piclist 1999\10\19\115138a >
Thread: AD and PIC interfacing problem
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face BY : Chris Fanning email (remove spam text)



> At 11:27 PM 10/18/99 -0400, Sean wrote:
> >How can a non-inverting follower work without at least a negative supply? I
> >interpreted "negative reference" to mean "negative supply" in this case.
> >
> >If we could use an inverting buffer, THEN it wouldn't need a negative
> >supply. However, good luck finding a high enough Rin,
>
> As far as I know, you never need to have bipolar supplies. You just need a
> Vss and a Vdd and a common point in between, typically at the midpoint.
>
> The common voltage becomes the signal ground. The full Vcc becomes the
> 'plus' voltage. The power supply ground becomes the 'minus' voltage.

>From what I can tell, you're suggesting to basically connect one end
of the electrode to 2.5V.  I'd then be running current through the
electrode and I'm not sure that's a good thing...

I found an interesting part in the Burr Brown INA116 differential
amplifier.  Not too cheap but seems ideal for this.  Looks really
easy to use too.  Just get a 2.5V reference, plug in a resistor for
gain and I'm set.  My concern would be ESD with this device though.
Any way to help control ESD across really sensitive inputs?

Unless there's a convincing argument otherwise, I think I'm going to
go with this part instead of DIYing a differential amp with lots of
external parts.

The LMC660 looks like a good cheap part.  I'll probably use that for
non-pH inputs.

Thanks for everyone that replied to help me get this input into a PIC.

Chris

<199910191550.LAA19998@jingoro.prevmed.sunysb.edu> 7bit

In reply to: <4.1.19991019102532.0358c810@mailhub.exis.net> from "Robert A. LaBudde" at "Oct 19, 1999 10:32: 7 am"
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