On Thursday 20 October 2016 10:56 PM, Paweł Jarosz wrote:
It is Negative Coefficient Thermistor (NCT) and so adc reads are
different.
Lower temp gives higher value.
So table should be
<7000 10
9000 8>;
temp1 = gti->lookup_table[2 * i];
temp2 = gti->lookup_table[2 * i - 2];
and then use in following equation.
adc_hi = gti->lookup_table[2 * i - 1];
adc_lo = gti->lookup_table[2 * i + 1];
temp = gti->lookup_table[2 * i];
temp -= (val - adc_lo) * (temp1 - temp2) / (adc_hi - adc_lo);
val = 9
adc_hi = 10
adc_lo = 8
temp = 9000 - (9 - 8)*(7000 - 9000)/(10 - 8)
temp = 9000 - (1)*(-2000)/(2)
temp = 9000 - (-1000) = 10000
still wrong ... temp for val = 9 should be 8000
Your temp1 and temp2 calculation is something wrong.
temp1 = gti->lookup_table[2 * i];
temp2 = gti->lookup_table[2 * i - 2];
so temp1 = 9000, temp2 = 7000
temp -= (val - adc_lo) * (temp1 - temp2) / (adc_hi - adc_lo);
temp = 9000 - (9 - 8)*(9000 - 7000)/(10 - 8)
temp = 9000 - (1)*(2000)/(2) = 8000 which is expected.
Maybe we could leave this patch as it is?
temp = gti->lookup_table[2 * i];
+ tlow = gti->lookup_table[2 * i - 2];
(modify) temp -= (val - adc_lo) * (temp - tlow) / (adc_hi - adc_lo);
This will gives you correct result.
Let me know if you can send the updated patch. Else I will send.
Thanks,
Laxman
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