Vallon VMH3CS Mine Detector

[Geo]

Lets wait.....

[6666]

Hi Eric just talked with our son in the army, he is a bit distracted right now he is getting bombs dropped on the camp by the bad guys, but he thinks he may have used a Vallon, but will get back in a few days when the locals settle down and he has time to talk.

[Ferric Toes]

Ever since than i am asking my self; is there any special reason to put electronics in sealed screened box?
Ok, one of the reasons may be "military" standard... or whatever.
But what if there is another more important reason?

The most likely reason for putting the electronics in a screened box is to thwart emi, both from the unit and coming from outside the unit. Military electronics has to be as immune as possible to outside sources of interference and not to emit spurious interference of its own making. A secondary benefit, in the case of the Vallon, is to make it difficult for prying eyes to unravel their technology by cementing the boards to the inside of the box. Maybe that is being cynical, and the real reason is to stop things shifting when being thrown into a truck and bounced across rocky and hostile terrain.

[ODM]

Jamming in a minefield is a possibility, after 90s, when placed by a modern military. Screening boxes are usual in devices that run switch mode supplies too.

So, the VMH3 coil current is constantly "jump started" by the charged flyback cap? I remember prototyping with a frontend based on the Fisher Impulse with a similar flyback snub/recycle some time ago. Using the same polarity pulse again, without charge in the cap to boost the current, gave a slower "generic PI" signal with a markedly different response in red brick powder soil. I wonder if they use a similar/multiperiod method for soil elimination, or a more clever software analysing approach. There was no change in the signal at all, it could very well be just an occasional cycle now and then, a similar period pulse with a lower rise, could look like just a glitch on an analog scope or not trigger if the level was low enough? Do you have a storage scope to check it with? Apologies if you've already exhausted this possibility

With the cap snubbed, lower voltage flyback, it was possible to use a virtual earth frontend amplifier instead of "generic PI" separate damping resistor and diode clipper.

[greylourie]

Table 2, pg. 20 indicates that the VMH3CS and the VMH3 have more differences than just changeable coils... look at the optimum speed and loss at hi and lo speeds.

The table also shows comparison for minimum-metal and uxo model of another well known marque (F1A4). This report suggests that the UXO version runs different tx/sample regime.
(http://www.geotech1.com/forums/showt...641#post193641)

But what impact would sweep speed have should a larger coil be fitted to an otherwise identical detector seeking the same small target? This subject would make for a separate, short but good, Qiaozhi tutorial.

Am enjoying this thread. The VMH3CS does look to be shaping up as a re-purposed hobby detector. Hope to see further reports on its life with the new coil.

[ivconic]

The most likely reason for putting the electronics in a screened box is to thwart emi, both from the unit and coming from outside the unit. Military electronics has to be as immune as possible to outside sources of interference and not to emit spurious interference of its own making. A secondary benefit, in the case of the Vallon, is to make it difficult for prying eyes to unravel their technology by cementing the boards to the inside of the box. Maybe that is being cynical, and the real reason is to stop things shifting when being thrown into a truck and bounced across rocky and hostile terrain.

Only obstacle that stops "prying eyes" is code in uPC. Anything else is less efficient. Other things you mentioned are making sense.
What else can be done in situation when you can't open the box?
Could be trivial and irrelevant; but also can be interesting: to check if screen is connected to minus pole of the battery or to virtual ground?
Check the relation between screen and coil pins too, by connecting black scope probe to screen and another to pins respectively and see what happens.
I am almost sure that all the smart things there are done in the code. And i am interested to find out how the "coil sensing" mechanism is done?
On what coil feature it relies on to sense if coil is proper or not? Resistance? Inductance? Altogether? None of those?
Most probably none of those but altogether gives proper voltage range and if custom coil is out of that range; than "mechanism" in code prevents it from running.
When you discover that; you will be able to make any custom coil you like.
And next interesting thing is how coil is damped?
As you described its behavior in your earlier posts; directly reminiscent of the behavior i am seeing at FelezJoo PI from another topic.
It has pretty similar coil sensing mechanism behavior.

[Chet]

Hi Eric just talked with our son in the army, he is a bit distracted right now he is getting bombs dropped on the camp by the bad guys, but he thinks he may have used a Vallon, but will get back in a few days when the locals settle down and he has time to talk.

Hi 6666


From an old US Army veteran pass on my appreciation on to your son for his service to your country. And remember all of the veterans this Memorial Day.


Have a great day,
Chet


Here is some information on a couple of newer Vallon mine detectors.


http://www.jmu.edu/cisr/journal/12.1...aunstein.shtml


https://www.youtube.com/watch?v=Bkz907P2MpE


https://www.youtube.com/watch?v=zfaKVwIGz6A


http://www.treasurenet.com/forums/ot...-detector.html

[Ferric Toes]

Only obstacle that stops "prying eyes" is code in uPC. Anything else is less efficient. Other things you mentioned are making sense.
What else can be done in situation when you can't open the box?
Could be trivial and irrelevant; but also can be interesting: to check if screen is connected to minus pole of the battery or to virtual ground?
Check the relation between screen and coil pins too, by connecting black scope probe to screen and another to pins respectively and see what happens.
I am almost sure that all the smart things there are done in the code. And i am interested to find out how the "coil sensing" mechanism is done?
On what coil feature it relies on to sense if coil is proper or not? Resistance? Inductance? Altogether? None of those?
Most probably none of those but altogether gives proper voltage range and if custom coil is out of that range; than "mechanism" in code prevents it from running.
When you discover that; you will be able to make any custom coil you like.
And next interesting thing is how coil is damped?
As you described its behavior in your earlier posts; directly reminiscent of the behavior i am seeing at FelezJoo PI from another topic.
It has pretty similar coil sensing mechanism behavior.

One easy thing to answer is that the screened box is connected to battery negative. As it is certain that there is a switch mode converter to generate the +6 and -6 required by the TX then all generated voltages can be referenced to battery negative as ground.
One way to check the coil on start up is to disable the damping and check that the resonant frequency is of the order of 150kHz. This would check L, C, and R by looking at the decaying envelope. If damped, then the presence of flyback volts of a certain amplitude would also be a check. Just surmising.

[Ferric Toes]

Two hours at the beach with VMH3CS

Last Friday morning I took the Vallon to a local beach for tests. It is not the best beach as it has quite a slope with little difference between high and low tide. A storm the previous day left the surf rough and generating a lot of noise. It also piled the sand up close to the cliffs. We went to the waters edge at first to test the effect of a wet beach. On the default high sensitivity, non-mineralised setting, the detector worked fine with no false alarms. The first signal dug was a small copper item shaped like a bead and about 4mm diameter. Various other small bits of metal, some lead fishing weights etc, but nothing significant. We retreated higher up the beach as the noise of the surf made it hard to hear the built in speaker. Headphones would be best in this situation, but the one piezo phone on a headstrap as supplied is not the best to wear. I need to fix up a proper set of piezo phones for the Vallon.
The next task was to bury coins and the first was a UK 10p buried in the wet gravelly sand at 10in. No doubt at the strong response from that, both with the stock coil and my 11in one. We then raised the head five inches and the 10p was still audible. The sensitivity was raised to max. and with my coil we got 17in and Vallon coil 16in.
Using a US nickel; we recorded 13in with Vallon coil on default sensitivity and 15in on highest sensitivity. My 11in coil gave an extra inch on both sensitivity ranges.

Back home the Vallon coil would not detect a 1in square of aluminium baking foil but would detect a 1.5in square at 8in. My 11in coil would only detect the 1.5in square at 3in. The detection of low conductors seems to fall off very sharply and seems more dependant on coil size than I have noticed before, with other PI detectors. It will however, easily detect a 4mm diameter phosphor bronze ball and a 0.3gm gold nugget with the Vallon coil but the 11in coil gives less range on those targets.

It is early days yet and I need to go to a better, flatter and sandier beach. Also, I need to compare the Vallon with a couple of my other detectors such as the TDi and Goldquest SS.

[Chet]

Hi Eric


Thank you for the update. Sounds like pretty good results except for the smallest aluminum targets. What kind of pinpointer is in your photo?


I have two 10 Pence UK coins; a 1970 = 28.5 mm diameter and a 1992 = 24.5 mm diameter. I believe that you were probably using the 24.5 mm diameter. I also have a UK 1/2 Penny; 1974 = 17.2 mm diameter. Next time you do some air testing could you add a 1/2 Penny to your target list?


Have a good day,
Chet

[6666]

Hi Eric
was the Goldquest SS your best beach machine ?

[Ferric Toes]

Hi Eric
was the Goldquest SS your best beach machine ?

'
There were two machines that were 'the best', depending on what you wanted to do. Aquastar was the most powerful and fully submersible, if you wanted to go into the surf and shallow water. Unfortunately the company making the housings decided to discontinued that particular submersible housing, unless one placed an order for 200 off. At £70 per housing that was not possible for me.

Goldquest SS V3 was the latest and continued to 2010 when I ceased manufacturing and just did consultancy. This was not submersible, except for the search head, and relatively low powered as it ran off 8AA batteries. That is what I will try, plus a TDi.

[Ferric Toes]

Hi Eric


Thank you for the update. Sounds like pretty good results except for the smallest aluminum targets. What kind of pinpointer is in your photo?


I have two 10 Pence UK coins; a 1970 = 28.5 mm diameter and a 1992 = 24.5 mm diameter. I believe that you were probably using the 24.5 mm diameter. I also have a UK 1/2 Penny; 1974 = 17.2 mm diameter. Next time you do some air testing could you add a 1/2 Penny to your target list?

The pinpointer is a PI unit I designed about 15 years ago. It has a range of 3in on a nickel.
1/2 penny coins came out of circulation a long time ago and I do not have one. I do have a set of US coins that I could do ranges on, including silver quarter, half, and one dollar.

[Asgard]

'
There were two machines that were 'the best', depending on what you wanted to do. Aquastar was the most powerful and fully submersible, if you wanted to go into the surf and shallow water. Unfortunately the company making the housings decided to discontinued that particular submersible housing, unless one placed an order for 200 off. At £70 per housing that was not possible for me.

Goldquest SS V3 was the latest and continued to 2010 when I ceased manufacturing and just did consultancy. This was not submersible, except for the search head, and relatively low powered as it ran off 8AA batteries. That is what I will try, plus a TDi.

Aquastar & DeepStar 3 have the same card, 100us TD WIDTH for 3200 PPS.

Goldquest SSV3 have a 10 000 PPS for 30us TD WIDTH.

Goldscan 5c issue 2 or 4 100us TD WIDTH for 3200 PPS. (but not the same amplification stage than deepstar 3)

TDI pulsescan is basically the same as the "goldscan 5c" but this is only theory. The reality is that there are many little secret goldscan that have not been included in the TDI.

After having spent several years develop and test the equipment across the French coastline with passionate people of eric materials, we can talk a little about that.

--------------------------------------

For french beachcomber is the 5c goldscan is best but can not be found, The sound is better thanks to its VCO and stability of the treshold. (2 analog channels for treshold),
The VCO also helps to feel the deep targets. There are a few more Current that is transmitted into the ground and the magnetic field is stronger!

The goldquest SSV3 has the advantage of many pulses, which allows for excellent integration, and to be sensitive to small constant target time.


However the disadvantage is that the differzential integrator window of noise and the Earth's magnetic field is very close (because the pulses are closely spaced).
Causing decrease signal to the targets of higher time constant (coins, big ring etc)

Alexandre

[Ferric Toes]

Vallon with Headphones

After the beach trip with all the surf noise, I fixed up a pair of old piezo phones for the Vallon. The audio was much too loud and raucous using a straight connection so I built an inline attenuator and filter to knock off the corners of what is almost a triangular waveform on the scope. You can of course turn the audio up or down with the + and - buttons, but when you switch off it defaults to loud when you come back on again. It is nice and sweet now. When the phones are plugged in, the internal speaker is muted.
To make the phone connection, I cut off and used the connector and 10in of lead from the single headstrap phone supplied. Then I made a housing with strain relief glands each end and two resistors and a cap. inside. The single phone won't be wasted as I will modify it into a bone phone for a diver held version I am planning.

The unit on the left in the photo has an improved armrest although they are both 2010 models.

The Vallon beats my Goldquest SS V3 hands down on a nickel but the Goldquest has no trouble seeing the 1in kitchen foil with 10uS delay The foil disappears at 25uS delay, so I figure the Vallon must be at least that figure, which is good for the wet beach and underwater.