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