EPE IB detector depth problem .. w/ schematic

[Astromic]

Hello,
I built the Everyday-Practical-Electronic's IB detector featured in oct.2002. I built the PCB and the coils as described, 150mm diameter, 100 turns with 0.26mm enameled wire, each. the "nulling" worked well and a good crackle sound on the edge and the humming is all gone now. the problem is it's sensitivity! it detects (air test) a penny only at ~50mm, and it must face in parallel with the coils, with no detection and complete silence (even to the crackling) if the penny got close to the middle of the coils in a vertical approach, and every other object seems to act that way, it need to approach to the coil in parallel. And bigger objects doesn't exceed 150mm rang to cause any sound.
Another thing about the coils, there's a tiny deference between the coils's diameter, TX is exactly 150mm and RX is 146mm, could it be the cause of this huge drop in sensitivity?

The discrimination By the way is sooo sharp by a stunning way, any ferrous metal like iron is NOT detected at all!! well, it's not an issue(isn't it?), but i would like to control that if anyone knows how, as i will use it mainly on meteorite hunting.

I don't know why the depth is so shallow, knowing that it should detect a 1" coin at 9.5" or so, and bigger objects at half a meter or more!!!
the only components i replaced is the capacitor, the author used those little 1n yellow metallised polyester film, i used the same value but a normal "red" polyester that has a larger voltage limit, because i didn't find his recommendation any place around here.. and also i used the TL082 instead of the TL072, but i checked the datasheets and they looks very similar in everything even their inner schematics..

Please help me on this one, i already spent days looking for parts and building it from A to Z, is it a tuning issue? is it a bad component?!
Thanks'

Mike

[Thomas]

This is a change I would make, Change pin selection for best arrangement

[golfnut]

Im unclear about how thim machine works - So I cant help.

If you still require a usable machine that would see large Iron - I would recommend the IDX kit from here sold via Silverdog.

Tidy kit will deliver - (although I found somewhat confusing documentation)

S

[Astromic]

This is a change I would make, Change pin selection for best arrangement [ATTACH]22444[/ATTACH]

Thanks', i would do this arrangement in a new PCB, i'm willing to make another one anyway.. but please explain more about this mod. as i'm learning along those projects..

Im unclear about how thim machine works - So I cant help.

If you still require a usable machine that would see large Iron - I would recommend the IDX kit from here sold via Silverdog.

Tidy kit will deliver - (although I found somewhat confusing documentation)

S

Is the IDX better for iron than say; surf pi and Tiny(from pulsdetektor.com)?, i'm thinking of building the tiny and use the surf kit as a back up!
about how the above device work, i don't know what do you mean exactly, but i will include the working principle if that what you're referring to..

As i said, i already spend too much time on this project and scavenging for components here is like looking for a nail in a haystack, so i would like to solve(or improve a specific component) it first before turning to another one..
thanks'

Mike

[Skippy]

It's possible that the screening of the coil could badly affect sensitivity if you do it wrong. Try it without the screen (foil?) and see of it improves. The op-amp substitution may be the cause, not having seen the whole article I can't say for definite, but the way C4 is joined to IC2b means that input currents may be important. The size difference between the coils that you mentioned is NOT important, and neither is the 1nF cap substitution.
Could you post pictures of your build, maybe we can spot the problem that way?

[eduardo1979]

Maybe the coils are not in resonance and so the detector is not working properly. Try playing around with the value of C2. Greetings.

[Astromic]

I played a little with the tuners, re-nulled the coil, improved the shape of them a little with no obvious improvement, it still has strong good operation but very low depth(sensitivity?).
I will post some pictures of the built today.
Here is the full article

1002- EPE Bounty Treasure Hunter_2.pdf

[Astromic]

It's possible that the screening of the coil could badly affect sensitivity if you do it wrong. Try it without the screen (foil?) and see of it improves. The op-amp substitution may be the cause, not having seen the whole article I can't say for definite, but the way C4 is joined to IC2b means that input currents may be important. The size difference between the coils that you mentioned is NOT important, and neither is the 1nF cap substitution.
Could you post pictures of your build, maybe we can spot the problem that way?

Thank's skippy, this narrow my issue a little (well, i guess),, i removed the shielding off the two coils and the depth does improve a bit more.. now a mid sized coin starts to crackle at about 150mm, larger copper objects makes it sing at ~30cm,, it's still way from "good", but still won't give up,, i see this device has great potentials, though..
The only kick back now is the coils is VERY sensitive to any interference, ever my hand when it close to them , and the pcb is also sensitive and a bit unstable, it took me like 10 minutes to fine tune!!

Mike

[Skippy]

Aluminium foil is, in my opinion, excessive for screening coils. It reduces sensitivity to targets, it's that excessive. Try it on the receive coil only (that is the most important coil), use as little as you can (minimal overlap) and LEAVE A GAP of 5 - 10mm, very important, that. Ideally you should use some graphite-based screen, such as painted on coatings or graphite-coated paper wrapping, but this is a beginners fun project, so leave that for your next project. It's worth pointing out that pot VR1 has a significant affect on sensitivity, minimum-resistance will give greatest gain and sensitivity (I hope) but you may not be able to run it thay way and still have 'stability'. I also recommend connecting IC2 pin 6 to pin 8 via 1 Megohm resistor, and to pin 4 via 1 Meg. This encourages pin 6 to stay at half-supply. Leaving it floating, as the Rev. has, is poor design practice.

[TH Jim]

Hi Astromic,

This is a very vey basic machine, you should not expect much from a simple design like this. I wouldn't waste any more time on it, just choose one of the many great projects you can find here on the forum.

Regards, Jim

[mahavir]

Hi friends..
I also make this project in this I made both coil tx &rx without aluminum foil. I got something better performance than the older design. This finds 1" coin at dept of 4" in air..
Now I wants to make the new project which has really good performance and better depth so I search for new project if u know than post here...
Thank regard...

[Davor]

Answer for you would depend on terrains (or beaches) and targets you want to hunt.

Give us some details.

[mahavir]

hellow friend,

I make epe bounty Hunter but not perform well..so make good sensitive metal detector..
I want to use metal detector in mountain areas and river areas so suggesting me a good depth and better differs between Fe and non Fe metal detector .
Thanks regards.

[mahavir]

Hi davor
I am again modify epe bonty such as changes in coil but results is it's depth range reduced and give continue sound so help me about this epe's coil or any other best MD for mountain and river areas so help me..
Thanks in advance..!!!

[maikl]

Hi mahavir.
This detector is a toy for children, do not help any "modifications"...
My advice is to do the second detector!