do-it-yourself nuclear magnetic resonance spectroscopy

Quote: Originally posted by not_important

The native field NMR systems must work with a __very__ low signal level and fairly high background noise, both manmade and natural.

disk drive magnet NMR

Quote: Originally posted by densest

Real NMRs have shim coils. How do you measure the nonuniformity?

Quote: Originally posted by densest

There are 20 disk drive magnets on my kitchen table. Pretty strong NIB... 0.2T maybe? [deletia] Or should I just go away and have some good wine instead?

Quote: Originally posted by 12AX7

Anyone suggesting strong magnets as a brute-force solution is disturbingly misguided.

Experimental pulse NMR: a nuts and bolts approach By Eiichi Fukushima, Stephen B. W. Roeder Westview Press 1981 has a lot of information. The Google Books excerpt is pretty helpful.

Using some course materials from various universities found on the net, a dropped-calculator no-envelope estimate of the signal from a 1 cm^3 sample of water using a 0.2T magnet is in the vicinity of 1 microvolt. The frequency is about 6 MHz, pretty easy to deal with. The power necessary for the stimulus pulse is painful - over 500W if I understood the very vague language in the one paper that defined it at all. At that frequency, a 10-turn (5 & 5) or fewer turns and a matching network would be needed. Electronics to quench the pulse quickly aren't -too- bad.

Modern chips & transistors would make things -relatively- easy. Given a 60Hz maximum for 10ppm allows the use of 24 bit A/D converters at baseband for $10 or so... getting 1 nV or less noise is harder. Significantly twisty signal processing might be necessary - then don't downconvert all the way to baseband, but instead maybe get 1000 - 1060 Hz out (where noise is less of a problem) and DSP the heck out of the data. Modern frequency synthesizer chips allow generating multiple very stable sources, so phase coherence shouldn't be a big problem. The current state of the art is would be to digitize directly at 6MHz and do everything subsequent to that in software. 12-14 bit converters run $25-30 or so. That might not be the least expensive way, though. Unless there is a reason I don't see, the traditional approach of frequency synthesis from two oscillators and double frequency conversion for the signal is probably a lot more trouble for no better results.

Machining pole pieces correctly would be a pain.

Mapping the field with an X/Y controlled force probe like an atomic force microscope would be amusing. Use a tiny search coil w/pizeoelectric vibrator giving either a force null when the search current matches pizeoelectric force or a signal generated in the coil at a voltage proportional to the field in the direction perpendicular to the search coil using a constant AC drive to the pizeoelectric actuator.

Anyway, I'm interested in this because NMR was my favorite way of identifying unknown organic compounds A desktop unit would be pretty amazing. It would probably be a 6-month to 1-year project, though. The less money, the longer time.

-----
http://www.magritek.com/lapspecspecifications.html is a portable NMR with specs very similar to the above... anyone in NZ have any idea what it costs?


[Edited on 1-9-2010 by densest]

Quote: Originally posted by densest

http://www.magritek.com/lapspecspecifications.html is a portable NMR with specs very similar to the above... anyone in NZ have any idea what it costs?

Quote: Originally posted by densest

Anyone in Australia (or maybe New Zealand) want an NMR? http://cgi.ebay.com/NMR-Oxford-200-Spectrometer-Superconduct... has no bids & an opening price of $1000...

I'll chip in if we find more Aussies wanting one. We could share it

I just drew up a rough sketch of what I'm talking about - instead of having the truncated-prism as the major component - ie. North-South traveling through them, why not use 6 10x10mm x 3.175(?)mm equilateral triangle-prisms and between them have 6 10x5mm x 3.175(?)mm long bars, which are magnetized through the 5mm edge, two of which would, in a Halbach array, form the North and South poles.

The design I've come up with would leave an approximately 10mm center (a hexagon with 5mm sides) for the coil and we could use grub-screws (provided they can be attached easily) to shim the magnetic bars inward/outward, thereby altering the field. The benefit is that the magnets I'm talking about are all Off-The-Counter designs, so there is no massive machining/purchasing overhead, it should cost under $30US for the lot.

The coil would have to fit in the center - but there are numerous coil designs (birdcage, etc.) and I'm thinking a capped centrifuge tube for the sample holder...



All up size, considering it would probably be best if the whole were encased in plastic, would be around 4cm (diameter) x 4cm (height). Anyone got some design ideas for the coil?

[Edited on 9-9-2010 by aliced25]

Have you considered modelling the field in FEMM at all? This would be a little better than guessing for dimensions and orientations. Eats up CPU power though...

http://www.femm.info/wiki/HomePage

Quote: Originally posted by aonomus

Have you considered modelling the field in FEMM at all? This would be a little better than guessing for dimensions and orientations. Eats up CPU power though...

AMEN

How to model the Gauss of a 10mm Equilateral triangle prism? It is N40 Neodymium, as is the 1/4" square prism... By the way, thank you very much for the program suggestion.

Can I import from GoogleSketchUp?

No, apparently - I have to work out how to draw it in the finite materials program

EDIT - sussed it out - from what the model is telling me there would be a solid 0.5-0.6T field right through the middle of the model.



Actually, that is pretty fucking spectacular - my design gives about the same results as the one in the paper by Danielli, et al (above), using off the shelf, cheap as fuck Neo magnets instead of specially machined/shaped Samarium Cobalt magnets and it is much smaller (while retaining the moving parts so as to allow for "tuning" of the magnetic field).

Who says amateurs have to be "amateurish"?

Check out what happens when the two top triangular magnets are turned inward... An actual peak of 0.6T in the center, with an average through the central area of ~0.58T

[Edited on 12-9-2010 by un0me2]

Amateurs may not be amateurish, but they can fuck up - when I went through the diagram of what I'd drawn I realised that despite setting the preferences in mm it had retained them in inches, so the diagram attached to the previous post is innacurate.

The one attached to this is an accurate (or roughly so) rendition of what FEMM makes of the model. Note that the section graphed is through the "middle of the model" where the coil would go and actually peaks in the center at just under 0.7T That pretty much matches what the pro's can do with much larger devices, this is approximately 4cm wide, by just over 3cm high, with a clear bore of about 6mm with a useable area in the center of about 2.5-3mm diameter (where the field is pretty well homogeneous & appears to average 0.68-0.69T, in fact I'd be prepared to state that it is so, the defects on the model are more likely from my drawing than from the "model" magnets).

It is rather higher nearer the poles so I may have to try out a couple of additional design ideas in order to increase it further. I also intend to contact the local school and get them to see if they can measure the flux once I build the same. The central part is so cramped due to the design incorporating aluminium framing (0.1", ie. 2.5mm - aluminium was one of the only choices offered, does anyone know enough about the plastics in this area? How well they conduct magnetic fields, etc.?)



[Edited on 13-9-2010 by un0me2]

Quote: Originally posted by un0me2

Note that the section graphed is through the "middle of the model" where the coil would go and actually peaks in the center at just under 0.7T That pretty much matches what the pro's can do with much larger devices [...] the field is pretty well homogeneous & appears to average 0.68-0.69T, in fact I'd be prepared to state that it is so, the defects on the model are more likely from my drawing than from the "model" magnets).

Instead of using such nasty shapes, you can build a halbach array using a ring of diametrically magnetized cylindrical magnets (available off the shelf). I ran a quick sim on FEMM, and got a much flatter field than in you sim above. Shimming is achieved simply by rotating the magnets. Size in sim is kind of random. magnets are N52.
More elements usually = flatter field.

Attachment: halbach.EMF (5kB)
This file has been downloaded 1317 times





[Edited on 13-9-2010 by Twospoons]

Be nice if that were so wouldn't it? But as your picture demonstrates, the magnetic field in the circular magnet designs is affected by there lack of density (both magnetic and otherwise). Your design pulls a nice field, there is no escaping that, but with heavier duty magnets, but the maximum field in the center is >0.5T (closer to 0.4 in fact). My "nasty shape" is pulling an homogeneous field with close to 0.7T (and I've designed others pulling over 1T, but without the homogeneity). I've tried nearly every design I can think of with circular magnets and without resorting to sizes & shapes that are outside what is easily available, I cannot break 0.5T (although with 8 Neo52 Discs, 1/2" dia, I can reach it with a "fairly" homogeneous field through the center with a 4mm useable region averaging from ~0.47-0.5T).

With an even nastier shape, which I will share directly, I can get a homogeneous field around 0.95-1T. I want to install some software so I can draw it in CAD & import it to FEMM first.

Here is one design - 10mm squares (1" high) & 10mm diameter discs (1" high), with the 4 circular magnets being used to tune the magnetic field. Across the 1cm center the field fluctuates from 0.82125T to 0.82110T which is pretty bloody homogeneous (0.82T right across) with further tuning available from turning the 4 circular magnets (all magnets are N40 - N52 would improve the field further).

[Edited on 14-9-2010 by un0me2]



[Edited on 14-9-2010 by un0me2]

Quote: Originally posted by un0me2

I've tried nearly every design I can think of with circular magnets and without resorting to sizes & shapes that are outside what is easily available, I cannot break 0.5T (although with 8 Neo52 Discs, 1/2" dia, I can reach it with a "fairly" homogeneous field through the center with a 4mm useable region averaging from ~0.47-0.5T).

Quote: Originally posted by un0me2

... As to the shim circuits, yes, they are going to be necessary, although I would hope to be able to build small servos (off 1 Integrated Chip) which could automatically manipulate the tuning magnets so as to get the field as homogeneous field as possible, thereby reducing the need for shim coils dramatically. [rquote] If those are PWM servo dirvers or similar, you'll need _really_ good filtering on their outputs. Quote: Originally posted by un0me2   ... @ Those & the rest, I am also trying to design the simplest possible electronic circuit to (a) convert Digital-to-Analog; (b) synthesize the signals using a programmable synthesizer (IC) which can sweep from several KHz to several MHz (the IC containing all of the components necessary to do (a-b are on one IC) so with minimal noise); (c) delivery of the synthesized signal to the radiating side of the double saddle coil; (d) collection of the signal at the receiving side of the double saddle-coil; conversion of that signal to (i) isolate the peaks from the transmission frequency while (ii) assigning the same to that frequency (all on one IC with the feedback loops, etc. all built in); (e) convert that information to from analog to digital (part of the same IC) and a USB 2.0 connection to drive the whole device. ... That's a fairly wide sweep range for good performance - precision, accuracy, and stability. Also, if I'm understanding what you're saying, you intend to use a pair of coils facing each other with the sample between them. If so, that will likely result in the driving signal swamping the sample signal; there's a reason that most NMR systems place the pick-up coils at right angles to the driving coils. Not only that, but the power levels needed for the drive side likely will induce excess noise in the receiver; it's better to pt power circuits on separate PCBs with good isolation - local regulators for the receiver one and all that. You can do it on one, but good board layout is needed. Note that FT NMR uses a short pulse to excite the sample, and it is possible to share the same coil for drive and pickup although you generally need protection for the receiver. The frequency range needed is fairly small, a ordinary DDS chip will do the job - the frequency base is independent of the sweep and generally covers a much wider range. http://www.analog.com/en/rfif-components/direct-digital-synt...

Yes Not_Important, that is precisely what I am saying, I was looking at using another integrated chip on the receiver side of the double-saddle coil, to filter out anything on the transmission frequency. By careful timing of the sweep I should be able to do so, taking any remainder as resonance at a particular frequency (ie. the necessity of the timing of the sweep, allows one to know what frequency the resonance belongs to). I'm busily looking for the partner IC to the transmission IC, I'm betting there is one.

Anyway, that has to wait for an answer in the reference request thread, here is the latest go - 1/2" Square & 1/2" Diameter x 1" high magnets with a 1/2" central area to give a 0.812 (+/-0.01)T field right across the 1/2" central area...




With further playing around with the tuning, I can get a dead flat line @0.84T, and I suspect I can get up to 0.85T with a +/-0.01 cross-section, now that is a permanent magnet

[Edited on 15-9-2010 by un0me2]

Quote: Originally posted by un0me2

...I was looking at using another integrated chip on the receiver side of the double-saddle coil, to filter out anything on the transmission frequency. By careful timing of the sweep I should be able to do so, taking any remainder as resonance at a particular frequency (ie. the necessity of the timing of the sweep, allows one to know what frequency the resonance belongs to)....

Quote: Originally posted by aonomus

I'm not sure if any of you guys have the equipment to do so, but if you have any semi-mainstream DSOs, you can always get labview to work with your DSO as the data capture device, and use a labview controlled signal generator to provide the IF for the mixer and RF amplifier for the excitation coils. Considering that DSOs are cheap now, no reason to try to reinvent the wheel if you have labview... Just my $0.02 adjusted for inflation.

$9k USD

Quote: Originally posted by 12AX7

Quote: Originally posted by aonomus   I'm not sure if any of you guys have the equipment to do so, but if you have any semi-mainstream DSOs, you can always get labview to work with your DSO as the data capture device, and use a labview controlled signal generator to provide the IF for the mixer and RF amplifier for the excitation coils. Considering that DSOs are cheap now, no reason to try to reinvent the wheel if you have labview... Just my $0.02 adjusted for inflation. You need megs of RAM and a full width FFT window to observe ppm shifts. This is pretty well a DAQ thing (data aquisition) requiring a PC, unless you have one of the incredibly massive mainframes that costs $50k and offers spectrum analysis this refined. Tim

Another thesis on the site said he passed away, but my bad (Glad he's ok) I do recall feeling bad reading his thesis after reading the other one Now I feel all good again, YAY

Now, there is a link to a calculator in this article, the DS1085L (the 3.3V version) can be programmed to the range needed.

As to the size of the DAC/ADC's needed, I suspect they are getting smaller as we speak. The DS1085L (above) has a DAC built into the IC (all silicon and TINY). The evaluation kit (DS1070K) appears to have everything needed to "evaluate" (ie. read, write, program and generate output = everything needed for one side of the spectrometer)

That has the outputs OUT0 and OUT1 which can be programmed to be the same (kind of a good idea) frequency and one could presumably be wired directly to the pulse generator (old school & programmable)

That and the synthesizer means you have the pulse pattern set, the frequency set and precisely what needs to be fed to the transmitter coil?

Does that mean we only have to work on the other half?

PS As to the DAC's being the primary concern, according to what I can glean from FGPA circuits can handle the signal processing.

[Edited on 20-9-2010 by un0me2]

Quote: Originally posted by 12AX7

Why the hell do you need a whole frickin DDS to generate exactly one frequency? Use an LC oscillator and be done with it. Besides cheaper and simpler, it's also smaller, being a coil, transistor, a few capacitors, resistors... Also, easy to build in through-hole, if you are so inclined. But SMD is easy enough, at least the wide pitch stuff. The NMR signal is about 100 Hz wide (for reaaaally shifted signals). This is not high bandwidth stuff. You don't need, and you don't want, a 50MHz ADC chopping up the whole thing, all it sees is the same damn sine wave. Instead of 10k datapoints in the audio range, you need 500M datapoints with ~100MB/s bandwidth. That's ludicrous! What is needed is precision frequency sources. An ovenized quartz oscillator should be good enough. IF frequencies can be generated with multiplier-divider-PLL blocks, which are tedious, but not difficult. Hmm, the ATmega series does 10kSa/s pretty easily. That's plenty for a 100Hz signal. It's no DSP chip, but with external SRAM to hold the data, and a few extra seconds between pulses to process it, you could easily run the works on a dinky little microprocessor. You could even pipe the output to a graphical LCD. Push a button, click click, wait a few seconds, there's your spectrum! Too bad the ADCs are only 10 bits. Lots of samples could be taken, using subtractive dithering to reduce error, to improve this. It would take a lot of sampling to get it up to 16 bit quality though (~4k passes!). An ARM something would be better suited to the math, and external ADC/DAC would improve performance (something for 16 bit audio would be fine). Or you can just use a PC's soundcard, which already has all this, plus oodles of RAM and HDD storage, plus gobs of processing power, plus familiar interfaces (if you're a Windows programmer anyway). Tim

Yet More NMR history

Quote: Originally posted by un0me2

Yes, but I want to be able to hook this up to other magnets as and when they are available, as the magnets change, so will the frequency.

Your fault in OS choice / watching too much porn. I have a copy of MS-DOS 6.2 if you're interested. Don't worry, you can find MS-DOS, protected mode, SVGA movie viewers so you won't even have to go without porn (though you may have to go without multitasking).

Quote:

The programmable on-chip-solutions are physically smaller and less complex than building a solution, they also require less board space Quote: Hmm, if I had the money and time (and probably the same problem for yourself), I might actually challenge you to a proper wager on that. We'd each build our own unit and compare board areas and total cost. That includes power supplies and anything else in the chain (computer, display, etc.)! Quote: the brute force solution is more accessible (in terms of time, space and money) Sorry, micro ITX boards are cheaper. Tim

Quote: Originally posted by 12AX7

Quote: Originally posted by un0me2   Yes, but I want to be able to hook this up to other magnets as and when they are available, as the magnets change, so will the frequency. So? Change the local oscillator. A very stable and very controllable oscillator can be built from a OCXO, a pair of programmable dividers and a PLL. The dividers can be hard wired for a specific frequency, or programmable for any reasonable rational ratio to the OCXO.

And a programmable oscillator is what? A few bucks? A board with it all pre-populated isn't that hard to ask for I'd imagine.

Quote:

Quote: Windows is known for it too, whenever it is short of RAM for XP/Vista, everything else slows down and Vista especially is a memory hog. Your fault in OS choice / watching too much porn. I have a copy of MS-DOS 6.2 if you're interested. Don't worry, you can find MS-DOS, protected mode, SVGA movie viewers so you won't even have to go without porn (though you may have to go without multitasking).

Quote:

The programmable on-chip-solutions are physically smaller and less complex than building a solution, they also require less board space Quote: Hmm, if I had the money and time (and probably the same problem for yourself), I might actually challenge you to a proper wager on that. We'd each build our own unit and compare board areas and total cost. That includes power supplies and anything else in the chain (computer, display, etc.)! Quote: the brute force solution is more accessible (in terms of time, space and money) Sorry, micro ITX boards are cheaper. Tim

Micro boards are cheap, but that is a personal choice. Integrated solutions do it for me, if you ask nicely people who know what they are doing will do a lot of the work for lazy fuckers like me, chip choice, board design, etc.

Anyway, I mean I've got the old Amstrad 64 green screen out the back somewhere (the 512 Orange Screen too) if I want a dedicated system to do it

Damn, remember when you didn't need "VISUAL" fucking anything? They've even fucked up Fortran (no more punch cards, WTF?)...

Yes, there are classes in it now, same as basic, but I remember writing in basic when you had to physically type in the numbers at the start of the line, GOTO, GOSUB, LET n=0, LET n=n+1, NEXT n ring any bells? Who needed stinking classes when you had routines & subroutines? I don't like writing shit into code "because that is what you do" I like to know "why"...

That said, I suck at soldering projects together, I'd rather buy minimal numbers of parts (I can understand electronics when it has a datasheet & tells me what it is & does) and pay some poor sod to do it for me.

EDIT

What does suprise me is that if we are going to use the sound-card, NVIDIA seems to be fairly ubiquitous, to receive and interpret the data, why can't it be used to synthesize (or alternatively simply play) a prerecorded pulsed signal? I mean, that is pretty much what it does - it sends pulsed signals to audio output and can receive the same/similar from audio inputs. No real hacks needed, that is its reason for being.

That would put the entirety of the spectrometer on the PC, except for the output & input wires & coils, and given the degree of amplification one can get out of a speaker, it really shouldn't need additional power sources. That would make for one trippy small fucking FT-H-NMR Spectrometer - with what? Two audio wires running to the spectrometer?

That would be smaller and more compact than any external spectrometer, and I know it could work, there is more fucking RAM on most machines than there was ROM on the fucking mainframe my mother used to program (and that sucker took up a building and used punchcards)

Hang on, DSD looks promising, it can transmit/record at the appropriate frequencies and samples fast enough. How to control it? Or better, build a control for both the input & output streams? A digital sound file could be synthesized with the pulse built in, and a digital sound file could be programmatically dealt with in next to real time...

There are some fucking wild ideas coming out of this thread Here's a wilder one, a sine/square/triangle/etc. wave generator and oscilope based on the sound card (here).

[Edited on 21-9-2010 by un0me2]

Quote: Originally posted by 12AX7

And under much more reasonable circumstances, like a dedicated machine having no other programs open, minimal services (e.g., no background antivirus pain) and no bothersome internet connection, the USB connection will respond in what, miliseconds worst case? Microseconds or better is probably typical, though I would be interested to see the actual time spread before putting much trust in that short a range.

Stelter Magnet array

Quote: Originally posted by 12AX7

Why the hell do you need a whole frickin DDS to generate exactly one frequency? Use an LC oscillator and be done with it. Besides cheaper and simpler, it's also smaller, being a coil, transistor, a few capacitors, resistors... ---------------------- r. A very stable and very controllable oscillator can be built from a OCXO, a pair of programmable dividers and a PLL. The dividers can be hard wired for a specific frequency, or programmable for any reasonable rational ratio to the OCXO. Tim

Quote: Originally posted by un0me2

... And a programmable oscillator is what? A few bucks? ... What does suprise me is that if we are going to use the sound-card, NVIDIA seems to be fairly ubiquitous, to receive and interpret the data, why can't it be used to synthesize (or alternatively simply play) a prerecorded pulsed signal? I mean, that is pretty much what it does - it sends pulsed signals to audio output and can receive the same/similar from audio inputs. No real hacks needed, that is its reason for being.

Uh, did you notice my scheme? Downconvert the signal to a ~1kHz carrier. Tons of bandwidth. 44kHz sample rate is good for what, 22,000,000 ppm of shift?

Easy enough to add a few latches, and a DAC or counter, to generate a programmable pulse. Obviously, generating the timing from a PC is stupid.

Tim

Quote: Originally posted by not_important

Simple programmable oscillators, even at the level of the DS1085, likely don't provide the needed level of stability (without the OCXO or at least TCO), tunablility and resolution.

Quote: Originally posted by un0me2

But I'm interested in how the SoundCard (and DirectSound) are going to deal with the output from the device, when the filters and inherent limitations of the SoundCard/DirectSound stop so much of the signal...

I'm watching and reading, meanwhile I am working on the magnets...

@12AX7

Yes, I did read the posts, I honestly didn't see the point you raised, sorry.*

@arsphenamine

Yeah, it is essentially an audio notch filter, you filter out the radiation you put in & what is left is noise+response (or that is my take). Hang on, why are we at 60MHz? I'm struggling with what frequency I need, do I or don't I need to put in a specific frequency, based upon the field strength (0.8T as you pointed out earlier is well below that (IIRC 44MHz/T?), or I've missed something basic, not unusual)?

That said, a digital input via the soundcard/DirectSound would be promising, that enables access without the vagaries of Windows OS prioritization getting in the way. A fast ADC is going to be needed, but I'm interested in seeing more about how to generate the signal in the first place.

* Why is generating the pulse from a PC so out of the question? Timers, like fan-type speed controllers, are on every board I can remember seeing, surely they can be reached programmatically? The pulse doesn't do anything but open the gates for the generated frequency to go through does it? The clock on the SoundCard, which is already going to be wired into one side of the unit, runs at how many hertz?

PS This ain't a College/University, more is learned by arguing points than most will ever acknowledge. Argument isn't bad per se.

NMR process control thots

Quote: Originally posted by not_important

Uh, Tim, did you notice the text about the sound card I commented on came from un0me2 , and it said "why can't it be used to synthesize (or alternatively simply play) a prerecorded pulsed signal" Ditto regards the programmable oscillator, and RF front end comments. By the time you add in the outboarded PLL and other stuff, you might as well go with a DDS chip.

Quote: Originally posted by arsphenamine

Soundcards and USB: If you up-convert by enough Hz to get out of the way of a soundcard's AC input coupling, then remove the upconversion digitally, a consumer grade soundcard can be plausibly used.

Just reading, this note caught my eye.

The biggest difficulty I am having is the amount of processing power that is being required off-board the PC/Laptop is increasing drastically as the designs progress. As this echoes the advent of the netbooks built on the same processors (once you go beyond ARM, etc. you get into the CAP end of the scale), all that will end up happening is that these will end up a mini-stand alone systems, with a display and keyboard & the magnet carefully tucked away inside the design.

Interesting thought process in fact, that leads to the thought that then the device (+ Li ion battery of course) would be truly mobile (whereas before it was going to be a USB device, not a standalone system). The yardstick keep shifting. FGPA's are dying a lonely death if they don't have a mini-CPU built onto the board to control them, so we are progressing into the prohibitively expensive end of the spectrum (pun intended).

Fuck, we were still reading about MOSFET based designs one or two pages ago.

As to the soundcard, why bother up & down converting into the Soundcard when you could more easily send a digital input stream in via ethernet/usb & deal with that using DirectSound (MS OS - so it will not be pushed aside easily).

Ok

How about 128K of memory and 16K of RAM? Shitloads of options, in a single chip in terms of control (its a USB 2.0 compatible microcontroller)? Nice. Then there is this, A signal processor IC with two amplifiers, two 12-bit ADC's, etc. all in one chip as well. That's what, $11 so far? With more timing signals, pulse width modulators & unused PLL's then you could poke 10 sticks at...

[Edited on 23-9-2010 by un0me2]

Quote: Originally posted by un0me2

The biggest difficulty I am having is the amount of processing power that is being required off-board the PC/Laptop is increasing drastically as the designs progress. (...) The yardstick keep shifting. FGPA's are dying a lonely death if they don't have a mini-CPU built onto the board to control them, so we are progressing into the prohibitively expensive end of the spectrum (pun intended).

Quote:

Fuck, we were still reading about MOSFET based designs one or two pages ago.

Quote:

How about 128K of memory and 16K of RAM? Shitloads of options, in a single chip in terms of control (its a USB 2.0 compatible microcontroller)? Nice. Then there is this, A signal processor IC with two amplifiers, two 12-bit ADC's, etc. all in one chip as well. That's what, $11 so far? With more timing signals, pulse width modulators & unused PLL's then you could poke 10 sticks at...

Quote: Originally posted by arsphenamine

At this point, the prospect of running a pulsed 100 watt RF amplifier in a manner that doesn't send the FCC into colonic spasms should get a little more pixel space.

Quote: Originally posted by 12AX7

Can't be too bad. The FCC would shit themselves if they had been checking out GSM cellphones while a clock radio played in the same room. Damn GSM gets into everything.

Just in case anyone is interested I am currently working on a large water cooled magnet with two 8.5 inch diameter pole faces. I am planning on generating a 1.2 tesla field in a 2.5 inch air gap.

Ok, well for the home-hobbyist, we really don't want to get too sidetracked onto electronics do we? How about starting from something like the CUI32 PIC32MX Development Stick which has it's very own open-source Stick-OS with a forum and a Google-code repository address. I mean, it is directly programmable from the USB 2.0 port, has the PIC32MX460F512L Microprocessor built in and is what, $40? Kicks the living shit out of Arduino doesn't it?

I'm thinking that the DDS/Programmable Oscillator with that (or have a good close look at the capabilities of that mini-CPU & see what it can do) then amplify the piss out of the signal to get it to where we want it, collect it, filter out the transmission, then convert the noise+resonance to digital and store them onboard for processing.

Quote: Originally posted by un0me2

Ok, well for the home-hobbyist, we really don't want to get too sidetracked onto electronics do we?

Quote: Originally posted by arsphenamine

There are inexpensive MCU that do both protocols in hardware, but throughput varies widely. With the AD7765 Sampling at 48kS/s, you need a ~1.5MHz SPI bus clock so must select the MCU accordingly.

Quote: Originally posted by watson.fawkes

Standard Arduino will do SPI at either 2 MHz or 4 MHz. Collect data at 2 MHz from SPI and ship data out the USB. Serial operations on each side have hardware control, so there's only a few instructions per byte transferred overhead. I'd guess that over half the CPU time is still available, plenty enough for other control tasks.

Quote: Originally posted by arsphenamine

Standard Arduino also has a 1ms Time-of-day interrupt to contend with the hoped-for repeatability, and an FTDI serial-to-USB chip that I'm not entirely happy with above 19.2 kBaud.

@ Arsphenamine

It got up to ~1T several posts ago, it doesn't appear to have been noticed (actually 0.989 +/- 0.001T based upon a hexagonal section through the sample area according to FEMM, the inhomogeneity is in the center of the design (east-west given the top & bottom are North & South)).


@not_important,

I hope the dsPIC does have the oomph to do the job, it is perhaps the most promising of the easily purchased designs in that regard. I would prefer, given the uncertainty as to transfer rates to (a) keep the data onboard & accessible as required and (b) if at all possible, perform the mathematical computations on the board prior to transferring the information to the main PC/Laptop. Given the amount of computing power involved and the speed of the sampling rate, I don't see why 10/12 bit sampling is sup-optimal. There is a HELL of a lot of information in a 10/12 bit digital record, particularly when the sample rate is as fast as is promised by the dsPIC chip. That MAXIM chip requires an external ADC, which would of course be provided by the dsPIC/PIC32 (it has shitloads of 'em to spare, plus then the digitized data is where we want it). The oscillator for the chip would also be ported from the dsPIC/PIC32 which has several of them spare.

On-chip signal conversion would enable there to be very few none-IC components on the board, the digital synthesizer then the on-chip conversion of the received signal takes care of most of it. The amount of binary data that can be stored in 32K of memory is HUGE (that is half the size of my first PC).