I would have thought there would be enough noise in the system to just over=
sample on the ADC, and add an appropriate number of samples together.

There is an appnote around about doing this to get higher resolution, but I=
 can't remember if it is a Microchip one.

Found it on my drive, it is an Atmel one - "AVR121: Enhancing ADC resolutio=
n by Oversampling". Probably find it as Doc8003 on their website.



> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf
> Of Neil
> Sent: 05 May 2016 15:03
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE] Increasing A/D resolution for low-voltage input signal
>=20
> Ah okay... but I'll have to investigate creating a noise source... which =
I
> believe I can do with a zener.
>=20
> The issue with the op-amp is finding a suitable one in my junk bin.
> Cringing at the thought of paying for overnight shipping for a $0.50 op-a=
mp,
> but I need to get this running this weekend.
>=20
> Will investigate the LED as a clamp.
>=20
> Cheers,
> -Neil
>=20
>=20
>=20
>=20
> On 5/5/2016 3:24 AM, Richard Prosser wrote:
> > 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 signa=
l.
> >> 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.
> >>
> >>
> >> --
> >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> >> View/change your membership options at
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