SI7021: Python class for the SI7021 Temperature and Relative Humidity sensor

(The MIT License (MIT) applies)

This is a very short and simple class. It uses the I2C bus for the interface.

Constructor

si7021 = SI7021(i2c)

i2c is an I2C object which has to be created by the caller.

Methods

temp = si7021.temperature(new = True)

Reads the temperature and returns a °C value. If the parameter new is set to new, a new reading is performed. When set to False, the Value taken during the previous readRH() call is returned.
The function raises 'OSError: SI7021 timeout' if after 100ms not value is returned from the device.
If the CRC of the data from the sensor is wrong, the call returns None.

rh = si7021.humidity()

Reads the relative humidity. The range is 0-100.
The function raises 'OSError: SI7021 timeout' if after 100ms not value is returned from the device.
If the CRC of the data from the sensor is wrong, the call raises 'OSError: SI7021 CRC Error'.

dew_point = si7021.dew_point()

Reads the dew_point temperature (°C) calculated from the actual temperature and humidity.
The function raises 'OSError: SI7021 timeout' if after 100ms not value is returned from the device.
If the CRC of the data from the sensor is wrong, the call raises 'OSError: SI7021 CRC Error'.

humid_ambient = si7021.humid_ambient(temperature, dew_point=None)

Calculate the relative humidity based on the supplied temperature and the optional dew_point. If no dew_point value is supplied, it will be determined. The range is 0-100.
The function raises 'OSError: SI7021 timeout' if after 100ms not value is returned from the device.
If the CRC of the data from the sensor is wrong, the call raises 'OSError: SI7021 CRC Error'.

si7021.set_resolution(index)

Sets the resolution for both temperature and relative humidity. Index in the range of 0-3 select the setting from the table below. The returned results of readTemp() and readRH() are truncated according to the resolution set. The conversion time also depends on the resolution.

Index	RH	Temp
0	12 bit	14 bit
1	8 bit	12 bit
2	10 bit	13 bit
3	11 bit	11 bit

si7021.reset()

Resets the device. The resolution is set back to maximum.

Properties

serial = si7021.serialnumber

8 byte serial number as a byte array. The fifth byte contains the the identification of the device. For the SI7021 it's 0x15.

serial = si7021.revision

Firmware revision as a single byte object.

Example

# Example for Pycom device.
# Connections:
# xxPy | SI7021
# -----|-------
# P9   |  SDA
# P10  |  SCL
#
from machine import I2C
from SI7021 import SI7021

i2c = I2C(0, I2C.MASTER)
si7021 = SI7021(i2c)

temperature = si7021.temperature()
humidity = si7021.humidity()
dew_point = si7021.dew_point()
serial = si7021.serialnumber