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 > [2] 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 [email protected]<javascript:>. > > To unsubscribe from this group, send email to > [email protected] <javascript:>. > For more options, visit this group at > 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 the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
