complete project Circuit diagram

[Sean_Goddard]

Tinkerer, I was a bit confused to see you had combined all the sample pulses into one point. I, personally, would have kept the 4 channels separate and multiplexed them, via a CD4053, into a single 12bit ADC (like the Eagle Spectrum does ADC804) then processed these signals relatively / comparatively like Minelab do. This would give you much more flexibility as regards the way in which the signals were handled, indeed different software tweaks would allow for real-time optimisation of the machine as a whole. you could also simply do away with the demodulators and use S/H like this http://schematics.dapj.com/2005/01/s...h-standby.html and implement the motion function in softwar

[Tinkerer]

At this days I had use the twisted wire between BU und TX coil to fine adjust the nulling. I had to twist or untwist it a bit more or less.

that is correct. On the Tinkerer_SB_NM_PSU&TX, I also added a fine adjustment for the Bucking coil current.

With 2 inductances in series, like the TX coil and the Bucking coil in the Tinkerer design, the current is the same in both coils. However, the Bucking coil current adjustment makes it possible to bypass some of the current so that the current in the 2 coils is not the same anymore, thereby adjusting any imbalance caused by magnetic ground.

[mschmahl]

At this days I had use the twisted wire between BU und TX coil to fine adjust the nulling. I had to twist or untwist it a bit more or less.

[Tinkerer]

nice work on the coils.
Which wires do you use for the fine adjustment for nulling?

[Tinkerer]

Here are some pictures of my experiments. But it it some time ago. These are with a big (50 cm) IB coil. Center taped RX.

Nulling is not good enough

[mschmahl]

Here are some pictures of the coil...

[mschmahl]

Here are some pictures of my experiments. But it it some time ago. These are with a big (50 cm) IB coil. Center taped RX.

[green]

Tinker, can you please post an updated scope capture of the pre-amp output (or a link to this). I have read all of your posts and know I've seen your experiments but not easy to put all the pieces together.

I build a modified Hammer Head PI but use IB coils which I null. If not properly nulled I have seen scope trace similar to what eclipse got.
Here is link to my post on IB for PI.
http://www.geotech1.com/forums/showt...237#post238237

Hi waltr, was looking at your scope traces and was confused until I noticed the scope trace goes right to left instead of left to right.

[Tinkerer]

Tinker, can you please post an updated scope capture of the pre-amp output (or a link to this). I have read all of your posts and know I've seen your experiments but not easy to put all the pieces together.

I build a modified Hammer Head PI but use IB coils which I null. If not properly nulled I have seen scope trace similar to what eclipse got.
Here is link to my post on IB for PI.
http://www.geotech1.com/forums/showt...237#post238237

You are correct, nulling is the most important part of IB coils. The smaller the residual of the nulling, the more gain you can apply.
Sorry I can not show you anything recent on these designs. I lost nearly all my files some time back, when I moved. The computer crashed and the backup hard drive with 240Gb of files stopped working when I moved. All I have is a few old backup DVD's with no index. It takes many hours of searching to find anything and I just can not find the time for that at present.
I posted a few things on the Forum, but, as you say, scattered and hard to put together. Probably the best way is to try to search for stuff of similar date, but a lot went lost when the Geotech forum reorganized.
If you can show me stuff I posted, usually I remember something.
Right now, I seem to remember, that the TX schematic posted earlier, with a single turn Bucking coil, was meant for a DD coil. After balancing the RX and TX coils, a single loop, stretching from about center coil, towards the rim, so that the 2 wires were lying about parallel 10mm apart, could then be moved like the finger of a clock, searching for the near perfect null.
Also on this TX design, I used a Mosfet as variable resistor to dampen the Flyback.
The RX circuit can be used for various TX. At some other time I can explain the several special features.

Thanks for your link, I will try to find some time to read it.

[waltr]

It is OK to use any kind of wire, but you must use the bucking coil for this design, otherwise your sensitivity will be very low.
the output of the preamp looks different, because this is not a traditional PI design. At the time I was designing and testing hundreds of different ways of making an induction balanced pulse induction metal detector. Most of the designs were innovative in some aspect or other.

Tinker, can you please post an updated scope capture of the pre-amp output (or a link to this). I have read all of your posts and know I've seen your experiments but not easy to put all the pieces together.

I build a modified Hammer Head PI but use IB coils which I null. If not properly nulled I have seen scope trace similar to what eclipse got.
Here is link to my post on IB for PI.

http://www.geotech1.com/forums/showthread.php?24251-My-take-on-the-HH2&p=238237#post238237

[eclipse]

Okay I will add the bucking coil and start readjusting the coil, maybe even try to build the concentric coil meanwhile.

[Tinkerer]

I've done adjustments by trial-and-error with the scope and this is currently the only way I've found it actually (somewhat) works, don't know if there's a better way.
I don't use the bucking coil and the wire is plain 0.56 enamelled wire because I didn't want to waste the litz wire before I know little more.

It is OK to use any kind of wire, but you must use the bucking coil for this design, otherwise your sensitivity will be very low.
the output of the preamp looks different, because this is not a traditional PI design. At the time I was designing and testing hundreds of different ways of making an induction balanced pulse induction metal detector. Most of the designs were innovative in some aspect or other.

[eclipse]

I've done adjustments by trial-and-error with the scope and this is currently the only way I've found it actually (somewhat) works, don't know if there's a better way.
I don't use the bucking coil and the wire is plain 0.56 enamelled wire because I didn't want to waste the litz wire before I know little more.

[waltr]

I hooked up test DD coil and here's few shots from the preamp out and TX. Signal looks quite different from the references I've seen.

Did you adjust the coil coupling?

[eclipse]

I hooked up test DD coil and here's few shots from the preamp out and TX. Signal looks quite different from the references I've seen.
I got no response change for before TX reaches 50uS (~50%TX ON) and goes to about 20uS-40uS after TX OFF.
Response to small targets like gold ring and silver coin is very low.
Scope is set to 50mV/DIV for both channels (TX is 1:100, preamp is 1:10) and 50uS/DIV.

Default signal (no traget)



Pair of pliers



Large tray