Tesoro Bandido - 18,5Khz - To find small gold nuggets

[bgs]

If you've been in electronics 40 years like me you'll know what's good.

[Andre]

If you've been in electronics 40 years like me you'll know what's good.

40 years in electronics mean nothing. The valve time is up! What matters is an open mind, as a good engineer or electronics technician knows that an ideal component is different from a real component. What I would like with this post is to offer one more project. Comments are welcome. Doubt too. Stubbornness, never!
I made my contribution. Nobody is forced to build it, but I want respect since I have shown that it works. The 40 years of electronics that you have, does not give you the right to discredit other people on this forum.
Sincerely

Andre

[Ruben2000]

Hi Andre, the video is very interesting. I've always wanted to have a nugget detector but they are very expensive. I hope to be successful in the construction. I do not have much knowledge about detectors but I have read several threads on this forum and I am more or less understanding. You are succeeding in your project, continue there.

[Andre]

Hi Ruben2000,

The project is really interesting, but there are people who don't give us credit. They think they are "the last cookie in the box!" ( A forty year old cookie)...
Tesoro Bandido occupied me for several weeks, but I was very pleased with the results.
I hope you will be satisfied!
Regards,
Andre

[MartyJ1963]

Looking forward to your progress Andre! @Ruben2000,,Hope you succeed in Sprint layout with the design,,,It will be a nice project to build. Great little video Andre! Regards, Marty.

[Andre]

Hi, MartyJ1963.
Encouraging words! I'm glad there are people like you on this forum!

[MartyJ1963]

No probs Andre,,,Looking forward to your Bandido as an eventual future project. Best luck and regards, Marty.

[bgs]

You want respect. Andre,YOU ARE GREAT! But on the schematic the generator does not work ...!

[Qiaozhi]

Forum friends! I decided to present here my project to modification the famous Tesoro Bandido II U-max, to find small gold nuggets. After countless attempts, I managed to arrive at this project that surprised me! I leave your outline published here for your analysis. A CA3140 op-amp was used to generate a sinusoid wave with adjustable frequency. I used a type D coil with 17cm in diameter and 28 AWG wire. 9.12mH for the receiver and 9mH for the transmitter. The receiving coil was covered with metallic adhesive tape and grounded to the circuit's GND. You may think that the set is out of resonance frequency, but, incredibly, that's how it worked best.
The op-amps must be the same as in the diagram shown. Attempts with equivalents left the circuit with less sensitivity.
I appreciate any comments or constructive criticism.
[ATTACH]54555[/ATTACH]

At first sight there does appear to be a problem with the oscillator as you have drawn it in the schematic. Since there is no positive feedback in the circuit it cannot possibly oscillate.
However, since you have a physical working circuit I thought must be a discrepancy between what you've built and what you've presented here.

But ... I then put the oscillator into LTspice, and (guess what?) it oscillates. The frequency of oscillation is nowhere near 18kHz, and the so-called Freq Adj cleans up the amplitude noise but has little control over the frequency.

I suspect this design is very dependent on the actual opamp used, as I did the simulation with an LT1007.

[Andre]

Dear master Qiaozhi!


It is true! It works! I have always used this configuration since my school days. Only works with the CA3140E! Try replacing the 47k trimmer for 100k for the 18Khz frequency.
The video and photos prove it works!

Thanks for your message!

[Qiaozhi]

Dear master Qiaozhi!


It is true! It works! I have always used this configuration since my school days. Only works with the CA3140E! Try replacing the 47k trimmer for 100k for the 18Khz frequency.
The video and photos prove it works!

Thanks for your message!

I tried different opamps in the simulation. Several of them fail to oscillate, whereas others oscillate at different frequencies.
It would no doubt work better and be more reliable if you used a Wien bridge oscillator configuration.
https://en.wikipedia.org/wiki/Wien_bridge_oscillator

[Andre]

I am satisfied with your performance. It has good stability and very little variation in its frequency, in the order of tens of millihertz. I don't know why there is so much suspicion. You have to build it in practice, not just by simulation. There is a possibility to replace this transmitter circuit with a similar configuration using the ic ICL8038, which will have the same practical result.
Regards,
Andre

[Andre]

Well,
I made my contribuition!
I Hope that you enjoy it!
End of line for me for on this topic!

Thanks all!

[SWL]

You do the right thing by closing the topic --- the project is hopeless. I watched the video. With such sensitivity in the air, in the ground, it will be useless.

[Andre]

You do the right thing by closing the topic --- the project is hopeless. I watched the video. With such sensitivity in the air, in the ground, it will be useless.

You must be a very happy person! Your kindness exudes from your skin like that exhaled from a skunk! Stupid criticism is very easy for you. However, you are unable to suggest an improvement. I think due to the lack of ATP!

As they says here in Brazil: "A inveja mata, seu fdp de pau pequeno!"