from machine import I2C, Pin
import time
__version__ = '0.2.1'
__author__ = 'Roberto Sánchez'
__license__ = "Apache License 2.0. https://www.apache.org/licenses/LICENSE-2.0"
# I2C address B 0x45 ADDR (pin 2) connected to VDD
DEFAULT_I2C_ADDRESS = 0x45
class SHT30():
"""
SHT30 sensor driver in pure python based on I2C bus
References:
* https://www.sensirion.com/fileadmin/user_upload/customers/sensirion/Dokumente/2_Humidity_Sensors/Sensirion_Humidity_Sensors_SHT3x_Datasheet_digital.pdf
* https://www.wemos.cc/sites/default/files/2016-11/SHT30-DIS_datasheet.pdf
* https://github.com/wemos/WEMOS_SHT3x_Arduino_Library
* https://www.sensirion.com/fileadmin/user_upload/customers/sensirion/Dokumente/11_Sample_Codes_Software/Humidity_Sensors/Sensirion_Humidity_Sensors_SHT3x_Sample_Code_V2.pdf
"""
POLYNOMIAL = 0x131 # P(x) = x^8 + x^5 + x^4 + 1 = 100110001
ALERT_PENDING_MASK = 0x8000 # 15
HEATER_MASK = 0x2000 # 13
RH_ALERT_MASK = 0x0800 # 11
T_ALERT_MASK = 0x0400 # 10
RESET_MASK = 0x0010 # 4
CMD_STATUS_MASK = 0x0002 # 1
WRITE_STATUS_MASK = 0x0001 # 0
# MSB = 0x2C LSB = 0x06 Repeatability = High, Clock stretching = enabled
MEASURE_CMD = b'\x2C\x10'
STATUS_CMD = b'\xF3\x2D'
RESET_CMD = b'\x30\xA2'
CLEAR_STATUS_CMD = b'\x30\x41'
ENABLE_HEATER_CMD = b'\x30\x6D'
DISABLE_HEATER_CMD = b'\x30\x66'
def __init__(self, scl_pin=5, sda_pin=4, delta_temp = 0, delta_hum = 0, i2c_address=DEFAULT_I2C_ADDRESS):
self.i2c = I2C(scl=Pin(scl_pin), sda=Pin(sda_pin))
self.i2c_addr = i2c_address
self.set_delta(delta_temp, delta_hum)
time.sleep_ms(50)
def init(self, scl_pin=5, sda_pin=4):
"""
Init the I2C bus using the new pin values
"""
self.i2c.init(scl=Pin(scl_pin), sda=Pin(sda_pin))
def is_present(self):
"""
Return true if the sensor is correctly conneced, False otherwise
"""
return self.i2c_addr in self.i2c.scan()
def set_delta(self, delta_temp = 0, delta_hum = 0):
"""
Apply a delta value on the future measurements of temperature and/or humidity
The units are Celsius for temperature and percent for humidity (can be negative values)
"""
self.delta_temp = delta_temp
self.delta_hum = delta_hum
def _check_crc(self, data):
# calculates 8-Bit checksum with given polynomial
crc = 0xFF
for b in data[:-1]:
crc ^= b;
for _ in range(8, 0, -1):
if crc & 0x80:
crc = (crc << 1) ^ SHT30.POLYNOMIAL;
else:
crc <<= 1
crc_to_check = data[-1]
return crc_to_check == crc
def send_cmd(self, cmd_request, response_size=6, read_delay_ms=100):
"""
Send a command to the sensor and read (optionally) the response
The responsed data is validated by CRC
"""
try:
self.i2c.start();
self.i2c.writeto(self.i2c_addr, cmd_request);
if not response_size:
self.i2c.stop();
return
time.sleep_ms(read_delay_ms)
data = self.i2c.readfrom(self.i2c_addr, response_size)
self.i2c.stop();
for i in range(response_size//3):
if not self._check_crc(data[i*3:(i+1)*3]): # pos 2 and 5 are CRC
raise SHT30Error(SHT30Error.CRC_ERROR)
if data == bytearray(response_size):
raise SHT30Error(SHT30Error.DATA_ERROR)
return data
except OSError as ex:
if 'I2C' in ex.args[0]:
raise SHT30Error(SHT30Error.BUS_ERROR)
raise ex
def clear_status(self):
"""
Clear the status register
"""
return self.send_cmd(SHT30.CLEAR_STATUS_CMD, None);
def reset(self):
"""
Send a soft-reset to the sensor
"""
return self.send_cmd(SHT30.RESET_CMD, None);
def status(self, raw=False):
"""
Get the sensor status register.
It returns a int value or the bytearray(3) if raw==True
"""
data = self.send_cmd(SHT30.STATUS_CMD, 3, read_delay_ms=20);
if raw:
return data
status_register = data[0] << 8 | data[1]
return status_register
def measure(self, raw=False):
"""
If raw==True returns a bytearrya(6) with sensor direct measurement otherwise
It gets the temperature (T) and humidity (RH) measurement and return them.
The units are Celsius and percent
"""
data = self.send_cmd(SHT30.MEASURE_CMD, 6);
if raw:
return data
t_celsius = (((data[0] << 8 | data[1]) * 175) / 0xFFFF) - 45 + self.delta_temp;
rh = (((data[3] << 8 | data[4]) * 100.0) / 0xFFFF) + self.delta_hum;
return t_celsius, rh
def measure_int(self, raw=False):
"""
Get the temperature (T) and humidity (RH) measurement using integers.
If raw==True returns a bytearrya(6) with sensor direct measurement otherwise
It returns a tuple with 4 values: T integer, T decimal, H integer, H decimal
For instance to return T=24.0512 and RH= 34.662 This method will return
(24, 5, 34, 66) Only 2 decimal digits are returned, .05 becomes 5
Delta values are not applied in this method
The units are Celsius and percent.
"""
data = self.send_cmd(SHT30.MEASURE_CMD, 6);
if raw:
return data
aux = (data[0] << 8 | data[1]) * 175
t_int = (aux // 0xffff) - 45;
t_dec = (aux % 0xffff * 100) // 0xffff
aux = (data[3] << 8 | data[4]) * 100
h_int = aux // 0xffff
h_dec = (aux % 0xffff * 100) // 0xffff
return t_int, t_dec, h_int, h_dec
class SHT30Error(Exception):
"""
Custom exception for errors on sensor management
"""
BUS_ERROR = 0x01
DATA_ERROR = 0x02
CRC_ERROR = 0x03
def __init__(self, error_code=None):
self.error_code = error_code
super().__init__(self.get_message())
def get_message(self):
if self.error_code == SHT30Error.BUS_ERROR:
return "Bus error"
elif self.error_code == SHT30Error.DATA_ERROR:
return "Data error"
elif self.error_code == SHT30Error.CRC_ERROR:
return "CRC error"
else:
return "Unknown error"
