[time-nuts] uC ADC resolution (was: Poor man's oven)

[Attila Kinali]

On Tue, 6 Jun 2017 16:43:30 -0700
Chris Albertson <albertson.chris at gmail.com> wrote:

> > . Heck, the STM32F4xx have so much internal noise that the ENOB
> > of their ADC is below 6bit... so low that they even had to write an
> > appnote on how to do averaging to get back to the 12 bits the ADC is
> > spec'ed for. (but don't mention that to an ST sales person, they will
> > hate your guts afterwards).
> >
> 
> Can you actually get back all of those bits? 

No

>  How many samples would you need?

White Gaussian noise goes down with the square root of the number of samples.
1/f^a noise does not average out the same way.

> My current use case for the STM32 ADC is to track battery voltage
> and maybe 6 bits is enough but if I can get to 12 with a software-only fix
> I'll take it.  Batteries volts charge slowly so I'd have time to take many
> samples.   It's a rather mundane application.  Controlling a battery
> powered motor and I can't let theLiPo battery dichange below a limit so I'm
> sampling voltage at 1Hz.   Got a link to or the name of the app note?

Keep in mind that you will need a good voltage reference as well
to reach anything close to 12bit. Your LDO is _not_ a good voltage
reference (depending on type and load/source conditions they vary
eaily by 1-2%... not to talk about their noise)


			Attila Kinali
-- 
You know, the very powerful and the very stupid have one thing in common.
They don't alters their views to fit the facts, they alter the facts to
fit the views, which can be uncomfortable if you happen to be one of the
facts that needs altering.  -- The Doctor