Recent Posts

1

General Technical Chat / Re: Questions about Adelaide Australia

« Last post by SmallCog on Today at 11:22:26 pm »

I've been pondering things for you to do, we don't really have a science and technology museum here, despite being quite a technical city.

We have Codan making radios, Redarc doing DC power equipment, and many other global defense brands present doing all sorts of stuff that would be interesting if we could actually hear about it.

There is however a temporary museum display happening of radio equipment, much of it brands that were manufactured here in Adelaide.

https://www.eventbrite.com.au/e/history-festival-exhibit-of-vintage-radios-more-bookings-not-required-tickets-878560236317

This display moves around, I'm not sure when you're visiting but hopefully it will be available somewhere to view when you're here.

Definitely put aside a day to explore the various institutions along North Terrace in the city. Well worth having a look at our museum, art gallery, and state library, all of which are free to enter.



https://guides.slsa.sa.gov.au/c.php?g=410288&p=2795746

If you like good food and wine then you're in the place for that, Adelaide Hills, Barossa Valley, McLaren Vale are all within an hour of the city center and have world class offerings.

2

Test Equipment / Re: Siglent SSA 3021X... Ooops

« Last post by Joel_l on Today at 11:17:54 pm »

Except that when using the antenna analyzer, I made no changes to any SA setting.

As far as what the SA is reading, thinking about it, it's all good. The SA knows what the attenuation is set to, so can always display the power being applied to the input port.

I did test my external attenuator and it is indeed bad.

The only potential issue left is why when using the antenna analyzer did I initially get several high SWR readings, when I tried the Smith chart I got the overload warning, then things worked fine. I did not change any SA settings during these tests with the antenna analyzer.

The SA still acts odd sometimes, so I think I will still replace those switches.

3

Projects, Designs, and Technical Stuff / Re: Accurate sine wave in terms of amplitude

« Last post by Majorassburn on Today at 11:17:46 pm »

What could be a proved single opamp for a wien oscillator?

Anything with sufficient frequency response, and output voltage swing, and drive capability.

Since you still haven't bothered to tell us those parameters, how do you expect us to help you?

In addition, ponder the second paragraph here.

More thread-choking negativity and useless crap from tggzzz. 
He's a real thread-killer if I ever saw one!

Your question about op amps?  I use T.I. OP07's with excellent results in my low frequency sine wave oscillators.
Data Sheet link: https://www.ti.com/lit/ds/symlink/op07c.pdf?ts=1714331934514&ref_url=https%253A%252F%252Fwww.google.com%252F

Also, check out the numerous TI App Notes for oscillator designs with sample circuitry you might use as starting points. Best Regards.

4

General Technical Chat / Re: Russia and China to Build a Nuclear Plant on the Moon.

« Last post by soldar on Today at 11:17:08 pm »

Which was what I meant to convey, but stuffed it up.
I was thinking about how the moon presents the same side to us, & that there was always some part of the moon lit by the sun.
I neglected the fact that we don't see all of the same side, all of the time.

The far side of the moon or the occult side of the moon, as opposed to the near side of the moon or the visible side of the moon.

5

RF, Microwave, Ham Radio / Re: fake MPF102s from AliExpress

« Last post by G0HZU on Today at 11:13:12 pm »

Farnell still have stock of the BF256B JFET in the TO-92 plastic package. The price here in the UK is £0.40 each but Farnell sell them for less than $0.20 each in the US.
This is a process 50 JFET like the MPF102 but made to a tighter tolerance for Idss.

6

Power/Renewable Energy/EV's / Re: DIY Battery Bank from Recycled 18650

« Last post by FinOminal on Today at 11:12:12 pm »

more pics from their add on facebook

7

Projects, Designs, and Technical Stuff / Re: Passing 2 wires into a hot water cylinder

« Last post by ejeffrey on Today at 11:07:29 pm »

Thermowells have a number of big advantages that make them the overwhelming choice.  They precent the hot liquid from attacking the sensor, wires or insulation.  They prevent the sensor from contaminating the liquid (important if it's food!) and avoid nooks and crannies that can trap liquid and make it difficult to clean.  It's much easier  to remove and replace broken sensors or just take them out to calibrate. There are enough advantages that it's the most common way to do this and thus the easiest.

If you really need a feed through, swagelock fittings can be used for this.  Just use a solid rod the right diameter for the ferrule and connect to it on both sides.

8

Projects, Designs, and Technical Stuff / Re: Linear acceleration of stepper motor

« Last post by moffy on Today at 11:03:10 pm »

Just an FYI for Andre, there is a project that might suit called GRBL: https://github.com/grbl/grbl
which runs on an Arduino, it takes GCode commands and controls the stepper motors, it is used quite extensively and would probably suit your application.

9

Power/Renewable Energy/EV's / DIY Battery Bank from Recycled 18650

« Last post by FinOminal on Today at 11:00:24 pm »

Someone on facebook is selling these:

I attempted to let the seller know this is a dangerous build, but they don't seem to care.

I thought it would be worth while getting opinions (technical and rational) from the community so they can see that it's not just me being annoying.

What are your thoughts on using random batteries that are soldered together in this way?

10

Beginners / Re: LC filtering for combined Vref/VDD of ADC

« Last post by temperance on Today at 10:54:59 pm »

An LM4040 shunt reference maintains a dynamic resistance below 0.25 mOhm with a bias current of 1 mA up to about 350 Hz. With a 270 R bias resistor this equates into a 60 dB PSSR. Below 200 Hz the dynamic impedance is even lower and close to 100 mOhm or about 68 dB PSSR.

Does it outperform an LDO? When bypassed with a 10 µF ceramic capacitor is does for freq. above 1...10 K. But some LDO's are better than others. Some modern ones are very good while some are just bad. The REF2030 I mentioned earlier is a series reference. (My mistake) When it comes to high frequency noise, the LM4040 when bypassed with 10 µF outperforms the REF2030 for freq. above 1 K.

Besides, at low currents, the PSSR plot might still be valid because the LDO is not operating close to or in saturation. But the way they specify drop out can be tricky. I usually calculate the MOSFET on resistance. That seems a more valid approach to me. But that only works for LDO's with output voltages > 2.5 V.

A shunt ref with a very low dynamic resistance is the AZ431L. 50 mOhm from DC up to almost 50 KHz. This would translate onto 75 dB PSSR from DC up to 50 K without a bypass capacitor. Not bad.

But your question is valid because this turns out to be an edge case.

I wouldn't know how to pick an LDO regulator with good PSRR, though. It seems difficult to make comparisons because the manufacturers all give specs according to different conditions. Some give it at 1kHz, some at 100kHz, etc. I'm not even sure what magnitude of PSRR is good. Is 50 dB good or poor? 70 dB? 90 dB?

The first question to answer is how many bits you need.