Any feedback from those who made HH or Gary's PI?

[Claude]

I would like to ask kindly those who already made Carl's Hammerhead PI or Gary's (Chemelec) PI to give us some feedback on this forum. I would like especially to know and surely others too, how they perform with a large coil.
Many thanks,
Claude

[Gary]

Re: Any feedback from those who made HH or Gary's PI?

I have recieved lot of good feedback for regular size coils, unfortunately not much on large coils. So I would also be interested.

Gary

[Goldfinder]

Re: Any feedback from those who made HH or Gary's PI?

I buit Gary's PI and with a 15 inch coil diameter the circuit can detect a 1 oz gold coin at 3 feet. I plan to build a larger coil. I have also converted Gary's PI to a PIC microcontroller based maching and am experimenting with frequencies and pulsewidths.

[Claude]

Whow! That's interesting

Thank you for the feedback. This was done after or before you modified the circuit? Did you have to modify it in order to use a large coil?
I also made a PIC controlled circuit, the one called Goldpic3, but I was unable yet to use a large coil with it.
Thanks again.

[Gary]

Re: Whow! That's interesting

PIC Controlling it does not change sensitivity.

Nor does it make any difference on large coil sizes.

[kt315]

Re: Whow! That's interesting

I agree. Pic controlling is using ONLY for commercialize of a project. As example, Schedrine's and Kolokolov's shematic is good project, but the Pic code is a commercial secret. There is some open code, but it has decrease in sensitivity. Even old programm versions was NOT still open (!).

[Gary]

Re: Whow! That's interesting

I believe the main reasons Manufacturers use PIC's is Cost, Less parts so its Cheaper! And Secrecy, as you have no access to the programming so you don't know what they are doing in there circuits and you can't change that program.

I think the only advantages in using PIC's on home built units is size and cost, but these are only minor savings. And Analogue usually allows for more versatility in changing frequencies and dead times, out in the field. These can be set with pots, rather then re-programming

As to detector Operation, with Both units at same Frequency, There should be no differences in sensitivity, coil sizes or anything else.

[Carl]

Re: Whow! That's interesting

I agree, PICs are cheaper. And they do provide some level of secrecy, although a determined engineer (read: competitor) can pick the lock.

However, there are other advantages. They are precise, compared to using RC time constants which have tolerances. They are more versatile, in that signals are easily inverted, delayed, etc., with no circuitry changes. And they can easily be field-adjusted, with fewer interface components.

I am currently learning PIC, for my next PI project. My goal is to use a pushbutton switch to select through, say, 6 or 7 variable settings, and a single rotary encoder to adjust the variables. Much better than 6 or 7 pots. Plus, I want to have an LCD display the current parameter name and exact setting. So I will know that when the display reads "Delay: 17us", the pulse delay is truly 17us. Exactly.

But non-PIC designs still have a lot of value, esp to the home-experimenter. Lotsa folks know nothing about them, and if the goal is to learn how a metal detector works, then using a PIC tends to hide some of the operation. That's why my first PI design was non-PIC (besides the fact that I was PIC-illiterate!).

Going forward, some of my ideas will either need a PIC, or a heaping gob of logic gates.

- Carl

[Thomas]

Re: Any feedback from those who made HH or Gary's PI?

Hello Claude,

about a year ago I built two GoldPic 3 of Trevor Hills design, and I've been experimenting with large coils since last summer. I have one 80*100 cm square coil that works rather good. Can easily detect 1 kg iron at ca 80 cm depth and a 15" steel pipe (1,5 mm wall) at a depth of 130 cm!
Working on improvements for the moment(I think both the programming of the PIC and coils can be trimmed). Next coil will be made of a multistrand, 12 leader shielded cable "cross-solded". No results yet!

Happy hunting!

Thomas

[Claude]

Re: Any feedback from those who made HH or Gary's PI?

Thank you Thomas, very good information. Could you tell us how many turns you used on that large coil? From a formula I reveived from somebody on these forums I made a 1mx1m 11turns, but I got no signal, all indicators on lcd panel were at 255.
Thanks

[Willy Bayot]

Re: Whow! That's interesting

It is true that commercial manufacturers are attracted by µP like PIC's to protect their R&D investment. At least for those who ARE making any R&D and not copying old analog circuits and adding in the µP a few timing controls and a bit of fancy/sexy LCD display.
It is however untrue that that the only advantages of µP for home-built units is size and costs. There is a whole field of experimentation with digital signal processing using fast but standard µP's like the 16F877A. If one forgets for a moment about analog signal timing/filtering/integration and concentrates on a clean pulse generation/amplification/AD conversion using fast modern components for the front-end module, the µP can then be used for every other functions.
Nowadays, it is not even necessary to be a PIC assembler gourou to make a good job since there are a few good optimizing C compile

[G.Gueorguiev]

Re: Any feedback from those who made HH or Gary's PI?

3 feet for 30-35mm coin :-()Fantastic! I would like to see that PI detector!
[email protected]

[Gary]

Re: Any feedback from those who made HH or Gary's PI?

If a 200 ua Digital meter is used in place of the analogue meter and with a good coil, you can get some pretty good distances with my unit.

[G.Gueorguiev]

Re: Any feedback from those who made HH or Gary's PI?

As I see "your unit" is the same as "Twin loop treasure seeker" by Robert&David Crone, which was patendet! Have you seen it :-(?
http://www.thunting.com/cgi-bin/geotech/pages/common/index.pl?page=metdet&file=/projects/twinloop/index.dat

[Willy Bayot]

Re: Whow! That's interesting

Claude,
If you reproduce with the large coil, the same inductance and approximate resistance as the originally described coil, you should be able to use the GoldPic with a large coil.
Connect first, a coil made according to the specs of Trevor.
Synchronize a scope with the PIC signal RB6, this is the transmit pulse. Put the first channel of the scope on PIC, RB5 or IC4, pin5, this is the delayed trigger given to the analog switch IC4.
Put the second channel of the scope on IC4, pin 4, this is the received pulse amplified by the OPAmp.
You should clearly see exactly in what region of the signal decay, the intergation and measurement are made.
Now, try to reproduce the same behavior with the large coil but only after you have carefully adapted the damping resistors R1,R2 to suppress any parasitic oscillations on the received pulse.
If you do not have any inductance meter, use coil inductance formula from the Web and refine by adapting the number of turns of the coil by experimentation while looking at the scope. When you are happy with what you see on the scope,outside of any target, adjust P1 until you get a value displayed on the LCD around 100 with VR1 at mid-position. If you can not find such a position of P1 (usually getting only 255), your coil is not near enough to the liking of the PIC program. Try more ajustments of the coil parameters.

Good luck,

Willy