field test unit no 001 "model T"

[moodz]

hello moodz,

maybe it's the chip itself that could be a little noisy on channel 5, are ypu going to use the internial ref, or would a externial vref be more stable ?

philip

...could be however if the ref was noisy you would expect it on all channels. The specs say the internal ref is 5ppm and low thermal drift. Fairly easy to supply an external ref ... I can always use channel 5 for battery volts ... dont need microvolt accuracy for that

Note that what I call channel 5 is actually channel 6 ( I number the channels from 0 to 5 in the code. ).

The latest update is that the SAT is working and available for all channels ... The pic below shows the SAT in action and tracking with a 20 second dwell and a 30 microvolt deviation. Its probable I wont need this sort of accuracy as noise from the coil will be higher ...eg 100s of microvolts ... we will see.

The other pic shows the ADC on the "test bench" where all the code cutting and probing is done ... not exactly your low noise lay out but certainly good enough to achieve microvolt accuracy and clock the data out at 10 mbit/sec.

moodz.

[moodz]

...correction that is a 3.0 microvolt deviation on the SAT not 30 microvolts.

[Aziz]

Hi moodz,

I get quite similar (well slightly better) results with the high quality 24-bit sound card.
The noise of the amplifier isn't often critical but the coil is picking up a lot more noise (at least where I live - so noisy here).

I often set the internal amplifier gain of the sound card to a low gain (-10 dB or more, the internal amplifier is noisy) and rise the front-end amplifier gain as much as the overall noise floor gets affected. So there isn't a high gain front-end required if you can detect the signals just above the noise floor.

To tame the coil's induced noise, a second "reference coil" is necessary to subtract out the induced EMI noise.

Cheers,
Aziz

[moodz]

Hi moodz,

I get quite similar (well slightly better) results with the high quality 24-bit sound card.
The noise of the amplifier isn't often critical but the coil is picking up a lot more noise (at least where I live - so noisy here).

I often set the internal amplifier gain of the sound card to a low gain (-10 dB or more, the internal amplifier is noisy) and rise the front-end amplifier gain as much as the overall noise floor gets affected. So there isn't a high gain front-end required if you can detect the signals just above the noise floor.

To tame the coil's induced noise, a second "reference coil" is necessary to subtract out the induced EMI noise.

Cheers,
Aziz

I agree ... however I wont be able to continue using the dspic30F4011 to do the DSP as it does not have enough memory for the DSP processing .... I have ported the main code to floating point and now using pic32. I am dropping the SAT and going to full frequency domain processing for the DSP as the 24 bit resolution allows sub microvolt levels. Processing in the FDM and an undisclosed innovation also removes the ground balance problem ( works on PIs and VLF ). There are so many variables involved now that the machine will have to be programmed via a usb port. So PC will be used for setup ... but wont be needed for operation. The good news is that the hardware will be extremely cheap .... around $50 for the backend CPU board and frontend in a box ... you will just need to add battery, stick and coil.
The good thing about doing everything in code ( as Aziz already mentioned ) with a simple front end is you can use all the patented methods done in hardware ( the "hard" way LOL ) by doing the same thing in software and there is nothing the patent holders can do.
...because you are not using their method/circuit in hardware but in software.

moodz

[Aziz]

I agree ... however I wont be able to continue using the dspic30F4011 to do the DSP as it does not have enough memory for the DSP processing .... I have ported the main code to floating point and now using pic32. I am dropping the SAT and going to full frequency domain processing for the DSP as the 24 bit resolution allows sub microvolt levels. Processing in the FDM and an undisclosed innovation also removes the ground balance problem ( works on PIs and VLF ). There are so many variables involved now that the machine will have to be programmed via a usb port. So PC will be used for setup ... but wont be needed for operation. The good news is that the hardware will be extremely cheap .... around $50 for the backend CPU board and frontend in a box ... you will just need to add battery, stick and coil.
The good thing about doing everything in code ( as Aziz already mentioned ) with a simple front end is you can use all the patented methods done in hardware ( the "hard" way LOL ) by doing the same thing in software and there is nothing the patent holders can do.
...because you are not using their method/circuit in hardware but in software.

moodz

You finally have recognized the crucial point!
I am looking forward to your cheap and good solution. If someone can do it, you sure will. Let's make the greedy monopolist's live (patent holders) a bit difficult. They deserve it.


Cheers,
Aziz

[hdphilip]

Paul,

The UNO32?


Philip

[moodz]

You finally have recognized the crucial point!
I am looking forward to your cheap and good solution. If someone can do it, you sure will. Let's make the greedy monopolist's live (patent holders) a bit difficult. They deserve it.


Cheers,
Aziz

he he ... it took a while but it is the only way to go.

moodz

[moodz]

Paul,

The UNO32?


Philip

yup ...it is the best bang for buck and the most available. The DSP code will compile with minimal effort in this processor, most any other processor with a GCC compiler or a laptop with a soundcard if required.

moodz

[hdphilip]

moodz

what kind of sampling rate are you getting? and do you plan on using all of the adc channels?

philip

[Aziz]

yup ...it is the best bang for buck and the most available. The DSP code will compile with minimal effort in this processor, most any other processor with a GCC compiler or a laptop with a soundcard if required.

moodz

I will provide the minimal hardware platform for the laptop/netbook/tablet/PC with a sound card solution soon. Oh shame! (on me), it is sooo much trivial & simple, that I barely dare to publish it.

Although it isn't a cheap platform (the netbook + USB sound card cost's at least 250 bucks), it makes up a good developing and analysing platform however.

Nevertheless, I would like to have the small form factor and portable one. So it is good to know, that someone is working on this issue.

Cheers,
Aziz

[6666]

Are you guys talking about this or something else ??

http://uk.farnell.com/digilent/chipk...ard/dp/1893211

[moodz]

moodz

what kind of sampling rate are you getting? and do you plan on using all of the adc channels?

philip

The sample rate can be anything you want from a few hertz to mega hertz ... its not the sample rate that matters its where and when you sample ... the maths is the same whether direct sampling with a fast ADC or demod and sample with slow ADC. The great revelation is that everyone has been barking up particular trees with all the techniques to date .... if you stand back and view the whole forest ( with a sprinkle of DSP) you can see all the detail of all the trees at the same time.

To answer your question ...there are main 3 sampling rates I will investigate ... dependant on front ends, time and funds available.

1. multichannel "Slow demod" with 8 Khz to 100 Hz sampling at 24 to 31 bits resolution.

2. multichannel "Fast demod" with 192 Khz sampling at 24 bits.

3. multiplexed "Fast direct sample" with 4 Mhz sampling at 24 bits.

1. is the cheapest and simplest to implement.
3. is the most expensive.

moodz

[moodz]

Are you guys talking about this or something else ??

http://uk.farnell.com/digilent/chipk...ard/dp/1893211

Thats the one. There is also a MAX32 version for more money and more memory.

[Aziz]

Hi all,

to give hdphilip an idea:
I'm using the second option with the sound card solution:
multichannel (dual-channel)"Fast demod" with 96 kHz sampling rate at 24 bits

When I get the 192 kHz sound card, it will support it as well of course. It will help to find easier the fly$hit targets.

Aziz

[moodz]

Hi all,

to give hdphilip an idea:
I'm using the second option with the sound card solution:
multichannel (dual-channel)"Fast demod" with 96 kHz sampling rate at 24 bits

When I get the 192 kHz sound card, it will support it as well of course. It will help to find easier the fly$hit targets.

Aziz

Dont forget the bacteria$hit nuggets with this card .... item no 220896231564 on ebay.

384 Khz sampling at 32 bits theres heaps of others too and the price is not too much for a high end card ( around $150 )

moodz.