TESORO GOLDEN SABRE

[dbanner]

By the looks of your VA picture, looks like the RX waveform is inverted, maybe you should flip the wires to Rx coil?

[dbanner]

So there's no need to go bending around your coils to tweak inductance.
Fix the tx in place and tune with capacitors. The lock it down so it can't move and forget about it.
Now focus on Rx.
In order to tune Rx, just hook it up the the tx circuit and tune it's resonance for the 1.6khz spread. See?

[dbanner]

If you notice, the tx resonance frequency is stated as 14.5khz and RX at 16.1khz.
This is important for everything to work correctly.

If you subtract 16.1khz - 14.5khz=1.6khz

This is known as " off resonance " tuning.

You should mantain the 1.6khz spread. Not so much the 14.5khz/16.1khz.

Let's suppose your TX is at 14.7khz, l am good with that, no problem. All l need to do is to tune my Rx coil to 16.3khz in order to maintain the 1.6khz spread. See?

So you don't have to be bang on 14.5khz and 16.1khz. More important is the "off resonance" spread between the tx and RX.

[dbanner]

I used a USB cable. It worked very good.

[Majster]

Hello again everyone,
And another idea came to my mind: at the time when I was winding and connecting these coils, I only had a shielded two-wire cable, i.e. 2 wires covered with an independent shield. So I connected these 2 cables with screens in parallel, thinking that it would be the same as one 4-wire cable in shield. The shields connect at the beginning and end of the cable, the RX wires are separated, one of TX wires connects to the shield, as in the second Don Bowers drawing. Or should I use a regular USB cable after all? It has 4 wires in the fifth screen, maybe it will be better? And maybe at the nulling stage I should connect them like in the top, first picture of the Don Bowers documentation? I think I need a USB cable. How do you think I should do that?
I greet everyone.

[Majster]

Hello again everyone
First of all, thank you very much for your help and involvement in my problem. It is always nice and uplifting, when people want to help, the world becomes much better. I really think so.


I did this today:


1. I made one more nullification attempt as you suggested, but I was very (realy very) slow and careful doing it, and it went a little better. I had both TX and RX coils connected. I was able to go down to 0.63V AC between IC101 / 7 and ground, and after a few different settings (coils high above the table) even to 0.53V AC. It doesn't get any lower. I did not move the coils with my hand, because I am not that dexterous, but with a plastic lever, and I think that the jumps / changes were not greater than 0.5mm shifting the position of one coil relative to the other. The frequency between IC101 / 7 and ground is 13.93kHz. DC under these conditions is 0.22V. I have noticed that the sensitivity has improved: ferrite and copper (pieces ~ 4-5cm) are already visible from 20cm, my phone 30cm or more. Under these measuring conditions, at a distance of 0.5 m from the coils, I have nothing metal, just the pieces that I use for testing. It's still rather poor, but I guess I'm going in the right direction.


2. As Carl-NC suggest, I disconnected the TX and first measured the AC voltage on the RX terminals. Regardless of which one I start with, it starts at ~ 1V and quickly drops to 0.1, then slower but still drops to a few mV, then it only fluctuates slightly. It is similar between IC101 / 7 and ground: 1.0V, down to 0.1, then almost to 0V AC. The DC voltages on the IC101 pins (TX coil disconnected) are:
1 0.77V 8 8.00
2 0.06 7 0.66
3 0.00 6 0.23
4 0.08 5 0.23


3. I connected the TX coil again and re-measured all the legs of the IC101. The DC voltages on the IC101 pins (TX coil connected) are:
1 0.29V 8 8.00
2 0.18 7 0.25
3 0.00 6 0.12
4 -6.30 5 0.10
Then I measured the frequencies in both terminals of both coils (not to ground, only pin 1/2 TX and 1/2 RX) and I got: TX 14.22kHz and RX 13.93kHz. My multimeter is very good: APPA 305, I'm sure you know this model. I know, maybe it's old, but it has served me for 20 years and it works great. I also use it for frequency measurements, it has a very wide working range. It also measures mV AC even at higher frequencies, but I haven't been able to get low enough to use this measuring range.


4. I have tried to use the VA program as suggested by dbanner. For the working system, I received the image as in the attachment. Looking at the oscillogram, I tried to nulate the coils manually, but failed to get the result in which one pass would be flat (I think that's what neulling is about). Still, I don't know how to get a 21 degree offset. Does it depend on the components on the PCB or only on the physical parameters of the coils? There is always some amplitude. When it is low, the sensitivity probably increases, is it good? As Waltr and dbanner write, it requires a really skilled hand. However, I suspect that maybe my coils are wrong? Or maybe something is wrong on the PCB?


5. If my coils are badly wound, I will probably have to rewind them. I figured it might be easier to adjust the inductance of the coils by bending them at a more convenient point, but that would require a different winding system, e.g. something like the picture (second attachment). What do you think about it?


6. What do you think I should do now?


I greet everyone.

[ArchibaldSTM]

Right here. Only with connected TX

[mawush]

hello, I'm new to this forum and sorry for my bad english. When I checked the schematic file, there is a regulator for -8V, but I couldn't see a regulator for -5V. In which part is -5V generated? . I plan to make the pcb design simpler.

[dbanner]

Since you have traced layout by hand and Sharpie, you are no doubt brave warrior.
The Hantek 6022be with Hscope software for Android tablet is excellent for our purposes.

[dbanner]

I balanced my the coil with ordinary multimeter. I didn't care about the reading the meter was putting out, I new it would be bandwidth limited. What l looked to see was the dip in voltage as l moved across the null. I just aimed for the lowest reading. So I knew that this was closest to where I needed to be. Then I began adjusting the gb trim for ferrite reject ( just on the edge of where ferrite is barely clicking). Then I wave various coins and metals to check discrimination range. All this time I am ever so slightly adjusting coil, gb trimmer and so on. Repeating until it is best.
Keep in mind that the tx frequency should be nailed down at 14.5khz( or was it 14.9khz, I don't quite recall)
Don't bend or deform the coils( you should glue in the tx coil so it can't move. Shift the entire RX coil left or right across the tx coil.
Don't bend or deform coil. When everything is to satisfaction, glue in place. The RX coil should be tuned to resonance at 16.1khz( if I can remember) this is important so phases and gb trimmer can be adjusted properly.
That's how I did it. No oscilloscope. I think I kept the meter connected while shifting around to get a feel for where I was in relation to the null point.
The trick is that so long as you can eliminate ferrite within the range of the gb trimmer while getting proper discrimination and good distance, then you can be assured that you've got close to the 21degrees phase balance required for the tgsl search coil since this performance could not be achieved otherwise. It is deductive logic.

[waltr]

In addition to Carl's and Dbanner's suggestions.

Coil null only happens within a very small physical range. So move one coil very, very little at a time to look for the null. The null will happen only within a few millimeters and best null within a fraction of a millimeter.
First time trying to null the coils is very hard but will be easier once you know how.

[dbanner]

Use VA software (visual analyzer). It has oscilloscope.
Sound card scope is limited, however by using VA there is a trick.
Open VA and go into settings/ scope. Click boxes designated Channel A full D/A and Channel B full D/A. Now your waveforms should be smooth.

[Carl-NC]

Disconnect the TX coil and measure IC101-7, see if the problem goes away. If it does, you have an imbalanced coil. If it does not, you have a different problem.
Keep in mind that ordinary multimeters are designed to measure AC at 50 or 60 Hz, not 14kHz. Building metal detector circuits really requires an oscope.

[Majster]

I try to add photos of my work:

It's working So, now the rest:

[Majster]

Hello again everyone
I did this: I picked up the RX coil and turned it over, then reassembled both DD coils. Again, I was looking for a setting in which the voltage between the indicated measurement point (pin 7 IC101 / ground) would be minimal. Unfortunately, nothing changes, I still have 4.6 - 4.7V AC. I'm beginning to suspect that the problem is on the PCB after all, but what could it be? I checked all the elements and connections 3 times, I have no idea. Maybe someone else has an idea?
I greet everyone.