complete project

[sido]

Forgot to mention that Paul's UNIPI chip has a dedicated audio output with user frequency adjustment. Maybe we should work on the rest of the audio circuit based on that.

Regards Sid

[sido]

In regards to the audio circuit.

Can a modified SD audio stage be sufficient? They seam smooth and represent the true audio output.

A smooth threshold and not the click type would be ideal. I think the click type lacks in performance and mostly is annoying.

Adding a clipping circuit is a must, on board or ext. user adjustable would be ideal.

Regards Sid

[sido]

Hi Ian,

i should have made myself clear what i meant of the module type, i was referring to the stacked module type side by side. In other words pcb modules mounted vertical to each other and connected to a main horizontal pcb board. I see the confusion.

Yes, you are right that the method being approached now with optimizing each stages is the only way to go. Gathering the best of all circuit stages and layed flat will allow for easy changes and adjustments to be made if need to be, then a final single board can be made when all bugs are ironed out.

I believe i saw a circuit from Tinkerer with a very basic manual ground balance. Similar approach to the M/L SD2000's system. If auto cannot be achieved then a manual G/B will be sufficient. Maybe running a second Pic chip dedicated in processing auto G/B??

I still like the higher TX voltage approach. If it saturates the ground with a larger signal and is able avoid instability to the receive circuits and also be able to G/B to some point, then i say that is a great achievement.

Remember Eric Foster's Goldscan 4 or 5 version had the issue of ground minerals interfering and swamping the detector which made it unusable in harsh soils. Even when the TX voltage was upped by Eric to 24 volts, it made no difference. if not worse.

I so much want to build these module circuits to add further input here, but most of me test gear and electronic parts have been placed in storage for now. Renovations have put me on hold, but this weekend i will dig out me other computer desk and dedicate it just to this project.

Regards Sid

[IBGold]

Hi I think the module idea was only meant as a development tool so that different ideas and topologies could be tried until the required outcomes were achieved then the idea was to put the optimized design onto one or two boards at least that is what we are working toward on the GG project it consists of a processor board a development of Moodz UNI-PI the GGRX board the TEM-TX board and a power-supply the prototypes boards have been made and are in the stage of smoke testing at present once we are happy with the outcomes we will try to put it all on one board but there is still a lot of work to do optimising the audio and ground balance regimes before this happens.

Regards, Ian.

[sido]

Hi Tinkerer, great thread and potential to be the best so far.

Have been following most of your great work and Pauls also.

For a detector with so many variables for individual needs is very hard to implement as a standard unit.

I believe that a module type or mother board type is very difficult to produce and may introduce local and external interference. Consider that some adjustments will probably be needed to be done and modular type can cause more headeches than its worth in doing so.

Best option would be a compromise for all as a final circuit to suit most peoples needs and made on a single Pcb board type. A few versions would be ideal.

Just so you understand what i would prefer.....mainly is a stable detector on harsh mineral ground with some form of GB and as powerful as possible. 24 volts sounds ideal.

I say get back on to the initial topic and not get sidetracked with exotic functions as the 2 box system a.t.m.

More than happy to help if either we decide on a modular type. Have some suggestions that may make it easier to produce though.

Cheers Sido

[Tinkerer]

I have heard from a TM808 user that when you tilt the front coil closer to the ground, it would react on small objects to some 10 cm depth. Which is what the hoard hunters usualy do not want.

You are right about the iron box, but usually you find silver coins in either leather pouches or ceramic pots here. Not that I have found one myslelf, but I have seen a few reports of these finds.

This is interesting and shows that one must know the purpose of a detector to be able to design it.

There are several ways to reduce sensitivity to small objects, while maintaining sensitivity to larger objects. It seems that a controlled size definition would be an improvement to the 2box type detectors.

Interesting.

Are there any 2box user on this forum?

Can they supply more information about the use and problems of 2box detectors?

Tinkerer

[pelanj]

I have heard from a TM808 user that when you tilt the front coil closer to the ground, it would react on small objects to some 10 cm depth. Which is what the hoard hunters usualy do not want.

You are right about the iron box, but usually you find silver coins in either leather pouches or ceramic pots here. Not that I have found one myslelf, but I have seen a few reports of these finds.

[Tinkerer]

I am slowly progressing in learning the PIC language. I hope to come up with more soon, I plan to create tone generating code and test it first.

Anyway, I was thinking if the detector could be used with the almost orthogonal coil configuration, aka "2box detector". Then, would it still discriminate large iron against large non-ferrous targets to say 1m depth? I am really intrigued to try a "hoard searcher", but with a useful discrimination. Would it find also shallow coind sized object?

I don't think that a traditional 2 box detector is capable of finding coin sized objects, but I have no personal experience with such detectors.

The way I see it, the target size corresponds mostly to the field strength, or we could say, the amount of field lines that the target intercepts.

With the almost orthogonal coil arrangement, the field inciding on the target is only a fraction of the total TX coil field. Therefore it needs a fairly large target to generate sufficient response.

It seems that 2box technology has been lagging a bit behind the general metal detector development, but I suspect that great improvements can probably be made.

Useful iron discrimination should be possible, but a treasure inside an iron box will only be detected as iron.

Tinkerer

[pelanj]

Almost orthogonal coil configuration

I am slowly progressing in learning the PIC language. I hope to come up with more soon, I plan to create tone generating code and test it first.

Anyway, I was thinking if the detector could be used with the almost orthogonal coil configuration, aka "2box detector". Then, would it still discriminate large iron against large non-ferrous targets to say 1m depth? I am really intrigued to try a "hoard searcher", but with a useful discrimination. Would it find also shallow coind sized object?

[Tinkerer]

OK, the programmer and small 16F690 board is at home. So it is time to think how to make the audio. What inputs will there to code the audio from?

I would use one of the PWM outputs to drive a FET to make a "class D" audio amplifier, if that is OK. Two tone audio - low tone for iron with volume modulation and high tone for non ferrous with volume and frequency modulation. The resulting mix would be a matter of a simple calculation and then it would be sent to the PWM output. I guess some averaging/filtering will be needed to tame the response a little. I think it could be used without a threshold tone, but it is possible to have it if needed.

I would maybe also include a selectable "mono tone", that is beep for nonferrous, silence for ferrous. Either with threshold or without.

Excellent.

I like your suggestion of the 2 tone audio. Please PM me with your email address, so I can send you the source code .asm file of the existing timing schedule.
Then we can see what changes we need to make in the use of the output pins.

Tinkerer

[pelanj]

OK, the programmer and small 16F690 board is at home. So it is time to think how to make the audio. What inputs will there to code the audio from?

I would use one of the PWM outputs to drive a FET to make a "class D" audio amplifier, if that is OK. Two tone audio - low tone for iron with volume modulation and high tone for non ferrous with volume and frequency modulation. The resulting mix would be a matter of a simple calculation and then it would be sent to the PWM output. I guess some averaging/filtering will be needed to tame the response a little. I think it could be used without a threshold tone, but it is possible to have it if needed.

I would maybe also include a selectable "mono tone", that is beep for nonferrous, silence for ferrous. Either with threshold or without.

[Tinkerer]

I was quite surprised that google translate makes a quite readable translation. If you have any specific question, I can help with understanding.

The translation is good enough for somebody familiar with IB coils to understand. I guess, the only way to see if there is an advantage over the concentric co-planar IB coils, is to build one of each of the same diameter and inductance and try them out.

Tinkerer

[pelanj]

I was quite surprised that google translate makes a quite readable translation. If you have any specific question, I can help with understanding.

[Tinkerer]

An interesting balanced coil idea: http://www.hq-elektronic.eu/data/patent_z_jarch.pdf
It is in Czech, but look at the pictures at the end of the document.

Very interesting coil arrangement. Let's see if I can translate the text.

Thanks

Tinkerer

[pelanj]

An interesting balanced coil idea: http://www.hq-elektronic.eu/data/patent_z_jarch.pdf
It is in Czech, but look at the pictures at the end of the document.