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Calculate temperature from thermistor resistance

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This commit is contained in:
Leon Krieg
2024-09-15 20:09:57 +02:00
parent ccbd964111
commit 1cc319cd38
3 changed files with 38 additions and 13 deletions
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27
src/bus/i2c.c
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@@ -2,7 +2,9 @@
#include "bus/i2c.h"
#include <avr/io.h>
#include <math.h>
// I2C status flags
#define TW_START 0x08 // Start condition transmitted
#define TW_REP_START 0x10 // Repeated start condition transmitted
#define TW_MT_SLA_ACK 0x18 // SLA+W transmitted, ACK received
@@ -12,6 +14,11 @@
#define TW_MR_SLA_NACK 0x48 // SLA+R transmitted, NACK received
#define TW_MR_DATA_ACK 0x50 // Data received, ACK returned
// NTC conversion constants
#define NTC01 1.009249522e-3
#define NTC02 2.378405444e-4
#define NTC03 2.019202697e-7
// TODO: Error handling and recovery besides watchdog timer.
// TODO: Add more documentation from the atmel data sheet.
// TODO: Implement TWI_vect ISR? This may not actually be
@@ -528,7 +535,25 @@ word I2C_ADS1115_Read(int channel)
// Single-shot conversion, active low, continous mode
config = os | rate | gain | mux;
I2C_ADS1115_WriteRegister(0x01, config);
return I2C_ADS1115_ReadRegister(0x00);
}
float I2C_ADS1115_ReadThermistor(int channel)
{
word raw;
float r1, t;
float logr2;
// TODO: Improve readability
// https://en.wikipedia.org/wiki/Steinhart%E2%80%93Hart_equation
raw = I2C_ADS1115_Read(channel);
r1 = (float) raw / 264.8f * 0.05f;
logr2 = log(10000.0f / (5.0f / r1 - 1.0f));
t = 1.0f / (NTC01 + NTC02 * logr2 + NTC03 * pow(logr2, 3));
return t - 273.15f; // Convert fahrenheit to celsius
}

3
src/bus/i2c.h
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@@ -28,6 +28,7 @@ int I2C_AHT20_Init(void);
int I2C_AHT20_Read(float *temp, float *rhum);
// ADS1115 analog to digital converter
word I2C_ADS1115_Read(int channel);
word I2C_ADS1115_Read(int channel);
float I2C_ADS1115_ReadThermistor(int channel);
#endif // MAD_CORE_BUS_I2C_H

21
src/main.c
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@@ -6,7 +6,6 @@
#include <avr/interrupt.h>
// TODO: Convert raw data from ADS1115 to usable values.
// TODO: Implement optional CRC8 sensor measurement check.
// TODO: Either implement software PWM for the FAN03 timer
// (which will be quite complicated) or pick a chip with
@@ -97,7 +96,7 @@ static int Init(void)
static void Update(void)
{
float temp[3], rh[3];
short adc[4];
float adct[3];
Info("Reading sensor values...");
@@ -110,16 +109,16 @@ static void Update(void)
I2C_SetChannel(AHT03);
I2C_AHT20_Read(&temp[2], &rh[2]);
adc[0] = I2C_ADS1115_Read(ADS01);
adc[1] = I2C_ADS1115_Read(ADS02);
adc[2] = I2C_ADS1115_Read(ADS03);
adc[3] = I2C_ADS1115_Read(ADS04);
Sleep(200); // FIXME: Poll config register until BIT(15) == 1
adct[0] = I2C_ADS1115_ReadThermistor(ADS01);
Sleep(200); // FIXME: Remove me - see above.
adct[1] = I2C_ADS1115_ReadThermistor(ADS02);
Sleep(200); // FIXME: Remove me - see above.
adct[2] = I2C_ADS1115_ReadThermistor(ADS03);
Info("TEMP0=%.2fC, RH0=%.2f%%", temp[0], rh[0]);
Info("TEMP1=%.2fC, RH1=%.2f%%", temp[1], rh[1]);
Info("TEMP2=%.2fC, RH2=%.2f%%", temp[2], rh[2]);
Info("ADC0=%04X, ADC1=%04X", adc[0], adc[1]);
Info("ADC2=%04X, ADC3=%04X", adc[2], adc[3]);
Info("TEMP0=%.2fC, TEMP1=%.2fC, TEMP2=%.2fC", temp[0], temp[1], temp[2]);
Info("ADCT0=%.2fC, ADCT1=%.2fC, ADCT2=%.2fC", adct[0], adct[1], adct[2]);
Info("RH0=%.2f%%, RH1=%.2f%%, RH2=%.2f%%", rh[0], rh[1], rh[2]);
}
int main(void)