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Implemented the heating commands for the SHT41.
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@linguini1
linguini1 committed May 14, 2024
1 parent e0f05b9 commit f782937
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Showing 3 changed files with 112 additions and 46 deletions.
3 changes: 2 additions & 1 deletion src/collectors/sht41_clctr.c
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Original file line number Diff line number Diff line change
Expand Up @@ -35,7 +35,8 @@ void *sht41_collector(void *args) {
};

// Reset SHT41
errno_t err = sht41_reset(&loc);
int err = sht41_reset(&loc);
usleep(100); // Wait just a little bit
if (err != EOK) {
fprintf(stderr, "%s\n", strerror(err));
return_errno(err);
Expand Down
142 changes: 103 additions & 39 deletions src/drivers/sht41/sht41.c
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Original file line number Diff line number Diff line change
Expand Up @@ -11,13 +11,9 @@
#include <time.h>
#include <unistd.h>

/** Defines positions of most and least significant bytes in the sensor's response for temperature. */
#define SHT41_T_MSB 0
#define SHT41_T_LSB 1

/** Defines positions of the most and least significant bytes in the sensor's response for humidity. */
#define SHT41_RH_MSB 3
#define SHT41_RH_LSB 4
/** Macro for early returning an error. */
#define return_err(err) \
if (err != EOK) return err

/** Defines the first byte to include in the CRC calculation */
#define SHT41_T_CRC 0
Expand All @@ -26,6 +22,9 @@
/** Defines the number of bytes to be included in the CRC calculation. */
#define SHT41_CRC_LEN 3

/** Defines the number of bytes into the returned sensor data that humidity starts. */
#define SHT41_HUMIDITY 3

/** The number of microseconds to wait before reading serial number after making a read request. */
#define SERIAL_WAIT 10

Expand Down Expand Up @@ -58,6 +57,13 @@ static const uint8_t PRECISION_READ[] = {
[SHT41_HIGH_PRES] = CMD_READ_HIGH_PREC,
};

/** The commands for heating and then performing a read. */
static const uint8_t HEAT_CMDS[3][2] = {
[SHT41_WATT_20] = {[SHT41_HEAT_1S] = CMD_HEATER_20_1, [SHT41_HEAT_P1S] = CMD_HEATER_20_P1},
[SHT41_WATT_110] = {[SHT41_HEAT_1S] = CMD_HEATER_110_1, [SHT41_HEAT_P1S] = CMD_HEATER_110_P1},
[SHT41_WATT_200] = {[SHT41_HEAT_1S] = CMD_HEATER_200_1, [SHT41_HEAT_P1S] = CMD_HEATER_200_P1},
};

/** Initial value of the calculated CRC. */
#define SHT41_CRC_INIT 0xFF
#define SHT41_CRC_POLY 0x31
Expand Down Expand Up @@ -87,9 +93,9 @@ static const CRC8LookupTable CRC_LOOKUP = {
* Checks if the calculated CRC for this section of data is equal to zero
* @param start The start of the data which ends with it's own 8-bit CRC
* @param nbytes The length of the data to be checked, including the CRC
* @return errno_t EBADMSG
* @return int EBADMSG
*/
static inline errno_t check_crc(uint8_t *buf, size_t nbytes) {
static inline int check_crc(uint8_t *buf, size_t nbytes) {
#ifdef SHT41_USE_CRC_LOOKUP
// Check the CRC to make sure we're not about to read garbage
if (calculate_crc8(buf, nbytes, &CRC_LOOKUP, SHT41_CRC_INIT) != 0) {
Expand All @@ -105,6 +111,35 @@ static inline errno_t check_crc(uint8_t *buf, size_t nbytes) {
}
}

/**
* Calculates temperature using the 16 bit word returned from the SHT41 sensor.
* @param data A pointer to the temperature data returned by the SHT41 starting at the beginning of the 16 bit word.
* @return Temperature in degrees Celsius.
*/
static float sht41_calculate_temp(uint8_t *data) {
int32_t t_ticks = (data[0] * 256 + data[1]);
return -45.0f + 175.0f * ((float)t_ticks / 65535.0f); // Degrees C
}

/**
* Calculates humidity using the 16 bit word returned from the SHT41 sensor.
* @param data A pointer to the humidity data returned by the SHT41 starting at the beginning of the 16 bit word.
* @return Relative humidity in percentage.
*/
static float sht41_calculate_humidity(uint8_t *data) {
int32_t rh_ticks = (data[0] * 256 + data[1]);
float humidity = -6.0f + 125.0f * ((float)rh_ticks / 65535.0f); // Degrees C

// Limit values of humidity, since values outside of 0-100 are invalid
if (humidity < 0) {
humidity = 0;
} else if (humidity > 100) {
humidity = 100;
}

return humidity;
}

/**
* Reads the specified data from the SHT41.
* @param loc The location of the SHT41 on the I2C bus.
Expand All @@ -113,50 +148,35 @@ static inline errno_t check_crc(uint8_t *buf, size_t nbytes) {
* @param humidity A pointer to store the relative humidity in percentage.
* @return Error status of reading from the sensor. EOK if successful.
*/
errno_t sht41_read(SensorLocation const *loc, sht41_prec_e precision, float *temperature, float *humidity) {
int sht41_read(SensorLocation const *loc, sht41_prec_e precision, float *temperature, float *humidity) {

i2c_send_t send = {.slave = loc->addr, .stop = 1, .len = 1};
uint8_t send_cmd[sizeof(send) + 1];
memcpy(send_cmd, &send, sizeof(send));
send_cmd[sizeof(send)] = PRECISION_READ[precision];

errno_t err = devctl(loc->bus, DCMD_I2C_SEND, &send_cmd, sizeof(send_cmd), NULL);
if (err != EOK) {
return err;
};
int err = devctl(loc->bus, DCMD_I2C_SEND, &send_cmd, sizeof(send_cmd), NULL);
return_err(err);

usleep(MEASUREMENT_TIMES[precision]); // Wait for the measurement to take place, depends on precision

// Read data from sensor
i2c_recv_t read = {.slave = loc->addr, .stop = 1, .len = 6};
uint8_t read_cmd[sizeof(send) + 6];
uint8_t read_cmd[sizeof(read) + 6];
memcpy(read_cmd, &read, sizeof(read));

err = devctl(loc->bus, DCMD_I2C_RECV, &read_cmd, sizeof(read_cmd), NULL);
if (err != EOK) {
return err;
};
return_err(err);

// Calculate temperature
err = check_crc(read_cmd + sizeof(read) + SHT41_T_CRC, SHT41_CRC_LEN);
if (err != EOK) return err;

int32_t t_ticks = (read_cmd[sizeof(read) + SHT41_T_MSB] * 256 + read_cmd[sizeof(read) + SHT41_T_LSB]);
*temperature = -45 + 175 * ((float)t_ticks / 65535); // Degrees C
return_err(err);
*temperature = sht41_calculate_temp(read_cmd + sizeof(read));

// Calculate humidity
err = check_crc(read_cmd + sizeof(read) + SHT41_RH_CRC, SHT41_CRC_LEN);
if (err != EOK) return err;

int32_t rh_ticks = (read_cmd[sizeof(read) + SHT41_RH_MSB] * 256 + read_cmd[sizeof(read) + SHT41_RH_LSB]);
*humidity = -6 + 125 * ((float)rh_ticks / 65535); // Degrees C

// Limit values of humidity, since values outside of 0-100 are invalid
if (*humidity < 0) {
*humidity = 0;
} else if (*humidity > 100) {
*humidity = 100;
}
return_err(err);
*humidity = sht41_calculate_humidity(read_cmd + sizeof(read) + SHT41_HUMIDITY);

return err;
}
Expand All @@ -166,7 +186,7 @@ errno_t sht41_read(SensorLocation const *loc, sht41_prec_e precision, float *tem
* @param loc The sensor's location on the I2C bus.
* @return Any error from the attempted reset. EOK if successful.
*/
errno_t sht41_reset(SensorLocation const *loc) {
int sht41_reset(SensorLocation const *loc) {
i2c_send_t reset = {.stop = 1, .len = 1, .slave = loc->addr};
uint8_t reset_cmd[sizeof(reset) + 1];
memcpy(reset_cmd, &reset, sizeof(reset));
Expand All @@ -181,15 +201,15 @@ errno_t sht41_reset(SensorLocation const *loc) {
* @param serial_no A pointer to the location to store the serial number.
* @return EOK if successful, otherwise the error that occurred.
*/
errno_t sht41_serial_no(SensorLocation const *loc, uint32_t *serial_no) {
int sht41_serial_no(SensorLocation const *loc, uint32_t *serial_no) {

// Prepare read command
i2c_send_t hdr = {.stop = 1, .len = 1, .slave = loc->addr};
uint8_t read_cmd[sizeof(hdr) + 6];
memcpy(read_cmd, &hdr, sizeof(hdr));
read_cmd[sizeof(hdr)] = CMD_READ_SERIAL;

errno_t err = devctl(loc->bus, DCMD_I2C_LOCK, NULL, 0, NULL); // Lock bus
int err = devctl(loc->bus, DCMD_I2C_LOCK, NULL, 0, NULL); // Lock bus
if (err != EOK) return err;

// Prepare sensor for read
Expand Down Expand Up @@ -221,13 +241,57 @@ errno_t sht41_serial_no(SensorLocation const *loc, uint32_t *serial_no) {
}

/**
* Heats up the SHT41 sensor.
* Heats up the SHT41 sensor and then performs a high precision read of temperature and humidity.
* WARNING: May draw a large amount of current.
* @param loc The location of the SHT41 sensor on the I2C bus.
* @param duration The duration to heat the SHT41 sensor for.
* @param wattage The wattage to use when heating the SHT41 sensor.
* @param temperature A pointer to store the temperature in degrees Celsius.
* @param humidity A pointer to store the relative humidity in percentage.
* @return EOK if successful, otherwise returns the error that occurred.
*/
errno_t sht41_heat(SensorLocation const *loc, sht41_dur_e duration, sht41_wattage_e wattage) {
return ENOSYS; // Not implemented yet
int sht41_heat(SensorLocation const *loc, sht41_dur_e duration, sht41_wattage_e wattage, float *temperature,
float *humidity) {

i2c_send_t send_hdr = {.slave = loc->addr, .stop = 1, .len = 1};
uint8_t heat_cmd[sizeof(send_hdr) + 1];
memcpy(heat_cmd, &send_hdr, sizeof(send_hdr));

// Select correct commands for argument combo
heat_cmd[sizeof(send_hdr)] = HEAT_CMDS[wattage][duration];

int err = devctl(loc->bus, DCMD_I2C_SEND, &heat_cmd, sizeof(heat_cmd), NULL);
return_err(err);

// Wait for heating duration to complete
switch (duration) {
case SHT41_HEAT_1S:
usleep(1000000 + MEASUREMENT_TIMES[SHT41_HIGH_PRES]);
break;
case SHT41_HEAT_P1S:
usleep(100000 + MEASUREMENT_TIMES[SHT41_HIGH_PRES]);
break;
}

// Read data from sensor
i2c_recv_t read = {.slave = loc->addr, .stop = 1, .len = 6};
uint8_t read_cmd[sizeof(read) + 6];
memcpy(read_cmd, &read, sizeof(read));

err = devctl(loc->bus, DCMD_I2C_RECV, &read_cmd, sizeof(read_cmd), NULL);
return_err(err);

// Calculate temperature
err = check_crc(read_cmd + sizeof(read) + SHT41_T_CRC, SHT41_CRC_LEN);
return_err(err);
*temperature = sht41_calculate_temp(read_cmd + sizeof(read));

// Calculate humidity
err = check_crc(read_cmd + sizeof(read) + SHT41_RH_CRC, SHT41_CRC_LEN);
return_err(err);
*humidity = sht41_calculate_humidity(read_cmd + sizeof(read) + SHT41_HUMIDITY);

return err;

return err;
}
13 changes: 7 additions & 6 deletions src/drivers/sht41/sht41.h
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Original file line number Diff line number Diff line change
Expand Up @@ -27,13 +27,14 @@ typedef enum {

/** The duration to heat the SHT41 sensor for. */
typedef enum {
SHT41_HEAT_1s, /**< 1 second. */
SHT41_HEAT_P1s, /**< 0.1 seconds. */
SHT41_HEAT_1S, /**< 1 second. */
SHT41_HEAT_P1S, /**< 0.1 seconds. */
} sht41_dur_e;

errno_t sht41_reset(SensorLocation const *loc);
errno_t sht41_read(SensorLocation const *loc, sht41_prec_e precision, float *temperature, float *humidity);
errno_t sht41_serial_no(SensorLocation const *loc, uint32_t *serial_no);
errno_t sht41_heat(SensorLocation const *loc, sht41_dur_e duration, sht41_wattage_e wattage);
int sht41_reset(SensorLocation const *loc);
int sht41_read(SensorLocation const *loc, sht41_prec_e precision, float *temperature, float *humidity);
int sht41_serial_no(SensorLocation const *loc, uint32_t *serial_no);
int sht41_heat(SensorLocation const *loc, sht41_dur_e duration, sht41_wattage_e wattage, float *temperature,
float *humidity);

#endif // _SHT41_H_

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