Volksturm SM + GEB

[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

[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 ?

[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!

[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

[mehdi]

Hi Qiaozhi and thanks a lot , ok i will try to keep my file size below 1MB and upload in Geotech.
regards
mehdi

[Qiaozhi]

Hi Don
here is some problem, i cant do wath you say, please see the video, may be you can find som error?!!!
http://www.upload4files.tk/download....021a7ecf50101d
Don, please send your email address by a PM to me.
thanks
mehdi

Please upload your attachments directly to Geotech, if possible, as the file sharing websites only hold these files on a temporary basis. Also, other members are sometimes reluctant to download from these (non-English) sites, as the advertising makes them look somewhat suspect. I know this particular file is over the 1MB limit for the rar format, so I have placed it here directly. If you can keep the file size below 1MB, you will not have a problem.

[mehdi]

Hi Don
here is some problem, i cant do wath you say, please see the video, may be you can find som error?!!!
http://www.upload4files.tk/download....021a7ecf50101d
Don, please send your email address by a PM to me.
thanks
mehdi

[dfbowers]

Hi Don
thanks for help
Don, can you explain how can i use a DVM to achieve a good null please?
i will try to do wath you say.

mehdi

Monitor pin #1 on U1a With a Voltmeter on the AC setting. With your coils just barely overlapping, move them closer together little by little. You will find a point where the Voltage will "dip" or "null" .. maybe 4mV will be the minimum. This is the point where you achieve induction balance. Next, if your coils are tuned, the area of your null will be very small.. less than 1mm!!

[mehdi]

Mehdi,

Nulling and tuning is what we must do next. My guess is that you have way too much overlap on your coils.

First, grasp your coil with your right hand, palm upward with your thumb extending in the direction of your Tx coil winding and your fingers wrapped around the coil. (Right hand rule). Your thumb represents the flow of current at some instant in time. The rest of your fingers represent magnetic flux at the same instant in time. Now notice that the magnetic flux (or your fingers) goes UP in the middle and DOWN on the sides.

The attached diagram may help as well. The green area would represent the magnetic flux going in one direction and the red will be the other. Notice that the Rx coil see both.
This is greatly simplified, but will help to illustrate.

If you position your RX coil overlapping in just the right spot, it sees magnetic flux going UP AND DOWN and the net signal is ZERO. So this will be the NULL point and hence IB Induction balance) - Little or no Tx signal induced in the RX coil and you will have a minimal residual signal from U1a Pin 1. You will want to move your coils around while monitoring pin 1 to achieve a good null. This can be done with a DVM on the AC setting.

Also, see the excellent article by Carl on coil types that may help you understand as well.

Once you null your coils we can work on tuning. Assuming that your tuning in not too far off to begin with, this should be easy.

Don

Hi Don
thanks for help
Don, can you explain how can i use a DVM to achieve a good null please?
i will try to do wath you say.

mehdi

[dfbowers]

my coil picture:

Mehdi,

Nulling and tuning is what we must do next. My guess is that you have way too much overlap on your coils.

First, grasp your coil with your right hand, palm upward with your thumb extending in the direction of your Tx coil winding and your fingers wrapped around the coil. (Right hand rule). Your thumb represents the flow of current at some instant in time. The rest of your fingers represent magnetic flux at the same instant in time. Now notice that the magnetic flux (or your fingers) goes UP in the middle and DOWN on the sides.

The attached diagram may help as well. The green area would represent the magnetic flux going in one direction and the red will be the other. Notice that the Rx coil see both.
This is greatly simplified, but will help to illustrate.

If you position your RX coil overlapping in just the right spot, it sees magnetic flux going UP AND DOWN and the net signal is ZERO. So this will be the NULL point and hence IB Induction balance) - Little or no Tx signal induced in the RX coil and you will have a minimal residual signal from U1a Pin 1. You will want to move your coils around while monitoring pin 1 to achieve a good null. This can be done with a DVM on the AC setting.

Also, see the excellent article by Carl on coil types that may help you understand as well.

Once you null your coils we can work on tuning. Assuming that your tuning in not too far off to begin with, this should be easy.

Don

[mehdi]

Ok. that sounds good. How about your coil? Did you decide on a 20" ?
Did your coils null OK? Your phasing might still be off. Tell me abbout your coils and anything that you have done with nulling and tuning. You can PM me if you wish.

my coil picture:

[mehdi]

Hi Don
i sent to you a PM.
with many thanks
Mehdi

[dfbowers]

Ok. that sounds good. How about your coil? Did you decide on a 20" ?
Did your coils null OK? Your phasing might still be off. Tell me abbout your coils and anything that you have done with nulling and tuning. You can PM me if you wish.

[mehdi]

Hi don
ok, volksturm sm+geb( your addition)
with sensitivity variable resistor and threshold.
in pin 8 of u6 and u2 i have +9v and in pin4 0v and all of other pin is about +4.5v, is it true?
i test with 9v.

[dfbowers]

Hi dear don and thanks for your fast reply
when i connect 12v battery, it sound but not any respond to metals but ehen i play with variable resistors, it can detect .5*.5meter AL metal at about 10cm!!
i hav not oscop but i have DMM. i hope you can help me
thanks
mehdi

Which variable resistor? GEB , Threshold or sensitivity? It will be important to be very specific with your questions.

Which version did you build?

Also, keep in mind that motion is required for detection of metal. It may be helpful to exchange videos.

To begin with, check your voltages on U6a. Do you have + and - 6v? If things are OK there we can begin to check other things.

Also, my Volksturm works just fine with a plain old 9V battery