Volksturm SM + GEB

[dfbowers]

I like this project.

I tried to make this detector a long time ago, but didn't have the right schematic. Could you explain your coil dimensions?

Thanks in advance.

Sure..

See post # 121

http://www.geotech1.com/forums/showthread.php?t=14595&page=5

[mehdi]

Hi don
i today finished my volksturm sm+geb and test it, it seem that work, but it dont any reflex and answer to metals! can you help me please?
mehdi

[dfbowers]

Hi don
i today finished my volksturm sm+geb and test it, it seem that work, but it dont any reflex and answer to metals! can you help me please?
mehdi

Sure, I can help. Could you please be more specific to what your problem is? You say that it "works". In what manner?

I'm not sure how the word "reflex" translates.

If your circuit is built correctly, then I would expect that we should have to work on tuning and phasing. I have built 3 of them, all have worked but I needed to tune the coils to get the detector to respond correctly.

Do you have an oscilloscope? If not, we may be able to figure it out with a DVM, but it will be more difficult.

[mehdi]

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

[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

[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]

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
i sent to you a PM.
with many thanks
Mehdi

[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:

[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]

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]

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]

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.php?file=442089cd82929eba6f021a7ecf50101d

Don, please send your email address by a PM to me.
thanks
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.php?file=442089cd82929eba6f021a7ecf50101d

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