From: John Brookes <haiticare2...@gmail.com> Reply-To: <beagleboard@googlegroups.com> Date: Saturday, May 10, 2014 at 3:31 PM To: <beagleboard@googlegroups.com> Subject: Re: [beagleboard] BeagleBoard Data Acquisition Platform
> And only 2000$ too! > j Yeah, but it is really amazing piece of technology running at 3.6GSPS. BTW, most of the DSP is done in the FPGA. Regards, John > > > On Sat, May 10, 2014 at 6:15 PM, John Syn <john3...@gmail.com> wrote: >> >> From: John Brookes <haiticare2...@gmail.com> >> Reply-To: <beagleboard@googlegroups.com> >> Date: Saturday, May 10, 2014 at 7:28 AM >> To: <beagleboard@googlegroups.com> >> Subject: Re: [beagleboard] BeagleBoard Data Acquisition Platform >> >>> My dear Penguin, >>> >>> Yes, the desired SPS rate is rather low, as I was feeling limited by the >>> actual possibilities here. I am a pattern recognizer >>> bird myself, and looking primarily at 2 problems: >>> 1. Non Invasive medical diagnostics. These use NIR, electronic noses, and >>> perhaps EEG, EMG. >>> 2. The quantum mechanical nature of consciousness. These onvolve detecting >>> signals like 1 above - coupled with AI, like 1. >>> >>> Both of these aims ask for rather many channels with rather low speeds. Why? >>> Because the combinatorial pattern recognizer asks for >>> a unique signature across many channels. Example (rough): Suppose you can >>> detect a signal in the NIR at .8 microns. It has 32 levels, >>> IOW a crappy signal. That's 2 exp 5. Now suppose you have 8 of these >>> channels. Suddenly, the degree of freedom is 2 exp 40. IOW >>> the signal is more unique, and noise has a harder time jamming. >>> >>> That's the justification for many channels. Now, I wonder what your desire >>> for high speed is. What would you use it for? I looked at the >>> microchip pic24fj128gc010. That can do only 20 MSPS, though. (from memory) >>> OTOH, I have a Tektronix scope that can do 10 GSPS on 4 channels. >>> So I am not aware of ADC chips that fast - It's an interesting problem >>> though - How would you design such a thing? >> http://www.ti.com/tool/adc12d1800rb >> >> Regards, >> John >>> >>> >>> Let's see - 120 MSPS would entail 240 MB/s at 16 bit res. (just for argument >>> here.). That seems well within SATA 3 and USB 3 type rates these days. >>> But this is not a vanilla ADC chip. >>> >>> A SAR-type design (speaking very roughly) will require 240x16x10exp6 >>> comparisons per sec. That's a comparator speed of 4x10exp9 per sec - >>> A comparator can get a speed (realistically) of 10 nanosec. Thats 10 exp 8 >>> comparisons per sec. So 4x10exp9/10exp8 = 40 comparators. >>> >>> Seems doable, but I have shied away from it as being beyond my practicality >>> (and needs) - since I am not skilled in high speed circuit design, as well >>> as >>> the issue of handling and data storage at the CPU level. >>> >>> I estimate that, in order to get that rate, you would have to build a desk >>> top super computer, made up of DSP board multiprocessors. (idea to get away >>> from >>> circuit design.) >>> Then the DSP memory would be connected to 1TB SSD drives to collect data. At >>> this rate, you are going to accumulate a gB in 4 seconds, so a 1TB SSD will >>> be good for >>> an hour of data collection. >>> >>> What do you want this speed for? High speed events? >>> JB >>> >>> >>> >>> On Sat, May 10, 2014 at 3:00 AM, sa_Penguin <soupi...@gmail.com> wrote: >>>> 32 channels is - a lot. At 16-bit, too. On the other hand, the actual >>>> sample rate is quite low: 200K sample/sec >>>> This sounds like the backbone of a 32-channel audio mixing desk. Which is >>>> fine, if that's what you are into... >>>> >>>> Personally, I'd prefer 2 [or even 1] ADC channel, with a MUCH higher sample >>>> rate. Say: 120 M sample/sec. >>>> Sure there are faster ADC's - but original [parallel] ATA cables were rated >>>> to 133MHz, so I'm aiming for a spec >>>> that reduces the need for matching length tracks etc. >>>> >>>> You'd probably need an FPGA to interface that with a Beagleboard, or >>>> Beaglebone Black [my device]. >>>> >>>> -- Alan >>>> >>>> >>>> On Wednesday, 12 May 2010 05:04:07 UTC+9:30, Ben Gamari wrote: >>>>> Hey all, >>>>> >>>>> For those who care, I have drawn up designs for the second iteration of my >>>>> BeagleBoard-based data acquisition platform[1]. >>>>> >>>>> This new design features 32 DAC channels and 32 ADC channels, both with >>>>> 16-bit >>>>> resolution. The ADC sampling rate is a little lower than I would have >>>>> liked >>>>> at 100ksamples/second (with the SPI bus running at 2MHz), but this should >>>>> be >>>>> more than enough for most tasks. The DACs on the other hand can run at up >>>>> to >>>>> 20MHz (limited by the level shifters). Additionally, the board now >>>>> exposes 8 >>>>> GPIO pins behind a level shifter, making it possible to directly interface >>>>> with >>>>> standard 5V TTL levels. >>>>> >>>>> The ADC part I'm using is TI's ADS8344 and the DAC is TI's DAC8568. The >>>>> level >>>>> shifters are TI's TXB0108 and the demultiplexer used for chip select is >>>>> TI's >>>>> SN74AHC139. Altogether, the board is quite expensive. Each of the four >>>>> DACs are >>>>> $25.00 and each of the four ADCs are $10. Thus, a fully populated board is >>>>> about $150 in parts alone. Far more expensive than I was hoping for, but >>>>> it >>>>> seems that these prices are pretty common in the world of converters. >>>>> >>>>> The board is designed to fit on a BeagleBoard XM-style expansion connector >>>>> and >>>>> thus sits beneath the BeagleBoard. >>>>> >>>>> One issue I encountered with the last design[2] was the large in-rush of >>>>> current at startup which seems to cause the BeagleBoard to brown-out. This >>>>> makes it necessary to remove the board while starting up the BeagleBoard. >>>>> While >>>>> I'm not certain of the cause of this, I suspect that the largish filter >>>>> capacitors (330uF IIRC) on the voltage rails might be at least in part to >>>>> blame. Anyone have any thoughts on this? I've reduced the value of these >>>>> to >>>>> 100uF, but it would be nice to have a slightly more certain solution. >>>>> >>>>> If anyone has any comments, I would love to hear them. I think this design >>>>> is >>>>> orders of magnitude better than the original, but there is no doubt still >>>>> room >>>>> for improvement. In particular, I would love to hear suggestions about the >>>>> PCB >>>>> layout. I took some steps to ensure good analog characteristics (e.g. >>>>> maintaining continuity in the ground plane), but I'm sure there are other >>>>> things that could be improved. Moreover, the reference supply is little >>>>> more >>>>> than a RC filter. Is this sufficient or could there be a better option >>>>> here >>>>> (perhaps an active voltage reference or Zener regulator)? >>>>> >>>>> Anyways, I look forward to hearing any feedback that folks have. Thanks >>>>> for >>>>> listening. >>>>> >>>>> Cheers, >>>>> >>>>> - Ben >>>>> >>>>> >>>>> [1] http://goldnerlab.physics.umass.edu/wiki/BeagleBoardDaq >>>>> <http://goldnerlab.physics.umass.edu/wiki/BeagleBoardDaq> >>>>> [2] http://goldnerlab.physics.umass.edu/wiki/BeagleBoardDaq/Version1 >>>>> <http://goldnerlab.physics.umass.edu/wiki/BeagleBoardDaq/Version1> >>>>> >>>>> -- >>>>> You received this message because you are subscribed to the Google Groups >>>>> "Beagle Board" group. >>>>> To post to this group, send email to beagl...@googlegroups.com. >>>>> To unsubscribe from this group, send email to >>>>> beagleboard...@googlegroups.com. >>>>> For more options, visit this group at >>>>> http://groups.google.com/group/beagleboard?hl=en >>>>> <http://groups.google.com/group/beagleboard?hl=en> . >>>>> >>>> -- >>>> For more options, visit http://beagleboard.org/discuss >>>> --- >>>> You received this message because you are subscribed to a topic in the >>>> Google Groups "BeagleBoard" group. >>>> To unsubscribe from this topic, visit >>>> https://groups.google.com/d/topic/beagleboard/TMxuNnQ4zOQ/unsubscribe. >>>> To unsubscribe from this group and all its topics, send an email to >>>> beagleboard+unsubscr...@googlegroups.com. >>>> For more options, visit https://groups.google.com/d/optout. >>> >>> >>> -- >>> For more options, visit http://beagleboard.org/discuss >>> --- >>> You received this message because you are subscribed to the Google Groups >>> "BeagleBoard" group. >>> To unsubscribe from this group and stop receiving emails from it, send an >>> email to beagleboard+unsubscr...@googlegroups.com. >>> >>> For more options, visit https://groups.google.com/d/optout. >> -- >> For more options, visit http://beagleboard.org/discuss >> --- >> You received this message because you are subscribed to a topic in the Google >> Groups "BeagleBoard" group. >> To unsubscribe from this topic, visit >> https://groups.google.com/d/topic/beagleboard/TMxuNnQ4zOQ/unsubscribe. >> To unsubscribe from this group and all its topics, send an email to >> beagleboard+unsubscr...@googlegroups.com. >> For more options, visit https://groups.google.com/d/optout. > > > -- > For more options, visit http://beagleboard.org/discuss > --- > You received this message because you are subscribed to the Google Groups > "BeagleBoard" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to beagleboard+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to beagleboard+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
