TGSL Experiments

[ApBerg]

Just as Don tells, speakers can give a problem, you can tray a Piezo speaker.( In PI detectors a must ?!)
There is not a strong magnetic field when using a piezo speaker?

Best regards.

Ap

And yes..... sheep can give side effects.....! do not tray to count them....

[dfbowers]

Hello Dennis,

Long leads can give problems, keep them as short as possible! For screening take care that only one side from the screen is connected to the pcb ground, do not twist wire's that go to the pots.

In the past I made a lot different teso's, at high sense they can give some noise but not at a level that it is a problem..

Koud hé...

Regards.

Ap

Agreed! Keep leads short. Pay particular attention to how the wires leave the coil. I have noticed better performance after I installed my coils in a shell and have the cable exit at 90 degrees. Keep wires as short as possible leaving the coil.

Use very thin shielding material such as metallized maylar (survival blanket works well),
You may want to try installing pots and external connectors in a ground plane as well (just a suggestion) as Ivconic has done with his projects. I have not done this though..

[simonbaker]

Inspired by someone who went to the mountains for a field test ( I guess at boiling temperatures ) and someone who went to the beach ( same temp ? ), I've decided to make my own fieldtest ( only at freezingpoint , must be out of my mind) due to lower detection depth as should on my TGS : 1 eurocoin > +/- 20 cm , probably caused by noisy workshop and sometimes 'motorboating' due to this noise.
The average workshop noise measured on the output of the LM308 is 40 - 60 mV ac

So gathered everything from my checklist : coils ( not potted yet but glued with hotmelt ) , borrowed a computer PSU ( 12v DC > 230 v AC ) so I could take my ancient scope in the field , batterypack for clean powersupply and Arctic Equipment etc etc.

The only living soul who passed was a shepherd with his herd of sheep and me arriving from the east ( is this a kind of christmass carol ?)

With great expectation I've started my test and got really disappointed by the results :
the noise in the middle of nowhere was even higher as at the workshop and continues 'motorboating' / falls detection - fals alarm .>> 70 mV ac

Even with the other set of coils ( shielded and unshielded ) same results, no matter the nulling ...quite a cold turkey

Back home ,after I was melted , reconnected everything for further investigation and guess what ....
noise at workshop about 30 mV and stable with a great detection depth : I've got about 29 cm on a 1 eurocoin in air .

What he heck is happening? It seems that somewhere internally noise is generated causing all these unwanted side effects.


Anyone with a clue ?

What should be considered as a normal noise average ?

Does the TGS operates below freezing points with windspeeds at 5 Bft ?

Can sheep cause side effects ?

The leads from the pcb to the commands at the front of my housing are quite long but shielded ( audio cable ) , is that a problem ?

regards ,

Dennis the Mennis

Dennis the Mennis Excellent Adventure!

Loved the pics, I could feel the cold... (enjoyed the humor too).

Ok, a few observations:

1. First, bravo for all the planning and execution! -- I'm sure you had that "what the hell am I doing out here?" feeling -- which is half the fun!

Excellent job with the table, scope, power supply, all the necessities...

I never took a scope with me. I would like to do that; I'm just afraid my old scope may rattle apart and never work again.

2. In my first attempt outdoors, I, like you, used unglued coils. But the slightest vibration or wind will make huge noise, so I decided I needed to pot the coils for real test. I think your next step is to pot a coil (glue it down).

Vibration is also a problem I think due to the cable slightly vibrating at times, or swinging. Again, any slight breeze can do it. When indoors, I believe building vibrations caused noise in my unpotted coils in my workshop too.

3. It is very difficult to know where noise exists (those darn submarine communications transmitters...). Underground cables can cause it, like for that lamp post. Sometimes we think we are far away from interference, but who knows? Only the TGSL knows. I had to go far into mountains as you know. It is possible there was some transmission energy, even in your field. Sometimes you have to try many different fields. Or different sheep.

But then, we need our detectors to work OK in such fields, don't we? However, remember, we don't necessarily need 30 cm air test for finding coins in ground, so it is an interesting question how much this noise affects practical treasure hunting. But theoretically, we believe it can. The truth is, if you need to hunt where there is EMI noise, depth may be limited.

But our air tests are mainly to check if we built our MD as well as possible, so we need to test that where there is no noise.

4. When you got home, you had less noise and a nice result of 29 cm. First -- good! Your TGSL is probably quite well made.

How good was the audio beep at 29 cm? You can make a video sometime too so we can see and hear.

But, you have a question: is the noise coming from your TGSL, or environment? Once in a while, the noise is less in my workshop. Once the power went off in the neighborhood and I got 30 to 34 cm! So environmental noise is very real I think.

Here is a quick test. Put a very short jumper across the RX coil leads where they attach to your PCB. Then look at the noise at the LM308 outputs. This at least gives you an idea if your PCB is making some noise. The noise should be very low, maybe 4 to 6 mV pp.

However, that test would not prove there is no "oscillator noise" that could be occuring.

A way to check for oscillator noise is to disconnect the TX coil and use a small "choke" coil instead, of same value (approx 6 mH) to make the oscillator run. Try to shield the choke coil from the RX coil as best you can.

Then check the noise at the LM308 outputs. That noise should be the noise picked up by the RX coil from the environment, not from the oscillator. Using the jumper across the RX coil, you can compare and see how much EMI noise the RX coil adds.

5. To test if the speaker is contributing to problems, disconnect it and just look at the scope. See if waveforms at output of LM308 change much.

6. dfbowers (howdy! good to know you're out hunting!) and ApBerg ideas sound good. I don't know how lead angles and such affect coils, but I need to improve my coils also.

So DtM, bottom line is: make a "potted" coil and keep trying. It looks encouraging. If you get 29 cm once, it means you are probably close and at least have a pretty good TGSL.

Oops, I'm writing too much again, need to get back to work... but very happy Dennis the Mennis is braving the elements to provide entertainment for the rest of us...

Hope to see some dfbowers relics soon also.

Cheers,

-SB

[simonbaker]

Hello Dennis,

Long leads can give problems, keep them as short as possible! For screening take care that only one side from the screen is connected to the pcb ground, do not twist wire's that go to the pots.

In the past I made a lot different teso's, at high sense they can give some noise but not at a level that it is a problem..

Koud hé...

Regards.

Ap

Hi ApBerg:

What happens if you twist leads to pots? I usually do that, but is it a problem?

Regards,

-SB

[WM6]

Dennis the Mennis Excellent Adventure!

Loved the pics, I could feel the cold... (enjoyed the humor too).

Agree!
Maybe there is an inner noice because of the shaking in the cold.

[Jerry]

The DC/AC converter could be a noise source. Try running a test with everything except the detector turned off just to help narrow things down. Just a thought.

I am just starting to get back with the tgsl experiments myself after several months off.

Jerry

[simonbaker]

The DC/AC converter could be a noise source. Try running a test with everything except the detector turned off just to help narrow things down. Just a thought.

I am just starting to get back with the tgsl experiments myself after several months off.

Jerry

Good, you have a really nice setup for good experiments.

-SB

[Tinkerer]

IB coils_induction balance field adjustment

Hi TGSL friends,

Induction balance coils are a pain to build. You can do everything right, then, while potting, a minute resin shrinkage can upset the balance.
It is much worst in the field. With your perfectly balanced coil you hit an area with highly mineralized soil. The Induction Balance is upset and you loose a lot of depth and sensitivity or the detector may not even work at all.

So what can be done about that?

Working on my Hybrid detector I ran into the same problem. I have found a solution that seems to be the answer. I can now adjust the Induction Balance of the coil in the field. A simple 25 turns pot is the interface. Eventually I intend to change this pot for a digitally controlled pot. Then the adjustment can be automatized with the MCU.

The system is still very crude but it looks very promising. Probably it would also work with a VLF, but I really don't know anything about the functioning of VLF's, so I need your input.

It will take some experimenting.

Anybody willing to give it a try?

Tinkerer

[pebe]

Hi TGSL friends,

........... With your perfectly balanced coil you hit an area with highly mineralized soil. The Induction Balance is upset and you loose a lot of depth and sensitivity or the detector may not even work at all.

So what can be done about that?

Working on my Hybrid detector I ran into the same problem. I have found a solution that seems to be the answer. I can now adjust the Induction Balance of the coil in the field. A simple 25 turns pot is the interface.........
Tinkerer

I am well advanced in the design of a PIC based detector. I would be most intersted in your solution.

If it's off topic here, could you send me a PM perhaps?

Peter

[Dennis the Mennis]

Side effects air test // 50 cm + detection on a 1 euro coin .....

Dennis the Mennis Excellent Adventure!


4. When you got home, you had less noise and a nice result of 29 cm. First -- good! Your TGSL is probably quite well made.

How good was the audio beep at 29 cm? You can make a video sometime too so we can see and hear.

Cheers,

-SB

Hi Simon ,


Here's my video of the airtest ...
Only those sheep keep hunting me , what is happening overhere ?
L.D.S.I ? Long Distance Sheep Interference ?
But I do get 50 cm +++ detection !

regards ,

Dennis the Mennis


http://www.youtube.com/watch?v=qL0oKDGaYV4

[nakky]

Good are you,Dennis.
Pefect distance.

Grt Nakky

[Dennis the Mennis]

29cm isn't too far off. I was getting just over 30cm until I came up with a mod. Now 36 to 45cm depending on how noisy the environment is.
http://www.geotech1.com/forums/showt...=14655&page=10

Question: Can you advance your sensitivity to the point where it chatters or does it motorboat?

The only times I have seen motorboating is when I get the coil too close to the speaker or I get close to 60Hz power.

Divide and conquor! Maybe we can try a different coil. Where do you live?

My experiments have grinded to a halt lately. Gone hunting (relics) and have been using mine lately!!


Don

Hi Don , Simon , Ap , WM6 and Jerry ,


Your 1M mod is sure on my list 'to do' ( for a long time ) , but first I wanted to make a basic stable TGS MD.

I live in Rotterdam Holland / the Netherlands / Ap Berg country .

Perhaps I've mis-interpretated ( is this correctly spelled ?: it's hard to write without a spellingscheck) the term 'motorboating' .

It did chatter however continuously during the 'field test' :

- I used a headset which was in my opinion far enough removed , I do remember some posts about the speaker problems.

- The psu dc/ ac convertor was turned of , as Jerry suggested and the ignition of my car was also switched of just in case ...( I whish I had a shed like Jerry , I could drive my car into it for a field test )

- I do think that those vibration influence by wind / shaking hands / or sheep on my coil are bigger as I expected so there's much to win for me overthere

- Ap Berg : ' Veel te koud hier hahaha ' : yes the leads are grounded only on 1 side , in the past I did read about the noise so I wanted to prevent the pcb injecting noise into the leads ( from pcb to pots ) perhaps there is also something to gain overthere , also on my list 'to do'.

- As Simon suggested to shorten the Tx coil : I do get then about 4 - 6 mV ac ...so my quest for the noise source continuous and I will post my findings
I was waiting to pot my coils : I just wanted to make sure that my coils are good enough and the nulling and phase shift is good enough , that's why they are partially glued down with ( I hope ) removeable hot glue

I must be close to the finish and barking at the right tree , at least I hope so .


regards and thanx everybody for the suggestions and feedback ,

Danny
Dennis the Mennis

[ApBerg]

Hi ApBerg:

What happens if you twist leads to pots? I usually do that, but is it a problem?

Regards,

-SB

Hello Simon,

Yes I now , in many applications we use twisted pair cable’s, For computer lines we all know the UTP cable (unshielded twisted pair) The twisting from the 2 cables is done to reduce external noise.
In the Tesoro coils also that twisted pair effect is in use, the receive signals ground is made in the sears coil (not at the circuit board) , that means that the receive cables from the coil going to the circuit board both see external noise in different faze and so cancel out that noise. ( I think it works that way...)

So why not use this twisted pair effect for the connection from potentiometers..??

When I had some problems with noise I have reduced the length from the cables that go to the potentiometers, this had some good effect !
Perhaps that twisting cables , that also works as making a capacitor, has a bad effect if you use it in a DC circuit ?

Well perhaps all nonsense ... if someone really knows.. shoot on it ..

Best regards.

Ap

[simonbaker]

Hello Simon,

Yes I now , in many applications we use twisted pair cable’s, For computer lines we all know the UTP cable (unshielded twisted pair) The twisting from the 2 cables is done to reduce external noise.
In the Tesoro coils also that twisted pair effect is in use, the receive signals ground is made in the sears coil (not at the circuit board) , that means that the receive cables from the coil going to the circuit board both see external noise in different faze and so cancel out that noise. ( I think it works that way...)

So why not use this twisted pair effect for the connection from potentiometers..??

When I had some problems with noise I have reduced the length from the cables that go to the potentiometers, this had some good effect !
Perhaps that twisting cables , that also works as making a capacitor, has a bad effect if you use it in a DC circuit ?

Well perhaps all nonsense ... if someone really knows.. shoot on it ..

Best regards.

Ap

Yes, maybe a possibility -- all observations are useful for trying again by others.

Regards,

-SB

[simonbaker]

Hi Simon ,


Here's my video of the airtest ...
Only those sheep keep hunting me , what is happening overhere ?
L.D.S.I ? Long Distance Sheep Interference ?
But I do get 50 cm +++ detection !

regards ,

Dennis the Mennis


http://www.youtube.com/watch?v=qL0oKDGaYV4

I'm still laughing...

That's one baaaad detector you got there...!

I want one!

-Bo Peep