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From: Joel Koltner on 13 Apr 2008 19:02
"Joerg" <notthisjoergsch(a)removethispacbell.net> wrote in message
news:Hp5Mj.77$I55.60(a)newssvr22.news.prodigy.net...
> david wrote:
>> National Instruments makes good-quality hardware, and excellent software
>> support.
> And it helps to have a bank account similar to Rockefeller's ...

N.I. pricing is in the same ballpark as Agilent and Tektronix... even a
little less in many cases.

But I would agree they're well out of the "hobbyist" price level.


From: Joerg on 13 Apr 2008 20:16
Frank Buss wrote:
> Joerg wrote:
>
>> Gets a lot more expensive though. But it's a good point, you can even
>> buy a LabJack for LAN connection. However, then they are north of $400.
>
> Why is it that expensive? There are nice small modules with integrated ADCs
> and ethernet for $67 :
>
> http://www.emacinc.com/som/somne64.htm
>
> Mounted in a box, it shouldn't cost more than $100.
>

Well, I guess they want to turn a nice profit :-)

The other reason may be that almost everyone (including me) buys the $99
USB LabJack so they have to amortize the NRE for the Ethernet version
over a much smaller number of produced units. Also, it's not a raw
module but it comes in a nice enclosure that can be bolted down to a
panel. It has screw terminals for many the I/O and a D-Sub for some
others. Those things are really practical.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
From: przemek klosowski on 14 Apr 2008 01:21
On Fri, 11 Apr 2008 13:39:07 -0700, Julian Vrieslander wrote:

> I'm looking for a simple data acquisition interface that will run on a
> Linux PC (Fedora Core 6). The requirements are very simple: 24 bits of
> digital output. We need to be able to flip single bits or groups of
> bits without causing glitches on unchanged bits. Data rate is slow -
> maybe one write every 2 milliseconds.

Three USB parallel ports and a minihub? You'd have to check for glitches
but it should work.



--
Przemek Klosowski, Ph.D. <przemek.klosowski at gmail>
From: Frank Buss on 14 Apr 2008 01:47
przemek klosowski wrote:

> On Fri, 11 Apr 2008 13:39:07 -0700, Julian Vrieslander wrote:
>
>> I'm looking for a simple data acquisition interface that will run on a
>> Linux PC (Fedora Core 6). The requirements are very simple: 24 bits of
>> digital output. We need to be able to flip single bits or groups of
>> bits without causing glitches on unchanged bits. Data rate is slow -
>> maybe one write every 2 milliseconds.
>
> Three USB parallel ports and a minihub? You'd have to check for glitches
> but it should work.

USB transfers packets in timeslots of 1 ms. I'm still learning the USB
protocol, but I think if all three USB ports are on the same hub, each
device will be accessed every 3 ms. And Linux is not a realtime system
(without additional work), so if the OS thinks it is a good idea to process
some network traffic, you might lost many milliseconds before the next
update.

--
Frank Buss, fb(a)frank-buss.de
http://www.frank-buss.de, http://www.it4-systems.de
From: panteltje on 14 Apr 2008 05:39
On 11 apr, 22:39, Julian Vrieslander
<julianvREMOVE_THIS_P...(a)u.washington.edu> wrote:
> I'm looking for a simple data acquisition interface that will run on a
> Linux PC (Fedora Core 6). The requirements are very simple: 24 bits of
> digital output. We need to be able to flip single bits or groups of
> bits without causing glitches on unchanged bits. Data rate is slow -
> maybe one write every 2 milliseconds.

On a multitasking OS 2 latency and task switching interrupts will
delay your signal much
more then 2 ms, even on real-time Linux.
If you only need to send every 2 ms that will work, but the data will
arrive very irregular
at the other end, both in case of par port, USB, or Ethernet,

As others mentioned, Ethernet has some advantages, I have a IIM7000A
module (on headers)
here that only cost me 25 Euro or so, including magnetics, it has a
W3100A chip in it.
Connect it to a 8052 (addressing) or perhaps PIC, and you have your
solution.
Source code is available free on the internet.

The simplest way (I do that also) is to connect a few PCF8574 IO
expanders to 3 bits of the par port.
I2C protocol is insensitive to long delays causes by task switching.
Par ports still exist, and it is possible to unload the par port
driver and do direct IO in Linux.


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