Bulding a GoldscanIV

[barry]

O.K. I have decided to build my first detector and decided on the GoldscanIV.

Got a few question I would like some help with...

From the original diagram I have found the circuit for the PSU I will add in so it runs of a 4 cell Li. I have also found the posts about the grounding mistake for the fet and the diode the wrong way around.

I have read the GS4 will be much improved with a AutoTune circuit. Where can I find this for the GS4 ?

Should some of the parts be replaced with more modern components with less noise and less power drain ? If so is there some details information on these mods.

Also any other mods I missed you can link me to the info.

Finlay I would like some build details on a PI 8inch shielded coil for it. If these a good build thread for this type of coil somewhere ?

[barry]

Forgot to mention. I also plan to use a Pic micro to do the timing and frequency. Have variable timing or 10us to 25us with a pot.

[Max]

O.K. I have decided to build my first detector and decided on the GoldscanIV.

Got a few question I would like some help with...

From the original diagram I have found the circuit for the PSU I will add in so it runs of a 4 cell Li. I have also found the posts about the grounding mistake for the fet and the diode the wrong way around.

I have read the GS4 will be much improved with a AutoTune circuit. Where can I find this for the GS4 ?

Should some of the parts be replaced with more modern components with less noise and less power drain ? If so is there some details information on these mods.

Also any other mods I missed you can link me to the info.

Finlay I would like some build details on a PI 8inch shielded coil for it. If these a good build thread for this type of coil somewhere ?

Hi,
the GSIV you can make with auto tune... but as I remember there isn't any schematic about, just a description by Reg, if I remember well.

The thing work like this: each minute or so a reset is performed and the MD is set to the original threshold level.

Why it's interesting ? Uhm... if you build GSIV as original schematic you'll have a pure no-motion PI so you'll see as side effect some drift appear in a few time (some minutes) to threshold, kind of slow drift.

That's as original works: Eric Foster, who designed the machine talk about that many times and suggest to retune threshold within few minutes... that could be boring to many people.

Note: consider that the original schematic is the one by Alex, that's B/W. The coloured one is by Vladimir and contains the self adjusting threshold... a couple of 470K resistors that make device act as motion MD. In Reg's version you have them wired by a switch, in a way you can select motion/non-motion by that according to soil conditions etc

Look here: https://www.geotech1.com/thuntings/s...light=goldscan

Now... the Reg's approach to autotune is to wire up some timer and let device retune by itself at fixed time, each minute if remember well.

You can use PIC for timing but must be jitter free, otherwise device will be very unstable. The cmos approach of original schematic is old, but without relevant jitters.

You sure can use modern e.g. op amps with lower noise than e.g. TL074 and similar, though you'll not find any document about I tell you it's not only possible but really good to do.

Also, first preamp was uA709 in original, today not any good and you could use (very good) the NE5534 by Philips, or another, very fast and low noise op amp (some OP37 is also good there).

Kind regards,
Max

[barry]

Thanks for the great info max. I have been working with the color one in proteus. Will make the mentioned changes and run a few sims.

The more I work with the PI circuits the more I see the benefits of a micro control PI. I might just go straight into build a fully micro controlled PI or even one ran by a laptop..