DSP in commercial prospecting and treasure hunting metal detectors ... and GPZ 7000 speculation

[Achillion]

Hi Wirelessguy,

I've looked into this just a little but found that the processor speed is the limitation. Many attempts have been undertaken and a uC can be very useful in providing programmable timing or high level processing. Even an Arduino can do some nice things. For adequate sampling microsecond pulse lengths however you need not only very fast ADC but also process this information in real time. I'm working with the LPC1768 and although this is a powerful microcontroller it will have no chance in adequately real time processing the fast signals. In my opinion the only way to go is utilizing uC in combination with FPGA's. Technology is around for a while but not really matured in the metal detector hobby space. We probably need people like yourself to progress the hobby community in this space. I can program a uC but FPGA programming is something I have to look into. When searching on google for FPGA oscilloscope you will find some interesting leads.

Cheers mate, Jacob

[wirelessguy]

I have 30 yrs professional experience in development of wireless products with various embedded microcontrollers and digital signal processors. I am new to metal detecting, and devoured Inside the Metal Detector the first Saturday after I received it. This website and forum have also been invaluable for expediting my education. Many thanks to all contributors!!!

I am puzzled by lack of application of digital signal processing to receiver circuitry in commercial prospecting and treasure hunting metal detectors. - insofar as I can tell -

Can anyone shed light as to why?

It seems to me that superior fine grade analysis of received signals using DSP over sample and hold analog techniques have myriad of possibilities yet untapped. My MD naivety results in no particular suggested algorithm to implement requiring the added complexities and downsides of production DSP over analog based analysis. Yet I find it puzzling that those professionals who have been doing this for years do not have core knowledge of physics involved with discrimination or ground noise reduction or sensitivity (as just a few examples) that could benefit from higher fidelity waveform analysis and statistics enabled by DSP.

for instance, in this 2007 post, Carl said

"I have some ideas that are only realistic in a DSP-based architecture."

The marketing blurbs of these two industrial metal detector companies tout their DSP prowess, so, DSP appears to be used in other metal detecting industries.

http://www.ceia.net/industrial/pdf%5CTTHSbrochureUS.pdf

http://www.fortresstechnology.com/company/history/

I'll wait for replies to debunk "cost" and "battery power" answers.

As part of my research into this personal puzzlement I looked at the FCC filing for the new Minelab GPZ7000. – An FCC Grant is required for the intentional radiator wireless audio link - Link to FCC OET exhibits list for GPZ 7000 Although most everything interesting is still under temporary or permanent non-disclosure, the test report noted the two microprocessors in the unit:
STM32F (no further details of PN provided)
IMX253

Well that’s potentially a lot of processing power in an MD. The Freescale IMX253 I am guessing is used for the display and other user interface. The ST Microelectronics STM32F is an ARM Cortex based controller with a very wide offering of peripherals processor speeds. Starting with the STM32F4 family (and up) has significant embedded DSP programming capability.

So, maybe part of the new super secret “new technology” in the GPZ7000 is using DSP?