Pirate Detector Waveforms

[MOR_AL]

Dear Sirs
I'm using Google Translate. Sorry if some sentences are not understood.

I'm retired here in Brazil and I can say that I understand analog electronics and know how to do some small projects with PIC microcontrollers.

I'm trying to understand how each step of the Pirate detector works.

I started changing the mosfet stage successfully. I included a source circuit, which limits the drain current to a chosen value, regardless of the period supplied by the collector of the first transistor (PNP) to the MOSFET gate and the value of the coil.

I would like to know the waveforms available in this detector.

Where can I get the full cycle at the output of the first OA op amp?
In my Protoboard assembly I am obtaining a waveform that interferes with the identification of this signal. I don't know if this is normal, as I can't find this waveform anywhere. For this reason I did not continue setting up the following stages. It is as if there was a negative voltage overshoot, with hundreds of microvolts on the diodes.

The strangest thing is that even by inserting a negative feedback capacitor into the first OA, which would reduce the high frequency range, the transition at the OA output remains fast, which would not be compatible with the theory.
It may be that the Protoboard assembly is producing interference between the stages. My next step is to assemble a PCB until including the first OA.

I would be grateful if anyone could tell me where I can find the waveforms found in this detector.

Thanks

[pito]

https://www.youtube.com/results?sear...�р+пират

[pito]

https://www.youtube.com/watch?v=txe78PQwzj8&t=23s

[ivconic]

What clearly caught my eye is the VOLTS-DIV potentiometer (or switch) which is very "loose" and does not turn properly but seems to be damaged or of very poor quality... hard to say.
Hantek is not too expensive, but I didn't expect it to be of the worst quality...
Or is it just an individual case, specifically that one loosened due to overuse...
Of course this has nothing to do with the topic... but the topic itself is not something interesting...
I wouldn't even be commenting on this if I hadn't been reminded of what I read on another oscilloscope thread last night.
And by the way, I have an almost new mid-range analog oscilloscope, which I am very happy with.
But it's big and takes up too much space in the very tight space of my workshop in the corner of the living room (where I'm violently crammed in by my wife).
So I'm thinking more about getting a smaller digital oscilloscope. And of course, due to the chronic lack of money; I pay attention to the cheaper models first.
And I dream of for example a Rohde & Schwarz model... which I will certainly never see in live...

[MOR_AL]

https://www.youtube.com/watch?v=txe78PQwzj8&t=23s

Good morning Mr Pito.
I had already swept almost all YouTube videos about the pirate metal detector.
But in your second link I found almost what I wanted.
The author actually showed the signal at the output of the operational amplifier. The detail is that it shows the small, but important, region of the useful signal. The section in which an inconvenient signal appears occurs later, within the same cycle.
I decided to assemble the original circuit just to observe the presence or absence of this signal.
By doing this I will be able to understand what is happening in the detection.
Thank you for your contribution.
MOR_AL

[MOR_AL]

.....
And by the way, I have an almost new mid-range analog oscilloscope, which I am very happy with.
But it's big and takes up too much space in the very tight space of my workshop in the corner of the living room (where I'm violently crammed in by my wife).
So I'm thinking more about getting a smaller digital oscilloscope. And of course, due to the chronic lack of money; I pay attention to the cheaper models first.
And I dream of for example a Rohde & Schwarz model... which I will certainly never see in live...

I wish you achieve your dreams.
Here is the video from my electronics lab.

https://www.youtube.com/watch?v=tk1kVgOglyg

MOR_AL

[Tinkerer]

I wish you achieve your dreams.
Here is the video from my electronics lab.

https://www.youtube.com/watch?v=tk1kVgOglyg

MOR_AL

A picture of your oscilloscope scren with your waveform and your schematic with the testpoint where you see the waveform would help us identifying your problem.

[ivconic]

I wish you achieve your dreams.
Here is the video from my electronics lab.

https://www.youtube.com/watch?v=tk1kVgOglyg

MOR_AL

Thank you sincerely, but that dream will be difficult to achieve.
Maybe in one of the next lives.
Hey you have so much space and a very nice workshop! I envy you!

[MOR_AL]

A picture of your oscilloscope scren with your waveform and your schematic with the testpoint where you see the waveform would help us identifying your problem.

My Circuit.

Ton of 555 = 500us; T = 11ms
Ton of MOSFET = 100us; T = 11ms
I(MOSFET) = 1,2Apk


MOSFET driving and flyback signal. Yellow: V2 (on diodes). Blue: V3 (OA output. Pin 1)
Both the blue signal and the yellow signal are AC




Same as the previous one but showing the entire cycle. Yellow: V2 (on diodes). Blue: V3 (OA output. Pin 1)
Note the undesirable signal between 2ms and 6ms.


MOR_AL

[Tinkerer]

Is this the original schematic you are trying to improve?

[MOR_AL]

Is this the original schematic you are trying to improve?

Yes it is the original circuit.
I'm trying to improve it. But there's still not much difference from the original.

The period of the 555 only differs at Toff = 500us (ton on the mosfet).

Q2, Q3, R6, R7 and C4 form an SCR, which limits the drain current to 1.2A (Ton on the mosfet with 100us), whatever the value of the L1 coil.
R9 = 10k. The value of R8 is such that the flyback pulse does not present overshoot, as can be seen in figure 2.
I increased the value of R9 (10k) to reduce the Icc current consumption. As a result, I had to change the signal for the positive input of the OA.
The value of the inductor L1 = 526uH is within the expected range for the Pirata detector.
Observing the blue signal at the OA output, in figure 2, the signal has 40us and when I place an iron box, this period increases, as it should be.
My only issue is that there is an undesirable signal between 2ms and 6ms (figure 3), which I believe makes it difficult to identify the useful signal.
I'm assembling a PCB for the Pirate detector. I intend to put the original values, just to see the complete cycle in the output of the first OA.
MORAL

[kt315]

I'm assembling a PCB for the Pirate detector.

anyway you will get great experience in the soldering. those skills will be needed for you for assembling Carl's HAMMERHEAD PI.

[MOR_AL]

I'm assembling a PCB for the Pirate detector.

anyway you will get great experience in the soldering. those skills will be needed for you for assembling Carl's HAMMERHEAD PI.

Thanks
I already had the opportunity to read about this metal detector.
My goal at this point is to find out if the inconvenient signal that appears in my project also occurs in the Pirata detector.
If so, I will try to eliminate it, as I believe that without this undesirable signal it will be possible to increase sensitivity.

I have some experience with electronics. In 1967 I took a radio and TV repair course. Since then, electronics have accompanied me on a daily basis.
I invite you to access my videos about electronics on YouTube.
They are in my native language (Portuguese), but electronics has its own universal language.

https://www.youtube.com/@MORAL1952/videos

Grateful.
MOR_AL

[MOR_AL]

OK!
I finally finished assembling the Pirata metal detector and I have some observations to make:
I photographed the Pirate detector waveforms from pins 1 (OA output) and pin 6 (comparator input). Follow the photo.



1 - The gain of the preamplifier in my circuit (non-inverter) is worth around 57 and is greater than that of the pirate (inverter). That's why the positive output of my circuit has almost 20us of saturation. The negative pulse of the Pirate preamplifier does not saturate, or is almost saturated.
2 - The preamplifier feedback resistor (1M8 or 2M or 2M2) of the Pirata detector has two purposes.
2.1 - Do not transform the preamplifier into a comparator.
2.2 - Establish the upper cutoff frequency. It turns out that depending on the OA used, this frequency may change, due to the open loop gain of each OA.
3 - Although this detector has a traditional circuit, I obtained better sensitivity by replacing the electrolytic capacitor at the preamplifier input, with a value 10 times greater.
4 - It would be interesting if the second OA, functioning as a comparator, was actually a comparator.
5 - The initial detection of small metals would be increased if there was a monostable stage between the comparator and the transistor driver. This monostable (555) could be driven by a current source instead of one of the resistors. This would maintain the signal frequency variation according to its intensity. This already occurs with the Pirata detector, but the beginning of detection would be more evident.
Finally.
I think a circuit with a small microcontroller (MC) could simplify the circuit.
1 - The signal generated by the 555 could be eliminated.
2 - The MC's DAC could read the exact period in which the presence of the metal appears. Furthermore, the comparator would also be eliminated.

At the moment I discovered (in my circuit) that both the Ton period and the decay period of the flyback pulse could be used to discriminate the material. Ferrous materials alter these periods differently than non-ferrous materials. However, this is practically only observed when the material is already larger and is closer to the coil.
Thank you to everyone who contributed to this topic.
MORAL

[Eddy71]

I think a circuit with a small microcontroller (MC) could simplify the circuit.

I thought the same thing, so I already did it.

https://www.eddy.com.ua/archives/784

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