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List:       comedi
Subject:    Re: Analog Input Board Recommendations
From:       Tim Holy <holy () pcg ! wustl ! edu>
Date:       2002-11-13 19:57:06
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Hi Calin,

On Wednesday 13 November 2002 12:51 pm, Calin A. Culianu wrote:
> I was just reviewing your email which recommends the 6071E from NI.  At
> any rate, I was wondering how you are doing signal conditioning for 64
> channels?  It seems that all the SCXI stuff NI offers likes to multiplex
> multiple inputs from multiple SCXI modules onto one physical AI channel
> that goes out to your DAQ device.  This means you have to de-multiplex all
> 64 channels in software.
>
> How are you overcoming this problem?  Are you doing your own homegrown
> signal conditioning?  Or are you using SCXI and de-multiplexing in
> software?

I bought a 64-channel amplifier from Multichannel Systems 
(http://www.multichannelsystems.com/). You can pick the gains and cutoff 
frequencies over a fairly large range. My amplifier is not 
software-adjustable (though they do sell one that is), as I find that a 
single set of parameters works well for me. It was something like $4500 and 
is so small it almost fits inside your shirt pocket (not including external 
power supply). I've built single-channel amplifiers that were bigger than 
that...

On input & output this amplifier uses 68-pin SCSI-3 connectors. You do have to 
do a little work to route the signals into the 100-pin connector of the NI 
board. I built a panel box that provides easy access to the digital channels, 
analog output channels, triggers, etc., as well as the 68-pin connector for 
the analog input channels. NI sells a breakout box (SCB100 or some such) that 
I used for this purpose, but if I were to do it again I would design a 
printed circuit board, so that I could build 2 or 3 setups with little extra 
effort. If you decide to go this route, let me know and maybe we can 
collaborate on a design.

Best,
--Tim

>
> Thanks for any help offered..
>
> -Calin
>
> On Wed, 2 Oct 2002, Tim Holy wrote:
> > Hi Calin,
> >
> > I use a NI PCI-6071E board to do 64 channel acquisition, 10kHz per
> > channel, to record spike waveforms from neurons. (It's only 12-bit, so it
> > may not be the board for you.) While the board specs say it can do
> > 1.25MS/s, implying that we could do almost 20kHz/channel, the errors due
> > to finite settling-time increase when we go that fast. NI is very
> > straightforward about this point in their specs and (with the tiny bit of
> > checking I've done) seem to be accurate in their measurement of the
> > errors as a function of scan rate. I certainly wouldn't shy away from
> > paying the extra $500 if it turns out to be the better board (I don't
> > know if it is, since I haven't tried any MC boards). Compare it to the
> > lost labor [& pigs :-)] for corrupt data.
> >
> > Your signals are well-buffered, right? I've occasionally seen weird
> > things with the multiplexer putting junk back on the channel when using
> > e.g. just a transistor to buffer signals.


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