Recent Posts

1

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

« Last post by G0HZU on Today at 12:22:25 am »

The J309 is a process 92 part and this is a bit different to an MPF102 as the MPF102 is a process 50 part.
The internal die is different and this means the capacitances will be different and so will the gm and the Idss.

2

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

« Last post by tggzzz on Today at 12:22:12 am »

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.

The context is these threads from MajorAssBurn:
https://www.eevblog.com/forum/buysellwanted/fs-affordable-dmm-checkers-ac-reference-dc-reference-ohms-reference-etc/msg5463700/#msg5463700
https://www.eevblog.com/forum/metrology/affordable-useful-ac-dc-references/msg5438690/#msg5438690
Anybody with too much time on their hands can read those. They will, no doubt, notice that many people have made negative comments about MajorAssBurn's claims in those threads.

3

Projects, Designs, and Technical Stuff / Re: more modern version of tl494?

« Last post by David Hess on Today at 12:21:08 am »

Unitrode had advanced replacements for the TL494, but after Texas Instruments bough them their selection guides were removed.  I think they had a current mode control version of the TL494.

4

Test Equipment / Re: Troubles with HP-8903B

« Last post by alan.bain on Today at 12:20:24 am »

Are you testing using the 8903 or an external frequency counter?  I've got an 8903A and the timebase is a fairly poor stability crystal (on mine I had to adjust the capacitative loading to be able to adjust it to within spec). However the output freq is counted with its own counter and this used to effect an adjustment so this should be stable!

It's obviously vital to know if your issues are in the source or the analyser.  The performance checks in Section 4 of the OSM are worth doing (at least the early ones).

Distortion in the source is often the fault of the ALC circuit - think mine had some leaky sample and hold caps.

Alan

5

General Technical Chat / Re: Is LinkedIn worth keeping?

« Last post by floobydust on Today at 12:19:07 am »

I have a few LinkedIn "connections" only with people I am really interested in and value, good peers. Instead of just anyone to jack up the number- which is a popular stunt.

I tried to add Dave as a connection, very long time ago. But it's only famous celebrities that are "on the list" lol. Didn't make it.
Also, making my connections visible to others is kind of shooting oneself in the foot if you are looking for work. You would likely have other peers, competitors to yourself on there and why aid recruiters? Why does knowing who you know matter? Seems like a zuckerburg strategy lol.

[...]  Unprofessional to use your employer's computer systems to search for other jobs (and potentially a breach of contract) for one. 

That is unprofessional?  I had a boss (married) using on-line dating site, another was checking out Sunshine Girls - with company computer. I walked in to their office a bit too fast for them to hide it. ICK. I've seen co-workers do their on-line banking, shopping, stream music as well.

I'll look at jobs using an employer's computer when confirming an opening got posted, to confirm that lazy HR is going to replace that guy and not overload me more.
If no hiring action is being taken, that is unprofessional IMHO. Then I'm looking for a new job, on company time lol.

6

Microcontrollers / Re: Has anyone used ASAN & MSAN, and relevance to embedded arm32

« Last post by djacobow on Today at 12:18:50 am »

At my company we have taken quite a bit of effort to be build out a hal that allows us to native compile our firmware projects on the host and run them against fake peripherals also on the host: things like UART and SPI show up as network sockets, timers are simulated with SIGTIMER, etc.

Anyway, we use clang for this and do use -fsanitize=address and we've caught a fair number of bugs this way.

You can achieve a lot of what these tools do by making your own instrumented memory guards. Create functions for allocating memory that allocate a larger chunk and return a pointer that skips the first 1/2 of the extra space, then have a registration function that colors the space at the beginning and and, and a checker that you run periodically on all the allocations to check for clobberage. This is very straightforward to do if you use malloc (just call this instead) but even if you use 100% automatic variables, you can achieve the same thing with some clever macros.

7

General Technical Chat / Relay trigger when voltage above 13v

« Last post by bigjoncoop on Today at 12:07:41 am »

Trying to create a simple circuit that will trigger a relay only when the monitored voltage is above 13v.

(the output voltage of the circuit is not important. Just needs to be 0v when the monitored voltage is below 13v)



I was able to find a couple of threads on this, but there was no clear answer in the end...



I was originally thinking of using a LM386 and a TL431 as a voltage reference since I have alot of these components. But was unable to find a detailed schematic on how to do so...

I do have a couple of low voltage disconnect modules I could use if all else fails connect a Buck converter on the output to trigger a 5 volt relay..

Specs:

Monitored Voltage Range: 12v - 14.6v

Trigger Voltage: ≥13v

Output voltage to control relay: Not Important

8

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

« Last post by cosmicray on Today at 12:07:31 am »

I was searching for an SMD replacement for MPF102. The one I found that (based on specs) seems to be close, and was available at LCSC, is an OnSemi MMBFJ309LT1G. I have not yet had the time to verify their utility for this purpose.

9

EEVblog Specific / Re: EEVblog 1612 - Siglent SDS1000X HD 12 bit Oscilloscope Teardown

« Last post by EEVblog on Today at 12:06:19 am »

Hi Dave, my 1204X-HD has microphonic inputs.

Wow. Why the difference?

10

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

« Last post by floobydust on Today at 12:05:43 am »

Name the Aliexpress store selling junk.
JFET's I've bought there have been meh. I had to because of the semiconductor shortages, ain't nobody makin' JFETS months back.
Shenzen IC Store - they were weird looking TO-92's, laser marked, a bit dodgy made me squirm.
Fantasy Electronics CO., Ltd Store - was good. FET's I've bought there have been OK, I_DSS in spec.