Question about tgsl

[dbanner]

I tried to make the Dbowers TGSL concentric coil, I followed all his instructions perfectly, using the correct size wire and everything, and guess what, The inductances were close, but I still needed to tinker endlessly to get the coil to its peak performance.
These coils are so finely balanced that if you build ten identical coils using the same size wire and all the rest, they will still end up being slightly different, requiring "personalized" treatment.
Precision requires a coil winder that stacks the wires side by side for a rectangular(square) cross section that comes out perfect all the time, while glueing the turns together in the process of winding at the same time, so when it is dry, the coil is perfect, one after the next.
Then the shielding process must be applied to the housing and NOT the coil so as not to interfere with inductances.

[dbanner]

I also did not ground the RX coil. Works great without falsing on wet grass.
In evaluating the design I see no reason to ground the Differential RX in.

I need to play with that Nautilus circuit. I have the question of why connect the RX coil to ground and will this circuit still work without that ground connection. Have a lot of other circuits to work on so won't be getting to this one soon.

The original tesoro coils, Rx is grounded, and there is no falsing on wet grass. So it stands to reason that there is something missing in the self made construction. I suspect strongly that it is in the shielding and the cable hookup configuration, but I can't be too bothered for now.

Grounding the Rx is supposed to make common mode between the shield and Rx, ironically to eliminate falsing.
Nautilus circuit Rx must be grounded I think.

[waleed]

Thanks dbanner and waltr also kt,now I have enough knowledge to build a good concentric coil with any size I want , I'll give feedback when I finish the 10" coil and attach it to the circuit

[dbanner]

Good luck!

[waleed]

Hello guys, after I finished my exams I start to continue working on my project ,anyway something weird happened well the last time that I said the device started to detect metals now when I tried it it didn't give any reaction, then I made the 10" concentric coil (Rx:6.5mh & Tx:6mh) and I attached it to the device and when I turned the device on it gave a single beep and when I moved a target on the coil nothing happened no reaction at all, I checked everything and all tests looks good except that I noticed something that I felt is wrong, when I test the point J2-1 the waveform looks normal but when I test point U101a-pin7 the waveform is square wave,is that normal?, it is possible that I broke the njm2068 IC (I'm using it instead of LF353).

[waltr]

1- The TX wave forms look good but the Frequency is only 13kHz. Should be 14.5kHz. This means either the TX coil's inductance is too high or the TX oscillator caps are to large. More likely the coil. Note: the TGSL will work at a different TX frequency.

2- The RX waveform is too large in Amplitude which is why (3) is a square wave.
The pre-amp has a gain of 220k/4.7k = 4.68.
The RX waveform is nearly 3Vpp and the pre-amp gains by 4.68 = 14V. But the per-amp's rails (power) is only 13V and can not output to the rails so it Clips the peaks.

The problem is that the Coils are not NULLED. You need to adjust the TX Buck Coil to get near the smallest RX p-p Voltage (and about a 20 degree phase shift relative to the TX).
Watch the RX input (J2-1) and play with the extra wire on the Buck coil. At some point the RX should reduce in amplitude.

Re-read the 101 pdf and other TGSL coil building docs.

Attached is one stuff:
My concentric eccentric adventure.pdf

[waleed]

1- The TX wave forms look good but the Frequency is only 13kHz. Should be 14.5kHz. This means either the TX coil's inductance is too high or the TX oscillator caps are to large. More likely the coil. Note: the TGSL will work at a different TX frequency.

2- The RX waveform is too large in Amplitude which is why (3) is a square wave.
The pre-amp has a gain of 220k/4.7k = 4.68.
The RX waveform is nearly 3Vpp and the pre-amp gains by 4.68 = 14V. But the per-amp's rails (power) is only 13V and can not output to the rails so it Clips the peaks.

The problem is that the Coils are not NULLED. You need to adjust the TX Buck Coil to get near the smallest RX p-p Voltage (and about a 20 degree phase shift relative to the TX).
Watch the RX input (J2-1) and play with the extra wire on the Buck coil. At some point the RX should reduce in amplitude.

Re-read the 101 pdf and other TGSL coil building docs.

Attached is one stuff:
[ATTACH]48942[/ATTACH]

Hey waltr, well I'm aware that the coils are not nulled and I know how to do that but the thing got me is the square wave maybe as you said the amplitude of rx is high, but if the coils are not nulled I'll not get any reaction right?, and I'm sure that Tx is 6mh but I'll check the caps, oki I'll null the Rx coil then I'll check the waveform of pin7

[waltr]

Hey waltr, well I'm aware that the coils are not nulled and I know how to do that but the thing got me is the square wave maybe as you said the amplitude of rx is high, but if the coils are not nulled I'll not get any reaction right?, and I'm sure that Tx is 6mh but I'll check the caps, oki I'll null the Rx coil then I'll check the waveform of pin7

Correct, pre-amp is Overloaded and so are the following stages so the slight amplitude change with a target passing the coil can not be detected. Once you have a better null and the pre-amp out is a sine then it will start detecting a target.

You also want to put the scope Ch1 of TX and scope ch2 on the RX pre-amp out. This is to compare the amplitude and PHASE of the RX relative to the TX. This is more important than have an exact TX frequency.
Also as I have said: checking the inputs, gates, to the FET switches in relation to the TX. dbowers shows these scope pictures in the TGSL 101 pdf.

[waleed]

Oki this what I did, first I removed some turns from Tx because the inductance wasn't correct, then while I was measuring U101a-pin7 I gradually removed turns from bucking coil until I reached 15mv ~ ,but I don't know why Rx waveform looks ugly, anyway even though that I'm so close from nulling and Tx is almost 14.3khz but still there is no reaction from the device at all when I move a target or touch anything.

https://i.ibb.co/pj7n6WB/20191231-153817.jpg
https://i.ibb.co/Pt4qmSd/20191231-171812.jpg
https://i.ibb.co/nBYrWtK/20191231-171425.jpg
https://i.ibb.co/qxgz23R/20191231-173050.jpg
https://i.ibb.co/JRjJYb9/20191231-173137.jpg

[waltr]

Oki this what I did, first I removed some turns from Tx because the inductance wasn't correct, then while I was measuring U101a-pin7 I gradually removed turns from bucking coil until I reached 15mv ~ ,but I don't know why Rx waveform looks ugly, anyway even though that I'm so close from nulling and Tx is almost 14.3khz but still there is no reaction from the device at all when I move a target or touch anything.

The wave forms look fine. RX is noisy due to electrical noise in you shop. My RX signal looks worse than that but TGSL works great.
I have read that with a concentric the RX phase shift is about 200 degrees.
Again use both channels of your scope to compare when the FET switches turn on relative to the TX and/or RX signal phase.

Next is check the outputs of the next two amps, U103 pins 1 & 7, then U104-6 & U105-7.
These should be very near to Zero Voltages.

Did you try All Metal Mode?
I am guessing it still beeps when powered on.

It did take me a while of fiddling to get my TGSL working. Keep at it.

[waleed]

The wave forms look fine. RX is noisy due to electrical noise in you shop. My RX signal looks worse than that but TGSL works great.
I have read that with a concentric the RX phase shift is about 200 degrees.
Again use both channels of your scope to compare when the FET switches turn on relative to the TX and/or RX signal phase.

Next is check the outputs of the next two amps, U103 pins 1 & 7, then U104-6 & U105-7.
These should be very near to Zero Voltages.

Did you try All Metal Mode?
I am guessing it still beeps when powered on.

It did take me a while of fiddling to get my TGSL working. Keep at it.

I'm really tired man but I'll not give up, I really wish that i can get it to work at any distance of detection I'll be satisfied, anyway yes I tried it in all metal mod and the device still beeps when power on and I'll check the poins you mentioned above when I back to uni because we are off until Sunday (I do test the device there because I don't have oscilloscope),

And I read this in the document "If the disc channel agrees with the ground balance channel at the
same instant, we have detection!".but how to know if the disc channel agrees with ground balance channel how to test that?,

Again use both channels of your scope to compare when the FET switches turn on relative to the TX and/or RX signal phase.

What you exactly mean by this and which pin of FETs to test to know if they are turns on ?

[waleed]

Omg this device really confused me, I tried it just now in my home with my low battery (it needs to be charged) and the device just worked and it start to detect metals and 1 euro coin at 20cm and it was quiet (no beeping when touching), I played with the small loop and the depth increased a bit, but the disc didn't work, I don't have a ferrite slug yet to adjust the ground balance. Anyway I'll wait to sunday when I go to uni to make sure first I have the correct resonance and the deepest null with the correct phase shift between tx and rx, because I think disc channel won't work until I have the correct phase shift.

[waleed]

Oki I'm done with it, just tried now to test it again to see if it still working and the same problem back again (no sound at all when moving a target on the coil) only beeping when power on. Now I'm pretty sure that my coils are oki and the problem is with the board itself or maybe some joints are not soldered properly.
I may buy the TGSL-EDU pcb from Silverdog, and rebuild it again with a good soldering.

[waltr]

What you exactly mean by this and which pin of FETs to test to know if they are turns on ?

The FET GATEs.

Omg this device really confused me, I tried it just now in my home with my low battery (it needs to be charged) and the device just worked and it start to detect metals and 1 euro coin at 20cm and it was quiet (no beeping when touching), I played with the small loop and the depth increased a bit, but the disc didn't work, I don't have a ferrite slug yet to adjust the ground balance. Anyway I'll wait to sunday when I go to uni to make sure first I have the correct resonance and the deepest null with the correct phase shift between tx and rx, because I think disc channel won't work until I have the correct phase shift.

Something very weird is going on. Usually something very simple and explainable once you find it.
This does take lots of persistence and patience like any electronic troubleshooting.

Without ferrite use a silver coin. Adjust GB trimmer until silver coin not detected in AM mode, then back the GB trim until it is detected.
The GB trim is normally adjusted with both ferrite and a silver coin so that ferrite is rejected and silver is not rejected.

[dbanner]

You have an intermittent connection from the coil to the pcb. Check the coil cable and the soldering. Touch the circuit all over the bottom side with your finger and see if you don't get a beeping response. I think your circuit is fine, just some poor connection somewhere.

Once you have sorted that out, the only thing remaining is to set the coils correctly (nulling and phase), then everything will fall into place quite nicely.

You must tap into your third eye and meditate. Take things one step at a time, methodically check things. Be meticulous.
This little circuit is a baby's food, you are big iron man. Are you gonna be defeated by such baby circuit, no way!
The pathway to success is littered with many failures.

I gave myself such pep talk, when I built my first TGSL, which took me one week to even get a single beep! I made horrendous self made PCB, and drilled hole in my finger too! When I finally got the thing working properly, I looked like a man who had been through hard times.
I'm glad I had those experiences, now I know the secret to a successful project is good PREPERATION. otherwise you may need PREPERATION H.