Re: getting full AD resolution between 2V and 8V

Greetings Vasile,

I am just getting started with the 12F675 A/D. I have 1 channel 
working, but I haven't checked accuracy yet. You mentioned other 
chips "87x ..." Would you care to list specifically those chips that 
you have found working good/better than the 12F675? I have several 
other parts, but the small size of the 12F675 appealed to me. But I 
hope I am not disappointed.

The approach I took was to operate the CPU with the 4 MHZ internal 
clock, but use the SLEEP mode and FRC while doing A/D operation.

I did notice the LSB jumping around, but I thought it was due to my 
poor breadboard, and I don't have a VREF hooked up yet. I was just 
working on the software at this point, later I plan to build a better 
board for the "real" project.

Thank you in advance for any suggestions.

bvwelch

--- In jallist@yahoogroups.com, Vasile Surducan  wrote:
> 
> Nice thought. Will not work exactly as you said (Vref-= Vss and
> Vref+=Vdd/2 as far I remember does not work with 10bit 
resolution)...
> But I'm using a PIC without vref-. :) like PIC12F675.
> BTW, I've discovered much more
> instability and offset in 675 AD than in 87x AD.
> Have anyone got the same conclusions ?
> 
> top 10 wishes,
> Vasile
> 

> 
> 
> On Sun, 29 Jun 2003, a3veyk wrote:
> 
> > How about increasing the resolution by doing this:
> >
> > First measure the signal with vref+=Vdd  and vref-=Vss
> > determine if the value is > Vcc/2
> > if this is true then set vref-= Vdd/2 and Vref+=Vdd
> > else set vref-=Vss and Vref+= Vdd/2
> > measure again, resolution should be increased by 1 bit now
> >
> > Unfortunately you can not select Vref- and leave Vref+ connected
> > to Vdd internally.
> >
> >
> > > And what about 14 bits from just one 10 bit AD-converter ??
> > > Or will it be too slow ;-)
> > >
> > > Stef
> > >
> > > >
> > > >
> >
> >
> >
> >
> >