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.