[oopic] Re: Signal levels for a2d objects

--- In oopic@yahoogroups.com, "Mike Smith" <msmith@...> wrote:
>
> I recently picked up a sensor that converts air pressure to voltage
> differential. You give the input leads a GND and a +5v, connect it
> to an air pressure line in the 0-3000 PSI range, and it produces a
> voltage differential on the output lines in the 3m-50mv range.
>
> I was hoping to be able to use this with my OOPic-R, but I'm
> concerned that the voltage diff may be too small for the OOPic to
> detect. I have the negative output of the sensor connected to line 3
> and am using the oA2D.ExtVRef2=1 so that it is used for the negative
> voltage reference. For now I have the postive refence just being +5v
> (oA2D.ExtVRef=0), but if I could find a suitable 50mv source I could
> set that to 1 and connect that source to I/O line 4. For now, it
> doesn't seem to be enough voltage to register.
>
> Any thoughts on whether this low of voltage can be used with oA2D?
>
> If not, does anyone know of any chips out there that could take a 0-
> 50mv range and amplify it to a level that would work better with the
> OOPic's A2D?
>
> Thanks,
> Mike
>

When you say 'differential' are you implying the output comes on two
leads independent of ground? Or is this just a single output that
varies between 3 mV and 50 mV? How about a link to the sensor datasheet?

If it is a single ended output, you can increase it with an op amp set
for a gain of 100 (50 mV * 100 = 5V).

Look at Chapter 4 of "Op Amps For Everyone" free at
http://www.ti.com/litv/pdf/slod006b

I really like the TLV247x series
of devices and use the TLV2474 when I want to offset, scale and buffer
a signal.

And the book is excellent!

Richard

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