sht3x v0.1.0

SHT30/SHT31/SHT35 temperature and humidity sensor.

Application scenarios

• Room climate monitoring.
• Greenhouse or enclosure humidity.
• A calibrated replacement for a DHT sensor.

Contract

typedef enum {
    SHT3X_HIGH = 0,
    SHT3X_MEDIUM,
    SHT3X_LOW,
} sht3x_repeatability_t;

uint8_t sht3x_init(sht3x_t *device, sht3x_port_t port, uint8_t i2c_address);
uint8_t sht3x_read(sht3x_t *device, sht3x_repeatability_t repeatability,
                   int32_t *milli_celsius, int32_t *milli_percent);

• read sends a single-shot command, waits, reads six bytes, and checks both CRCs.
• Temperature is millidegrees Celsius; humidity is millipercent RH.
• Returns 1 on success, 0 on a bus error, a busy sensor, or a bad CRC.

Parameters

• I2C address 0x44 or 0x45.
• Repeatability high/medium/low changes the measurement time and noise.
• Conversion: T = -45 + 175 * raw / 65535,

RH = 100 * raw / 65535.

Memory and timing

• About 8 bytes; one 6-byte read.
• Measurement takes about 15 ms (high), 6 ms (medium), or 4 ms (low).

Integration

sht3x_t sensor;
sht3x_init(&sensor, board_i2c_port(), 0x44);
int32_t temperature, humidity;
if (sht3x_read(&sensor, SHT3X_HIGH, &temperature, &humidity)) {
    show(temperature / 1000, humidity / 1000);
}

Adapters

• The adapter writes two command bytes and reads six data bytes.
• Reference: DFRobot_SHT3x (MIT) and the Sensirion SHT3x datasheet.
• This implementation is original.

When not to use

• A sensor on a long cable without a buffer.
• Condensing environments; use a protected sensor.

Verification

make test covers both CRCs, the conversion, repeatability commands, and a

bad CRC.

void *context;
uint8_t (*write)(void *context, uint8_t address, const uint8_t *data, uint16_t length);
uint8_t (*read)(void *context, uint8_t address, uint8_t *data, uint16_t length);
void (*delay_ms)(void *context, uint16_t milliseconds);

SHT3X_HIGH = 0,
SHT3X_MEDIUM,
SHT3X_LOW,

sht3x_port_t port;
uint8_t i2c_address;