Well, I found my first mistake.  I trusted someone else's drawing.  The datasheet
calls for about a 5K not a 50K for the correct amplification of this baro sensor.  Now
to figure out why it's going the wrong way.  I am sure if I keep reading.  Thank
goodness for Hooked on Phonics!  Perhaps reversing the inputs would be more meaningful
now.


Alice Campbell wrote:

> Date sent:              Tue, 1 Feb 2000 11:18:22 -0700
> Send reply to:          pic microcontroller discussion list <PICLIST@MITVMA.MIT.EDU>
> From:                   Greg Hartung <ghartung@ADT.COM>
> Subject:                Re: OT: pressure sensor -> PIC
> To:                     PICLIST@MITVMA.MIT.EDU
>
> um, what happens when you connect vref on inamp to vcc instead
> of ground??
>
> alice
>
> >    I finally got the AD working and the input from this circuit fluctuates 20%
> > also.
> >    I can't believe I'm doing ASCII art, but I'm desperate...
> >    Thanks
> >    When I try reversing Out- and Out+, the output voltage still hovers around 1V
> > from the amp at atmospheric pressure, but it won't go up or down under a vacuum.
> >
> >
> >                         47K
> >   SX15             ___/\/\/\____
> >  _______          |   _______   |
> > |   Out-|______   |__|Rg   Rg|__|
> > |   Vdd |__Vcc |_____|In- Vdd|____Vcc
> > |   Out+|____________|In+  Vo|____to PIC AN1
> > |   Gnd |____________|Gnd Ref|____
> > |_______|     |      |_______|    |
> >               |        INA122     |
> >              Gnd                 Gnd
> >
> >
> >
> > Tom Handley wrote:
> >
> > >    Greg, I've used SenSym's SCX series absolute sensors in a PIC-based
> > > barometer (interfaced to an AD620 IA). If you are using an absolute sensor,
> > > the polarity is reversed. As far as your results below, the output is biased
> > > between ground and your bridge excitation voltage or whatever the voltage is
> > > at the top of the bridge. The output increases with pressure. I would have
> > > to see your circuit to be of further help.
> > >
> > >    - Tom
> > >
> > > At 08:16 AM 1/31/00 -0700, Greg Hartung wrote:
> > > >   I guess I should've mentioned that I tried that.  The voltage was at about
> > > >1v and would rise to about 2.5v.  Proper output should be about 4.5v dropping
> > > >to about 2.5v, but even reversed it still started at 1v.  By "starting", I
> > > >mean atmospheric pressure.
> > > >
> > > >Wagner Lipnharski wrote:
> > > >
> > > >> I think the subject is of general interest to the list.
> > > >> Just reverse the polarity of the sensor output or the INA122 inputs.
> > > >> Wagner.
> > > >>
> > > >> Greg Hartung wrote:
> > > >> >
> > > >> >    I know this is way off topic, but it really has quite a bit to do
> > > >> > with my last coupla posts...  I am trying to connect a sensym baro
> > > >> > sensor to an F877 thru a BurrBrown INA122 instrument amp, and it appears
> > > >> > to inverting my voltage so that when pressure goes up, the voltage goes
> > > >> > down.  Anyone with any experience in this area could e-mail offlist...
> > > >> > Thanks.
> > >
> > > ------------------------------------------------------------------------
> > > Tom Handley
> > > New Age Communications
> > > Since '75 before "New Age" and no one around here is waiting for UFOs ;-)
> >