htu21d.py

# -*- coding: utf-8 -*-
#
# For module GY-21, or sensor HTU21D
#
# refer https://cdn-shop.adafruit.com/datasheets/1899_HTU21D.pdf
# refer https://github.com/jasiek/HTU21D/blob/master/HTU21D.py
# 
# © Takeyuki UEDA 2018 - 

import smbus
import getrpimodel
import geti2caddress

# htu21d command
RDTEMP  = 0xE3
RDHUMID = 0xE5
RESET   = 0xFE

# select bus info
if getrpimodel.model() == "A+":
  i2c_bus = 0
else:
  i2c_bus = 1

# make smbus
bus = smbus.SMBus(i2c_bus)

class HTU21D:
	def __init__(self):
		# get i2c address of sensor
		self.I2C_ADDRESS = int(geti2caddress.addr(),16)

		# select bus info
		if getrpimodel.model() == "A+":
			self.I2C_BUS = 0
		else:
			self.I2C_BUS = 1

		# make smbus
		self.bus = smbus.SMBus(self.I2C_BUS)

	def temp(self):
		msb, lsb, crc = self.bus.read_i2c_block_data(self.I2C_ADDRESS, RDTEMP, 3)
		self.t = -46.85 + 175.72 * (msb * 256 + lsb) / 65536
		return self.t

	def humid(self):
		msb, lsb, crc = self.bus.read_i2c_block_data(self.I2C_ADDRESS, RDHUMID, 3)
		self.h = -6 + 125 * (msb * 256 + lsb) / 65536.0
		return self.h

h = HTU21D()

def read():
	temp   = h.temp()
	humid  = h.humid()
	result = {"temp":			       ('%.1f' % temp),
						"humidity":	       ('%.1f' % humid),
						"humiditydeficit": ('%.1f' % humidityDeficit(temp,humid))}
	return result

# http://d.hatena.ne.jp/Rion778/20121203/1354546179
def humidityDeficit(t,rh): # t: 温度, rh: 相対湿度
	ret = absoluteHumidity(t, 100) - absoluteHumidity(t, rh)
	return ret; 

# http://d.hatena.ne.jp/Rion778/20121203/1354461231
def absoluteHumidity(t, rh):
	ret = 2.166740 * 100 * rh * tetens(t)/(100 * (t + 273.15))
	return ret

#  飽和水蒸気圧
#  function GofGra(t){};
# http://d.hatena.ne.jp/Rion778/20121126/1353861179
def tetens(t):
	ret = 6.11 * 10 ** (7.5*t/(t + 237.3))
	return ret

if __name__ == '__main__':
	print (read())