VLF MD (by Sascho - Varna)

[aft_72005]

Sascho and other people that built this detector

Hi
Sascho and other peoples that built this detector
Built search coil with 0.4 mm cu wire with insulate. as Sascho determined at in
Circuit diagram. Also shield tx and rx coils with aluminum foil and both connected
To circuit ground . wire between coils and circuit was shielded type .
my test with this detector , detected one coin with 28mm diameter from 30cm at air .
Working like as motion type detectors. Also check and correct phase displacement
For ground reject and discrimination by oscilloscope . as Sascho said -5 to 25 degree for
Ground and 20 to 120 degree for discrimination . discrimination didn’t work correctly .
Also I working for better result .
Best regards.

[Ultimate_Haze]

0,31mm!!!

[aft_72005]

0,31mm!!!

Hi Ultimate haze
Are you built this detector?
Yes, also I built other coil with 0.3mm cu wire .
Total dc resitance for tx and rx coil is 14.9 ohm. And finally coils shielded with AL. foil .
With it transmitter frequency when apply power running around 730-740 KHZ ???!!!
At the first produced harmonic frequency . for solving this problem
also I added other 150nf cap. To tx coil and then osc frequency reduced
to 5.5-5.7 khz . but work with harmonic , wave shape not complete sinus
on oscilloscope screen .
then I built other coils with 0.4mm cu wire , total dc resistance is 8.4 ohm
for tx and rx . with this coil osc at the first when apply power works on main
resounace ,5.7 khz . for tune it exactly added other cap with tank circuit at osc .
Wave shape is complete sinus without harmonic, p to p out pout voltage
Was 50 volt .
Also receiver tuned at full resonance mode and ………
What is your opinion ?
Also I hope Sascho reading this message.
Sascho , where are you ?
Best regards.

[aft_72005]

Hi Sascho and Leto .........
and ......To people that built this detector
Please upload waveform pictures from various sections of receiver .
Best regards.

[Ultimate_Haze]

Hi,
Aft
I hope Sasho answer here its his work.

But you shouldnt search fot solution like that.Dont change the tanks.

You should shield and type the windings.Then find minimal residual voltage in RX.Ccomp is not conected!!!Like this you seal with epoxy.Afther the resin is setled you compensate the coil with right Ccomp value.This type of coils are more stabile then compensated buy fazeshift and amplitude onces.
Hope this helps.
Please post results later
Dont lorry about the frequency.When right nulled its came on its place.5,7kHz.

[aft_72005]

Hi Ultimate Haze
Yes, all of your statements is right and I working seem.
In my opinion oscillator should be running on 5.7khz undependable to
Coils displacement.
Coil Displacement at null area ,shouldn’t any changes of oscillator frequency.
Oscillator contain two transistor . oscillation frequency determined by
RC section at base of transistors . the LC tank( parallel resonance) tuned
On main frequency . I didn’t changes LC section ,only optimum it at 5.7 KHz .
I think my problem at receiver. At the best and minimum null, I read 1.2
Volt peak to peak in receiver in put ..(by oscilloscope )
What is your measurement at receiver input?
Best regards.

[Ultimate_Haze]

Hi,
Aft.
I sill wait for my scope to reach me within few weeks.Plus this project is in box and stored.
But if you read the Leto post you will see that when coil nulled right the frequency goes to 5,7kHz like it should be.

[aft_72005]

Ultimate haze
I did read all of this thread and what’s Leto said exactly.
Please say about your detector. Air test, discrimination,
Was it work motion mode ?
Best regards.

[Ultimate_Haze]

Its motion type.
Air tests were around 25cm for 1euro coin.
I haven't chance to test in soil and no free time to finethune the device.
Disc were ok.
If you look schematic there are some components labeled with *,try to change those values.This might help.
I will search for the box and remake the setup but without oscilloscope I wont be able to asist you further.
What TRs you used for TX?
My coil were made from 0,25 wire.

[aft_72005]

Its motion type.
Air tests were around 25cm for 1euro coin.
I haven't chance to test in soil and no free time to finethune the device.
Disc were ok.
If you look schematic there are some components labeled with *,try to change those values.This might help.
I will search for the box and remake the setup but without oscilloscope I wont be able to asist you further.
What TRs you used for TX?
My coil were made from 0,25 wire.

Ultimate haze
I remember Sascho said this detector can be detect coin with 2cm diameter
From 30-35 cm in the ground .
When compares my detector ,seem as my detecting was lower than Sascho made .
Another problem is , discrimination .
What type discriminate your detector ? meter needle at center , discrimination
Divided in two section , Ferro and non ferro
Or be able rejected ferro items complatly seem as Tesoro detectors ?
Transistors of Transmitter is 2N 2907A
Also thanks for your attention .
Best regards.

[Ultimate_Haze]

No,
Problems Aft.
But it looks like I wasnt able to help you.
Disc were for fero /non-fero and Al I think.
I will check.
30-35cm with 19 oo is inposible I think.But with larger maybe.
I have to tell you that this results are most probaly for loosed normal soil.

[Unregistered]

Hi,I made this schematic OO coil 19 cm. 27/27/54 Tx and 108 Rx. With 100nF - 6,5kHz. With shielded coils -instead of 3,3nf cap for adjust ground -270pf to me. Disc work.Air test 1euro -about 35cm. I have no box yet to make tests in the field.Tx power is 22V. I use 7809 stabilizer.Power consumption about 28-30 mA.Coil resistance is 14,5 Om - like Cu -wire is 0,35mm. But I was given wire for 0,31.I tried first 0,22 -100 turns -it didn`t start to generate,so you need at least 0,28 mm I think.With almost fine tuned coils,without C comp. air test as I said -1euro - 35cm.Ground I made with a little ferrite.For osciloscope I used sound card of my pc and pc -oscilloscope program -freeware -from a german cite I think.

[aft_72005]

No,
Problems Aft.
But it looks like I wasnt able to help you.
Disc were for fero /non-fero and Al I think.
I will check.
30-35cm with 19 oo is inposible I think.But with larger maybe.
I have to tell you that this results are most probaly for loosed normal soil.

Hi Ultimate haze
Thank you , please check your detector discrimination ,
And say me more .
Best regards.

[aft_72005]

Hi,I made this schematic OO coil 19 cm. 27/27/54 Tx and 108 Rx. With 100nF - 6,5kHz. With shielded coils -instead of 3,3nf cap for adjust ground -270pf to me. Disc work.Air test 1euro -about 35cm. I have no box yet to make tests in the field.Tx power is 22V. I use 7809 stabilizer.Power consumption about 28-30 mA.Coil resistance is 14,5 Om - like Cu -wire is 0,35mm. But I was given wire for 0,31.I tried first 0,22 -100 turns -it didn`t start to generate,so you need at least 0,28 mm I think.With almost fine tuned coils,without C comp. air test as I said -1euro - 35cm.Ground I made with a little ferrite.For osciloscope I used sound card of my pc and pc -oscilloscope program -freeware -from a german cite I think.

Hi unregistered
Also thanks for your data ,
Can you upload some waveform pictures from receiver section ?
What is your reading ( better if by oscilloscope) at null point of coils?
Please say more about discrimination test .
Best regards.

[Unregistered]

Hi,Aft!I think that you may even without oscilloscope to null the coils -pin1 NE5532 -less reading.With oscilloscope I measure exactly wire from Rx coil .First by changing cap 100nf(or 150nf) of Rx coil -you must achieve biggest amplitude in Rx (Coils must be nulled before making that)After achieving most amplitude in RX -try to null coils again to make minimal reading in RX.Then your detector must work like it should.Try to make ground balance by trimer.If is not possible-sound appear only in one direction -then change da cap 3,3* nf.Change this cap so the potentiometer 10k must be somewhere in the middle when the ground is adjusted.Discrimination - I put varistor 100k to adjust discrimination.DIscrimination must be adjusted once time - without extended potentiometer.Adjusting disc affects the ground balance.
1. Make the coils nulled.(shielded coils)
2. Try to make Rx in full resonanse by changing cap* (max amplitude in Rx)
3. When max amplitude is achieved in Rx -try to null again by slightly moving coils for less reading in NE5532 ,or directly otput RX (with oscilloscope)
4.Now for the test you may put C comp (from 10 to 100 pf) to get amplitude in rx most minimal.If adding C comp* increases amplitude-you must move coils to make null,but from other side - then C comp decreases amplitude in Rx.
5.Try with a little ferrite to adjust ground.(to me ferrite is about 8mm diameter and 3sm long.Don`t move ferrite too close to the coils.If sound appears only when ferrite goes to the coils ,you must increase 3,3nF* cap To me -270pf.(Disc varistor must be set in the middle).When you make ground -try with little iron - meter should go left when sound appears,and for coloured metals -right.If no,or sound is no like should it be,or you can not adjust the ground -you must turn around the Rx coil and again 1,2,3,4,5 If everything correct by varistor 100k (discrimination) you should get the place where meter start to move left for irons,and right for coloured metals.Once adjusted -make the ground again and your detector is ready :P.Disc. 100k must be in the pcb,not outside the box.Once adjusted you don`t need to adjust again.outside the box must be Ground pot,SENS,VOLUME and meter ofcourse
I`m not expert this is my third pcb -that was the way which I used to get my detector to work.I hope all that will at least little help you.