PSN-L Email List Message

Subject: RE: OP-Amp with ADC only give positive values
From: "Stephen Hammond" shammon1@.............
Date: Tue, 8 May 2012 10:48:08 -0700


Here is an op-amp design by Pete Rowe (here in the group) that works =
very
well. http://pw2.netcom.com/~shammon1/compressed/PSN_PreAmp.jpg  and =
here is
the filter design that goes with it.
http://pw2.netcom.com/~shammon1/compressed/PSN_FilterAmp.jpg=20

Regards, Steve Hammond PSN San Jose =96 Aptos, CA

=20

From: psnlist-request@.............. =
[mailto:psnlist-request@...............
On Behalf Of Tiago A.
Sent: Tuesday, May 08, 2012 9:03 AM
To: psnlist@..............
Subject: OP-Amp with ADC only give positive values

=20

Hi.

I=B4m struggling with this issue for some days:=20
Using a "pickup coil" that i get from a car relay (310ohm), when i =
connect
it directly to the ADC i have positive/negative values, but when i =
connect
the "pickup coil" to a OP-Amp (OPA227) and the ouput from the amp to one =
ADC
inputs i only have positive values.

This is the results with a magnet using OPA227 :
http://dl.dropbox.com/u/15802004/immm.png

Rudimentary schematic (i=B4m not using any kind of resistor/capacitor in =
the
amp)
http://dl.dropbox.com/u/15802004/circ.png

I really wish to use the OPA227 because it=B4s much more responsive than
connecting the "pickup coil" directly to the ADC.


Thanks.













Here is an op-amp design by Pete Rowe (here in the group) = that works very well. http:/= /pw2.netcom.com/~shammon1/compressed/PSN_PreAmp.jpg=A0 and here is the filter design that goes with it. htt= p://pw2.netcom.com/~shammon1/compressed/PSN_FilterAmp.jpg

Regards, Steve Hammond PSN San Jose – Aptos, = CA

 

From:= = psnlist-request@.............. [mailto:psnlist-request@............... On Behalf Of Tiago A.
Sent: Tuesday, May 08, 2012 9:03 AM
To: psnlist@..............
Subject: OP-Amp with ADC only give positive = values

 

Hi.

I=B4m struggling with this issue for some days:
Using a "pickup coil" that i get from a car relay (310ohm), = when i connect it directly to the ADC i have positive/negative values, but when = i connect the "pickup coil" to a OP-Amp (OPA227) and the ouput = from the amp to one ADC inputs i only have positive values.

This is the results with a magnet using OPA227 :
http://dl.dropbox.com/= u/15802004/immm.png

Rudimentary schematic (i=B4m not using any kind of resistor/capacitor in = the amp)
http://dl.dropbox.com/= u/15802004/circ.png

I really wish to use the OPA227 because it=B4s much more responsive than connecting the "pickup coil" directly to the ADC.


Thanks.


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