TESORO GOLDEN SABRE

[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.

[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.

[ArchibaldSTM]

Right here. Only with connected TX

[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.

[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.

[dbanner]

I used a USB cable. It worked very good.

[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]

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]

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

[dbanner]

Here is a little circuit for setting up the null. It is derived from magnum metal locator project. Read the text. Connect to output of Rx preamp.

[Majster]

Welcome back,

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?

I tried to use your tips. I thought I understood them. But it doesn't work. My TX coil in TX port (J1.1 and J1.2) has a frequency of 14.2kHz. Attempts to add a capacitor to it only lower the frequency. I used a 1nF capacitor. By no means does the capacitor raise the frequency. The frequency only goes down. This is logical because the theory says f = 1 / (2Pi SQRT (LC)), so if L = const (because I don't bend the coil like you said), and if C = x (initial value, I don't even know which is a capacitor, but I think it's the harmonic mean of C1 and C1, which is close to 20nF), then f (C = x + 1nF) <F (C = x).


I figured I would tune the RX to f = 15.8kHz then (because 14,2 + 1,6 = 15,. But that doesn't work either. The RX coil in the TX port (J1.1 and J1.2) has a frequency of 13.8kHz. Attempts to add a capacitor to it only lower the frequency. By no means do the capacitors raise the frequency.


Don Bowers' documentation shows that after assembling the coils and testing them in the TX port, the frequencies should be 14.5kHz (TX) and 13.95kHz (RX). My values are quite close. They are 14.2kHz and 13.8kHz as I wrote above.


I don't think I understand your tips though. I am really a beginner.


Greetings.

[dbanner]

Firstly, tx coil is tuned to 14.5khz and RX coil is tuned to 16.1khz resonance.
However even though it is tuned to 16.1khz, the RX coil will pick up a signal of 14.5khz being transmitted by tx coil. This happens when a metal object is placed in the field and disturbs the null.

The tx circuit is a colpitts oscillator, so there are 2 capacitors, which makes up the total tank capacitance. So I think it is C1xC2/C1+C2.

[dbanner]

To raise frequency of TX, add a large capacitor in series with C2. Or maybe change C2 to lower value. That should raise it to beyond the 14.5khz. then you can parallel a cap across the coil to bring it back down as required.

Maybe I said too much, l do not wish to confuse things. Good luck.

[Majster]

Let's simplify it:
The picture shows my layout.
How do I tune the coils with capacitors?

[dbanner]

Put a 470nF capacitor in series with C2 (you'll have to desolder one leg of C2 from PCB and join a 470nF in series. Connect the tx coil.
That will raise tx frequency to 14.5khz.