M
@maamar
sh31 lib
from machine import I2C
import time
R_HIGH = const(1)
R_MEDIUM = const(2)
R_LOW = const(3)
class SHT31(object):
"""
This class implements an interface to the SHT31 temprature and humidity
sensor from Sensirion.
"""
# This static map helps keeping the heap and program logic cleaner
_map_cs_r = {
True: {
R_HIGH : b'\x2c\x06',
R_MEDIUM : b'\x2c\x0d',
R_LOW: b'\x2c\x10'
},
False: {
R_HIGH : b'\x24\x00',
R_MEDIUM : b'\x24\x0b',
R_LOW: b'\x24\x16'
}
}
def __init__(self, i2c, addr=0x44):
"""
Initialize a sensor object on the given I2C bus and accessed by the
given address.
"""
if i2c == None or i2c.__class__ != I2C:
raise ValueError('I2C object needed as argument!')
self._i2c = i2c
self._addr = addr
def _send(self, buf):
"""
Sends the given buffer object over I2C to the sensor.
"""
self._i2c.writeto(self._addr, buf)
def _recv(self, count):
"""
Read bytes from the sensor using I2C. The byte count can be specified
as an argument.
Returns a bytearray for the result.
"""
return self._i2c.readfrom(self._addr, count)
def _raw_temp_humi(self, r=R_HIGH, cs=True):
"""
Read the raw temperature and humidity from the sensor and skips CRC
checking.
Returns a tuple for both values in that order.
"""
if r not in (R_HIGH, R_MEDIUM, R_LOW):
raise ValueError('Wrong repeatabillity value given!')
self._send(self._map_cs_r[cs][r])
time.sleep_ms(50)
raw = self._recv(6)
return (raw[0] << 8) + raw[1], (raw[3] << 8) + raw[4]
def get_temp_humi(self, resolution=R_HIGH, clock_stretch=True, celsius=True):
"""
Read the temperature in degree celsius or fahrenheit and relative
humidity. Resolution and clock stretching can be specified.
Returns a tuple for both values in that order.
"""
t, h = self._raw_temp_humi(resolution, clock_stretch)
if celsius:
temp = -45 + (175 * (t / 65535))
else:
temp = -49 + (315 * (t / 65535))
return temp, 100 * (h / 65535)
