LM35DZ reading

[Ttelmah]

To get 0.1C readability, you would need to use an external Vref of say
3.072v and add an op-amp amplifier to the output of the sensor giving
*3 gain. You'd then have a step size on the ADC of

3.072/1024 = 3mV/step

and an output from the amplified sensor of 30mV/C

[temtronic]

You'll need to take several readings and average them, that's why I suggested the 'Olympic averaging' method. it's easy to implement and fast. There are 100's of ways to get 'precise' readings but 'temperature' is generally a 'slow' moving measurement, so you can take 10 readings and consider them 'one' reading. My energy control systems did this, once every 15 seconds THEN took whatever action was needed. You do NOT want to rely upon only one reading !
A lot depends upon the 'project' and the 'goals' of what is required. The LM35 a reliable, stable, slow response devices, which should have a 'calibration' done if you want 'accuracy'. (ie: that 21*C read IS the actual 21*C room temperature). Each LM35 is slightly different response,even within 'batches' of them. Connect 2 to the PIC's ADC and sample 1000 times displaying the raw data (ADC bits), they will NOT be identical....

[MCUprogrammer]

What I don't understand is if VREF_1v024 doesn't work, isn't it unreasonable for them to put it as a feature inside the processor? Here I solved the problem. It didn't work because I made an installation mistake. It's working fine now.
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MCUprogrammer
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[Ttelmah]

Multiple things here.

All ADC's have minimum working voltages for their full resolution. In the
case of the older PIC ADC's (yours is an old chip), this is typically about 2.5v.
So pointless to even think about working with a 1.024v reference.
Many of the newer chips support a range down to about 2v, and a few
support down to perhaps 1.5v. However I don't think any will work down
to 1.024v.

Second thing though you could get a step size 1/4 the existing ADC, by
switching to a chip with a 12bit ADC. Some of the very oldest chips have
these and a lot of the newer chips.

Third thing though you can't have an option to specify the ADC Vref in
your chip, since it does not have a built in Vref to give this. You can't
specify a reference voltage, since there is not a reference to give
this. You can only select the supply, or an external Vref.

Even on chips that do have a reference, you would not get the accuracy
needed, since the internal Vref will not be that accurate. Understand that
really accurate Vref's are expensive chips. They need a huge amount of
laser trimming as part of the manufacture. Not economic to build such
a device into a cheap chip like a PIC. A 0.05% Vref, will typically cost
at least five times what a PIC costs.

PIC ADC's in general are 'general purpose' ADC's not high precision
devices.

Have a look at some prices for the LTZ1000, if you want to see a Vref
suitable for say a 14bit ADC. The reason it is wire leaded is otherwise
mechanical stresses into the unit will degrade the accuracy.

[MCUprogrammer]

Ttelmah and temtronic are very important to me. I take them all seriously. And I will try.
_________________
Best Regards...
MCUprogrammer
_______________________________
Work Hard