Bipolar PI design

[Carl-NC]

The most important thing is that it not detects (but it should) that small silver "Ottoman" coin, which is about 6-8mm in diameter but is very thin and is made of pure silver.

This type of subtractive GB always results in a target hole and it's possible the Ottoman coin is in this hole. Turn off the GB and see if it can be detected. If so, it is in the hole. You can move the hole around by changing the timing parameters but then something else will end up in the hole. The book describes how to eliminate the hole.

[Orbit]

Hello Orbit
Which part of the world are you from?

https://youtu.be/j09lv2ugzww?si=cW-XgsZGO0Q_JYTE

[ivconic]

Ok, I'm happy for now. The detector worked from the first, without any problems.
Now to recap...
What would I like to see better on this detector?

1) Much softer audio without the "sharp" sound and without the background quiet "buzz" ... which may not be heard in the video.

2) To improve it so that it detects those coins from the video that it does not currently detect.
The most important thing is that it not detects (but it should) that small silver "Ottoman" coin, which is about 6-8mm in diameter but is very thin and is made of pure silver.
(The Minelab Vanquish 340 detects that coin incredibly deep, noticeably deeper than the Deus 1)

[ivconic]

Before watching the video, a mandatory note:

- Not a single decoupling capacitor was fitted...
- Coil is "random", totally inadequate... 18cm diam.
- The damper resistor is 390 ohms, rather randomly chosen, probably inadequate.
- The frequency is set to 1.1kHz
- Gain is at approximately 75-80%
- Delay is at a minimum.
- Mosfet transistors are 2 x IRF840 and 2 x FQP3P50.
- I also couldn't buy a 74HCT4053 anywhere so I put in a 74HC4053 instead.

The set of opamps was the same as on the original schematic, and then I replaced them with TLC274 and TLC272.
I did not notice any major differences in performance.
I assume that the differences will be noticed only when the device is arranged more neatly
(addition of a decoupling capacitor and a more adequate coil with a damper).

At one point, two very similar ancient Roman coins, the so-called "Antoninian" can be seen;
one has a good patina and the other is "burnt" and without patina.
You will notice that it is the one with better patina and quality; much better detected.
Yes, there is a noticeable "cut" and "chirpy" audio as well as a very quiet "buzz" in the background.
The speaker is 8 ohms.
Ground balance works great! No objections!
Before shooting the video I did a GEB adjustment on the piece of antique brick from the video.
Otherwise, that brick is detected by all detectors when GEB is not performed on it.

[pechkata]

Works great! But I think some people were still disappointed.. It was thought that it would be equal to Smart Pulse Hybrid or better than it.. Still needs work?!

Hello Orbit
Which part of the world are you from?

[ivconic]

Not to spoil this topic, fun here: https://www.geotech1.com/forums/foru...elmholtz-coils

[algan]

Hi Eduardo, will you post the layout of your board?
To build your project. Thank you.

[Carl-NC]

That's curious, I wouldn't think it would matter all that much. I've made monopolar designs that cancel hot rocks quite well.

[eduardo1979]

Thanks, Carl, for answering my question.
I've noticed that ground balancing is more effective with the bipolar design than with the monopolar one. I have a highly mineralized stone, and the only detector capable of canceling it out is the bipolar one. The monopolar detectors I have aren't capable of rejecting it.

[Carl-NC]

The bipolar TX has more parasitic capacitance than a mono TX so usually the sample delay cannot be as aggressive. This will limit the smallest nuggets you can see. On the other hand, bipolar can be run at much higher pulse rates than mono and this can improve integration gain, but this won't make up for the later sampling.

[eduardo1979]

Hello Detectorist 1.
Thanks for the feedback. The black stone is very hot, and the other object is a piece of highly mineralized brick. If you bring a magnet close to it, it sticks. There's no need to touch the GEB potentiometer. I don't know if it's because the mineralization of the two objects is very similar, or because the GEB has a lot of margin and isn't as sensitive to small changes in mineralization. I've built many PI detectors with very good results for detecting small gold nuggets. This detector isn't as sensitive for small gold nuggets as the ones I've built in the past, and they weren't bipolar pulse detectors. I don't know why. I don't know if bipolar detectors are less sensitive to small nuggets or not, but the results are clear. Surely Carl would clear my doubts if he read this post.

[Orbit]

Hi Orbit,
Yes, but you must have in mind that Smart Pulse Hybrid uses IB coils and this project uses more simple mono coil with very good results. The difference in the coils is very important for DIY projects.

Hi Detectorist! Let me understand what you're talking about! I also know that some expected exactly what I wrote... That's why I'm sorry for some who thought it would do the same.Again the translator does not translate realistically.. Let me understand that Smart uses an ib coil!

[Detectorist#1]

Hi Orbit,
Yes, but you must have in mind that Smart Pulse Hybrid uses IB coils and this project uses more simple mono coil with very good results. The difference in the coils is very important for DIY projects.

[Detectorist#1]

In my PI-MD project with IB coil, I also use VCO for high-low tone for Fe/non-Fe targets discrimination and different threshold stage, but I'm not sure for GB capabilities of my design until the field tests.

[Orbit]

Works great! But I think some people were still disappointed.. It was thought that it would be equal to Smart Pulse Hybrid or better than it.. Still needs work?!