lobo improved

[maxbiri]

Hi all

Finally copper wire arrived! it's 0.22 mm.
I started same fast test and seem i have same problem around disc channel.
All metal seem working in good way.
In disc and gb channel i can follow signals with oscope on second lm358 and they are good but i lost them around 308 and 393, it seem i have same problem in this part of schematic.
I hope solving problem in the next days.
Bye Max

[aft_72005]

Hi Maxbiri
It is good news, that your homemade lobo running .congratulate.
Can you upload waveforms pictures?
Best regards.

[maxbiri]

I aft72005

Sorry now i havent photos of signal, after i will try with a digital camera, never tryed before take a picture from oscope tube.
It seem that W.L. schematic of year 1990 have sames errors around last 393 comparator .
I need more time for investigate but if is what i suspect it will be a big problem because i designed a very compact ss pcb and i need change a lot of tracks!

Bye Max

[aft_72005]

Hi Maxbiri
Please see attached pictures .my opinion schematic 1 correct. Try
It.
Best regards.

[maxbiri]

Yes, the problem was the incorrect connession of e10 k and 1n4148, i wired them as 1 and now it's working, i dont use the 3.6 M resistor in parallel at 1n4148.
Now i have problem with oscope, after 1-2 minutes it go on strike!
I need fix problem on oscope or find a new oscope!


Bye Max

[aft_72005]

and now it's working

Hi Maxbiri
Very good ,please more inform us .
Best regards.

[maxbiri]

I found a new error in disc stage, this time it's a my error!
I will correct it and than post what i presume will be the definitive schematic.
At moment device is not too performing, but i need again well test for tx- rx phase.
The strange thing is that i have a double ritarded ring with non ferrous target and a single well centered ring with ferrous target, this happen in all metal and disc mode.
I presume this is a phase problem.

Bye Max

[maxbiri]

This is last schematic revision.

rx coil is 1 mh + 47 nf
tx coil is 10 mh +4.7 nf
i reversed rx coil and now no more double ring on target.
Disc now seem working, not perfet but working.
coil test not shielded, DD eliptical about 22*14 cm.
rx phase -10,-20° respect tx, tx signal about 9 volt PP rx about 4-5 mv PP.

[simonbaker]

Hi, did you successfully build Lobo? Any test results?

Cheers!

-SB

[maxbiri]

Hi Simon

Yes i built newlobo as in last schematic, it work but with same problems.
I'm testing a DD eliptical coil 14*22 cm.
The problems are:
1)Poor deep, i can detect a 50 eurocent at about 20-22 cm in disc.
2) if i set newlobo for best perfomance in all metal i have poor perfomance in disc and viceversa.
3) disc work in strange mode; at minimun disc set i disc big and smal iron target( e.g. hammer head 250 gr.)but i can ear, in clear mode, smal alu foil like this in cigaret box, if i increase disc i lost alu foil but even 50 € cent!
Is not sensibile at smal target e.g. small lead sferic 4.5 mm diameter.
I presume i have phase problem in coil or around lm339 comparator.
I need change small capacitor from ceramic NP0 tipe to polipropilene or polyester type and try a new coil.

Bye Max

[simonbaker]

Hi Simon

Yes i built newlobo as in last schematic, it work but with same problems.
I'm testing a DD eliptical coil 14*22 cm.
The problems are:
1)Poor deep, i can detect a 50 eurocent at about 20-22 cm in disc.
2) if i set newlobo for best perfomance in all metal i have poor perfomance in disc and viceversa.
3) disc work in strange mode; at minimun disc set i disc big and smal iron target( e.g. hammer head 250 gr.)but i can ear, in clear mode, smal alu foil like this in cigaret box, if i increase disc i lost alu foil but even 50 € cent!
Is not sensibile at smal target e.g. small lead sferic 4.5 mm diameter.
I presume i have phase problem in coil or around lm339 comparator.
I need change small capacitor from ceramic NP0 tipe to polipropilene or polyester type and try a new coil.

Bye Max

Thanks for update. I am interested in Lobo because Tesoro made Lobo super for depth and I've seen results of person who uses it every day. Excellent for both coins and small gold nuggets. I hope we can get a circuit working as well as Tesoro. Only drawback is big heavy box on original.

Cheers,

-SB

[porkluvr]

Maxbiri, how did you decide that you needed 4.7nF capacitor for your TX coil?

I think that 4.7nF in the receiver tank will resonate slightly higher than the circuit is intended. I look for 6.2nF to resonate with 10mH at about 20.2kHz - (with the frequency trimmer set approximately at mid point). Why have you chosen 4.7nF?

The Lobo manual indicates an operating frequency of "about 20Khz". Your tank circuit wants to work at 23.2kHz . I think that 23.2 is almost beyond the high end range of the RC components on the 555, certainly not mid-range.

[Unregistered]

. I think that 23.2 is almost beyond the high end range of the RC components on the 555, certainly not mid-range.

If you are relying on simulation results, then you are probably not accounting for cable and coil capacitances to lower the output frequency to within range of the RC timing network.

[maxbiri]

Hi Simon

I forget said that all my test are done feeding tx stage at 5v so all circuit can be powered at 9 volt, 6 AA or AAA battery or even a single 9v block so i presume a light device.
With new power stage i have a stable simmetrical +/- 4.95 volt, less than 5 mv difference.


Bye Max

[maxbiri]

Hi porkluvr

I decide 4.7 nf by testing with oscope.
Before i set tx at 20 khz and after try different capacitor try finding resonance.
My measure are with oscope so mybe not very exactly, i presume +- 10 %.
I try even reverse tx and rx and device work more oe less in the same way.
On rx coil we need a tank capacitor for decrease noise, rx must not be at 20 khz resonance for best perfomance, i need more test for finding better solution.

Bye Max