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Discussion Groups | Piclist | hi ned to sense 1mV by an 16F877

A discussion group for the PICMicro microcontroller. Also called the Microchip PIC, this list is dedicated to the use and abuse of this fine, simple, microcontroller. Close to topic posts are welcome, ie. general electronics.

hi ned to sense 1mV by an 16F877 - R Ramesh - Nov 12 0:24:00 2003

Hi all
I m using 16F877. I need to sense 1mV changes  input variation . But I coundnot.
Because 5V/ 1024 = 0.004V per bit. Is there anyway to sense 1mV by 16F877.
Thx
Ramesh


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Re: hi ned to sense 1mV by an 16F877 - rtstofer - Nov 12 0:26:00 2003

Not over the entire 5V range. If you don't need the entire 5V range
then use an op amp (or two) to rescale and amplify the signal. If
you do need the range then you can use an external 12 or 14 bit A/D
converter.

--- In , R Ramesh <ramesh_21_in@y...> wrote:
> Hi all
> I m using 16F877. I need to sense 1mV changes input variation .
But I coundnot.
> Because 5V/ 1024 = 0.004V per bit. Is there anyway to sense 1mV by
16F877.
> Thx
> Ramesh > ---------------------------------
>





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Re: hi ned to sense 1mV by an 16F877 - Dave Mucha - Nov 12 1:37:00 2003

very true, but don't forget that a 4096 count ADC will read 4096
counts, but not offer 1mv changes since it has a error of +/- 1 count
so in reality, it is within 3mv. you would need to be 4 times more
accurate than your desired accuracy to claim to have a valid reading
of the 1mv.

Also, monitor the board voltage and correct for errors there too.

is it Metrabite or Keithly-Metrabite that offers a free book on how
to read low voltage signals ?

Dave --- In , "rtstofer" <rstofer@p...> wrote:
> Not over the entire 5V range. If you don't need the entire 5V
range
> then use an op amp (or two) to rescale and amplify the signal. If
> you do need the range then you can use an external 12 or 14 bit A/D
> converter.
>
> --- In , R Ramesh <ramesh_21_in@y...> wrote:
> > Hi all
> > I m using 16F877. I need to sense 1mV changes input variation .
> But I coundnot.
> > Because 5V/ 1024 = 0.004V per bit. Is there anyway to sense 1mV
by
> 16F877.
> > Thx
> > Ramesh
> >
> >
> > ---------------------------------
> >




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Re: hi ned to sense 1mV by an 16F877 - Scott Lee - Nov 12 2:13:00 2003

--- In , "rtstofer" <rstofer@p...> wrote:
> Not over the entire 5V range. If you don't need the entire 5V
range
> then use an op amp (or two) to rescale and amplify the signal. If
> you do need the range then you can use an external 12 or 14 bit
A/D
> converter.

If you don't need the entire 5V range then I have one word to say --
"Vref". If you don't know what I'm talking about read the A/D
portion of the datasheet. Basically you don't need to have the
range of readings reflect 0-5V.

Comments previously made regarding accuracy still apply. However if
the required operating range is small enough then using Vref might
make the built in 10bit A/D more than sufficient.

--Scott




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Re: Re: hi ned to sense 1mV by an 16F877 - Milton Medicinteknik KB - Nov 12 4:39:00 2003

Hi

... also...

there is a 4.096 ref available that only requres 5 V input. Great
device: MAX 6141 !

Also - as you turn on the AD - clear the ADIF flag first, run the AD
and set let the Pic SLEEP. This reduces noice. As ADIF rises when
Analog value is taken, the Pic wakes up (not necessarily from an
interrupt). Then -- read values.
> --- In , "rtstofer" <rstofer@p...> wrote:
> > Not over the entire 5V range. If you don't need the entire 5V
> range
> > then use an op amp (or two) to rescale and amplify the signal. If
> > you do need the range then you can use an external 12 or 14 bit
> A/D
> > converter.
>
> If you don't need the entire 5V range then I have one word to say --
> "Vref". If you don't know what I'm talking about read the A/D
> portion of the datasheet. Basically you don't need to have the
> range of readings reflect 0-5V.
>
> Comments previously made regarding accuracy still apply. However if
> the required operating range is small enough then using Vref might
> make the built in 10bit A/D more than sufficient.
>
> --Scott > ------------------------ Yahoo! Groups Sponsor ---------------------~-
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Re: hi ned to sense 1mV by an 16F877 - bg3009 - Nov 12 11:24:00 2003

If he is talking about 1024, then he is talking about the ADC. The
best way is to amplify the signal, and then feed it. Giving it a Vref
means you dont have to amplify the signal too much. Amplification
would mean u reduce the signal-to-noise ratio. Even with a 1V signal,
u get plenty of resolution which I think should be fine.

--- In , "Scott Lee" <midl_man@y...> wrote:
> --- In , "rtstofer" <rstofer@p...> wrote:
> > Not over the entire 5V range. If you don't need the entire 5V
> range
> > then use an op amp (or two) to rescale and amplify the signal.
If
> > you do need the range then you can use an external 12 or 14 bit
> A/D
> > converter.
>
> If you don't need the entire 5V range then I have one word to say --
> "Vref". If you don't know what I'm talking about read the A/D
> portion of the datasheet. Basically you don't need to have the
> range of readings reflect 0-5V.
>
> Comments previously made regarding accuracy still apply. However
if
> the required operating range is small enough then using Vref might
> make the built in 10bit A/D more than sufficient.
>
> --Scott




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Re: hi ned to sense 1mV by an 16F877 - Dave Mucha - Nov 12 12:03:00 2003

--- In , "bg3009" <bg3009@y...> wrote:
> If he is talking about 1024, then he is talking about the ADC. The
> best way is to amplify the signal, and then feed it. Giving it a
Vref
> means you dont have to amplify the signal too much. Amplification
> would mean u reduce the signal-to-noise ratio. can you elaborate ? I thought that if the signal was noisy, an amp
would increase everything ? Dave




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Re: Re: hi ned to sense 1mV by an 16F877 - amir hossini - Nov 12 20:08:00 2003

hi
de..
please .PLC  NO  PIC 
HOWEVER   THANKS.
PLEASE  DONT  SEND EMAIL




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