29 lines
942 B
C
29 lines
942 B
C
#include <math.h>
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#include <stdint.h>
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#define USE_CALC
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#ifdef USE_CALC
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#define NTC_A1 0.003354016f // see NTC RT csv from Vishay
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#define NTC_B1 0.000300131f
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#define NTC_C1 5.08516E-06f
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#define NTC_D1 2.18765E-07f
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#define VREF 3000.0f // 3V
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#define TEMP_CONV 1000.0f // 65.535°C max; maybe 100 for better safety against overflow
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#define CELSIUS_TO_KELVIN 273.15f
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#define CELSIUS_TO_KELVIN_SCALED CELSIUS_TO_KELVIN * TEMP_CONV
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// More efficient (?) calc using:
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// R_T = R_Pullup / (V_REF / ADC - 1)
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// With R_T/R_0 and R_0 = R_T@25C
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// R_T/R_0 = 1 / V_REF / ADC - 1
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[[gnu::optimize("fast-math")]]
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static inline uint16_t ntc_mv_to_celsius(int16_t adc) {
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float log_ohms = logf(1 / ((VREF / adc) - 1));
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return (uint16_t) (TEMP_CONV / (NTC_A1 + NTC_B1 * log_ohms + NTC_C1 * log_ohms * log_ohms + NTC_D1 * log_ohms * log_ohms * log_ohms) - CELSIUS_TO_KELVIN_SCALED);
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}
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#else
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// Lookup Table coming soon; not really needed but fun?
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#endif |