NEW !!! Full differential PI front end.

[Aziz]

Hi Moodz,

that is too much difficult for a beginner.

The ADC is a 14 bit I think. Anyway, it should even be enough to make a time-domain digital integration / processing.

But nothing for me. It's beyond my scope. I also like analog signal processing.

Aziz

[bklein]

I am seeing a synergy here where most of my electronic interests are being now served by a FPGA design platform. Although the results are often very superior the DIY nature of them are too demanding on my time to learn. The thrills of FPGA programming are ...well, programming thrills.
I've touched those waters but they are pretty different from the experiences gained in analog electronics.
The fpga based design is easily modified and usually becomes very cost effective. The oldschool hands-on electronics nature of it however I think is lost.
An example of this is a portion of what you describe - the digital oscilloscope. Check out www.seeedstudio.com for their nano digital scope. $89 with color display. I had to order one - knee jerk reaction.
Should be perfect for field tests as you suggest. That's pretty cheap for a complete product. This fpga-based detector should really fall under $150 (as a product/kit) when the hardware design is finalized. A manufactured detector using this technology much less.
So hey guys, here may be a platform that can do anything you want to try, just learn how to program it. Somehow such "electronics" is losing its appeal for me. The issue I think is that with traditional electronics the product is built in modular design fashion. Each section can be understood visually and modified etc. But with FPGA design the concepts are in the code. Not easily understood. Easily lost to new-comers. Such code is likely very poorly or uniquely documented. An example of my problem is say you just want to replicate the PI two sample detection scheme. When I start to think about how to do that in code my mind tweaks. When I think about doing it in analog I know how and there are a ton of books that detail the parameters of such modular designs. Problem may be that these analog electronics books may go the way of databooks... Too few and far between. Too expensive for a hobbyist to buy. Won't be found in a Borders. In fact, in the Borders by me most of the electronics book section has been eliminated... Such is life.
Ignoring the above, I look forward to seeing this succeed. Maybe I'll even buy what's necessary to make one - but no guarantee it will win over the other similar projects that fill the shelves of my garage.

[simonbaker]

.... after a few months of busy times in the coalmine ... I now have time to return to this project. Below is a picture of the backend of the balanced PI. The foundation is a generic FPGA development board. The system supports a 50 Mhz 32bit soft RISC system with 16 Mb of RAM 4 Mb of Flash, ether port, USB, 2 x serial, 1 x VGA, rotary switch, LCD etc. ( ie everything you need for a detector box ... just add code )
Code is well developed to implement an inbuilt Digital Oscilloscope that will be able to display TX and RX waveforms in the field without lugging a real one around. The display, timing and triggering will be specially adapted for displaying the interesting parts of a PI detector waveform on a small vga display. The input is a full differential 24 bit ADC sampling at 4 Million samples per second ... this greatly simplifies the frontend electronics ( Goodbye to analogue sample and holds ).
All the housekeeping code is programmed in C ( future plans basic interpreter ) whilst all the time critical stuff is programmed in HDL ( hardware descriptor language .... goodbye nasty assembly code )
All rx processing is done in the digital domain and tx is also generated using programmable state machine to produce arbitrary waveforms including a "listen" function where the detector can receive the TX waveform of another detector and reverse resolve the timing to clone the pulse waveform no matter how complex. All timing clocks are programmable and the test version can implement a 5ns resolution TX PWM modulation wave form with upto 32000 pulse transitions in a single TX cycle. The board utilises high efficiency low noise switch mode supplies to support battery operation.

The total cost of the project to purchase new modular components is pegged at $US 300. ( make your own coil / wand and no cost for software image ).

moodz

moodz has kicked some *** with this design.. nice job.. looking forward to whatever comes out of it... we'll learn some stuff when moodz and aziz get their boxes in gear... I'll keep playing with transistors in the mean time ha...

-SB

[simonbaker]

I am seeing a synergy here where most of my electronic interests are being now served by a FPGA design platform. Although the results are often very superior the DIY nature of them are too demanding on my time to learn. The thrills of FPGA programming are ...well, programming thrills.
I've touched those waters but they are pretty different from the experiences gained in analog electronics.
The fpga based design is easily modified and usually becomes very cost effective. The oldschool hands-on electronics nature of it however I think is lost.
An example of this is a portion of what you describe - the digital oscilloscope. Check out www.seeedstudio.com for their nano digital scope. $89 with color display. I had to order one - knee jerk reaction.
Should be perfect for field tests as you suggest. That's pretty cheap for a complete product. This fpga-based detector should really fall under $150 (as a product/kit) when the hardware design is finalized. A manufactured detector using this technology much less.
So hey guys, here may be a platform that can do anything you want to try, just learn how to program it. Somehow such "electronics" is losing its appeal for me. The issue I think is that with traditional electronics the product is built in modular design fashion. Each section can be understood visually and modified etc. But with FPGA design the concepts are in the code. Not easily understood. Easily lost to new-comers. Such code is likely very poorly or uniquely documented. An example of my problem is say you just want to replicate the PI two sample detection scheme. When I start to think about how to do that in code my mind tweaks. When I think about doing it in analog I know how and there are a ton of books that detail the parameters of such modular designs. Problem may be that these analog electronics books may go the way of databooks... Too few and far between. Too expensive for a hobbyist to buy. Won't be found in a Borders. In fact, in the Borders by me most of the electronics book section has been eliminated... Such is life.
Ignoring the above, I look forward to seeing this succeed. Maybe I'll even buy what's necessary to make one - but no guarantee it will win over the other similar projects that fill the shelves of my garage.

I must agree with sentiment - there is beauty in analog circuits, like old mechanical machines. Software seems so dry. On the other hand, software is tinkerer's delight -- you can adjust any parameter tiniest bit in an instant and retest. Software can be designed to be adaptive, you can make it tune itself and adjust to hardware, such as different coils. But you need to know a lot of mathematics and stuff for software, digital filters, FFT, numerical methods, programming tricks -- not for the beginner.

I still prefer analog for fun. Maybe these software based designs will discover ways to improve and optimize the analog designs because faster to experiment different parameters.

We'll see.

Cheers,

-SB

[moodz]

Hi Moodz,

that is too much difficult for a beginner.

The ADC is a 14 bit I think. Anyway, it should even be enough to make a time-domain digital integration / processing.

But nothing for me. It's beyond my scope. I also like analog signal processing.

Aziz

ads1675.pdf

Hi Aziz .... ADS1675 ... 24 bit 4 Ms/s ADC this is located on my frontend board. The FPGA board is the backend. This is not beyond your scope IMHO .. the HDL language is just like procedural except each 'subroutine' works in parallel / runs at same time. In a way it is a quantum leap over procedural languages in what you can do.
I have worked with analog for over 30 years .. that is why I like CA3130 ... however if we are ever to produce a 'state of art' detector that offers user customisation then we must go down this path. You could not customise a finely optimised / designed analog circuit as it would break in some way as we see many times in these forums.

Regards,

Moodz

[moodz]

moodz has kicked some *** with this design.. nice job.. looking forward to whatever comes out of it... we'll learn some stuff when moodz and aziz get their boxes in gear... I'll keep playing with transistors in the mean time ha...

-SB

Simon ... I hope you are not implying I actually made that board ... It is one of the standard FPGA development boards available from www.digilentinc.com for about 160 - 220 $US ... I am only supplying some ideas and code and the frontend and the coil and the stick and the box and the battery. (did I leave anything out )

[moodz]

I am seeing a synergy here where most of my electronic interests are being now served by a FPGA design platform. Although the results are often very superior the DIY nature of them are too demanding on my time to learn. The thrills of FPGA programming are ...well, programming thrills.
I've touched those waters but they are pretty different from the experiences gained in analog electronics.
The fpga based design is easily modified and usually becomes very cost effective. The oldschool hands-on electronics nature of it however I think is lost.
An example of this is a portion of what you describe - the digital oscilloscope. Check out www.seeedstudio.com for their nano digital scope. $89 with color display. I had to order one - knee jerk reaction.
Should be perfect for field tests as you suggest. That's pretty cheap for a complete product. This fpga-based detector should really fall under $150 (as a product/kit) when the hardware design is finalized. A manufactured detector using this technology much less.
So hey guys, here may be a platform that can do anything you want to try, just learn how to program it. Somehow such "electronics" is losing its appeal for me. The issue I think is that with traditional electronics the product is built in modular design fashion. Each section can be understood visually and modified etc. But with FPGA design the concepts are in the code. Not easily understood. Easily lost to new-comers. Such code is likely very poorly or uniquely documented. An example of my problem is say you just want to replicate the PI two sample detection scheme. When I start to think about how to do that in code my mind tweaks. When I think about doing it in analog I know how and there are a ton of books that detail the parameters of such modular designs. Problem may be that these analog electronics books may go the way of databooks... Too few and far between. Too expensive for a hobbyist to buy. Won't be found in a Borders. In fact, in the Borders by me most of the electronics book section has been eliminated... Such is life.
Ignoring the above, I look forward to seeing this succeed. Maybe I'll even buy what's necessary to make one - but no guarantee it will win over the other similar projects that fill the shelves of my garage.

Agree totally with what you say ... the FPGA development environment can seem very challenging ... I mainly have used the ISE webpack from XILINX ( large but free download ) and beginners can start in schematic mode. You literally draw a conventional ( digital ) schematic and connect the inputs / outputs of your design to the the particular chip you are using .... fairly straight forward if you have used LTSPICE or Eagle or similiar schematic layout. The HDL coding is a bit less intuitive but arguably more powerful. There are lots of free code blocks on the web that are fairly easy to glue together. I still think alot of the viewers out there would be interested in a machine that even if they dont want to put all the code together themselves can at least get an understanding of how the box works and ask questions on an informed basis ... you dont have to be an artist to be an art critic and still be respected.

Moodz

[Aziz]

Hi Moodz,

[ATTACH]11384[/ATTACH]

Hi Aziz .... ADS1675 ... 24 bit 4 Ms/s ADC this is located on my frontend board. The FPGA board is the backend. This is not beyond your scope IMHO .. the HDL language is just like procedural except each 'subroutine' works in parallel / runs at same time. In a way it is a quantum leap over procedural languages in what you can do.
I have worked with analog for over 30 years .. that is why I like CA3130 ... however if we are ever to produce a 'state of art' detector that offers user customisation then we must go down this path. You could not customise a finely optimised / designed analog circuit as it would break in some way as we see many times in these forums.

Regards,

Moodz

the ADC is pretty much fast for a serial interface. Looks interesting.

Nevertheless, the platform is still beyond my capabilities (money, money, money). I even have simple problems in getting basic VCA's and J-Fet MUX chips (only C.O.D. orders possible to me at the moment).

You probably need an additional DSP to process all the huge data. I am looking forward to your results and would like to see you working on this platform.

Aziz

[moodz]

THE FUTURE OF MD IS HERE!!!!!!!!

Fantastic moodz. Congratulation!

What is proper ordering code of your TI Spartan -3E board?

How to get your software image?

Hey thanks ... some way to go yet ...

http://www.digilentinc.com/Products/...h=2,400&Cat=10

pick your weapon ! almost any of these boards can be pressed into service but the S3E kits are the best in terms of peripherals like LCD display and switches for doing stuff.

So far I am still hammering the code together so not ready for release 1.0 however hope to share progress with the group shortly.

Regards,

Moodz.

[simonbaker]

Simon ... I hope you are not implying I actually made that board ... It is one of the standard FPGA development boards available from www.digilentinc.com for about 160 - 220 $US ... I am only supplying some ideas and code and the frontend and the coil and the stick and the box and the battery. (did I leave anything out )

Ok, wasn't sure what was what, but understanding how to use such a board is a big leap and how to interface to it -- definitely looking forward to how it goes. Battery life and weight will be an interesting issue - maybe an area where stripped down analog designs still have an edge.

One you master this board, the ability to play with parameters will be amazing, like Aziz's work also.

We'll stay tuned in...

-SB

[WM6]

So far I am still hammering the code together so not ready for release 1.0 however hope to share progress with the group shortly.

What of frontend schematic you apply? Something new or one of here posted?

[mts]

Why wouldn't you use a cheap microcontroller instead of a FPGA chip costing $200? FPGA is fine for implementing discrete logic functions. But they aren't that good for algorithms that require "programming" such as FFT's and such. You can get a microcontroller with a built in ADC, memory, and even various peripheral support for around $5. The programmer costs $49. Once you have the programmer you can buy various different chips with differing capabilities so the possibilities are virtually endless.

Maybe I missed something earlier in the discussion as to why you are considering FPGA over a microcontroller. If so, I apologize.

[moodz]

Why wouldn't you use a cheap microcontroller instead of a FPGA chip costing $200? FPGA is fine for implementing discrete logic functions. But they aren't that good for algorithms that require "programming" such as FFT's and such. You can get a microcontroller with a built in ADC, memory, and even various peripheral support for around $5. The programmer costs $49. Once you have the programmer you can buy various different chips with differing capabilities so the possibilities are virtually endless.

Maybe I missed something earlier in the discussion as to why you are considering FPGA over a microcontroller. If so, I apologize.

I was using a cheap microcontroller ( dspic4102 ) which is fine and more than adequate for driving a PI detector however it is not ideal as a sandbox for developing more exotic functions like descrimination in the digital domain.
... the FPGA chip itself is about $10 - $20 ... the boards with RAM, FLASH, ethernet, power supplies, switches, LCDs etc cost $59 - 200 or more depending on application.
Apart from the fact that you can 'build' a microprocessor in an FPGA or a number of them simultaneously if you wish one of the fundamental limitiing factors of a uP is that it can only execute instructions sequentially. Insruction 1, Instruction 2, Instruction 3 etc etc. On the FPGA it would be something like ON CLOCK EXECUTE ( inst 1,2,3 ) .... ie all the instructions would execute in one clock. In other words a FPGA can trash a microprocessor applied to a SPECIFIC APPLICATION. On the other hand a microprocessor will probably trash an FPGA on a GENERAL APPLICATION. ( ie you would probably not write a word processor on a FPGA )
It is interesting that you mentioned FFT calculations ..... An FPGA will trash a CPU at FFT no matter how optimised the code in the microprocessor is. This is because something like FFT is ideally suited to parallel hardware that the FPGA provides. Also you can set up multiple parallel FFT process units in a FPGA to further increase speed.

An FPGA is no more than a digital breadboard .... it allows you to program not just conventional microprocessor code but to rewire the whole circuit if you wish. You cant do that on a conventional microprocessor board.

If anyone remembers space invaders ... the arcade game .... an enterprising individual mapped the original game logic board ( ie the chips ) and ROMS into the Spartan s3e FPGA as mentioned above. So if you ever want to take a break in the field ... you can play the original game .. sounds and all. www.fpgaarcade.com/games.htm The point I am making here is that one minute your box could be a metal detector ... the next it is a game box all without changing a single component or wire.

Moodz

[mts]

I see. I guess I just wouldn't look forward to implementing a "microprocessor" in a FPGA. Just because you CAN do something doesn't mean that you should.

But I'm an old software guy from way back so I'm more familiar with programming microcontrollers. Thus that would be my preference. It sounds like FPGA isn't nearly as expensive as what I originally thought so that makes a lot more sense. To each his own I guess.

Thanks for the explanation.

[moodz]

I see. I guess I just wouldn't look forward to implementing a "microprocessor" in a FPGA. Just because you CAN do something doesn't mean that you should.

But I'm an old software guy from way back so I'm more familiar with programming microcontrollers. Thus that would be my preference. It sounds like FPGA isn't nearly as expensive as what I originally thought so that makes a lot more sense. To each his own I guess.

Thanks for the explanation.

I will post a cheeky reply .....

A microprocessor is a pre-programmed FPGA.

Seriously though if you are an old hand you would remember the Z80, 6809, 68000 etc .... these are all available precoded for FPGA platforms ... they just run alot faster than the original chips plus all the peripherals like UARTs etc that occupied board space are in the chip.

Regards,

Moodz