michael brown wrote:
> Crist=F3v=E3o Dalla Costa wrote:
>
>   =

>> Yes, a problem with the PIC's hardware. Maybe it's just the
>> particular PIC I'm using. But I don't think that it's a problem with
>> my hardware since I plugged in a 16 bit AD from Analog Devices and it
>> has just about 1 lsb noise, and the PIC's 10 bit AD has at least two.
>>     =

>
>
> I have used a 16F88 on a solderless breadboard to measure and log temps =

> from an LM34.  I didn't sleep during the conversion and I still had no =

> trouble obtaining consistant 10 bit readings.  I used an external Vref =

> that was simply a variable resistor and a filter cap.  1.024V well =

> outside the minimum allowed by the datasheet ;-), but hey I wanted .1 =

> degree resolution so I needed 1mV resolution in the ADC.  Seemed to work =

> just fine.
>
> I don't think you should see that kind of noise in your readings, unless =

> you have it in your power supply as well. =

>
>   =

Yes, I have had no trouble either. To REALLY get an absolute reading, =

sum 8 readings then divide them by 8
(shift right three times). This is- in effect- a way to cancel noise =

out, as one  sample might be taken below the value,
another time above the value.

The biggest problem people have with PIC's ADC is that they don't allow =

the input sampling cap to charge up
properly before they  take the measurement.  If the impedance on the PIN =

is high (> 5K) then you might need
5ms  before the input cap can obtain a reliable sample.

--Bob
-- =

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