Geotech Baracuda - REV-A - Coils

[waltr]

Thanks,
I currently am running non-shielded for several reasons:
1- I didn't have good shielding material
2- Read some that PI detector coils really do not need shield (been wondering if shielding is just a hold over from VLF coils). Tinker's threads are also very interesting.
3- In the KISS principle- start with the minimum needed then test. My coils are not glued so easy to pull apart to change (add shield, etc).

When weather is warm enough to get outside I'll be testing and reporting in my thread.

[Chiv]

Thanks Waltr I have been reading your posts with intrest

[waltr]

Sounds like the resin changed the dielectric considerably which increase the inter-winding capacitance thus slowing the coil's decay.

Check the Coil articles here:
http://www.geotech1.com/cgi-bin/page...&file=info.dat
http://www.geotech1.com/cgi-bin/page...e=projects.dat

Also check my thread "my take on the HH2" in the HH II sub-forum about coils.

Note: The HH (Hammer Head) is also a PI detector and coils would be the same.

[Chiv]

I think your going to find the figure 8 coil also cancels out target signal on a PI.

you where totally right with this, I made up a 320uh figure 8 coil and almost nil pick up on my targets, also had no emi or end swing noise from the earths magnetic field either.
I could detect a spoon sinker (1'3/4" in size) about 3 inches above coil, and a bean sinker number3, 3/4inch in length only by rubbing very close to coil, so scrapped that one and started on a new coil.
this coil was a lets see what happen type coil at random winding spots in a cheep housing.

It started out with two strands of .236mm enamelled wire 19meters in length and after wind is come out at 356uh, then added cable witch brought it up to 540uh 2 ohms, for shielding I use some type of sticky ally foil that found at local tip shop only on the edge of coil housing, some quick scope work and fitted a 550ohm resister in for damping and tested it on led sinkers, getting a good hit @12inches with bean sinker which for some reason is the hardest shape sinker to get a nice clean sig, and the spoon sinker best I can get is 17inches as in air test, and 9crt mens ring @ 9 inches good sig after that sig gets iffy.
So I filled it with model resin and to my surprise that inductance had risen a fair bit to 651uh and 825.1pf and still 2ohms and resonance frequency @541991hz if I got that measurement right.
with reasoned filled coil now hard as I have basically lost 2inches of depth on all my test targets and still no EMF effect with the swing of the coil, so on with next project and that's to make my own litz wire and build another coil with only edge shielding.
This barra is getting a good work out on different coils and has not let me down

[Chiv]

I shall do the test for you as soon as I get a US 5cent coin, but aussie 5cent piece 140mm air test and beach sand non black sand 130mm ish wet, and heavy mineral beach sand (black sand) 90mm wet but that with playing around to find just 5cent coin when I set up reject for 5 cent coin then I loose depth for gold ring so that means I might be loosing of few coins down a bit deeper as I use a gold ring to set up on the beach as every beach here has different amount of mineral sands mixed in to it. one beach here I cant even pick up my test ring as barra just cant settle down but even the neo magnet will pick up the dirt, lucky it a national park or the mining companies would be mining it

[ionut_mtb]

just an update on this project as its all working sweet, good depth with the mono coil as in image with graphite shielding. 9kt mens ring in the beach sand 220mm .Have a flat spiral coil @250mm dia that pick up the gold ring @390mm in beach sand, so happy days. thanks to all who helped along the way to build my first PI detector. Now to silver dog in the new year for my next kit or may be kits
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[ATTACH]41265[/ATTACH]

good job! Can you make tests with us 5cent coin? Air and sand? And what diference you have on gold ring air test/sand. Thanks

[Chiv]

just an update on this project as its all working sweet, good depth with the mono coil as in image with graphite shielding. 9kt mens ring in the beach sand 220mm .Have a flat spiral coil @250mm dia that pick up the gold ring @390mm in beach sand, so happy days. thanks to all who helped along the way to build my first PI detector. Now to silver dog in the new year for my next kit or may be kits

[Chiv]

Battery pack down to 11.5v U5 pin5 -11V...................so found new battery and now 12.8 U5 pin5 -12.1, now with the agm battery hooked up I get-4.9V and just to clear up all so get 5V on other rail, all so u7 pin 1 now get -1.9v so between the battery pack not so new battery's which they are have not lasted more that 1hours worth of testing at 12v, and the board likes a good clean supplied 12v has helped with the V situation

[Qiaozhi]

Yes it was at -5v , could of U6 have been damaged by the short? or C22 C23. I know in the automotive game relay and alike do burn contacts and give false readings to what they should be with age or too higher current, after a google to find how these (u6 U7 type of chips work) they are basically a multi switch of sorts. any way I like to problem solve I just have to wait for oscilloscope to turn up, as you all say it is a invaluable tool to tune and problem solver (maybe)

What is the voltage on U5 pin5 (LT1065)?

[Chiv]

Yes it was at -5v , could of U6 have been damaged by the short? or C22 C23. I know in the automotive game relay and alike do burn contacts and give false readings to what they should be with age or too higher current, after a google to find how these (u6 U7 type of chips work) they are basically a multi switch of sorts. any way I like to problem solve I just have to wait for oscilloscope to turn up, as you all say it is a invaluable tool to tune and problem solver (maybe)

[Qiaozhi]

thanks Qiaozhi and Homefire, MMM I don't know why I put -2.7v in my statement just not thinking to straight when typing this up,should have type -2.1v. When I was building the project I thought I was doing it step by step. every thing was right on the $$$ with the build to as written out in the pdf, Untill I stuffed up and shorted a couple of pins out on U5, so got a new LT1054. now I only get -4.7v now I'm not the bright spark in this type of electronics but step 6 lead me to step 7 with out oscilloscope, so with the voltage with in a few .V of where the preferred v should be lead me to think that is why I cant get -2.1v on pin u7 pin1 and I shorted out pl2 pin 2 shorted to pin 3, I can make voltage change not a problem just could not get the -2.1v and the instruction states, other than that the detector work quite well. hope this made more sense on what I was trying to get across

When you were following the step-by-step instructions (before you shorted something out) was the negative supply voltage at -5V?

[homefire]

I use 1% resistors on all my projects and still have quite some variations at times. The Differences your seeing would be fine I think. March On.

[Chiv]

thanks Qiaozhi and Homefire, MMM I don't know why I put -2.7v in my statement just not thinking to straight when typing this up,should have type -2.1v. When I was building the project I thought I was doing it step by step. every thing was right on the $$$ with the build to as written out in the pdf, Untill I stuffed up and shorted a couple of pins out on U5, so got a new LT1054. now I only get -4.7v now I'm not the bright spark in this type of electronics but step 6 lead me to step 7 with out oscilloscope, so with the voltage with in a few .V of where the preferred v should be lead me to think that is why I cant get -2.1v on pin u7 pin1 and I shorted out pl2 pin 2 shorted to pin 3, I can make voltage change not a problem just could not get the -2.1v and the instruction states, other than that the detector work quite well. hope this made more sense on what I was trying to get across

[homefire]

Emmmm Where do you get this -2.7 voltage from ? It calls for -2.1 and your -1.7 is quite close. Did you short PL2 ?

""STEP 7
Sampling integrator (see Fig. 10):
Fit R19, R20 (270k), R26, R27 (1k), C10, C11 (470n), C16, C24 (100n), Q2, Q3 (2N5485) and U7
(LF412A) .
Monitor U7 (pin 1) with an oscilloscope or a voltmeter, and confirm the DC voltage level increases
when a target is placed near the coil.
If you did not make the adjustment to R14 (Step 6) using an oscilloscope, then do it now while
monitoring U7 (pin 1) with a voltmeter. Set the DC voltage level to around -2.1V. Make sure you
attach your coil and short pin2 of PL2 to either pin 1 or pin 3 (before adjusting R14) otherwise the
voltage will not change.""

[Qiaozhi]

Have finished the board with the every thing in place, tested for volts and found negative rail only getting -4.7v is that a problem? In step 7 trying to get the volts to -2.7v can not make that voltage only -1.7v now I'm thinking it because of the -4.7v supply!! After reading forum over and over I have decided to buy a oscilloscope to help with this build as my automotive oscilloscope is not good enough to dial in my coils to the barra. the barra dose pick up sig with every thing connected but only 10cm on screw driver which I'm not to concerned about until I can hook up on the oscilloscope. my main question is- dose the -4.7v rail a real problem that need to be repaired so it is a true -5v

I'm guessing that you didn't read the part in the Build Document where it says:

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If you go through the following steps carefully, and in order, you will have a greater chance of
ending up with a detector that actually works. Please do not proceed to the next step until you have
solved any problems encountered in the current step. If you get stuck at any stage during the build,
then seek help in the Geotech forums before moving on. Do not simply populate the whole board;
discover it doesn't work (which will be the most likely result) and then post in the forums: “I've
built the Geotech Baracuda, and it's not working. What's wrong?” .... as you will receive little
sympathy from other Geotech members.
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I would advise going over each step in a methodical manner, and fix any issues you find before proceeding to the next step.If the power supplies are not measuring close to 5V, then you'll need to fix that first. An oscilloscope will very useful.