Thank's Thys but my problem is to simplify the hardware.
You have right, if 0...5V is 1024 bites 10mV is 2.048 bit.
But this is right only if the input signal is scaled from 0 to 5V
I don't want to scale usind OA the output of lm35.
This tehnique I've used for interface the lm35 with oldest 7107
http://www.geocities.com/vsurducan/4temp.htm
I was thinking to the same method with pic, changing both references
at desired values.
But my test shows it wouldn't work.
Or probably we talking about different versions of LM35 ?
Vasile


On Wed, 7 Feb 2001, Thys Van Tonder wrote:

> Vasile
>=20
> The LM35 gives you an output of 10mV/=B0C so you do not have to convert K=
elvin
> to Celcius. So
> you get 2 bits/=B0C. If you use a opamp X5 you get 50mV/=B0C and 5v at 10=
0=B0C
> (Maybe X5 is a bit too match) The code can do the rest.
> Hope it helps you?
>=20
> Thys
>=20
>=20
>=20
> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Vasile Surducan
> Sent: 07 February 2001 02:50
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [PIC]: LM335
>=20
>=20
> Thys, can you tell me how do you scale the output signal of LM35 to obtai=
n
> full AD pic resolution and how do you convert for displaing celcius
> degrees. AT 0C LM35 output is about 2.7315V and depends of biasing
> current. At 100C will be about 3.73V For a 0..5V AD input, probably you
> need a diferential amplifier or for a pic16F877 to set -ref at 2.73 and
> +ref at 3.73 but in this case you will not have 10 bit AD resolution.
> Is there any more simple method to do that without external amplifiers
> and of course without any one wire or i2c temperature measurement devices=
=2E
> Thank's very much,
> Vasile
>=20
>=20
> On Wed, 7 Feb 2001, Thys Van Tonder wrote:
>=20
> > Hi there Peter
> >
> > The LM335 gives you 10mV/=B0K. So you better use shielded cable. I used=
 the
> > LM35 with about 4m
> > of cable and it worked fine for our application, a bit of switching noi=
se
> > from the motors we were probing. You can average out your reading in th=
e
> > software.
> >
> > Regards
> > Thys
> >
> > -----Original Message-----
> > From: pic microcontroller discussion list
> > [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Peter May
> > Sent: 07 February 2001 08:13
> > To: PICLIST@MITVMA.MIT.EDU
> > Subject: [PIC]: LM335
> > Importance: Low
> >
> >
> > I gave up on the DS18S20's and went to a simple LM335. It says in the d=
ata
> > sheet I can run a long cable to it and use it remotely. In the finished
> > product it will be within a couple of inches of the PIC but for bench
> > testing I want about 20 feet of cable. Would this introduce much noise
> into
> > the analogue input?
> >
> > --
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