NEW !!! Full differential PI front end.

[Rov]

Hi Paul,custom made from a batch local.
they use lightweight metal tube with twistlock extention,alloy armrest,plastic T an grip.have a Bill Hayes made insert for coil at the end.Have used these even to fit ML an other detectors to the pole/stem assembly with Chrome springclips or caphead machine screws.some have the handle assembly inclined 30degree forward for better balance.
regards Rov

[moodz]

FPGA progress

... adding the first filter bank for ground balance .... below are traces from the built in scope funtion showing the TX pulse ( yellow ) the input signal ( purple ) the target signal ( white ) and the reference ( red ) I have demonstrated a target showing how the target signal white moves away from the red reference. Note how the digital filters have extracted the clean reference ( red ) from a very noisy input .... cant even see it on the input signal ( purple )... that is one smokin filter even if I say so myself.

The input signal is depends to some degree on the TX pulse, the target signal is derived from the input signal and so on.

The red reference is the equivalent of sampling with a 28 bit ADC ... moodz filter function .. and to think I hated maths at school.

This milestone shows a number of things ....
1. all four channels are working correctly on the built in scope function
2. sync lock is rock solid
3. the filters work better than I expected.

Moodz


NO TARGET below


with TARGET below

[moodz]

Easier than you think.

All this FPGA stuff seems terribly confusing for some hobbyists .... even though this whole project is coded in VHDL ( hardware description language ) ... you can look at it as a schematic ... and you can actually edit the schematic and not write any code at all if you want to.
Below is the actual schematic for the TMPI project that is the FPGA backend .... This particular schematic was drawn automatically from my code. ...each chip is a code module and the wires connecting it are signals that are defined in the code. You can expand each "chip" into a sub schematic till you get down to gate level ( AND, OR etc ) The main "chips" in this schematic do the VGA function for the scope, the filters, Freq counter, LCD control, pushbuttons, filters, 32 bit CPU, ADC control and memory controller. All these "chips" are programmed into the FPGA chip.
All the VHDL code does is describe the connectivity and behaviour. Each time you write a block and connect it to others a new "chip" will appear on the schematic. So if you are used to working with schematics and chips its not that hard....

Mooodz

[IBGold]

Hi Moodz,
I cant help you with the shafts the only ones I have played with are the Otto ones for obvious reasons but I think it may be to your advantage to contact Rov's suggested supplier and see what they can offer they may be the same supplier that made the original Goldseekers ones I owned a business in Adelaide in that field until I sold up and retired in 2004 but it is not rocket science I would suggest fibreglass shafts give Western Fibreglass a call and see if they can help If I think of any other I will PM you.
My Electronics knowledge is not great I have been a ham since the early 1970's (VK5KIB) but only know enough to be dangerous Hi but if I have the layouts I can build it but the new technology is over my head.

Tinkerer,
I have read your other post and will reply there when I get a minute it will be something different to try all my forms are for elliptical or 3 to 1 rectangular either mono or DD but I do have one round one of 325 OD and I like a challenge.
Regards, Ian.

[moodz]

Thanks Ian .... I have been toying with the idea of using a modified crutch as they have the right ergonomics and come in pairs at a reasonable cost. I would have to replace the lower section with a non metallic shaft.
I will investigate the Adelaide connection ... thanks Rov.

Moodz.

[IBGold]

Rov,
Would you let me know the manufacturer in Adelaide as I will be there next week and if time permits I might be able to check out what they have and report back to Moodz as I thought he was in Adelaide as well but now I see he is not I probably know the company anyway and have probably dealt with them before as Adelaide is a small place business wise, You can PM me if you like.
Regards, Ian.

[Rov]

PM sent Ian.

[Andygold]

Detector stems

Also check out Bill Quinn from Plugger rods in California. He makes excellent stems with quality handgrips and stands from only US$68. Easily a match for Andersons but only half the price. You'll find him on Ebay USA.
Cheers, Andy

[Rov]

Yes Andygold,Bills plugger rods,look hard to beat at these prices,Thanks!

[moodz]

FPGA progress and EMI reduction.

posted in

http://www.geotech1.com/forums/showt...143#post111143

moodz

[moodz]

FPGA progress report

.... after another session of slaving away over a hot computer more progress on the FPGA project. The 32 bit cpu can now 'see' the DSP rams ... which is pretty cool since the DSP is running at several mips and writing / reading those rams continuously ...however we dont want the CPU to interfere with the DSP process. The DSP processing will have a very analogue feel to it ..... I am even considering feeding some of the channels out of a DAC into a conventional meter for a bit of nostalgia.
The digital CRO function now has more controls with vertical channel offset controls from the CPU and will be controlled by command via internal GPIO ports from the CPU. The CRO function is the best idea I have ever had ... it just makes checking the coil performance so easy ... you can see straight away if there is anything wrong with your rig. The DSP timing now autotracks within microvolts however there will be a track locking button that will track lock user selected sample channels from the 512 available. ( ie any of 1 to 512 channels can be selectively locked. ) This is important because with huge effective oversampling the really faint targets can be resolved in huge noise ( EMI, hotrocks, ground effect etc ).
All the code still fits into the cheapy FPGA chip .... a battery powered generic board slightly larger than a matchbox is available for less than $50 that will run the current build with all DSP / CRO features enabled. All that is required is the front end ( switching mosfet, ADC and protective diodes) and coil of your choice. The total cost of a detector would truly be below $100 but would rival a machine that costs 50 times more ( presuming you make your own coil )

cheers for now.

Moodz.

[simonbaker]

Outstanding stuff. I expect we'll be seeing some new performance benchmarks from these designs, especially discrimination.

-SB

[WM6]

..

All the code still fits into the cheapy FPGA chip .... a battery powered generic board slightly larger than a matchbox is available for less than $50 that will run the current build with all DSP / CRO features enabled. All that is required is the front end ( switching mosfet, ADC and protective diodes) and coil of your choice. The total cost of a detector would truly be below $100 but would rival a machine that costs 50 times more ( presuming you make your own coil )

cheers for now.

Moodz.

Great work moodz. Thank you to deal with us.

Only, after all your and Thinkerer threads I am a bit confusing at the end.

What parts, boards or module to use/buy and what of stages (eg. frontend) to build and how interconnected all this?

Can you be a little more explicite and give us some summary of project?

A lot of good ideas in the future.

[Tinkerer]

Great work moodz. Thank you to deal with us.

Only, after all your and Thinkerer threads I am a bit confusing at the end.

What parts, boards or module to use/buy and what of stages (eg. frontend) to build and how interconnected all this?

Can you be a little more explicite and give us some summary of project?

A lot of good ideas in the future.

Hi WM6,

you make a valid observation. The FPGA signal processing is only a part of a whole detector.

The detector also needs hardware.
It needs an ergonomic stem assembly.
A good coil.
An efficient power supply and battery combination.

The detector also needs an operator interface.

How should this interface be? Only audio? There are many variations in audio output possible. single tone? dual tone? variable pitch?
What about FE identification? Just a red LED? An "ignore FE" setting?

This is where YOU and other experienced metal detector operators come in. What are YOUR wishes? How would YOU like the detector to be?

The more bells and whistles are added, the higher the cost.
Color screen with back light? GPS interface?
The lists are endless.
In general bells and whistles sell better, even if cost is higher.

What about a high efficiency, high sensitivity detector, with only essentials, to keep cost down?

There are many questions that ask for answers. Feedback will generate the best results.

Any suggestions?

Tinkerer

[Tinkerer]

COILS FOR THE TMPI

.... after another session of slaving away over a hot computer more progress on the FPGA project. The 32 bit cpu can now 'see' the DSP rams ... which is pretty cool since the DSP is running at several mips and writing / reading those rams continuously ...however we dont want the CPU to interfere with the DSP process. The DSP processing will have a very analogue feel to it ..... I am even considering feeding some of the channels out of a DAC into a conventional meter for a bit of nostalgia.
The digital CRO function now has more controls with vertical channel offset controls from the CPU and will be controlled by command via internal GPIO ports from the CPU. The CRO function is the best idea I have ever had ... it just makes checking the coil performance so easy ... you can see straight away if there is anything wrong with your rig. The DSP timing now autotracks within microvolts however there will be a track locking button that will track lock user selected sample channels from the 512 available. ( ie any of 1 to 512 channels can be selectively locked. ) This is important because with huge effective oversampling the really faint targets can be resolved in huge noise ( EMI, hotrocks, ground effect etc ).
All the code still fits into the cheapy FPGA chip .... a battery powered generic board slightly larger than a matchbox is available for less than $50 that will run the current build with all DSP / CRO features enabled. All that is required is the front end ( switching mosfet, ADC and protective diodes) and coil of your choice. The total cost of a detector would truly be below $100 but would rival a machine that costs 50 times more ( presuming you make your own coil )

cheers for now.

Moodz.

Thanks for the update, Moodz,

I would like to add to your last sentence:COILS

The best signal processing will not be able to make a good detector out of a bad coil. A GOOD COIL IS NEEDED.
Anybody is capable of building a more or less coil. but to build a good coil, considerable experience is needed.
To build a really good coil cost efficiently, proper installations and testing facilities are needed.

I therefore propose:

We build a few coils of different parameters as open source projects, here on the forum.
Once the FPGA signal processing block is fully developed and for sale, some of the excellent coil manufacturers may be interested in producing the specific coils for the TMPI.

In fact, I would be much interested to know who the coil manufacturers are.

Which coils are recommended by forum members?

Which coils are the best?

Is it worth paying for the best coil? How much difference is there in coil performance with the same machine?

Tinkerer