htu21

README

HTU21 (SHT21, SI7021) golang package

This package allows you to connect and read environmental data from HTU21 (SHT21, SI7021) sensor. I guess it could be qualified as a Periph.io driver, because it tries to comply with periph.io sensors interface like bmxx80 in terms of the ways to access I²C, function calls and data returned.

Example

You can find an example in cmd folder, it works on RPi 4 with HTU21 connected to 4-th I²C bus, sensor address is 0x40. List of I²C buses can be obtained with

i2cdetect -l

Once you know the bus number, connected devices can be enumerated with

i2cdetect -y 4

Additional links

Some links you can find useful working with this sensor, RPi GPIO and I²C:

• Sensor datasheet is here - https://www.te.com/usa-en/models/4/00/028/790/CAT-HSC0004.html
• Wonderful Raspberry Pi pinout guide - https://pinout.xyz/
• How to define additional/alternative I²C buses on RPi GPIO - https://www.instructables.com/Raspberry-PI-Multiple-I2c-Devices/
• "Access GPIO pins without root. No access to /dev/gpiomem. Try running as root!" problem solution - https://raspberrypi.stackexchange.com/questions/40105/access-gpio-pins-without-root-no-access-to-dev-mem-try-running-as-root

Why does this package exist?

This package is a heavily rewritten idahoakl/HTU21D-sensor library. Main differences are:

• periph.io i2c package to access I²C instead of proprietary one, idahoakl used
• periph.io physic package for environmental data (temperature and relative humidity)
• one function Sense() instead of separate functions for each measurement
• no proprietary logging package
• no write/read user registry functions for now

I'd really like to get rid of proprietary CRC checking dependency as well.

Documentation

Index

• type Dev
  • func NewI2C(b i2c.Bus, addr uint16) (*Dev, error)
  • func (d *Dev) Reset() error
  • func (d *Dev) Sense(e *physic.Env) error

Types

type Dev

type Dev struct {
	// contains filtered or unexported fields
}

Dev is a handle to an initialized HTU21 device.

func NewI2C

func NewI2C(b i2c.Bus, addr uint16) (*Dev, error)

NewI2C returns an object that communicates over I²C to HTU21 environmental sensor.

HTU21 I²C device address is 0x40, according to the datasheet https://www.te.com/usa-en/models/4/00/028/790/CAT-HSC0004.html

func (*Dev) Reset

func (d *Dev) Reset() error

Performs soft reset of the device 0xFE - code for soft reset 15 milliseconds delay follows

func (*Dev) Sense

func (d *Dev) Sense(e *physic.Env) error

Sense requests a one time measurement as °C and % of relative humidity. 0xF3, delay 50 ms - temperature 0xF5, delay 16 ms - humidity