NEW !!! Full differential PI front end.

[simonbaker]

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

In my next life I'm going to learn that stuff... wicked slick...

-SB

[WM6]

Seriously though if you are an old hand you would remember the Z80, 6809, 68000 etc .... these are all available precodet

Are there a down-loadable FFT module for FPGA?

[moodz]

Are there a down-loadable FFT module for FPGA?

Have a look here ... lots of stuff .... http://www.opencores.org/projects



Moodz

[bklein]

Someone I know did some work with the Digilent board and then moved to this 3A board for $49:
http://www.em.avnet.com/evk/home/0,1...53DEVK,00.html
It doesn't have the display but way cheaper...
Also another friend mentioned an Actel Igloo Icicle board for $49 that may be lower power.

[moodz]

Someone I know did some work with the Digilent board and then moved to this 3A board for $49:
http://www.em.avnet.com/evk/home/0,1...53DEVK,00.html
It doesn't have the display but way cheaper...
Also another friend mentioned an Actel Igloo Icicle board for $49 that may be lower power.

Good find ! ... only look through Avnet now and then .... this board would make an excellent PI controller engine ... it hasn't got much RAM though for bigger apps.

[revmaster]

One of the problems with sensitive PI detectors is earth field. If you wave a coil through a static field ( eg the magnetic field of the earth ) a slight voltage is induced that is proportional to the rate of change of flux through the coil. eg at type of generator. This leads to false target detection. However if the PI is driven by an alternating Tx pulse the receiver will see two things ...

1. Targets will respond with an alternating field as the eddy currents alternate in track with the stimulating tx pulse.

2. The earth field will produce a steady ( like DC ) response depending on the motion of the search head.

The only thing that would fool this would be if you sweep the search head at the same frequency as the alternating Tx pulse. ( if you drink lots of coffee you might be able to reach a 1000 Hz sweep speed )

The other benefits ? .... have you heard of chopper stabilised amps ? ... read up .... if you want to measure really small voltage changes like in a PI this definitely is better.

Coupled with the differential coil this system changes the PI landscape forever .... bisymmetric differential drive system schematic is published below ....

... wait till you see the ground balance system I have devised ... more soon.

Moodz

Hi Paul,

Very nice... Lately just started tracking this thread.
Any success on field trials reg ground balance system using bi-symmetric differential drive system.

Cheers,
Michael.

[moodz]

Hi Paul,

Very nice... Lately just started tracking this thread.
Any success on field trials reg ground balance system using bi-symmetric differential drive system.

Cheers,
Michael.

Hi Michael,
some success ... however I am moving the whole design into an FPGA backend. I have teamed up with Tinkerer to do move the analogue processing into digital processing. I hope to do field testing shortly.

Best Regards,

moodz.

[moodz]

FPGA progress

.... The RX filter banks, the oscilloscope function and the TX pulse functionality are operational. Have not built frontend yet so the shot below shows the output from the chip with no coil / frontend connected. The purple trace is the unfiltered input the white trace is the output from the digital filter ... I no longer need my Tek CRO

Note the whole display is generated by about 6 digital outputs on the FPGA and few resistors...... basically a 'free' scope.

The TX pulse ( yellow trace ) is the MOSFET driving pulse and is 127 uS duty cycle in 512 uS.

Sorry about the flash on the screen but it takes a much clearer picture of the traces with the flash on ... must be the lighting in my 'lab'

moodz

[hobbes_lives]

Nice work moodz! This project is really coming along!

I had looked into FPGAs a while back, but it seemed very cost prohibitive for the general hobbyist. Watching your work with them has renewed my interest.

BTW, are you programming in Verilog or VHDL? I've learned Verilog to some extent, but have not had any experience with VHDL to this point.

[moodz]

Nice work moodz! This project is really coming along!

I had looked into FPGAs a while back, but it seemed very cost prohibitive for the general hobbyist. Watching your work with them has renewed my interest.

BTW, are you programming in Verilog or VHDL? I've learned Verilog to some extent, but have not had any experience with VHDL to this point.

Thanks hobbes ... FPGA boards and tools are alot better and cheaper than they were a few years ago. You can certainly get cheaper Microprocessor development boards however you cant do the sort of real time things that the FPGA can do .... there are boards from Digilent and Avnet that for about $75 that are perfectly adequate. Coding is no more difficult than a micro IMHO and might even be easier if you are used to building stuff in the old days from discrete logic like TTL and CMOS. I found it harder and longer to set up the Microchip PIC IDE and get coding than the FPGA development ISE from Xylinx. ( Have not tried Altera but it looks similiar )
This project uses VHDL which has a more structured format than Verilog .. however I have built up big microprocessors in the past using Verilog and it is easy to convert code from one to the other automatically or even use mixed code modules.

Moodz.

[IBGold]

Hi Moodz,
I like the way you are going about your design will you be making available the coil design specs when all completed as I build all my own coils I live over the water from you on the peninsular.
Regards, Ian.

[moodz]

Hi Moodz,
I like the way you are going about your design will you be making available the coil design specs when all completed as I build all my own coils I live over the water from you on the peninsular.
Regards, Ian.

Thanks Ian ... I dont have any secret coils so I see no reason why not .. I am still doing alot of work in the coding department ... and as I dont have an example to copy some of it is new ground ... In the background do you or anyone know of anyone selling the shaft to hold the coil and the bit box ... I found this product which looks cool ... not sure if there is a dealer in Oz .... http://www.andersondetectorshafts.com/27.html
Moodz.

[Rov]

how about this,is a simple pole/stem assembly with a twist lockextension,as used for PulseMate PI detectors here in Oz.Pm if you interested in one Moodz.they made in S.A.as well.even to small lots if required.
regards Rov

[moodz]

how about this,is a simple pole/stem assembly with a twist lockextension,as used for PulseMate PI detectors here in Oz.Pm if you interested in one Moodz.they made in S.A.as well.even to small lots if required.
regards Rov

Hi Rov what are they made of. All plastic or top metal bottom plastic. Who stocks them or are they custom made ?
Thanks for the info ... much appreciated.

Regards,

Paul.

[Tinkerer]

Coils for TMPI

Hi Moodz,
I like the way you are going about your design will you be making available the coil design specs when all completed as I build all my own coils I live over the water from you on the peninsular.
Regards, Ian.

Hi Jan,

Moodz has given the TX and cycle times as TX, 127uS and cycle 512uS. I am starting to build a coil for this.
Since you are a very experienced coil builder, you are probably well aware that it takes a few tries to get the perfect coil for a specific detector.
If you (and others) are interested, we could each build some coils of different sizes, designed for the TMPI, exchange information and compare results.
We would quicker reach the goal of a perfect coil.

As a starter I suggest:

DD coil of 30cm diameter
Concentric IB coil of 30cm diameter
concentric IB coil of 45cm diameter

There are many factors to be taken in account. Coil wire, coil cable, shielding etc.

I am posting information and pictures on the 45cm coil at----today.
http://www.geotech1.com/forums/forumdisplay.php?f=53

Any suggestions are welcome.

Tinkerer