Question about tgsl

[waleed]

Omg, waltr don't hit me please Haha, well I just found that I put the 2n2222 instead of 2n9207, and 2n2907 instead of 2n2222, not all of them only the ones which close from the -5v circuit, I know that they are complementary of each other one is npn and the other is pnp,and they work opposite each other right?, well I'll replace them back and check the charge pump again.

https://i.ibb.co/7tKDYjF/20200215-190348.png

[waleed]

Finally the problem is solved, I replaced the transistors and then I connected the TX coil and when I turned the device on its gave a single beep only and this is normal, and I measured the charge pump it was almost -6v,I'll not connect the RX coil until I go the the uni and I'll do it there with oscilloscope testing

[waltr]

Finally the problem is solved, I replaced the transistors and then I connected the TX coil and when I turned the device on its gave a single beep only and this is normal, and I measured the charge pump it was almost -6v,I'll not connect the RX coil until I go the the uni and I'll do it there with oscilloscope testing

Ok, Progress.
You are not the first to mix up transistors or other parts.
I put one IC in backwards when I first built the TGSL. Found this when it burned my finger.

Go try connecting the RX coil now. It could just work.

[waleed]

Ok, Progress.
You are not the first to mix up transistors or other parts.
I put one IC in backwards when I first built the TGSL. Found this when it burned my finger.

Go try connecting the RX coil now. It could just work.

Oki I couldn't wait until tomorrow so I connected both coils and then I turned the device on, well the device acted normal and I really don't know the frequency of both coils exactly but when I pass a target on the coil it give a reaction but the depth wasn't satisfying,I switched the disc switch and it rejected iron only, I didn't null the coils yet nor even play with GB pot, I want to check the frequency of each coil tomorrow and I'll try to null it,
Waltr is really there a difference between the concentric and the DD coils in the depth? Because I have concentric and it's really hard to null, what you think?

[waltr]

Sounds all good. The circuits are now working properly.

Both DD and Concentric ARE very hard to null. A fair null to a great null can be moving a wire less than 1 mm.

I haven't yet built a concentric for the TGSL but Dbowers has told me the concentric goes deeper and this is true of the concentric verse DD on my PI detector. However the difference is maybe a cm or so.

I did build two DD coils for the TGSL. The first had a completely wrong Phase due to bad nulling but also shielded with alumium foil. The second has near perfect phase and null but shielded with graphic paint.
The second coil's Air distance is a few cm greater.

Building these coils is very tricky and can take building more than one to learn how to do them correctly.

When you get to the O'scope Use Ch1 on the TX output and trigger.
Then ch2 signals are Referenced in time/phase to the TX signal. This is Very important when observing the RX (at pre-amp output) and any of the switching signals (GB & Disc).

[waleed]

Sounds all good. The circuits are now working properly.

Both DD and Concentric ARE very hard to null. A fair null to a great null can be moving a wire less than 1 mm.

I haven't yet built a concentric for the TGSL but Dbowers has told me the concentric goes deeper and this is true of the concentric verse DD on my PI detector. However the difference is maybe a cm or so.

I did build two DD coils for the TGSL. The first had a completely wrong Phase due to bad nulling but also shielded with alumium foil. The second has near perfect phase and null but shielded with graphic paint.
The second coil's Air distance is a few cm greater.

Building these coils is very tricky and can take building more than one to learn how to do them correctly.

When you get to the O'scope Use Ch1 on the TX output and trigger.
Then ch2 signals are Referenced in time/phase to the TX signal. This is Very important when observing the RX (at pre-amp output) and any of the switching signals (GB & Disc).

Thanks waltr your comments are always useful to me, well then I'll stay on the concentric I'll try hard to get it best nulling, I'll give feedback when I check it on the oscilloscope.

[waleed]

Hey waltr, today I did some test at uni, I found that I really need to add some turns on the bucking coil because the amplitude of the RX is high and when I remove a turn from the bucking coil the amplitude increases and when I place it back the amplitude start to decreasing, so can I solder the end of the bucking coil with the same wire and add some turns?,it is ok to do that?.

TX=5.9mH /13.9khz
RX=6.65mH /14.9khz

What you recommend me to do?

https://i.ibb.co/tYyMLk2/20200216-131221.jpg
https://i.ibb.co/y6vdWF4/20200216-135938.jpg
https://i.ibb.co/hLt8m5j/20200216-140056.jpg

[waltr]

Yes, solder extra length of wire to find how many turns are needed on the buck coil to get a null.
Just make the solder joint as small as possible. A simple lap joint with a piece of heat shrink will work.

[waleed]

Yes, solder extra length of wire to find how many turns are needed on the buck coil to get a null.
Just make the solder joint as small as possible. A simple lap joint with a piece of heat shrink will work.

Ok seems fair, but what you think about the frequency of both coils?

[waltr]

Ok seems fair, but what you think about the frequency of both coils?

Ideally, the TX coil AND Oscillator should be 14.5kHz with the RX coil running at 13.9kHz on the TX's Oscillator circuit as in Dbower's TGSL 101.pdf.
What is actually important is the TX and RX coils have a difference of about 0.5mH. The actual TX Frequency can be different from the ideal 14.5kHz.

TX=5.9mH /13.9khz
RX=6.65mH /14.9khz

How did you measure these frequency? Are you sure you didn't mix them when posting?
The lower inductance would oscillate at a lower frequency if connected to same oscillator circuit.

[waleed]

Ideally, the TX coil AND Oscillator should be 14.5kHz with the RX coil running at 13.9kHz on the TX's Oscillator circuit as in Dbower's TGSL 101.pdf.
What is actually important is the TX and RX coils have a difference of about 0.5mH. The actual TX Frequency can be different from the ideal 14.5kHz.

How did you measure these frequency? Are you sure you didn't mix them when posting?
The lower inductance would oscillate at a lower frequency if connected to same oscillator circuit.

I think I measured RX wrong, I should connect the RX to the TX oscillator alone and then check the frequency it should be almost 13.9khz right?

[waltr]

I think I measured RX wrong, I should connect the RX to the TX oscillator alone and then check the frequency it should be almost 13.9khz right?

Correct.
But remember it is the difference that really counts.
So if TX oscillates at 14.9kHz, the RX Coil connected to the oscillator should be near (14.5-13.9kHz = 0.6kHz) 14.9 - 0.6 = 14.3kHz.

You can also TUNE the TX oscillator by adding C across the tank cap to bring the frequency down. I did do this on my TGSL. Try adding 1nF across C2 and measure TX coil frequency.
Add more until you get 14.5kHz.
Then the RX coil on this oscillator should run at 13.9kHz.

By using the same oscillator to check the coils you are actually check that the TX verse RX coils have the correct difference in inductance. This is the important value to obtain GB, disc and depth.

[waleed]

Waltr, the concentric coil doesn't seem to work properly so I decided to make the dd one, but I have some questions going on my mind make me not comfortable, first I did use the tl081 instead of lm308 it is ok or ne5534 would give better performance?, second I used 4 pins connector and soldered the cable wire shield to the TX end from both sides of the cable it is fine?

https://i.ibb.co/br5fq1N/1582242261519.jpg

[Nandor]

Hi

TL071 ot TL081 is a good replacement, I use booth maybe 071 is better because of low noise. NE5534 does not work here it gives continous sound.

4 pin connector is good as you showed.

[waleed]

Hi

TL071 ot TL081 is a good replacement, I use booth maybe 071 is better because of low noise. NE5534 does not work here it gives continous sound.

4 pin connector is good as you showed.

Much love Nandor thanks.