Sorry, don't agree on that the output is independant of supply voltage.
The output of a Wheatstone-bridge is /proportional/ to the supply
voltage. The sensitivity is usually given as=20

mv(bridge diff. output)/V(bridge exitation voltage)/kPa(physical
property, e.g. pressure)

Regards
St=E5le Freyer



/*  St=E5le Freyer                 mailto: staale.freyer@tn.his.no
  Stavanger University College, POB 8002, N-4068 Stavanger    *
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-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Michael Rigby-Jones
Sent: Wednesday, April 09, 2003 10:48 AM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC]:A/D problem w/16F877 - reduced range (Vref+/-)


> -----Original Message-----
> From: St=E5le Freyer [SMTP:staale.freyer@TN.HIS.NO]
> Sent: Wednesday, April 09, 2003 9:16 AM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      [PIC]:A/D problem w/16F877 - reduced range (Vref+/-)
>=20
> My application measures a pressure via a Wheatstone-bridge; the result

> is reliant of the battery voltage, and with the battery also connected

> to vref+/-, the system "auto calibrates".
>=20
The output from a wheatstone bridge is differential and is inherently
independant of supply voltage.

Mike


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