[Openec] temperature sensor

[Frieder Ferlemann]

Hi Richard,

Richard A. Smith schrieb:
> Start at the DC power jack and move up until you see the connector for
> the speaker. R363 is just below it.

thanks, found it:)

>> - how does ADC reading translate into degC?
>>   (or preferrably: which part is used and how does it connected to
>> GPIAD0)
> 
> Its a 10k_NTC hooked up in the classic voltage divider setup.
> 
> <Fixed width font>
>   10k ohm          10k NTC
> 3.3V --/\/\/\--|--/\/\/\/--- gnd
>                |
>                |
>              Vout
> 
> </Fixed width font>
> 
> I don't have any data on the beta and whatnot of the NTC. I've asked but
> never got a response.  I suspect the values in the EC code are
> empirically determined.  You will just have to generate the calibration
> curve with data readings of know points.


Ok, I just committed the code with adc reading and interpolated table lookup:
http://dev.laptop.org/git?p=projects/openec;a=blob;f=temperature.c

I arbitrarily picked a curve for an NTC with beta=4100K from an application note.

Press 'c' within the monitor to see the temperature (gives 32degC here) and
'C' to see the interpolation.


We need to know the beta of the NTC. It makes little sense to
invest time into inaccurately measuring the voltages at a subrange of the
temperature span while endangering the XO and still not being sure that this
sample would be representative.

Greetings,

Frieder