PI from Poland ???

[sonar]

Yes. You're absolute right Max. PI for military is the best. Jabel works good. About thats bombs. Here is still to much fireworks. PI realy like this bloody-junk and its very dangerous (sic).

Thats why I like VLFs with discrimination

Greeeetz!

[Unregistered]

Ok, 4 years programming is good.
You waste your time by writing programs for the such PIs.
I suggest you to write programs for Goldscan4 or Sniffer-XR71.

Have fun,
1843

arnt they PI's GS4 or XR71

[Max]

arnt they PI's GS4 or XR71

?
Do you mean they aren't GS4 and XR71 !? Sure... GS4 and XR are very nice PIs...

Actually writing a program for those is not required... cause they use CMOS to generate clock etc...

If someone would like to change (simplify) GS4 he could do this way: cutting all the CMOS timing section of 4538s and using an MCU to control everything : any pic or atmel will do that job pretty easy and with not degradation if the care required are taken... like stopping interferences from MCU to the analog path...

But the problem is at disc/reject: digital processing of disc/reject in GS4 in totally impossible... cause schematics came from another age... and so you have no ADC... you have no smaple/hold etc etc just op. amps.

One must remove about half of analog path and then use adc to feed a second MCU and instruct it to do that process: VERY HARD STUFF

Kind regards,
Max

[pelanj]

My Jabel built

Hello all,
I have built my Jabel kit and it has cost me some 60 USD in total excluding the AA accumulators I already have had before. I am using 8 AA cells, I have added a charger jack and a headphone jack. The coil is made from 2,5 m (+ 2 x 10 cm extra for leadouts) CAT5 cable in 4 turns (gives around 21 cm diameter). The cores are soldered to form 32 turns. The cable is bound together with plastic cable ties and wrapped in three layers of insulating tape. The connecting wire is 2 x 1,5 mm2 round speaker wire. I guess you can recognise from the pictures what the mechanical construction is made from Worked at the first power up, I have modified R18 to 100 kOhm as advised on hq-elektronics forum 200 k was too much for my coil.

The gallery is here.

I visited a danish beach that I scanned in December for some 30 coins with a Velleman CS120 toy-like detector, however it had a thick layer of new sand, the tide was high and waves as well. I was able to find a small ring (unknown alloy) and two coins, a totally eaten 20 DKK and a quite nice 50 ore. On another beach I have found a fish-shaped brass Møre-silda fishbait without a hook. Then some old beer bottle caps and lots of iron nails, some even very small. While digging I could see the old layer of sand, so I have to wait for a low tide to get to the treasures, I was just exploring the old-wood-and-nails-and-screws-line

The detector is very stable compared to my VLF machines, however the non-discriminating nature makes me dig a lot, which is not always fun. A pinpointer would be handy - the nails and bottlecaps at up to 15 cm depths give a signal at the whole coil diameter and sometimes even more. Sounds like another project for me

[Pepe LeMiau]

You should replace P1 with multi turn pot (expensive solution) or add another pot (I used 470R) in series with either R16 or R17. I believe that it's the most common Jabel mod, known here in Poland as "precyzer". It helps to set precisely the point of highest sensitivity, which is almost impossible with the default 10k pot.
I didn't realise it's so important until I did some test with my small pinpointer-type (65mm) coil. Setting the detector just on the edge of oscillations, where it makes knocking noise every now and then, increased sensitivity by about 30% and with some skills even more, because you can hear the "noise" frequency going up before it changes to continuous tone.

[pelanj]

Thanks! I was reading some polish forums with the help of google transator and I remeber seeing similar info, but later I could not find it again.

I will try to get a small multiturn pot here.

[Pepe LeMiau]

You could also gain a bit of depth by replacing the AA cells with small 12V battery. Higher voltage helps a bit and 1,2 or even 2,2Ah sealed lead-acid battery is cheaper than large pack of AA cells. I bought mine for like 5$.
Some of the users who replaced AA's with 12V battery reported that they had to replace 78L05 with it's larger version, 7805, because the small one ran very hot. I haven't noticed anything like that, but who knows, there are at least two revisions of Jabel (the older one has faulty PCB and it comes with additional page of manual which says how to fix that), maybe the other one draws more current.

[pelanj]

A lead acid battery would be too heavy and I have fixed AA holders in the box I have. The depth is satisfactory as it is, but things like this are good to know. My current battery pack is most of the time around 10 Volts and it is still light enough to carry on the stick.

However I have noticed another thing - after 2 days in my car (there is a few degrees below zero here), I had to turn down the threshold. Detection distance did not seem affected, only the threshold shifted. I suspect maybe some water got into the coil and I am trying to dry out.

And other thing - would there be any gain if I made a Faraday shield for the coil?

[Pepe LeMiau]

I didn't bother to try the coil shielding and I doubt that it will have a signifficant effect on detection range, however I might be wrong.

About the coil: try to make it waterproof. Mine is sealed in epoxy, a bit heavy but I can use it submerged, not to mention that it isn't afraid of rainy conditions.
By the way, I think that your coil has too many turns, however that's not critical. The rule of thumb for Jabel is to use around 19 metres of 0.7mm wire, for my smaller 24cm coil that meant about 24 turns if I remember correctly. For a 21cm coil I would wind 26 turns. The kit manual says 20 turns at 25cm.

About the sealed lead-acid battery, you're wrong.
Take a look at the photo below, my 1.2Ah 12V batt is relatively small and it's not that heavy, it weights about the same as the 8xAA pack, maybe a bit more. It lasts for about 10 hours of continuous usage with my Jabel.
On the bottom right corner there's my experimental Li-Ion pack. I took it from dead laptop, it is rated around 3,5-3,8Ah if I remember correctly, 10,5V nominal voltage (around 12,5 fully charged). I'm going to repack it in a plastic case and then I'll have a nice power source for the detector.




One more thing: I see that you're using the chinch connector that came with the kit.
If I were you, I'd start looking for another type of connector. Chinch is not reliable here, specifically not the cheap type that came with the kit. Most of users I know either replaced it with another plug type or soldered the wire directly to the PCB.

[pelanj]

This coil is more or less experimental, I plan to do it the correct way next time. Although it has 32 turns, it is 20 m of wire length in total (8 x 2.5 m), that should not make much difference. I was also thinking of using a LiIon battery pack, but I have had those 2,5 Ah AAs to use and I have a really nice charger for them.

I bought a new cinch but an exchange for a HF connector (F-type or another) is planned. I wanted to put everything together as soon as possible.

I still think I need a different coil - maybe a flatwound and a bit smaller - because it seems that the reach for coins gets worse in the middle. Today on the beach I have had almost no signals - maybe a not very popular beach. Not even rusty nails and screws. Just one or two new metal hooks and 2 or 3 bottle caps. My Whites 3900 got a better score on another nearby beach - but just by two pulltabs and one 8 cm diameter steel ear ring - this beach was quiet as well. Tomorrow I am heading to a more popular beach (I hope) for another test.

[Pepe LeMiau]

Take a look > here < - I posted photos of my coil design somewhere in the middle, and if you scroll to the bottom of the page, there's one of two kits I built recently, almost finished (waiting for nylon screws); this one will be used by my friend.

The larger coil has 29cm diameter (it's the black one on the finished detector), the other one 24cm. Both coils went through long test procedure, I tested detection depth (and compared it to other coils), detector stability etc. before we decided they're good enough to use - that's because later both coils were sealed in expensive epoxy, the best we could find/afford. It made them completely waterproof and quite strong (and heavy ).
The larger coil has absolutely no problems detecting small coins, gold rings, and various other small things, however the smaller one seems to be a bit better at this.

[pelanj]

A nice construction - the coil holder middle "T" is just pushed in to adjust the angle? The pipes are pressure water or sewage pipes?

Also, on that page, some other Jabel mods are suggested - do you know more about them? Are they worth trying out?

Just to be sure, 0.7 is the wire diameter, not crosssection area, right?

My today's score with Jabel is 2 x 5 DKK and a small silver baby ring compared to 1x 5 DKK, 3 x 50 Ore and 1 Eurocent with 3900. Then countless pulltabs, bottlecaps, bobby pins. With Jabel I got more rusty iron pieces as the 3900 when ground balanced on the salty beach is starting to discriminate iron a little bit. With both detector I have found one or two tiny paperclips - that was another + for Jabel.

I again had to reduce the threshold because I left the coil in the car over night - there is definitely some water/salt problem. My next coil will be fully waterproof and most probably done in your way, I like it.

All in all, the Jabel proves to be a great detector for cheap money - and if I succeed with a better coil, it will become my primary beach hunting detector while travelling by plane.

[Pepe LeMiau]

The "T" is not glued, it can be moved to adjust angle and requires reasonable amount of force to do that. The pipes are 3/4 inch cold water pressure pipes, they're super cheap (about $3 for all the pipes and stuff shown on the photo) and relatively strong.

The wire I used is 0.7mm diameter (well, actually 0.74 because the copper core has 0.7 and the insulation adds 0.04). The diameter is not critical, as long as the coil resistance does not exceed ~1 Ohm.

About the other mods - there are basically two types, enhancements and fixes for unstable units (as you've probably noticed, Jabel does not contain even a single low tolerance element - everything is 5 to 20%). I'll provide translation of the most interesting changes and user comments to them, perhaps tomorrow.

BTW, which PCB do you have ? As far as I know J-267 has minor glitch on the PCB and the newer, fixed version is 267N, should be printed under C12.

[pelanj]

I have the capacitor glued in, but I bought my unit two months ago and I think I remember seeing 267N. There was no mention of bad PCB (or how to fix it) in the manual.

I definitely need to change the threshold pot - not to loose sensitivity. I am looking forward to see the mods, there are not many Jabels here in CZ (or at least I do not know).

[Pepe LeMiau]

First the changes suggested by Mrand (I believe that he's also registered here under the same nick) http://www.poszukiwanieskarbow.com/f...p?f=46&t=22072
Please keep in mind that it's not exact translation, as my english isn't very good and I'll also skip what's not important.

He built Jabel for hist friend and from what he says, they were both shocked by it's performance. The stock kit was modded as follows:

Coil: 18 turns at 350mm, twisted pair telephone wire, looks like this http://www.kablesklep.pl/telefonikan...x0-5-2112.html
Coil to detector connection: RG-58, 1.5m (it's 50 Ohm concentric cable)
12V 1.3Ah power supply
R1 4.7Ohm -> 1 Ohm
P1 10k -> 4k7
R16 & R17 both changed from 1k to 27k
R18 10k -> 47k
C2, C3, C4 changed to 220n

Detection ranges after tuning : beer can 95cm, helm 120cm [too bad he didn't say anything about smaller items]

Two posts below he says, that with his mod treshold tuning is very smooth [the default treshold regulation doesn't work very well, I believe that his mod is an alternative for multi-turn pot]. Answering stelf1's question, he also wrote that it's possible to experiment with LF353 instead of LM358.
He also suggests changing R8 from 1M to 470k, it improves stability at the cost of slightly reduced detection range. However, few posts below someone said that changing R8 didn't help at all, it just decreased range.
Another post or two below, he wrote about the coil, that it's shape is not critical as long as it's inductance is around 300µH and resistance 1 to 1.5 Ohm. He also suggests using 1% tolerance R12, R13, R14 & R15 and C2, C3 5% or better.
Several posts later someone noticed, that changing the capacitors as mentioned above changes the time constants of the detector, after the change it's seeing metal longer when sweeping the coil over target, so it's harder to miss something

There was also a short discussion about rectangular coils, especially the "legendary" 3:1. I verified usefullnes of such coils with Jabel myself, I tested 4:1, 44:11cm square coil. Unfortunately it wasn't as good as I expected, the detection range was shorter than my round coils (I compared it to the 29cm one), however it was easier to find the exact location of the item.