felezjoo PI(the best pulse induction metal detector that I made until now)

[Detectorist#1]

Hi ivconic,
For you, experienced guy in metal detectors, is very strange to write for the problems with RX amplifier for this very simple detector. It is easy to see with oscilloscope if the signals on the output the RX amplifier stage haves some problems. In this project, the author make attempt to move all problems to the software, but the speed and the properties of used microprocessor haven't enough power for producing of really good results. But, the attempts continue so many years....

[ivconic]

I am extremely grateful to you for being willing to teach me, thank you very much!
Could you do me a huge favor and explain how to use an oscilloscope?
Little is clear to me from what you are talking about!?
Thanks in advance!

[latcakir]

Aliexpress is death. I from Turkey and i used aliexpress 10 from years. AliExpress is banned in our country. Now I can't even log into my old account.

[Tanu]

ivconic can you give your coil details?

thank you

[ivconic]

In advised range... 0.38mH/1.7R

[algan]

Very dissatisfied I wrote an official complaint to Aliexpress.
After a few days, I received a reply that "I am not right and that my complaint is rejected"... !??
So much for how Aliexpress protects its customers.
A gang of thieves, liars and robbers! Generally speaking.
There are also positive examples, of course, but they are rarer.
This is a link for a damn thief, remember this seller well and NEVER BUY ANYTHING from that scumbag!

https://www.aliexpress.com/item/1005...%21%211%210%21

I've also bought ICs from Aliexpress that don't work. Nothing can be done, they're cheap and people get scammed, there have been some that work, you can't be sure until you test them.

[ivconic]

Last year I ordered 30 pieces of J113 and they all arrived ... FAKE!
And then I ordered 20 pieces from another seller and they all arrived... OK!
You never know what you're going to win, like the lottery!

[ivconic]

[nejdet]

Last year I ordered 30 pieces of J113 and they all arrived ... FAKE!
And then I ordered 20 pieces from another seller and they all arrived... OK!
You never know what you're going to win, like the lottery!

Can I have a link to a legitimate seller? Thanks!

[ivconic]

I can't be sure, the link is missing from my "order" list, because it was last year.
It looks like Aliexpress doesn't keep those listings longer.
I did not save the seller's name.

[Detectorist#1]

Hi ivconic,
Don't be so quick to thank me in advance for teaching! We haven't agreed on my fee yet. It's important to use our sense of humor!

[ivconic]

The whole point is that until the original LF357 arrives to me; any further story makes no sense.

[latcakir]

Is it possible to build an original LF357 test circuit?

[ivconic]

Very good question.
The answer is conditional; it depends on what you want to test with the opamp, which characteristics.
In this case, the best test circuit is precisely the FelezJoo PI detector. And "debug" numbers on the LCD.
Otherwise, the general opamp tester circuit would be very complex with the addition of not very cheap measuring equipment.
I do a lot of different things, the least detectors in recent years.
I mostly make musical equipment.
And I have the perfect "tester" for single opamps for those applications.
Similar case as here with FelezJoo PI.
I have a small simple "echo/delay" pcb that has a mic input and an amp output.
In addition to LF357 being faked, TL071/TL072 type opamps are most often faked. At least that's what caught my eye.
When I put the fake TL071 on that pcb, I turn on the mic and amp; I can clearly hear the huge differences right away.
Fake TL071 produces an unprecedented amount of noise, various squeaky harmonics, etc.
When I put a good TL071; the sound is perfect.
LF357 and FelezJoo PI pcb can be tested in the same way.
Either you get solid behavior right away or you can't get anything even after a few hours of setup.
And the fastest symptom to suspect the LF357 is a constant "Coil Error" printout on the LCD.
Provided that you made the coil according to the instructions.
You don't have to be overly intimidated by coil making.
For room rehearsals, an 18-20cm coil is sufficient. 0.35-0.4mH, 1-2 ohms.
There is no need for various acrobatics with "spider", "basket", "mosquito", "crocodile", whatnot coils...
Ordinary Cu lacquer wire, 0.35-0.6mm and a couple dozen windings, until reach the mentioned specs; will do just fine.

[ivconic]

I posted this picture somewhere on the forum before, I keep it as a reminder for a few hours of annoyance and stress; until I discovered that it was a fake TL071 (whole batch of 50pcs!).
The reason I didn't find out right away was because I found it hard to believe that there was even one moron in this world who would fake the TL071; the cheapest opamp in the world!
The trick of the mind is such that I always first doubt my own mistakes in my work, in the style: "What did I do wrong?".
Last on the list of possibilities is that there is a moron out there who is going to fake the TL071!
But there... still there are such idiots!