Jim,
Have you done any analysis to see if the data rate would be=20
sufficient to close your loop at high frequencies?  One thing I have
wondered about is whether the delay produced by these high-resolution
A/Ds is longer than is implied by the sample rate, i.e. is there a
pipeline of data coming through and your output is a few samples
behind the real world.  This could cause stability problems. =20

Actually, it might be worth someone calling up Analog Devices,=20
a friendly applications engineer might have some useful information.

I can only speak for myself, but I'm interested in hearing developments
in this area.

Jack

-----Original Message-----
From: psn-l-request@.............. [mailto:psn-l-request@...............
On Behalf Of James Hannon
Sent: Thursday, April 13, 2006 11:57 AM
To: psn-l@..............
Subject: Re: AD7142 ?

I hope this list does not mind the traffic. This sort of stuff is why I
am on the list.=20
My interest started with Dr Peters posts to the list about his
capacitive seismograph.=20
The parts I have are actually AD7747 which is capacitive and allows one
side of the capacitor to be grounded. I will be hooking the part up to a
DLP2232M http://www.dlpdesign.com/usb/2232m.shtml This will require some
windows software to talk to the AD7747 and log the data but all the
device driver stuff is already done.=20

I have looked into using a DSP for a force feedback system. Have the DSP
do all the feedback calculations etc. I have talked it over with some
DSP experts and we agree it is possible. I am however not sure it is
worth the effort.=20

My current application would not have any feedback and a PC is quite
capable of doing what I need to do with the low frequency signals.=20

My next step is to get some PC board that I can solder the fine pitch
part to so I can hook it up.=20

Jim Hannon=20

---------- Original Message ----------------------------------=20
From: Brett Nordgren =20
Date:  Thu, 13 Apr 2006 11:14:50 -0400=20

>Jim,=20
>=20
>I'll also reply off list, just to keep the noise level down.=20
>=20
>Are you doing your own digital interface to the USB chip?  That's more
than=20
>I'd want to try, but would be interested in what results you get.=20
>It's clear that I need to learn enough about DSP to build something=20
>useful.  Was wondering if perhaps inserting a DSP chip between the
AD7745=20
>and USB adaptor might not have some advantages.=20
>=20
>I keep having the feeling that there's something in this whole approach

>that's waiting to bite us, but so far haven't been able to figure out
what=20
>it might be.=20
>=20
>Good luck,=20
>Brett=20


--
Jim Hannon
http://www.fmtcs.com/web/jmhannon/
42,11.90N,91,39.26W
WB0TXL
--
__________________________________________________________

Public Seismic Network Mailing List (PSN-L)

__________________________________________________________

Public Seismic Network Mailing List (PSN-L)