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'[PIC]A2D Vref Diode'
2006\10\03@150426 by genome

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hello,
Anybody can recommend 3 volt Vref Diode.. I cant use a 2.5volt such as
LM336BZ-2.5 as the datasheet for pic18f242 says:
(VREFH - VREFL) must be minimum of 3V when Vdd >= 3V..
is this correct as I've heard on other PICS its 2.5volts.. maybe I could use
a zener but unfortunately I could not find any zeners here that has 1%
tolerance..

thanks..



2006\10\03@155226 by David VanHorn

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On 10/3/06, genome <spam_OUTjtroxasTakeThisOuTspamgmail.com> wrote:
>
> hello,
> Anybody can recommend 3 volt Vref Diode.. I cant use a 2.5volt such as
> LM336BZ-2.5 as the datasheet for pic18f242 says:
> (VREFH - VREFL) must be minimum of 3V when Vdd >= 3V..
> is this correct as I've heard on other PICS its 2.5volts.. maybe I could
> use
> a zener but unfortunately I could not find any zeners here that has 1%
> tolerance..


Your VCC is probably at least that accurate.

2006\10\03@162506 by genome

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I'am trying to match 0.5-1.05 volt sensor output using a single supply opamp
to a 0.05-3volt references.. the 0.05trim is to acount for the opamp output
not being able to swing exactly to the voltage level on its powerrails..
i.e. I'm using a virtual ground..

> Your VCC is probably at least that accurate.

I dont want to waste a2d counts as I need to have good A2D resolution so I
cant exactly use the VCc as a reference. If I simply use 0-1volt sensor
output and amplfy it to 0-5volts.. I would be losing counts and will not be
able to detect voltages close to 5volts and 0volts as I know of no opamp
that can swing to their rail voltages.. even those rail-rail opamps cant do
that..

thanks..

"David VanHorn" <.....dvanhornKILLspamspam@spam@microbrix.com> wrote in message
news:25b178740610031250n66006c55u996ef14d8d1bbc67spamKILLspammail.gmail.com...> {Quote hidden}

> --

2006\10\04@012557 by Vasile Surducan

face picon face
16F series need somewhere between 2.5V to 2.8V.
I doubt 18F philosophy on AD is different.
The best choice could be a 3V linear regulator which gives you both
the supply and the reference. Like LT1763-3 ?

Vasile

On 10/3/06, genome <EraseMEjtroxasspam_OUTspamTakeThisOuTgmail.com> wrote:
{Quote hidden}

> -

2006\10\04@030757 by genome
picon face
will it posible be posible to just amplify 2.5volt refrence to 3volts using
an opamp.. If I do it this way will it not be unstable and susceptible to
logic load noise.. anybody did somthing like this..

thanks..

"Vasile Surducan" <piclist9spamspam_OUTgmail.com> wrote in message
news:@spam@5eeda4c20610032225k7d0f1b0bta4c7c1b24c2e7871KILLspamspammail.gmail.com...> {Quote hidden}

>> --

2006\10\04@033000 by Mark Rages

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On 10/4/06, genome <RemoveMEjtroxasTakeThisOuTspamgmail.com> wrote:
> will it posible be posible to just amplify 2.5volt refrence to 3volts using
> an opamp.. If I do it this way will it not be unstable and susceptible to
> logic load noise.. anybody did somthing like this..
>
> thanks..
>

This will work fine.  You can even buy a precision reference and
amplifier combined in the same package. This combination is called a
"linear regulator."

Regards,
Mark
markrages@gmail
--
You think that it is a secret, but it never has been one.
 - fortune cookie

2006\10\04@041547 by Alan B. Pearce

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> Anybody can recommend 3 volt Vref Diode..

Use an LM317L and two resistors ... You should be able to set it up much
more accurate than 1% by resistor selection or trimming.

2006\10\04@045932 by Mohit M. (Lists)

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I am not sure if this will help you...

Connect the 2.5V reference to any AD pin. Take a reading. Use this as
a reference standard.

Lets say, your AD reads 500 (0x1F4) for 2.5V reference. At another AD
pin, if you get a reading of 1000 (0x3E8), the input is 5.0V.

HTH,
Mohit.

{Original Message removed}

2006\10\04@092913 by Russell McMahon

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face
> You can even buy a precision reference and
> amplifier combined in the same package. This combination is called a
> "linear regulator."

For some outlying values of the set [precision].


   Russell

2006\10\04@092914 by Russell McMahon

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flavicon
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> able to detect voltages close to 5volts and 0volts as I know of no
> opamp that can swing to their rail voltages.. even those rail-rail
> opamps cant do that..

Some r-r opamps have inbuilt power supply inverters to give them
internal rails greater than rail so they can do the impossible.  You
can often do the same yourself if you don't mind being naughty or
clever by having some dropping resistance in the supply or using
voltage upstream of the regulator. Applicability varies with
application.


       Russell

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