Hi Neil,

You can add dither (noise) to the wanted signal and then average the
results to give intermediate steps. Generally OK for a couple of bits
of extra resolution.

Low voltage zeners tend to have a fairly soft turn on point - not what
you want. You may even find a LED of the right type could be better,
or a string of  std. diodes. Better again might be an opamp to clamp
the maximum level. (And amplifiy).

RP


On 5 May 2016 at 17:53, Neil <picdude3@narwani.org> wrote:
> Hi all,
>
> I'm looking for a way to get more resolution on a PIC32 A/D input (I'll
> actually be using a Chipkit board) for a low-voltage input signal.
> Official spec =3D as good as I can get it (in limited time). The
> sensor/amp puts out a 0-10V signal for 0-to-10 Kg force, but I only need
> to measure about 0 to 0.5kg (up to 0.5V), so only 5% of the full range.
> Voltage-dividing the signal reduces the resolution/range, so I'll
> protect the A/D input with a zener to clamp the signal instead.
>
> Now, with a 2V external reference (lowest allowed by datasheet), 0 to
> 0.5V nets only 8-bit resolution.  I'd really like to get better. Other
> than adding an op-amp into the circuit, is there any other trick to bump
> the resolution up?
>
> If I do happen to have a workable op-amp on hand (though I doubt) to
> amplify the signal x4, I know that the zener will affect the linearity
> of the signal as it gets close to the zener voltage, but would a 3-ish
> volt zener cause any noticeable error at around 2V? Or is there some
> parameter that indicates that a zener would have a "sharper" knee?
>
> Cheers,
> -Neil.
>
>
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