Question about tgsl

[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]

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]

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]

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

[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.

[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]

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]

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]

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

[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]

Waltr I bought an multimeter today, well I measured the regulator output it was 7.9v it is ok, and then I measured the charge pump before I connect the TX coil it was 0.7 volt and after I connected the TX coil while it beeping the voltage also was the same (0.7v), it didn't change to -5v or so, well now we know where to start solving problems, and tomorrow at uni I'll check the TX frequency and I'll see the waveform, but for now why I didn't get the -5v when I connected the TX coil?, it is possible the problem with the 4024 ic? Because I took it from my old board it's not a new one or maybe the transistors is reversed?, but I'm sure I placed them as the datasheet.

[waleed]

Hi
Yes you need B version. The difference is the resistance over distance, I hope you understand. Listen if you have a 100kB linear pot at middle position it will have 50k because its half of 100k, but if you use logarithmic 100kA at half position you will have maybe 20-30k and the rest of 70k is on that other half because this type is for volume control not for level control! Very important difference. Now you need level control for Disc Geb and Sens, so you can properly adjust the detector.

Thank you for the explanation I'll change them to the linear ones and then I'll do the tests that waltr mentioned above..

[Nandor]

Hi
Yes you need B version. The difference is the resistance over distance, I hope you understand. Listen if you have a 100kB linear pot at middle position it will have 50k because its half of 100k, but if you use logarithmic 100kA at half position you will have maybe 20-30k and the rest of 70k is on that other half because this type is for volume control not for level control! Very important difference. Now you need level control for Disc Geb and Sens, so you can properly adjust the detector.

[waleed]

And yes all my potentiometers ends with A letter, look at the image below you mean like this one right?

https://i.ibb.co/p2RfMnV/20200214-161536.jpg

[waleed]

Mod seems ok. I played with that mod and found it didn't do much to improve performance.
There are a few things you can check using a DVM.
1- Is there -5V (-6.2V)?? A TX coil MUST be connected to have the TX Oscillator run which is used for the charge pump.
Without -5V the circuit will not work.
I would disconnect the speaker so the noise does not drive you crazy. Also some speakers may not work causing problems in the rest of the circuit.

2- Voltage at the outputs of U104 & U105 need to be very close to Zero. It is these outputs that trip the comparator, U106, to cause output to speaker.
3- Check Voltage at inverting inputs of U106. The Voltage here should change when you turn the Sens. pot.

Check the POTS as Nandor stated. Log pots will kinda work but they really should be linear pots.

Thank you waltr, I understand now what to do first, I'll provide feedback when I'm done.