IGSL

[simonbaker]

Hi, any ac voltmeter will give you something useful Id imagine

Your looking for a relative measure, of how much signal is coming thru - matter of tweaking caps about for max. Works very well.

An old AVO 8 will go out 100kHz !


The meter I use here is a tektronix DMM914

Has a cap meter
frequency counter to 2MHz
True RMS etc
Steve

Even though measuring the peak is "relative" and absolute voltage doesn't matter, the voltage "fall-off" with frequency will bias the peak frequency of your LRC circuit slightly -- but probably not too much. If your LRC circuit is very high Q (sharp peak), then pretty accurate.

Looks like your DMM has AC range up to 10 kHz +- 3.5%.

Better than mine, I have to use oscope instead.

Regards,

-Sb

[der_fisherman]

Check this post demonstrating target phases with lissajous: http://www.geotech1.com/forums/showp...56&postcount=2

What specifically do you want to try?

-SB

I would like someone with a scope to attach an accurate signal generator to the X and with X-Y selected, attach the other channel to the Tx coil. Set the signal generator to the correct frequency (14.6 KHz) and then switch on the MD and see just how accurate the Tx frequency is.

The link I posted showed a demo.

Its an old fashioned method, but as accurate as the Sig Gen is accurate, way of testing for the correct frequency.

The video you posted demonstrates something else with Lissajous. Not the accuracy of the frequency.

Regards

Andy

[ivconic]

It is irrelevant whether frequency will be 14.6 or any other closer value.
In the past, making TGSL and many coils, i never had exactly the same freq at each one i made.
Simple because coils are hand made, not 100% identical.
Also there is certain tolerance in components. So all the coils&detectors were in mentioned range, but not exactly the same.
Insisting on exact frequency is not so important.
Look White's Eagle series and Classic as an example; all those models can work in some range, usually from 6 to 7 kHz. Same coil.
Also Tesoro's from 10 to 15 kHz, same coils.
etc..etc..
I suggest you not to waste to much time and energy examining frequency.
What's going on with your hand made?
Any progress?
Would be nice to see some more concrete works here, photos, videos.... any progress?
...
I deliberately stopped working on IGSL further, just made 3 devices so far. Those are working just fine, i am very satisfied.
But i stopped and am waiting winter.
In meantime i do not think much on IGSL and further mods.
I noticed much better creativity when i make longer pause, month or two, and later back to same idea.
Also i could use your experiences gained with IGSL, so am waiting some of You to finish it and give us here first impressions.
So? Any impressions?

[petravka]

With my DIY coil i got 27cm for 1e coin in air, golden ring 2gr at 29-30cm. I tested it on my improvized test bed and compared with branded models that i could obtain at the time.



It detects 2 din. coin burried in soil at 10cm depth the very same as it was in air, nail and coin close to each one nicely separated with both tones, at 12cm depth. Further, 2 din coin (18mm) can detect burried at 20cm in soil with bit weaker signal, while 5 din coin (24mm) it is detectng at same depth, burried in soil, but with coil some 3-4cm over soil surface. Garrett Ace 250, at same testings, detected same 2 din coin at 10cm and nail&coin at 12cm depth. DIY Classic 3 with branded Fisher 27cm coil also detected all the items - but with no discrimination at all. Keep in mind that this was preliminary testings on real soil and fact that my first DIY coil for IGSL is not so perfect so i had to lower gain because of it.

[simonbaker]

I would like someone with a scope to attach an accurate signal generator to the X and with X-Y selected, attach the other channel to the Tx coil. Set the signal generator to the correct frequency (14.6 KHz) and then switch on the MD and see just how accurate the Tx frequency is.

The link I posted showed a demo.

Its an old fashioned method, but as accurate as the Sig Gen is accurate, way of testing for the correct frequency.

The video you posted demonstrates something else with Lissajous. Not the accuracy of the frequency.

Regards

Andy

Hi der_fisherman -

Ok. Then your description of how to use it is not quite right. When the frequencies match, the pattern will become "stable" (not changing shape) and simple (oval) -- which will be difficult to achieve unless you have two stable frequencies to start with and a very fine tuning dial on your signal generator. To get a straight line (degenerate oval), the phases would have to match also.

.......

Ok, I just tried it. My signal generator is too lame for it to work. I could not get a stable pattern, it was just a blur. I could see flashes of a pattern as I crossed the TX frequency, but my tuning is not fine enough to land on the exact frequency.

I think if you have a really good signal generator (probably digital) where you can dial in an exact frequency down to the .1 Hz it would work as you expect. However, if you have no idea what frequency the target signal is, you might spend some time searching before you find the stable pattern. On the other hand, since you have an oscilloscope anyway, you can measure the target frequency pretty accurately with that to get in the ballpark, then use your lissajous to nail down the exact frequency.

Another technique is to use your signal generator signal as the oscope trigger input and tweak the frequency until the target signal is not drifting left or right.

As Ivconic said, we usually don't need to know frequency too exactly -- oscope measurement sufficient. But most multimeters have a frequency counter anyway, and that is so easy to use.

I had fun using the x-y inputs of my scope and playing with Lissajous though. It is a handy way to monitor phase relationships, might find more uses for it.

Regards,

-SB

[Jerry]

Hi der_fisherman -

Ok. Then your description of how to use it is not quite right. When the frequencies match, the pattern will become "stable" (not changing shape) and simple (oval) -- which will be difficult to achieve unless you have two stable frequencies to start with and a very fine tuning dial on your signal generator. To get a straight line (degenerate oval), the phases would have to match also.

.......

Ok, I just tried it. My signal generator is too lame for it to work. I could not get a stable pattern, it was just a blur. I could see flashes of a pattern as I crossed the TX frequency, but my tuning is not fine enough to land on the exact frequency.

I think if you have a really good signal generator (probably digital) where you can dial in an exact frequency down to the .1 Hz it would work as you expect. However, if you have no idea what frequency the target signal is, you might spend some time searching before you find the stable pattern. On the other hand, since you have an oscilloscope anyway, you can measure the target frequency pretty accurately with that to get in the ballpark, then use your lissajous to nail down the exact frequency.

Another technique is to use your signal generator signal as the oscope trigger input and tweak the frequency until the target signal is not drifting left or right.

As Ivconic said, we usually don't need to know frequency too exactly -- oscope measurement sufficient. But most multimeters have a frequency counter anyway, and that is so easy to use.

I had fun using the x-y inputs of my scope and playing with Lissajous though. It is a handy way to monitor phase relationships, might find more uses for it.

Regards,

-SB

I also agree with Ivconic about the frequency. However getting any two oscillators exactly on the same frequency and keeping them there is way more effort than it is is worth. In the days before we had all these nice digital meters, two way radio techs always had to measure against some known standard and it was not all that easy.

For the purposes of our metal detectors, the frequency meter built in to most multimeters now days is more than accurate enough. In particular if you look at one of the 4025 divided outputs.

Jerry

[der_fisherman]

Using Lissajous for frequency tests.

Hi der_fisherman -

Ok. Then your description of how to use it is not quite right. When the frequencies match, the pattern will become "stable" (not changing shape) and simple (oval) -- which will be difficult to achieve unless you have two stable frequencies to start with and a very fine tuning dial on your signal generator. To get a straight line (degenerate oval), the phases would have to match also.-SB

Dear Simon, that is the crux of the matter, once you have the frequency generator stable, the display will also become relatively stable and slowly change between a circle and a flat line, the angle of which will depend upon the stability of the two sources.....
.......

Ok, I just tried it. My signal generator is too lame for it to work. I could not get a stable pattern, it was just a blur. I could see flashes of a pattern as I crossed the TX frequency, but my tuning is not fine enough to land on the exact frequency.

I think if you have a really good signal generator (probably digital) where you can dial in an exact frequency down to the .1 Hz it would work as you expect. However, if you have no idea what frequency the target signal is, you might spend some time searching before you find the stable pattern. On the other hand, since you have an oscilloscope anyway, you can measure the target frequency pretty accurately with that to get in the ballpark, then use your lissajous to nail down the exact frequency.

Another technique is to use your signal generator signal as the oscope trigger input and tweak the frequency until the target signal is not drifting left or right.

As Ivconic said, we usually don't need to know frequency too exactly -- oscope measurement sufficient. But most multimeters have a frequency counter anyway, and that is so easy to use.

I had fun using the x-y inputs of my scope and playing with Lissajous though. It is a handy way to monitor phase relationships, might find more uses for it.

Regards,

-SB

Dear SB,

Well done. Many thanks for trying it out and I do feel that your results were worth the effort.
I already tried it with my scope and I think the X-Y function needed is broken as all I got was two dots at an angle, maybe its right but as i was using the same frequency source, with no phase change..........but I will try again in the near future once I have some sort of frequency generator, I am going to try first with a software generator on my PC.

As I mentioned, the test will only be as good as the stability of the frequency generator, I do not think that the IGSL will be changing as much as you mention....e.g. a good sig gen will actually work doing this. But the sig gen must be as stable as IGSL.

I am pleased to recently read from Ivconic that its not so important to have an exact frequency, though mine should be pretty good as I tailored C2 to fit as exactly as I could. I was under the (wrong) impression that it needed to be really exact, thanks all for clearing that up!!

I have not got my 12 volt supply organised at this time, that will have to wait (financially) till the beginning of next month at the earliest...

I am also still searching for a plastic tube for the lower part of my stem, nothing I have found fits anywhere near.......though I still have some ideas.....

I am guessing, but I am hoping that my IGSL's lack of good sensitivity is mainly due to being close to mains electricity and the use of a (stabilised) power supply for testing, so I am putting it away for a time till I have the battery problem fixed......

Many thanks again SB for trying that out for me (us!!)....

regards

Andy

[golfnut]

Even though measuring the peak is "relative" and absolute voltage doesn't matter, the voltage "fall-off" with frequency will bias the peak frequency of your LRC circuit slightly -- but probably not too much

Hi, I was measuring at the output of the U1a Op amp of the receive front end - I would expect no loading of the tuned cct

Steve

[ivconic]

"...I am also still searching for a plastic tube for the lower part of my stem, nothing I have found fits anywhere near......"

You are not the only one!
I am searching for such thing also.
Ordinary plastic tube/pipe will not do. Must be strong and robust plastic.
I tried to use some plastic pipes and those are deflecting on each coil swing. Annoying!
So it must be made from pretty robust plastic and with fat walls.
Haven't founded such thing yet...

[der_fisherman]

"...I am also still searching for a plastic tube for the lower part of my stem, nothing I have found fits anywhere near......"

You are not the only one!
I am searching for such thing also.
Ordinary plastic tube/pipe will not do. Must be strong and robust plastic.
I tried to use some plastic pipes and those are deflecting on each coil swing. Annoying!
So it must be made from pretty robust plastic and with fat walls.
Haven't founded such thing yet...

Hi Ivconic,

when I get a chance, I am going to a special shop about 20KM away that deals in high pressure plastic water pipe. I used some a few years ago (35mm though) and it is relatively stiff. If it looks good and the sizes are also good, i will let you all here know as to what it is called, maybe even send some if you cannot find it locally!!!!

regards

Andy

[ivconic]

Hi Ivconic,

when I get a chance, I am going to a special shop about 20KM away that deals in high pressure plastic water pipe. I used some a few years ago (35mm though) and it is relatively stiff. If it looks good and the sizes are also good, i will let you all here know as to what it is called, maybe even send some if you cannot find it locally!!!!

regards

Andy

Nice! You do that and test it (against deflection) good.
If it shows as good solution, than just inform me on it's exact model, type, manufacturer etc.
Because most probably it is available here too - only i don't know what to ask at local suppliers.
And usually it is like that; much of materials already are available - i only need to "discover" it at some local supplier.
Need exact "name", model, type, manufacturers specs etc..etc..
...
How to test it against deflection, to suit our needs?
Simply; take piece of pipe, 40-50cm long and on one end somehow attach 500gr weight and swing left and right.
If it deflects much - no good.
If it's not deflecting at all - SPLENDID!

Write down manufacturers specs and inform us here. Usually specs are already printed on pipe surface.

[bernte_one]

Hi Ivconic,

when I get a chance, I am going to a special shop about 20KM away that deals in high pressure plastic water pipe. I used some a few years ago (35mm though) and it is relatively stiff. If it looks good and the sizes are also good, i will let you all here know as to what it is called, maybe even send some if you cannot find it locally!!!!

regards

Andy

i have made a stem from that ist is high pressure water pipe 16bar presuure and more
it is stiff plastic
with different diameter (upper part and lower)
in the middle a connecter from 20 to 25 dia so you can adjust the lenght i will post in other thread

[der_fisherman]

Free software to turn a breadboard circuit into a real PCB.

Hi All,

this post may not be in the best place, apologies if true, but I know you Guys best, so I post here first.

I stumbled across some open source (free) software that you use to design a "Breadboard" layout, and I know many of you, like myself, test things out on a breadboard first.

Now the following is where things change, once your breadboard circuit is working correctly, the software will design an Eagle compatible PCB layout from the breadboard (I knew I could get you Guys more interested in Eagle one way or another!).

Also there is a company that then produces PCBs cheaply from the designs, a one off if needed and charges very little as they wait till they have enough orders to fill a full PCB sheet(s).....

Now I haven't tried it yet, that is all read from the multi language web site!! Here:-

http://fritzing.org/

Download and have fun (I hope!). Lets compare notes at a later date.

Regards

Andy

[der_fisherman]

Nice! You do that and test it (against deflection) good.
If it shows as good solution, than just inform me on it's exact model, type, manufacturer etc.
Because most probably it is available here too - only i don't know what to ask at local suppliers.
And usually it is like that; much of materials already are available - i only need to "discover" it at some local supplier.
Need exact "name", model, type, manufacturers specs etc..etc..
...
How to test it against deflection, to suit our needs?
Simply; take piece of pipe, 40-50cm long and on one end somehow attach 500gr weight and swing left and right.
If it deflects much - no good.
If it's not deflecting at all - SPLENDID!

Write down manufacturers specs and inform us here. Usually specs are already printed on pipe surface.

Exactly right Ivconic,

I will try and get there sometime in the next couple of weeks....

Some tubing can be made stiffer by placing a drop or two of builders foam in it......once it expands it weighs nothing, but the tube gets really stiff.

Regards

Andy

[ivconic]

Exactly right Ivconic,

I will try and get there sometime in the next couple of weeks....

Some tubing can be made stiffer by placing a drop or two of builders foam in it......once it expands it weighs nothing, but the tube gets really stiff.

Regards

Andy

I tried that too!
I had no success.
I filled pipe with "styrofoam" (not sure about name, here we call it "purpen"), yet it still deflects, maybe a bit less, but still annoying much!