Volksturm SM + GEB

[mehdi]

Hi
ofter change q3 and q4 to tip31 and tip 32 and change lf353 with a new one, now it work and can detect 1 inch coin at 14cm but phase(geb) variable resistor adjustment is very hard and critical!! only at one point of geb knob it can detect metal, is it usual?!
i am using 500k variable resistor instead of sens 390k+100k in series. and let me know, i must use R? 8K2 or not? i did'nt use that.
i hope you can help me dear Don.
best regards

[dfbowers]

I seem to remember that when phasing is just right, ferrous metal will increase the volume and non ferrous will cause a sharp dip in volume followed by an increase. So, you CAN discriminate but not GB at the same time. When phasing is set to eliminate ferrite then your setup is pretty close for actual use. You are corrrect that the GB setting is very critical so I use a 10 turn Bourons pot.

You do not need th 8k2 pot.. That's just a fancy VCO option.

Sounds like you are getting closer!

[taliesin]

ok

here is the volkstrum + geb in proteus schematic and pcb, the part list, top (pdf), bot(pdf), included, can anyone to revise it is correct or not?, i replaced the kt8xx for the tip3x, and the kt315 for 2n2222 the pins are not the same, and i have a question... can i include a class a amplifier 10w in the tx coil to do more power more depth? and a mic booster in the rx? for 4ohm coil? anyone tried this? im crazy!

ps. my english is weaker
[edit]i forget to put the battery holes , you need to drill the holes for the battery [/edit]

has this pcb board version been tested ?

[mehdi]

I seem to remember that when phasing is just right, ferrous metal will increase the volume and non ferrous will cause a sharp dip in volume followed by an increase. So, you CAN discriminate but not GB at the same time. When phasing is set to eliminate ferrite then your setup is pretty close for actual use. You are corrrect that the GB setting is very critical so I use a 10 turn Bourons pot.

You do not need th 8k2 pot.. That's just a fancy VCO option.

Sounds like you are getting closer!

Hi and thanks Don
my coils null is ok now , so please help me to fine tuning the coil, since it seem 14 cm for 1 inch coin is a little short distance! or not?!
and any other info will be very great help.
Don, what is maximum detection depth of your volksturm sm for 10'' coil? ( for big object)
other thing; i am testing indoor (at home) so is it possible that my test was not correct?!

with many thaks for your help
mehdi

[dfbowers]

Hi and thanks Don
my coils null is ok now , so please help me to fine tuning the coil, since it seem 14 cm for 1 inch coin is a little short distance! or not?!
and any other info will be very great help.
Don, what is maximum detection depth of your volksturm sm for 10'' coil? ( for big object)
other thing; i am testing indoor (at home) so is it possible that my test was not correct?!

with many thaks for your help
mehdi

Yes, that is a little short. Detection distance should be at least twice that for a 1" coin.
How "big" for a large item? For example, I just checked mine for a 10cm x 10cm copper PCB and detection range is about 60cm.

Questions:

Can you find the "threshold" (slight audio hum)?

Where do you have your "sens" set to? I have mine fixed at 460K ohms.

Can you reject ferrite??

Don

[mehdi]

Yes, that is a little short. Detection distance should be at least twice that for a 1" coin.
How "big" for a large item? For example, I just checked mine for a 10cm x 10cm copper PCB and detection range is about 60cm.

Questions:

Can you find the "threshold" (slight audio hum)?

Where do you have your "sens" set to? I have mine fixed at 460K ohms.

Can you reject ferrite??

Don

Hi Don
yes i can find "threshold" but hardly, ((if you remember my video))
my "sens" is fixed at about 480K ohms.
no, i can not reject ferrite , but as i told, phase(geb) variable resistor adjustment is very hard and critical so i cant find true point but to night i will use two 5K variable resistor in series to easy adjustment. i will post here the result after change.

again thanks a lot for your helps
mehdi

[mehdi]

Hi Don
after many trying, finaly i can not reject ferrite and my detection depth is poor yet.
please let me know, what is your coil detail; TX and RX diameter details and etc.
i think my problem is the poor coil!!

all the best

[dfbowers]

Hi Don
after many trying, finaly i can not reject ferrite and my detection depth is poor yet.
please let me know, what is your coil detail; TX and RX diameter details and etc.
i think my problem is the poor coil!!

all the best

I do not think that exact coil parameters are important, as long as you are close. It sounds like you are just not tuned to resonance, or close to it. That would explain why you cannot reject ferrite.

What you could try to do is add or remove tuning caps to your Rx coil for a maximum signal on pin 1 U1a while seeking a minimum while nulling. I usually get the null close and then start adjusting the tuning caps, then go back and null again.

The tricky thing with trying to tune a squarewave it that you can hit a harmonic that gives you a peak in signal amplitude, but adjusting to the fundemental will give you the highest peak.

Also, for initial tuning, I would suggest bypassing your op-amp that you are using for phase adjustment just to make sure that is not causing a problem as well.

Anyway, everything would become obvious if you had a scope. If you are going to do many more projects it would be well worth the investment, even a cheap one


Hope this helps!!

Don

[mehdi]

I do not think that exact coil parameters are important, as long as you are close. It sounds like you are just not tuned to resonance, or close to it. That would explain why you cannot reject ferrite.

What you could try to do is add or remove tuning caps to your Rx coil for a maximum signal on pin 1 U1a while seeking a minimum while nulling. I usually get the null close and then start adjusting the tuning caps, then go back and null again.

The tricky thing with trying to tune a squarewave it that you can hit a harmonic that gives you a peak in signal amplitude, but adjusting to the fundemental will give you the highest peak.

Also, for initial tuning, I would suggest bypassing your op-amp that you are using for phase adjustment just to make sure that is not causing a problem as well.

Anyway, everything would become obvious if you had a scope. If you are going to do many more projects it would be well worth the investment, even a cheap one


Hope this helps!!

Don

Hi Don
thanks for reply
i think that my problem of can not reject ferrite is in critical adjustment of phase variable resistor, now i am going to use 10 off 1Kohm pot in series may be solve the problem.
ok, i will do what you say and i will post the results after that.
again, thanks a lot for your considerable helps.

mehdi

[stergeol]

ok

here is the volkstrum + geb in proteus schematic and pcb, the part list, top (pdf), bot(pdf), included, can anyone to revise it is correct or not?, i replaced the kt8xx for the tip3x, and the kt315 for 2n2222 the pins are not the same, and i have a question... can i include a class a amplifier 10w in the tx coil to do more power more depth? and a mic booster in the rx? for 4ohm coil? anyone tried this? im crazy!

ps. my english is weaker
[edit]i forget to put the battery holes , you need to drill the holes for the battery [/edit]

hello in this pcb what is R2 R22 and C7???????

[mehdi]

Hi dear Don
thanks for your helps
it work perfect now and can detect 1inch coin at 29-30cm and about 60-65cm for 12.5*16cm one side copper board, but it can not reject ferrite at all, and the sensitivity for ferrite is better than other metals! Is it good?

my problem was poor coil; i make new one a few little than first.
my null is good now( pin 1 of LF353 is about .4v) and for tuning cap i use 100nf for first time and i dont want to change it because the performance is good now.

what cable i must use for coil connection?

btw, volksturm sm+geb is excellent MD.
thanks a lot dear Don to your help.

all the best
mehdi

[dfbowers]

I suspect that you are not tuned to resonance. You must be able to reject ferrite or you will not be able to reject ground. Also, when you find resonance your depth will be even better!

[mehdi]

I suspect that you are not tuned to resonance. You must be able to reject ferrite or you will not be able to reject ground. Also, when you find resonance your depth will be even better!

Hi
one time with 75nf the sensitivity for 8cm ferrite rod reduced to about 5cm but sense reduced for coin to about 15cm.
nulling is simple, because i can measure volt of pin1 lf353 but tuning is very hard, is there any test point to measure that tuning is in right way or not? or may be i must change the cap's often to get best sens to coin and less sens to ferrite?
any idea is great help
regards
mehdi

[dfbowers]

Hi
one time with 75nf the sensitivity for 8cm ferrite rod reduced to about 5cm but sense reduced for coin to about 15cm.
nulling is simple, because i can measure volt of pin1 lf353 but tuning is very hard, is there any test point to measure that tuning is in right way or not? or may be i must change the cap's often to get best sens to coin and less sens to ferrite?
any idea is great help
regards
mehdi

If no scope, it may be a little bit of trial and error. But, if tuned too far one way, you will get a negative response from ferrite, too far the other it will be positive, just right will be almost nothing. Now what you could really use is a "decade" box with a rotary switch and a bank of caps that can quickly switch them into place, say from 15 - 100 nF.
You may be able to narrow it down quickly that way. Just and idea.

[taliesin]

ok

here is the volkstrum + geb in proteus schematic and pcb, the part list, top (pdf), bot(pdf), included, can anyone to revise it is correct or not?, i replaced the kt8xx for the tip3x, and the kt315 for 2n2222 the pins are not the same, and i have a question... can i include a class a amplifier 10w in the tx coil to do more power more depth? and a mic booster in the rx? for 4ohm coil? anyone tried this? im crazy!

ps. my english is weaker
[edit]i forget to put the battery holes , you need to drill the holes for the battery [/edit]

hi and,
i just checked your pcb .the original schematic shows the tx q's driven from pin 12 of the 4013.on your pcb it's driven from pin 1 of the 4013.is this a mod or mistake ?