TESORO GOLDEN SABRE

[tiktak]

Leto,
This LM388 can't be found!!!
I spend all day going to all the stores that I now to search for this with no results!!!
I see that LM390 is similar can it be used?
Or LM3900?

[Max]

A better coil for detecting 1cm coin at good depth is maybe 25cm DD.
Think it could detect coin at 28-30 that way.

Hi,
Max.
What you sugest?I just bought coil housing and ined diameter is 25cm!!
So will be glad to test this.But how much turns should be wounded for TX and RX?
I will have this 0,25 without the varnish wire in monday and will go buy some other multimeter that have 2v range and will try to make another coil.
Thanks

Hi tiktak,
I don't know how many turns it need ... have to calculate. You can do also using e.g. the posted coil calculator program. Then use 10-15% more turns and cut away turns till you match tx frequency.

Best regards,
Max

[tiktak]

Hi,

Hi,
Max.
I now but dont trust myself because I do stupid mustakes!
Please calculate proper number of windings.You will make this coil anyway!
Thanks
p.s. Can't find TLC2262!!!
I dont now why?!??!?Should I change TL062 with TL072 or TL082 for now or this wont make any differance?
I now that become boring with all those questions but will find a way to ramach you somehow?
I am here until tuesday and then going for some field tests so have to make good coil!!
Can't wate to see how will this detector performe.

[tiktak]

Hi,

How can I measure frequency?
I dont have mant tools.
I am entusiastet beginer,thats why its better for me to folow your leads and learn.

[Max]

How can I measure frequency?
I dont have mant tools.
I am entusiastet beginer,thats why its better for me to folow your leads and learn.

Hi,
replace TL062 with TL072 or TL082, cause they have less noise.
No big improvement but if you have them... why not ?
Same performance and less noise, good.

TL062 is a very obsolete product now... noisy. Can't do any good there.
That's my point of view.
Someone could say you that's good enough there... for my taste is too noisy.
Take you choice.

To measure frequency, well...
you need one of these things:
- scope
- frequency meter
- multimeter with frequency meter built-in (some have it and are cheapy)

(well there are other methods but these are direct and easy!)

First 2 are for a more advanced approach... as beginner I'll find a good multimeter capable of reading e.g. 200KHz or more, cheap stuff, good enough to understand what's going on at oscillator... you just need reading its frequency.

Or you could buy something e.g. on ebay... there are a lot of these instruments (scopes, meters...) for few us dollars there, and also quality ones.

Best regards,
Max

[nelson]

Thanks Max.
Ok i ll do all that and see whats happend.

With the 15nF cap on RX coil leads, i got much sensitivity, but i also notice that on discrination, my wedding ring has almost no detction at minimum setting, while without the 15nF cap i get less sensitivity and my gold ring is detected at half turn on discrimination mode.

Perhaps all this, what else i can check to get more sensitivity. I ask this, cause you did 27 cm with 22 cms coil or this is ok. May be i need to check the TX stage to get more power, what do you think?
Another question, changing the TX coil inductance, changes the frequency too?
Do you have any formula to calculate the resonant frequency for the coil?

Regards

Nelson

Hi Nelson,
you can use a cat5 stp cable (the one used in ethernet works, flexible) to make internal connection from board to the panel connector. Other shielded cables are fine too... e.g. two pieces of RG-58 and the like or also some quality audio cables.
For coil cable you must use a shielded cable with at least 1 shield and two wires inside. You can use also e.g. 120cm of cat5 stp flexible. Only things needed are a good shield and low capacitance per lenght.

Is normal that when you touch leads unshielded you increase capacitance and so variation is seen by detector as a signal... you imbalance input stage that way. If use shielded cables the effect is reduced to minumum.

Another important thing is that cables must stay wounded e.g. on coil pole... expecially true for the lower end of them that goes to coil housing.

You have to avoid that cable moves during sweeping or you'll have a false signal from that movement relative to the coil.

Keep in mind that this is not a minelab/coiltek coil... where preamp is inside the potting at coil dish (but also minelab suggest to keep it fixed for similar reasons related to tx field radiation from cable). In our GSabre we have preamp on control unit... so also coil cable is "sensitive" to metal... not only the tx wire floating problem like in others...that's the clear reason of keeping it fixed to the pole.

Also in Tesoro' manuals there are instructions for that, in the assembly of detector part is explained how to wound coil cable to the lower end of pole.

1cm diameter 22cm depth ? I got about that too, maybe few more...
can't remember now.
Anyway, my reference is always 1eur coin... got something 27cm for that.

A better coil for detecting 1cm coin at good depth is maybe 25cm DD.
Think it could detect coin at 28-30 that way.

Think that I can reach BandidoII performance with some cap mod. and a bit of luck, have to find time!

Best regards,
Max

[tiktak]

Hi,

Hi,
Max.
I try but cant find right solution with this calculator....................
Its look like its for oo coils?
Please advice me.How much turns for this DD25cm./inner diameter 25cm/

And one more thing:
I have this multimeter.I cant null my coil with this right?
ACV:0-200V-600V±1.2%
RANGE 100mV-700V AC;

I see that Ivconic use VC9805A.
I will search for something according my poket.
THANKS

[porkluvr]

supplier?

Hello Tiktak -----

I don't know where you are located but Digikey evidently has a multinational presence. They might be able to ship to you.
You might give them a try for TLC2262.

http://search.live.com/results.aspx?...=AS5&q=digikey

[tiktak]

Hi,

Hi,
Thanks porkluvr!!
I am glad you help me.Unfortunatly they can send 2,500 pieces minimum!
But anyway thanks!
Isnt there any more easy to find good replacement?

[Leto]

Originally Posted by tiktak
Leto,
This LM388 can't be found!!!
I spend all day going to all the stores that I now to search for this with no results!!!
I see that LM390 is similar can it be used?
Or LM3900?

I have not tried but it looks the same, also the pinout is identical..
download LM390 datasheet and you will see (FIGURE 1) same circuit I used...

about multimeters:
Your multimeter needs AC voltage range starting from 0mV (DT-830B starts with 100mv). Look for Max post somewhere about tuning with different multimeters there are quite big differences.
If you do not have frequency meter - that's also very much needed.

[Qiaozhi]

Hi,
Max.
I try but cant find right solution with this calculator....................
Its look like its for oo coils?
Please advice me.How much turns for this DD25cm./inner diameter 25cm/

No - the calculator is not specifically for OO coils, but it is designed for circular coils. This means it is good for mono, OO or concentric coils. If you want to use it for calculating DD coils, then you need to do some mathematics.
First - estimate the circumference of the D coil you want to make. You can easily do this by laying out one turn of wire in the correct shape. Then measure the length of this one loop. If you were to reshape this loop into a circle, this is the size of coil you must enter into the calculator. In other words, take the length of the single loop and use this value as the circumference (C) for a circular coil. Then use R = C / (2*pi). The value R is the length of the radius to be entered in the calculator.
Lastly - wind the correct number of turns onto the D-shape. There is no need to wind a circular coil and reshape it, because the circumferences of both are the same.
And yes, there will be a margin of error, but after some practice you can work out the correct fudge factor.

[porkluvr]

meter facts

Tiktak
I am sorry about the minimum order from Digikey. What country are you in where they want you to buy 2500 each??

Look, about your meter: what Leto said is correct - your multimeter's lowest voltage resolution is 100mV and that is not so great. But, you might still be able to use your meter. Measure AC current, instead of AC voltage.
It looks like your meter's current (amps) scale can resolve to 0.1 microamps. AC current resolution is good enough. A 10mV residual signal would push 10 microamps through a 1kΩ resistor, and that should be plainly readable on your meter's 200uA scale.

Now, this should work:
De-solder the ground end of the 1kΩ resistor on the far side of the .22 capacitor from the receiver opamp output. (look at the picture.) Connect the red meter lead there. Connect the black meter lead to PCB ground.

Using the existing 1kΩ resistor should give an OK trade-off between circuit loading and meter display resolution. Set the meter's scale to 200uA and null according to previous instructions.

With the suggested set-up using a 1k resistor, simply multiplying the measured current X1000 will tell you the AC voltage. This is an indirect method of measurement, but it should work reasonably well (unless the fuse in your meter is blown). So, now you may be able to afford to buy a better frequency counter (hmm, I need one too, come to think of it). $$Get a better multimeter some other day.

Be careful when the meter in the milliamps test mode. I don't know your particular unit, but It may be more succeptible to damage. It is easy to blow a fuse - or worse when measuring current. You should definately THINK about what you are doing before you apply power, more so than usual.

[Max]

Thanks Max.
Ok i ll do all that and see whats happend.

With the 15nF cap on RX coil leads, i got much sensitivity, but i also notice that on discrination, my wedding ring has almost no detction at minimum setting, while without the 15nF cap i get less sensitivity and my gold ring is detected at half turn on discrimination mode.

Perhaps all this, what else i can check to get more sensitivity. I ask this, cause you did 27 cm with 22 cms coil or this is ok. May be i need to check the TX stage to get more power, what do you think?
Another question, changing the TX coil inductance, changes the frequency too?
Do you have any formula to calculate the resonant frequency for the coil?

Regards

Nelson

Hi Nelson,
I said 27cm depth (at now) with DD22 for 1eur coin....

1eur coin is about 23mm diameter, bimetallic coin.

With 1cm diameter coin (silver alloy) I get about your depth.

About disc... if you put much capacitance on the RX side... you'll lose some disc. That's why I said max 4-5nF increase or decrease respect to original 15nF.

You could experiment e.g. from 10 to 20 nF for rx cap. But if you keep it close to original and get good performances is even better.

Yes, changing the TX inductance change the frequency.

It's a colpitts osc. Formula is below.

Kind regards,
Max

[tiktak]

Hi

Hi,
Leto.
I have found LM3900 ,but its look like its not the same???!
What do you think?

[tiktak]

Hi

No - the calculator is not specifically for OO coils, but it is designed for circular coils. This means it is good for mono, OO or concentric coils. If you want to use it for calculating DD coils, then you need to do some mathematics.
First - estimate the circumference of the D coil you want to make. You can easily do this by laying out one turn of wire in the correct shape. Then measure the length of this one loop. If you were to reshape this loop into a circle, this is the size of coil you must enter into the calculator. In other words, take the length of the single loop and use this value as the circumference (C) for a circular coil. Then use R = C / (2*pi). The value R is the length of the radius to be entered in the calculator.
Lastly - wind the correct number of turns onto the D-shape. There is no need to wind a circular coil and reshape it, because the circumferences of both are the same.
And yes, there will be a margin of error, but after some practice you can work out the correct fudge factor.

Hi,
I am BEGINER!
In this calculator there are inner diameter/I understand former size?!?/;wire thicknes and number of turns!
What is the (2*pi)?
I can't get the point?