PI metal detector with energy recuperation

[WM6]

Maybe you are right , maybe not , who knows .... but as for me , I just found a strange and as it seems to me beautiful path in a big world of metal detecting What I did - I followed this path , explored it as I could ... but whether people go this way - I don't know

This is great electronic creations, no doubt. Once complete teams used to work for months on such projects. Unrepeatable for most of us. I hope we will get more great ideas and constructions from you in future. Thanks.

[golfnut]

Good to see a block diagram !

S

[WM6]

Hi deemon, did you take some sensitivity tests on different targets?

Are you satisfied?

1,5 mA current consumption only is really a great achievement.

[deemon]

Hi deemon, did you take some sensitivity tests on different targets?

Are you satisfied?

1,5 mA current consumption only is really a great achievement.

Of course , I am not satisfied , because sensitivity is quite medium now ... for example , search distance for coca-cola can is about 50 cm , nickel coin of 2,3 cm diameter - is something about 12 cm . But my sensor coil in this experimental device is far from ideal now , so I hope to improve the parameters after ferrite core replacement . I couldn't find a good monolithic core and made it from 3 pieces with total length 27 cm , and of course it's not good . I think that it's better to use longer monolithic stick , if I find it - about 40 cm must be OK for such a portable metal detector . Of course , for special deep search purposes one can make an even longer sensor - because a search depth depends here not of diameter of the coil ( like it does in conventional search coils ) but of the length of the coil - longer coil makes magnetic field to penetrate deeper into the ground .

And another important thing here - is magnetic permeability of the core . Now it's 2700 ( ferrite core for power pulse transformers ) , but there are much better ferrites , as I know . Another idea - to use amorphous iron core - it can have permeability of 50000 or even more - such a coil must be a real champion . What I think to do - is to find something better than I use now and perform more experiments ... anyhow , I hope that my sensitivity result is not a limit for this kind of PI detectors .

About power consumption - 1,5 ma is consumption of signal processing circuit only ( gain stages , correlators , etc - all shown on page 2 of schematics ) , and the power chain with compensation circuit ( page 1 ) eats about 11,5 ma , and about 1,5 ma for sound ( page 3 ) , so the total consumption is something about 14,5-15 ma from 24 V supply . But because of switching mode stabilizer all device does consume 13 ma from 3 fresh 9V batteries . And of course , this power saving recuperation technology can be used in different manner - not to save a battery with the same pulse energy ( like I did ) , but to rise pulse energy with the same power from the battery . And this can be useful with the big coils for deep search , as I think .

[WM6]

, search distance for coca-cola can is about 50 cm , nickel coin of 2,3 cm diameter - is something about 12 cm . But my sensor coil in this experimental device is far from ideal now ,

.

Not bad for ferrite core antenna. Max. detecting field is in front (axial) of coil?

[deemon]

Yes , maximum of sensitivity is directly on the axis . And this is why I like this ferrite antenna - it can sense big and deeply buried objects like the conventional search coil does and at the same time can sense and precisely locate little objects ( coins , etc ) near the surface . But if we don't need to sense little metal junk - we can reject it electronically , using information from 2 detector channels . In another words , we don't need a special pinpointer with this device ...

[straton]

Maybe you are right , maybe not , who knows .... but as for me , I just found a strange and as it seems to me beautiful path in a big world of metal detecting What I did - I followed this path , explored it as I could ... but whether people go this way - I don't know

"Professional" gold seekers go for what works best. No question about it. Researchers and scientists like yourself, I suppose, try a lot of different paths.

[WM6]

Yes , maximum of sensitivity is directly on the axis . And this is why I like this ferrite antenna - it can sense big and deeply buried objects like the conventional search coil does and at the same time can sense and precisely locate little objects ( coins , etc ) near the surface . But if we don't need to sense little metal junk - we can reject it electronically , using information from 2 detector channels . In another words , we don't need a special pinpointer with this device ...

Can we say that surface covered by such ferrite antenna is about circle of 3cm in diameter, or maybe 10cm in diameter, or ... more?

And deeper in soil, I am curious about ferrite antenna radiation field diagram.

[deemon]

Can we say that surface covered by such ferrite antenna is about circle of 3cm in diameter, or maybe 10cm in diameter, or ... more?

And deeper in soil, I am curious about ferrite antenna radiation field diagram.

Yes , on low distance it's a spot about 3 cm diameter , and when we go deeper it becomes wider . But anyhow , we have a clear maximum on the axis , so the antenna is pointing directly to the target when the sound has maximum pitch .

[Alexismex]

With this ferrite monster it will be great :
http://www.stormwise.com/page26.htm

[Midas]

Yes , on low distance it's a spot about 3 cm diameter , and when we go deeper it becomes wider . But anyhow , we have a clear maximum on the axis , so the antenna is pointing directly to the target when the sound has maximum pitch .

I can't help but feel that a ferrite core antenna is not optimal as far as depth is concerned. Perhaps you already know that but are prepared to sacrifice depth for pin-pointing ability. Still it would be very interesting to see its performance with a more regular coil. If its performance improved enough maybe it would be worth your while to switch coils and make a dedicated pin- pointer.

Oh btw as others have noted it is indeed a work of art.Congratulations.

Midas

[Woody.au]

Wow! I just felt like i had a flash back to the early 1970's I would give up on the idea of using a Ferrite loaded coil as it does not have a large amount of capture area to get any appreciable depth. Sure its ok for pinpointing but what a complicated pinpointer with all that discrete electronics connected to it..

[deemon]

2Midas

Yes , I have the same thought now ... but I really did it for some purpose . This design did have a three main goals - to test this "current-reverse and recuperation" concept , to test some specific schematic solutions and to test a ferrite as a search coil core . What does we know about ferrite ? It has 2 main drawbacks - magnetic instability and nonlinearity And these drawbacks makes almost impossible to use it in high-class metal detector . On the other hand , ferrite search coil looks quite attractive in some specific conditions , such as hollows , caves , fractures , etc . And what is interesting , it seems that this circuit is the one and only that can use a ferrite quite correctly and push it to the limit .

What I mean by this - it's instability and nonlinearity cannot make a harm here . You see , when the current is changing in the coil ( charge and discharge intervals , A-B and D-E on timing diagram ) - we don't measure anything , and when we measure the incoming signal ( measuring interval C-D ) - the current doesn't change When we receive , the current is constant , we are sitting on the one point of the magnetization curve , so if the permeability does change , it's not a problem at all . Even if the permeability of our ferrite drops to 1/2 of initial value - it can't disturb the demodulation process of the circuit . All we need from our ferrite core is to "suck" magnetic force lines into the coil , and it's enough ...

So I cannot stop myself to try it anyhow and look how can it work . What about the concept - it works OK , so the schematics does , but about ferrite I am hesitating now . As I think - this performance of course isn't the best because of mediocre quality of the ferrite that I used ( and the core isn't monolithic , it's not good too ) , but what can I achieve when I use the best ferrite - it can show the future experiments , of course .

So the best idea now is to assemble the same device with the same schematics , but optimized to use a conventional search coil ( simple round coil with air core ) - it needs some minor changes in the power chain circuit , and direct compare it's performance with the existing one . And if I find the good long ferrite core with high permeability and good Litz wire , I will be able to replace my search coil in this device and compare them again in order to make a final conclusion .

[deemon]

Wow! I just felt like i had a flash back to the early 1970's I would give up on the idea of using a Ferrite loaded coil as it does not have a large amount of capture area to get any appreciable depth. Sure its ok for pinpointing but what a complicated pinpointer with all that discrete electronics connected to it..

Ferrite is not a problem for this concept , because this circuit can work with usual search coil as well , with all its features such as power saving , 2-channel metal discrimination , etc . By the way , its low sensitivity to the ferrite permeability inside the coil makes it quite insensitive to the any ferromagnetics outside the coil The circuit does have inherent "ground tolerance" , because if the soil does content iron oxide , it works like "weak ferrite" outside the coil , and the demodulation circuit just ignore it .

[Sean_Goddard]

WOW

Now THAT is a work of art Deemon!!

Behold the work of a TRUE Engineer, not just someone who connects IC's together and hopes the results work (although I'm getting better at it these days ).

**RESPECT**