cleanup main pt1

fw/ntc.h

@@ -0,0 +1,31 @@
+#ifndef _NTC_H
+#define _NTC_H
+
+#include <stdint.h>
+
+// LUT for converting NTC readings to degrees celsius
+// Nominal: 10kOhm, Beta: 3380, Step: 64
+// TODO: Add a fixed offset to account for toollerances
+const uint8_t ntc_step_size = 64;
+const int16_t ntc_lut[] = {
+	1316, 197, 155, 133, 119, 108, 100, 93, 87, 82, 77, 73, 69, 66, 63, 60,
+	57, 54, 52, 50, 47, 45, 43, 41, 39, 37, 35, 34, 32, 30, 28, 27,
+	25, 23, 22, 20, 19, 17, 15, 14, 12, 11, 9, 7, 6, 4, 2, 0,
+	-1, -3, -5, -7, -9, -11, -14, -16, -19, -22, -25, -28, -32, -38, -44, -55,
+	-55 // extra value to not have an extra if statement
+};
+
+// Convert the raw adc reading to a temperature in celsius with the ntc lut,
+// linearly interpolating between positions
+static inline int16_t get_temp_c(uint16_t adc_reading)
+{
+	if (adc_reading > 4095) return 0;
+	uint8_t index = adc_reading / ntc_step_size;
+	uint8_t remainder = adc_reading % ntc_step_size;
+	int16_t temp_base = index < ntc_step_size ? ntc_lut[index] : 0;
+	int16_t temp_next = ntc_lut[index + 1];
+	return temp_base + ((temp_next - temp_base) * remainder)/ntc_step_size;
+}
+
+
+#endif