[TriEmbed] ATTiny84A internal temp sensor: how good?

[Scott Hall]

On 01/28/2014 01:08 PM, Pete Soper wrote:
> On 01/27/2014 11:47 PM, Scott Hall wrote:
>> Are you trying to use it to measure atmospheric temperatures?  It was
>> designed to measure chip temperature, to help you program a shutdown or
>> minimizing sequence before the magic smoke comes out.  At work last year we
>> used it to activate a peizo cooling element as needed, but minimized
>> activation for longer battery life.  We always used an external sensor for
>> environmental conditions.
> I'm trying to understand how calibration relates to the accuracy of this
> sensor and the 84A datasheet is worthless for that. Ron Craig pointed me to
> exactly the right Atmel app note <http://www.atmel.com/images/doc8108.pdf>
> that makes it clear that the sensor isn't at all linear and to get to +/- 2C
> takes a pair of calibration points for *each* span of 10-20 degrees across the
> range of interest. I would have guessed that support for temperature
> compensation is the aim of this kind of sensor in this kind of chip.
>
> -Pete

You just rang a big bell: I remember that from work last year -- we had a table
of 16 data points for calibration from -20°C to +55°C for our main temperature
sensor.  And similar tables to adjust CO_2 , humidity and pressure sensors.  I
forgot about it because by the time I had to deal with the data, values were
already converted to °F, percent relative, parts per million, and millibars Hg.

-- 
Scott G. Hall
Raleigh, NC, USA
ScottGHall1 at GMail.Com

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