eddys_snippets/I2Csensors

Reading information from different T/P/H sensors

Supported sensors: AHT10, AHT15, AHT21b, BMP180, BMP280, BME280, SHT3x, SI7005

Sensor	Precision H/T/P	Address	Max speed	Comment
AHT10	2%/0.3°/-	0x38/0x39	400k	ADDR selects lowest address bit
AHT15	2%/0.3°/-	0x38	400k	what is the difference from AHT10?
AHT21b	3%/0.5°/-	0x38	400k
BMP180	-/1°/12Pa	0x77	3.4M	could also works by SPI
BME280	3%/1°/0.2Pa	0x76/77	3.4M	SDO allows to select lowest I2C address bit; supports SPI
SHT30	3%/0.3°/-	0x44/0x45	1M	SHT31 have higher humidity precision (2%); ADDR selects address lowest bit; hav ALERT pin
SI7005	4.5%/1°/-	0x40	400k	~CS can select sensor if several are on bus

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Install library

1. Download: git clone or other way.
2. Create building directory: mkdir mk. Go into it: cd mk.
3. Run cmake: cmake ...
4. Build and install: make && su -c "make install".

Cmake options

Marked options are ON by default:

• DEBUG - compile in debug mode;
• EXAMPLES - build also examples (they won't be installed, you can use them just in build dir).

How to use

After installing library you can use it including i2csensorsPTH.h into your code and linking with -l i2csensorsPTH. Also you can use pkg-config after installing library:

pkg-config --libs --cflags i2csensorsPTH

Base types

sensor_status_t

Status of given sensor. SENS_NOTINIT means that you should init device; also if you get SENS_ERR you should try to reinit it. Receiving error on init function means that there's troubles on the bus or with sensor.

typedef enum{
    SENS_NOTINIT,   // wasn't inited
    SENS_BUSY,      // measurement in progress
    SENS_ERR,       // error occured
    SENS_RELAX,     // do nothing
    SENS_RDY,       // data ready - can get it
} sensor_status_t;

sensor_props_t

Properties: if the corresponding field sets, the device have this ability. flags allows to use all together as bit fields.

typedef union{
    struct{
        uint8_t T   : 1; // can temperature (degC)
        uint8_t H   : 1; // can humidity (percent)
        uint8_t P   : 1; // can pressure (hPa)
        uint8_t htr : 1; // have heater
    };
    uint32_t flags;
} sensor_props_t;

sensor_data_t

Gathered data. The fields that are zeroed in sensor's properties are undefined.

typedef struct{
    double T;    // temperature, degC
    double H;    // humidity, percents
    double P;    // pressure, hPa
} sensor_data_t;

Functions

int sensors_open(const char *dev)

Open I2C device by path dev. Returns TRUE if all OK.

void sensors_close()

Close I2C device.

char *sensors_list()

Returns allocated string with comma-separated names of all supported sensors. Don't forget to free it later.

sensor_t* sensor_new(const char *name)

Search name in list of supported sensors and, if found, returns pointer to sensors structure. Returns NULL if sensor not failed or some error oqqured.

void sensor_delete(sensor_t **s)

Delete all memory, allocated for given sensor.

sensor_props_t sensor_properties(sensor_t *s)

Allows to check sensor's properties.

int sensor_init(sensor_t *s, uint8_t address)

Try to find given sensor on the bus and run initial procedures (like calibration and so on). The address argument shoul be zero to use default I2C address or non-zero for custom. Returns TRUE if all OK.

int sensor_heater(sensor_t *s, int on)

Turn on (on == 1) or off (on == 0) sensor's heater (if sensor supported it). Returns FALSE if sensor don't support heater or some error occured during operations.

int sensor_start(sensor_t *s)

Start measurement process. While measuring, you should poll sensor until data would be ready (or you get timeout error).

sensor_status_t sensor_process(sensor_t *s)

Polling sensor and gathering all data in simple finite-state machine. Checks if sensor is still busy and asks for data portion on each measuring stage. Returns current sensor's state. If you get SENS_RDY, you can ask for data.

int sensor_getdata(sensor_t *s, sensor_data_t *d)

Get data into your variable d. Returns FALSE if data isn't ready (e.g. you didn't run start or sensor is still measuring).

I2C functions

Of course, you can wish to work with I2C directly (e.g. to switch multiplexer's channel and so on), so here are some usefull functions.

int sensor_writeI2C(uint8_t addr, uint8_t *data, int len)

Write data array with len of len bytes with device address addr. Returns FALSE if failed.

int sensor_readI2C(uint8_t addr, uint8_t *data, int len)

Read len bytes of data from address addr. Returns FALSE if failed.

int sensor_readI2Cregs(uint8_t addr, uint8_t regaddr, uint16_t N, uint8_t *data)

Read content of N 8-bit registers starting from regaddr to array data. Returns FALSE if failed.

int sensor_writeI2Creg(uint8_t addr, uint8_t regaddr, uint8_t data)

Write data to single register regaddr. Returns FALSE if failed.