Equipment / Re: Hacking the Rigol DHO800/900 Scope

« Last post by mrisco on Today at 04:20:22 am »

Is it possible to remove the RIGOL logo in the top left corner to save some space ?

If you want more space for wave, you can use full screen mode.

4

Microcontrollers / Re: Reset esp8266 when alarm circuit path *broken* with minimal power draw at rest

« Last post by Kasper on Today at 04:18:58 am »

I've used a mosfet for a few similar circuits.

Do you really just need to drive reset low or do you need a pulse: high -> low -> high?

If you need a pulse, an RC delay and 2 mosfets can do it.

5

RF, Microwave, Ham Radio / Re: High bandwidth FM signal generation

« Last post by radiolistener on Today at 04:10:32 am »

are you trying to build a cell phone "blanker" ?!?

maybe he is trying to design some kind of military RF jammer to shut down GSM, WiFi, GPS and other communications 

6

Microcontrollers / Re: How do you search for a microcontroller ?

« Last post by Kasper on Today at 04:05:21 am »

I use Digi-Key for more serious searching but if I just want something quick and easy, I'll see what Adafruit and Sparkfun have.

They seem good at selecting components and their example code is usually helpful. 

Into RP2040 lately, Adafruit has nice boards with extra features and example code.
 Seeed has very small $5 boards.

7

Test Equipment / Re: Siglent SDS3000X HD and upgraded SDS1000X HD

« Last post by ebastler on Today at 04:00:25 am »

As expected, the core architecture seems very similar to the 800X HD series. The front ends differ, of course, due to the 50 Ohm support in the 1000 series.

I am still puzzled by the dual ADCs. Why did Siglent splash out on those, given that the total sampling rate across all active channels is always 2 GSa/s maximum in the SDS1000X HD? Does this imply that the scope could technically run at 2*2 GSa/s (or 4*1 GSa/s) and is just throttled to keep the higher-end models differentiated?

It's the same for the 800X HD platform, of course. But I don't think we ever reached a conclusion there? 

8

Beginners / uCurrent Gold Schematic

« Last post by uf29857 on Today at 03:55:58 am »

I am working on my university project to design current meter to measure currenst from nano amps to 3 amperes positive DC only. Design is based on Dave's ucurrent gold and videos designing a better multimeter. Components being used are, MAX4239,CSD16340Q3(NMOSFET), ADS1115, ESP32 ucontroller. Charging circuit for battery, and usb to uart (CP2102). I have attached my schematic. Please review it and feedback will be highly appreciated.

9

Projects, Designs, and Technical Stuff / Re: "practically smallest" debug connector on tiny pcb

« Last post by Kasper on Today at 03:54:10 am »

If you include an extra pin, you can use it as a key, to reduce the chance of someone plugging the programmer in backwards.

10

Microcontrollers / Re: RIP Z80

« Last post by CatalinaWOW on Today at 03:50:13 am »

The high volume markets drive the chips (and the SW toolsets).  The low volume folks have to dodge around and try to figure out where the high volume people are going so that their choices will meet their market needs.  And there is a big split in the low volume market.  Those who will be producing for years or even decades, and those who make a production run or two and then move on to the next model or product.  That first group is the one that really needs to be clairvoyant or clever.  Fortunately many of those old chip designs can be adequately emulated on current hardware allowing transparent to software and user replacements for ones that have gone EOL.