29 lines
895 B
C
29 lines
895 B
C
#include <math.h>
|
|
#include <stdint.h>
|
|
|
|
#define USE_CALC
|
|
|
|
#ifdef USE_CALC
|
|
#define NTC_A1 0.003354016f // see NTC RT csv from Vishay
|
|
#define NTC_B1 0.000300131f
|
|
#define NTC_C1 5.08516E-06f
|
|
#define NTC_D1 2.18765E-07f
|
|
|
|
#define VREF 3000.0f // 3V
|
|
#define TEMP_CONV 100.0f // 655.35°C max
|
|
#define CELSIUS_TO_KELVIN 273.15f
|
|
#define CELSIUS_TO_KELVIN_SCALED CELSIUS_TO_KELVIN * TEMP_CONV
|
|
|
|
// More efficient (?) calc using:
|
|
// R_T = R_Pullup / (V_REF / ADC - 1)
|
|
// With R_T/R_0 and R_0 = R_T@25C
|
|
// R_T/R_0 = 1 / V_REF / ADC - 1
|
|
|
|
[[gnu::optimize("fast-math")]]
|
|
static inline uint16_t ntc_mv_to_celsius(int16_t adc) {
|
|
float log_ohms = logf(1 / ((VREF / adc) - 1));
|
|
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);
|
|
}
|
|
#else
|
|
// Lookup Table coming soon; not really needed but fun?
|
|
#endif |