TESORO GOLDEN SABRE

[Aiko]

my Tesoro

Hello everyone,

This is my Tesoro GS Light by Ivconic. This is very nice project – many thanks to Ivconic, Max and to other guys.

My coil is DD with 210 mm inner diameter of each RX and TX coils, with 0.3 mm wire. I calculate the number of winding with Coil Calculator and receive 113 windings for RX and 107 windings for TX.

Unfortunately I unable to obtain a good shielded cable for the coil.

The best coil balance that I able to obtain is about 5 mV – is this good enough? I use digital multymeter to measure it.

The detection in air for 20 euro cents is about 18 centimeters. In normal soil the detection for 20 euro cents is about 15 centimeters. For large metal objects (metal mug) in air about 50-60 cm.

I know that the secret is hiding in the coil. I think that my coil is very good prepared and shielded, but I am not sure about the numbers of windings.

I will be very grateful for any advices which will help for increasing of the detections depth.

[ivconic]

Very nice work. Congratulation.
Also your results are not bad at all.
Yet, instead 0.3 wire i would rather use 0.25mm (0.28 with resin layer).
Do not try to achieve less possible residual voltage on RX coil by demand. Not obligated. Mutually you should balance coil and check air detection by swinging coin over coil. Measure, balance than check with coin, again and again. It is possible to achieve excellent air distances on coin with a bit higher residual voltages. All this can also be related to components quality and their tolerances. Of course; all the "secrets" are in coil itself.
But at the end..you will find out that best coils are must be 6mH for TX and 6.5mH for Rx. Resistances between 18ohms to 25ohms (depends of coil dimensions and wire).
You are almost there. Pay a bit more effort. Change a wire. With 0.25mm try 98 windings for TX and 107 for Rx. (D shape dimensions should be 255x137mm)
Regards!

[Max]

Hello everyone,

This is my Tesoro GS Light by Ivconic. This is very nice project – many thanks to Ivconic, Max and to other guys.

My coil is DD with 210 mm inner diameter of each RX and TX coils, with 0.3 mm wire. I calculate the number of winding with Coil Calculator and receive 113 windings for RX and 107 windings for TX.

Unfortunately I unable to obtain a good shielded cable for the coil.

The best coil balance that I able to obtain is about 5 mV – is this good enough? I use digital multymeter to measure it.

The detection in air for 20 euro cents is about 18 centimeters. In normal soil the detection for 20 euro cents is about 15 centimeters. For large metal objects (metal mug) in air about 50-60 cm.

I know that the secret is hiding in the coil. I think that my coil is very good prepared and shielded, but I am not sure about the numbers of windings.

I will be very grateful for any advices which will help for increasing of the detections depth.

Hi, I like it. Good made !

Congratulations.

About performances you're right : trick is in tuning, of coil mostly and circuit also.

About coil you need match params nad tx frequency, sure phase shift also for good disc. All this require you use a scope for finest possible tuning, multimeter is good but you have to play much with coil... experiment with slight variation of nulling...also not all multimeters are the same... so what's indicated by e.g. Ivconic's one it's sure different from your readings... so it's a bit tricky way of tuning coil.

Nulling seems good at 5mV , usually under 15mV coil plays good... sure the best for e.g. being ummune to soil false is achieving small nulling voltages and overnulling...a bit. But, again, you need scope for that.

The fact is, indeed, if you use an original tesoro coil with your circuit you could be surprised you'll don't get much more performances than your actual handmade... easy: they don't tune for maximum perf but much about stability and best discrimination... that's why so many wrote about weakness in performances of uMax mds in past and even today.

The circuit is really good old analog... if you tune coil and reduce noise you'll get a top-md for really cheap, but requires work and dedication... and much hours of testing... much coils you have to make etc to gain practice.

I suggest , now that you know it works, make other coils, following advices here... use 30AWG (0.25mm bare) wire, make required number of turns and match frequency... try to phase it good etc... shield properly and wire properly etc
You'll discover the hidden potential of your golden sabre.

PS: also remove any flux stuff from soldering layer... use cotton and isoprophilic alcohol for that stuff... device will be more stable then.

Kind regards,
Max

[Aiko]

Hi guys! Thank you very much for your advises . I will try them, but first I should find an oscilloscope. I don’t have it.

Regards to both of you!

[Ultimate_Haze]

Hi,

Nice work Aiko.
Can you use one euro coin for test?And tell us results.
Also I see that the cable from speaker goes trough some pot.Is this 100k for volume adjust?Is this working good.Have you added other components there?Or just 100k?

[Aiko]

Thank you Ultimate Haze!

One euro detection is about 20 cm in air and about 17-18 cm in normal soil. This is not good enough, but this is my first self-made metal detector and coil in my life. I will try everything possible for me to optimize it.

The forth potentiometer is a 10k, with 330 ohms resistor parallel to the potentiometer. This is switching off/on potentiometer and I use it also for sounds volume. Unfortunately this is not working well for the sound volume. In fact with this pot I have two positions of the sound – strong and weak in the two ends of the potentiometer. I do not know haw to connect this potentiometer for smooth sounds volume. I am not very proud with this solution

I forget about the discrimination – it is excellent – with insignificant depth decreasing.

Regards!

[ivconic]

Maybe that potentiometer is cause of some problems there? In the past i also experienced some problems with Vol pot and earphones socket. Later i realized that and ever since i am not using Vol pot any more. I am using earphones sockets, but large plastic ones, not small metalic! Exclude Vol pot and wire up speaker directly to output on pcb. If there are some differences than, tell us.

[Aiko]

Maybe that potentiometer is cause of some problems there? In the past i also experienced some problems with Vol pot and earphones socket. Later i realized that and ever since i am not using Vol pot any more. I am using earphones sockets, but large plastic ones, not small metalic! Exclude Vol pot and wire up speaker directly to output on pcb. If there are some differences than, tell us.

I try it now, but I did not feel any difference. But thank you Ivconic! At first I will try a coil with your parameters and to replace the coil cable with a good one, because the current one is much improvised .

[simonbaker]

I try it now, but I did not feel any difference. But thank you Ivconic! At first I will try a coil with your parameters and to replace the coil cable with a good one, because the current one is much improvised .

Can you measure the voltages on both .22uF capacitors C12 and C15 that are connected to JFet source pins? I think I have identified the voltage points in your attached photos.

These voltages should be positive. If they are negative, it probably means your coil is nulled improperly, and maybe someone can help with some suggestions.

Can you give us the following additional measurements, if your meter can do it?

1. Oscillator frequency (measure at TX coil lead that is not grounded).

2. TX and RX coil inductances and resistances.

-SB

[Aiko]

Of course simonbaker .

The voltage is positive – 75 mV for C12 and 40 mV for C15.

The frequency, if my multymeter measures properly is 13.6 kHz. Unfortunately I can not measure the inductance with my multymeter.

Resistance on RX is 19.3 ohms and for TX is 17.7 ohms.

Regards!

[simonbaker]

Of course simonbaker .

The voltage is positive – 75 mV for C12 and 40 mV for C15.

The frequency, if my multymeter measures properly is 13.6 kHz. Unfortunately I can not measure the inductance with my multymeter.

Resistance on RX is 19.3 ohms and for TX is 17.7 ohms.

Regards!

(Damn, lost the message, starting over)

Here is a possible small tuning your could try, no guarantees.

I will make some guesses based on your measurements. I hope others will check and correct any mistakes, so don't try this for a while.

Based on your oscillator freq of 13.6 kHz, I am guessing your TX coil is 6.5 kHz (by playing with LTSpice).

Based on coil resistances, I am guessing your RX coil is (19.3 / 17.7)**2 * 6.5 = 7.7 mH. (I hope others can check and correct that).

Based on RX inductance and assuming RX capacitor C6 is .015 uF, your RX resonant frequency is about 14.8 kHz.

You may be able to pick up about 8 dB gain (hardly much, but hey) by lowering your resonant frequency a little, but not so much to cause a phase shift that would mess up your discrimination. My calculations with LTSpice show that 14.0 kHz would be a reasonable choice.

If you change the RX capacitor C6 to .017 uF that should come close. Ivconic left space to add a capacitor to PCB, so you could add .002 uF there. But be careful, a little too much capacitance will start shifting your discrimination knob settings, so measure your original .015 uF cap as closely as possible and any cap you add.

Anyway, something to fool around with.

Cheers,

-SB

[Molzar]

Hi Molzar:

1. Were you ever able to remeasure the TX frequency of your Tesoro TGS? Your first measurement was 13.985, but you had question about meter.

2. Can you measure the resistance and inductance of the 8" coil RX and TX coils?

3. Can you confirm that the RX capacitor is 15 nF on the actual PCB?

I would greatly appreciate it.

Regards,

-SB

Simon,

1) Yes, Frequency for Tx is correct. ~13.98KHz

2) 8" Concentric coil (open centre)

Tx = 23.04 ohms, 5.43mH, Q 1.48
Rx = 23.37 ohms, 6.36mH, Q 1.71

3) Yes, .015 uF (15nF)

Hope this helps,

Molzar

[simonbaker]

Simon,

1) Yes, Frequency for Tx is correct. ~13.98KHz

2) 8" Concentric coil (open centre)

Tx = 23.04 ohms, 5.43mH, Q 1.48
Rx = 23.37 ohms, 6.36mH, Q 1.71

3) Yes, .015 uF (15nF)

Hope this helps,

Molzar

Thank you very much, I'm interested in original phase information.

13.98 kHz is strange, but explained if .022 uF cap in oscillator is actually .0253 uF (15% high) according to my simulations.

Regards

-SB

[Aiko]

Hello simonbaker,

Your proposal is tested. Thank you!

15n is best value for now, but I can not try lower values of this capacitor because I do not have smaller then 15n capacitors. I have only 15 n and 1n. With 16n the difference is small and with 17n and 18n are unstable.

Regards!

[ivconic]

You also not need to "hunt" exact frequency. It can work just fine with frequencies from 13kHz up to 16kHz. In the past i also made one pretty funny coil which gave 12.1kHz with TGS setup and it worked just fine with very good depths. Later, working more and more i established (for my needs) exact number of turns and exact wire with wich i usually gain 14.1 to 14.6kHz.... Personally i dont mind and dont bug myself much with exact frequency. So...just try to respect proper inductances (6mH and 6.5mH) and dont worry.