Thanks Chris,
Yes, it (they) are bridge style, some have + swing, others both + and
- swing.  I'm trying to follow your description with my feeble brain,
but im not sure what a servo setup is.   Because of the millivolt
levels  out of the bridge, i still need some amplification to get the
signal into the range the adc0831 can read.  yes,
i will put in a better adc once i understand what im doing.  I rather
suspect that the wobbly voltage will turn the readings to mush but
its easy enough to put together on the breadboard and see.

I like the idea of using the pic to generate the voltage for
the bridge, and maybe the amp, yet still let the rest of the circuit
use lower voltage.  i am already controlling power to the peripherals
with the pic and i still have 2 free pins on port b.  anything to
squeeze a bit more out of the batteries...


alice

>
> Ah! you want to drive a pressure transducer.  Is it a bridge style?  And you h
ave
> a 1.5V rail?  Why not connect the + on the transducer to the rail and generate
 a
> negative on the - side?  If you use an op-amp in a servo setup, you could driv
e
> the - terminal until one of the return terminals is regulated to 0VDC, and the
> other terminal would then be a ground referenced signal.  Linear Technology (r
ef
> Jim Williams, bridge transducer circuits) is fond of these methods.  If you st
ep
> up to 3V, you would have to deal with a 1.5V common mode with a 1.5V rail, whi
ch
> is ugly.  With the ground reference, you can then avoid an instrumentation
> amplifier.  If you need to measure bipolar signals, you could be in the thick
of
> it again, as your PIC HATES any negative voltages on an analog pin.  Whacks th
e
> other analog readings REAL fast.  Would this circuit have poor performance in
> light of the total V applied to the sensor varying?  Do you have to use a brid
ge
> with four varying elements to avoid this?  Hmm...
>
> Chris Eddy
> Pioneer Microsystems, Inc.
>
> Alice Campbell wrote:
>
> > > Date:          Mon, 8 Nov 1999 17:26:08 -0500
> > > Reply-to:      pic microcontroller discussion list <PICLIST@MITVMA.MIT.EDU
>
> > > From:          Wagner Lipnharski <wagnerl@EARTHLINK.NET>
> > > Organization:  UST Research Inc.
> > > Subject:       Re: [OT] Ringing Chokes and batteries
> > > To:            PICLIST@MITVMA.MIT.EDU
> >
> > Well, i'm about to replace the 9v battery in my datalogger with two
> > AA 1.5v and a stepper to 5v, but i was curious how they worked, and
> > wanted to see for mysef.  I've been messing with switched capacitor
> > circuits, and saw the inductor circuit, but couldnt get it to work.
> > Then i wondered if i could run it at 3v, stepped up from 1.5v, and
> > let the pressure transducer work ratiometrically. The pressure sensor
> > only pulls a few mA, the pic and adc and memory chip only a few mA.
> > The problem with the switched cap design is the oscillator part, the
> > self-oscillation of the coil looked nicer.
> >
> > alice
> >
> > > Hello dear Alice, looking for a small step up conversion circuit?
> > > What are you trying to power up?
> > > What is the input and output Voltage x Current?
> > > :)
> > >
> > .
>