GoldScan IV

[Max]

Hi
I didn't leave a gap.what is the gap use?
thanks.

I didn't see it!

WRONG! YOU MUST MIND THE GAP!

You cannot make a continuos shield turn there... or you'll get an enormous eddy current flowing in it! It will totally damage your detection ability there.

So, make a gap from 5mm to 1cm long and connect the shield wire at one extrem of shield.

Purpose of shield is avoid capacitive effects with ground/soil and prevent too external noise being detected at coil (e.g. from RF sources in VLF range, like e.g. switching regulators noise).

Kind regards,
Max

[zzy]

I didn't see it!

WRONG! YOU MUST MIND THE GAP!

You cannot make a continuos shield turn there... or you'll get an enormous eddy current flowing in it! It will totally damage your detection ability there.

So, make a gap from 5mm to 1cm long and connect the shield wire at one extrem of shield.

Purpose of shield is avoid capacitive effects with ground/soil and prevent too external noise being detected at coil (e.g. from RF sources in VLF range, like e.g. switching regulators noise).

Kind regards,
Max

Hi
Good answer.I made a 2cm gap.Now the GS4 works properly.The last problem
is drift.When sense at max, only after one minute silence. It'll begin to beeps.Why GS4 uses so much pulse width? It need more power.And produce a lot heat. I decrease the pulse width to half. The sensitive seems not be affect.

[Unregistered]

Technical question

Hi,


It's not so important unless you put there something that will create too much interferences like a little speaker could do.

Kind regards,
Max

Heres a Technical question for professionals

One question on 555 driving a mosfet, 555Ic's do not jump to 0V while going low (as per data sheets the 555IC's low level will be at 1.2 Volts ie above reference at 10V supply) and we are switching off the Fet with 555, but the low level is 1.2 volt not 0V, here the voltages are -10and 0V, Will the fet switch off completely due to -1.2V.

Another question the Fet Drain in Twin Loop Treasure seeker is connetced to 0V thru the resistor R17 and cap C13 high pass filter, we have to take this as drain connected to 0V, and the gate driven from the 555 @-1.2V above reference at off condition will the fet switch off completely.

[Max]

Hi
Good answer.I made a 2cm gap.Now the GS4 works properly.The last problem
is drift.When sense at max, only after one minute silence. It'll begin to beeps.Why GS4 uses so much pulse width? It need more power.And produce a lot heat. I decrease the pulse width to half. The sensitive seems not be affect.

Hi,
all Eric Foster's designs are power oriented: the use lot of power in the coil switchoff but to "charge" that energy there you waste it also.

During inductance loading (energy is stored in the magnetic field) the current rise following a well known equation... after 3-4 time constants you'll get it rise with less speed than before... so obtaining a fairly large current at coil is not easy or inexpensive task... you waste energy just to gain relative few rise on current after that initial large/fast rise.

Why GS4 is so ? Answer is realy simple: you need more current cause you cannot speed up di/dt by components ...over particular limits with that components (e.g. the IRF740) cause capacitive effects are always there... in the switching device and at coil itself.

Now... if you cannot increase the di/dt by e.g. components your choice to increase the effects of magnetic field collapse... so an higher di/dt is by increasing the current in a way you'll force a larger spike on switchoff. The increased collapsed energy will produce a larger di/dt at parity of other params that will produce fairly larger eddy currents in the target... so an opposing magnetic field you'll detect by integrators.

Is that increase in peak current and energy required to obtain it that waste much of your battery stored energy... not the peak current itself.

It's a design choice... but you can simply reduce TX on time to force it to lower battery drain... but mantaining descent performances. In GS4 you can easy put tx on time at 50% of design value and save lot of power: sure detection will be less than when at 100%. The same thing you can made opposite way... increasing tx on time, but wasting more energy to gain just a few more cms.

So , it's up to you...depends of what you need: in some Eric Foster's machine there's a switch to actually select the amount of power delivered to coil... just for that purpose of make battery last more...

You cannot notice a sensitivity decrease on some items... e.g. large ones are detected about at same distance even with 50% power at tx... but on some e.g. gold stuff the effect is fairly visible. Try with a small gold ring.

So why GS4 uses all that dang power ? It's Eric's design... and purpose was 1st for nugget hunting in australian soil... worse than hell! 2nd purpose was maybe beach oriented... cause device share many things with other MDs for beach hunting... and in such hunting you look for e.g. small gold rings ... so the BIG power is a key of success in most places... cause sand moves fast and rings are located often also at 40cm under the sand level!

In such things... like deepstarII the power selector is a very good option: if needed you'll work at 50% power... otherwise you'll search with full power but for less time... due to the hi-consumption... that's around 500mA !

If you find it too power addicted... add that switch... and commutate tx on time with it.

Kind regards,
Max

[Max]

Heres a Technical question for professionals

One question on 555 driving a mosfet, 555Ic's do not jump to 0V while going low (as per data sheets the 555IC's low level will be at 1.2 Volts ie above reference at 10V supply) and we are switching off the Fet with 555, but the low level is 1.2 volt not 0V, here the voltages are -10and 0V, Will the fet switch off completely due to -1.2V.

Another question the Fet Drain in Twin Loop Treasure seeker is connetced to 0V thru the resistor R17 and cap C13 high pass filter, we have to take this as drain connected to 0V, and the gate driven from the 555 @-1.2V above reference at off condition will the fet switch off completely.

Hi,
I'm not "professional" about MDs... but try to give an answer: depends on mosfet. The VGSoff is the param you must check... if e.g. it's 4V and you put 1.2V you'll be sure device will be totally off state at such low voltage.

That param is about strict and if you put even 1volt less in most cases your mosfet will not conduct any valuable current.

In other cases , depending on what you have to do, could be necessary using a mosfet driver device... there are many and they are made expecially to avoid that problems with mosfet switching control that could be really worse in e.g. SMPS converters and the like. Some pulsdetektor projects use them so you'll maybe could take a look there to see how they are employed to avoid such problems.

I don't remember well the twinloop now, sorry...I cannot give a answer about it.

Kind regards,
Max

[barry]

Whats the total current drain in normal operating mode ? Trying to work out a battery pack to use in my machine.

[zzy]

Whats the total current drain in normal operating mode ? Trying to work out a battery pack to use in my machine.

Hi barry
About 220mA,
Have you built one? Did you test it?

[barry]

Still haven't built mine. Working on changes to the schematic based on all the bits of hints on this forum. Think I will use a 4 cell lithium 2200mHa for the battery. Might build a balance charger into the whole setup.

[Max]

Still haven't built mine. Working on changes to the schematic based on all the bits of hints on this forum. Think I will use a 4 cell lithium 2200mHa for the battery. Might build a balance charger into the whole setup.

Hi,
the zzy value is right: 220mA (when no sound)

That's about what you get from that default tx pulse width: you can change tx width to save battery (reducing it and losing some depth) or increase tx power (but not being too aggressive...cause are troubles and doesn't pay much and lose about power consumption).

The GSIV is so powerful at default setup... nobody really need to push it UP... but I've made some tests at increased power... and I still can't belive my eyes.

Problems are on soil: it's already so powerful and aggressive that at default it will sound on any brick fragment!

Kind regards,
Max

[jamal]

GOLD DETECTOR DISIGEN

hi max
I am question about detector the depth for goldscan 4 if the target is 10 KG. how many distance

[Max]

hi max
I am question about detector the depth for goldscan 4 if the target is 10 KG. how many distance

Hi,
it's not weight the issue...it's like with radar stuff... what important is volume... or, better, "effective area"... effective area is the projection of surface of the target exposed to search coil and field-lines of md.

The larger the effective area the more the detection range at several times the coil diameter distance (when field is about decreasing very fast with few lateral components).

An example, a coin... suppose you can detect e.g. a 30mm diameter coin at 50cm with a particular PI md when flat under the search coil , in air... if try to tilt 90° the coin (so having its plane 90° apart from search coil plane) you'll see you can detect at much less distance... try that.

The coin is always same mass... and same weight... but its "effective area" to the md is maximum when flat and least when tilted 90°.... so , in physical terms you get when flat a very large conductive area for eddy currents to flow in or least conductive area when tilted... the more the eddy currents, the larger the eddy current circuit(s), the more the magnetic opposition to tx collapsing field, the more range you have for detection. That apply to buried items , of course, too.

Also, is very different then... if that 10Kg are for e.g. a large and relatively thin 1mx1m silver plate flat... than for a small 1Kg silver ingot buried at same depth! Mass is the same,weight is the same but detection wouldn't be the same!

Anyway... the GSIV need have a large coil (1mx1m or more) for depth work... if so you can get 5-6meters depth on soil for very big objects... like 1m^2 of e.g. iron effective area.
That are indicative data... much depends also on timing and height you suspend coil... components you use (effective S/N of your GSIV) etc

You can obtain similar results with good 2boxes too in ideal conditions, but 2boxes suffer from void detection and too many false signals, so I do not suggest you unless you're on a budget.

Kind regards,
Max

[jamal]

GOLD DETECTOR

hi max

I suggest you are Add variable capacitor on parallel
for coil, for it increase twanging in the circuit as you are know.
and I like know how much is cost to build device GSIV


Kind regards....
jamal

[Max]

hi max

I suggest you are Add variable capacitor on parallel
for coil, for it increase twanging in the circuit as you are know.
and I like know how much is cost to build device GSIV


Kind regards....
jamal

Hi Jamal,
cost ? for parts ? not much I think... maybe 100usd for everything , maybe less... I made using parts I already own... made all the work by myself... so cannot say for sure... but component bill is wide so maybe you need really 100$ for to build.

If have already resistors, caps etc the cost could be much lower I think... ics are not recent stuff can buy at few $ or fraction of $ each.

The GSIV requires much skills to be built and tuned successfully but can be done by motivated people I think. Big trouble is pcb... can't find suitable design for it you must do yourself.

So far I know at least Alex and zzy made it, so I do too... so at least three successful clones of it! But probably are more.

Kind regards,
Max

[jamal]

gs4

hi max
I want make GS4 but I need you help.
but I have questions before made it.
1- what is the (HP) . and how operate function in the circuit
2- what is advantage from (1MA)
3- CH1 , CH2 - how are operate.
4- what is function this switch (sw1c, sw1a, sw1b)
thanks my friend .
Kind regards....
jamal

[Max]

hi max
I want make GS4 but I need you help.
but I have questions before made it.
1- what is the (HP) . and how operate function in the circuit
2- what is advantage from (1MA)
3- CH1 , CH2 - how are operate.
4- what is function this switch (sw1c, sw1a, sw1b)
thanks my friend .
Kind regards....
jamal

Hi Jamal,
ok... will try to help:
1. the HP is headphone... if wanna use them just wire up a socket and use something headphone set , better if quality one, of at least 32ohm impedance... you know like old philips big ones with ear cover, like dj stuff I mean... that have 32 or more ohm impedance... that's fine using well higher also (some 150ohm could work also good, but need volume pot on the headphones)
You can also leave it out... use just speaker stuff.

2. 1mA is the instrument for visual indication of detection... don't really nead it... doesn't add much cause your finest sens output is always at sound change... you regulate MD to provide a slow pitch...pulsating frequency... then when metal is near the pitch rise quickly... the meter also move but for far/deep stuff you get audible indication much more useful... so can also omit meter.

3. there are two channels... labeled sometimes "gold" and "iron"... well actually one (gold) is the signal path for targets... the "iron" one is employed when you operate in "disc" mode... but also plays a role in ground balancing of MD. If you don't use iron channel...removing from schematic... the MD is like simple PIs without ground balance or "disc".
Now... when talking about disc... disc is not as it is in VLFs ... not comparable... it gives you some iron ignoring but few and it's not reliable in reality of random searchfield... you may also miss stuff using it cause reduce sens of MD.
The GSIV was made with in mind Australia gold-fields... Victoria state I think.... where there's lot of magnetic stuff in the soil matrix... including powders of iron oxides... magnetite... and hot rocks... fired-magnetic-material from volcanic activity etc... along with the gold nuggets. So it's not really a disc machine for general purpose...

4. the selector 3-ways and 4-positions is for mode of operation... no/all-metal/sel1/sel2 : it's about disc mode of operation... sel1 and sel2 are preset modes used for particular disc setting... all-metal is for all-metal search including small stuff like gold rings at beach... no offers just ground-balancing... all is due to the change in timings and the presets made with some trimpots in critical points of circuit.
I say that in sel2 (differently from other modes) you get a very long delay about 250uS in one of the paths that enable a particular kind of disc/matrix rejection... in practice can ignore also big amounts of flat mineralization but still find targets like copper items or brass... useful for Australia soil... or very mineralized soil in general.

Kind regards,
Max