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

[Carl-NC]

Which part?

Cortex M4 is very attractive for even high-end metal detectors, lots of parts are around 100uA/MHz core power.

[scrungy_doolittle]

Cortex M4 is very attractive for even high-end metal detectors, lots of parts are around 100uA/MHz core power.

Yeah. The GG group is using a STM32F411. The nucleo board is cheap. 10.33

[Achillion]

I think you are quite wrong. The STM32F405/7 for example, has a 2.2 megasample pipelined triple ADC at 12 bits. The pic24FJ128GC010 has a 10 Megasample ADC. Either of these are adequate. Using DMA to directly transfer the data, and running at 168 mhz, there is more than enough processing to do multiple filters and analysis.

Well, I would like to see a working example of adequately direct sampling and processing with this microcontroller and have sufficient sampling speed and resolution to give meaningful results.

[bklein]

I'm not sure if this is 100% relevant but check out the DSP audio software here:http://www.dspconcepts.com/sites/def...urnal_DSPC.pdf
Ask for a free download. It looks cool for audio manipulation so may add value for the hobbyist with analog front end with Dsp based discrimination features.

[golfnut]

It would be nice to have this as a cut down freebie that did decent filters.

Ashamed to say although Ive used dsp filters in SW radios and work, Ive not made one for a detector !

[Carl-NC]

Well, I would like to see a working example of adequately direct sampling and processing with this microcontroller and have sufficient sampling speed and resolution to give meaningful results.

2MSps is more than enough speed, but 12 bits isn't enough resolution. The Minelab X-Terras are direct sampling, and the White's Prizm 6T/CoinGT is a direct quadrature sampling. I believe that both use 24 bit ADCs. You could do a reasonable direct sample with as little as 64kSps (8X for 8kHz).

[bklein]

If you contact them they will give you a download link for a full featured copy. They are trying a new business model which i think works on a royalty basis if you productize what you are working on. The STM32F discovery board is a supported eval platform for it. It looked fun to try playing with so i'm set to go but have other things taking priority before I do...
I have a CTX - which I think has the depth needed but the processing can cause target misses and innaccurate identification. I think the future will bring better algorithms that perhaps sequentially ID/screen targets better.

[wirelessguy]

Cortex M4 is very attractive for even high-end metal detectors, lots of parts are around 100uA/MHz core power.

Yeah. The GG group is using a STM32F411. The nucleo board is cheap. 10.33

The Cortex M4 family was publicly released by ARM in 2010. STM32F4 family is Cortex M4. I am not sure when ST Microelectronics had the STM32F4 in production, however you can be sure they had early libraries from ARM since they are an enormous ARM customer. Carl and scrungy_doolittle have referenced DSP used (in some manner) in commercial detectors to answer my original Q. Thx folks!

I'll opine that the use of DSP seems relatively slow to adopt in this industry relative to say, audio consumer products. More than anything, I'll opine this is mostly an economics issue. The world-wide metal detector industry is but a minuscule fraction of the worldwide consumer audio industry. For every Carl and Bruce Candy, there are several orders of magnitude more equally sharp engineers with proportionally more $ behind them developing audio products (as just one consumer product example extensively utilizing DSP for many years).

Maybe the "STM32F???" in the GPZ 7000 is a STM32F4 (or higher end) using direct sampling?

[greylourie]

Sample images of the audio rx module show a STM32F102C8T6 working in conjunction with a T.I CC2500 transceiver ic.

[Taktyk]

It is the cortex M3 core. For direct sampling you need fast ADC converter (conversion time + aquisition time <= 4uS) 16-24 bits and DSP algorithms - also implementations of digital filters.

[greylourie]

Taktyk, the data available from the FCC mentions 3 devices used in this detector. How accurate or uptodate this information is, is anyones guess ?

The wireless audio reciever module uses the STM32F.
Also a Freescale IMX253, probably running some flavour of linux. For user interface, gps, etc.

And listed as well is a Microsemi M2S010-FGG484 fpga/SoC. How or what means are used to pipeline sensor data is unknown and would be speculation. Direct sampling, who knows ? ADC or comparator ?

https://apps.fcc.gov/oetcf/eas/repor...cc_id=Z4C-7000

[wirelessguy]

Sample images of the audio rx module show a STM32F102C8T6 working in conjunction with a T.I CC2500 transceiver ic.

greylourie, where do you see these sample images ? I do not see them in the "internal images" link at the FCC site https://apps.fcc.gov/oetcf/eas/repor...cc_id=Z4C-7000

[greylourie]

Hi wirelessguy

greylourie, where do you see these sample images ? I do not see them in the "internal images" link at the FCC site https://apps.fcc.gov/oetcf/eas/repor...cc_id=Z4C-7000

On the third page of the "Internal Photos" pdf.

[Carl-NC]

I'll opine that the use of DSP seems relatively slow to adopt in this industry relative to say, audio consumer products. More than anything, I'll opine this is mostly an economics issue. The world-wide metal detector industry is but a minuscule fraction of the worldwide consumer audio industry.

Yup, this pretty much nails it. Also consider the enormous resources that go into cell phone design. There are probably more people in the world designing 35mm cameras than metal detectors.

Maybe the "STM32F???" in the GPZ 7000 is a STM32F4 (or higher end) using direct sampling?

I can't imagine that the GPZ would use direct sampling. If you want to squeeze out every drop of performance, direct sampling is definitely not the way to go. It is more useful for implementing multiple modes, as in software-defined radio. With the hardware available right now, I would only use direct sampling in low-to-mid range detectors.

[Davor]

Ah, so many people have troubles grasping this. Thanks.