Bipolar PI design

[ivconic]

One less dilemma, thanks Altra!

[Carl-NC]

Carl, apparently the frequency adjustment range is very wide, going from about 330Hz to as high as 1.8kHz.
A simple question: "is it safe?"

As the frequency increases you should also see the pulse width decrease. Because the relationship is non-linear, it actually burns less power at higher frequencies.

[eduardo1979]

Hello everyone.
I've finally been able to finish the PI Bipolar detector. Everything works correctly, just as shown in the video. The sound is very similar to the GPX series. The Hi-Low discrimination is very good, as is the GEB.
https://www.youtube.com/@eduardofern...pez7868/shorts

Best regards,
Eduardo.

[ivconic]

Excellent Eduardo!
Dunno why Carl is "complaining", the detector works quite alright!
(Carl is too modest)

[algan]

Perfect Eduardo and you act quickly. Now can you tell me what the oscilloscope diagram is with your project? Is there still the bug that Carl showed in the video or is it gone? Can you make a clip of the oscilloscope? Thanks.

[eduardo1979]

The error has disappeared, as using a 4066 as a demodulator with its corresponding level translators worked perfectly. The VCO was also modified and replaced with a 4046. The Threshold stage was also modified. In any case, this is a project that can be further improved. For now, it detects a gold wedding ring 30 cm in the air. It also detects gold nuggets, but at a shorter distance than the TDI. As a learning base, this project is very good, giving people the opportunity to try out a Bipolar PI. Carl has done a great job, as always.

[Detectorist#1]

Hi eduardo1979,
Congratulations for you and for Carl. How hot are the two stones in your youtube video? It is interesting - you not change the GB setting pot between waving of them.

[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?!

[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.

[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.

[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!

[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.

[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]

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]

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