Python script to turn a fan on and off based on SHT31 temperature and temperature from the internet

ventilate.py

from Adafruit_IO import *
import json
import requests
import RPi.GPIO as GPIO
import smbus
import time

aio = Client('XXXXXXXXXXXXXXXXX_ADAFRUIT_API_KEY_GOES_HERE_XXXXXXXXXXXXXXXXX')

GPIO.setmode(GPIO.BCM)           # choose BCM or BOARD
GPIO.setup(26, GPIO.OUT, initial=0) # set a port/pin as an output

WEATHER_URL = 'http://api.openweathermap.org/data/2.5/weather?zip=02144&appid=fa50fc1b8864b5ca05d05995712c8728'
last_time = time.time() - 100 # pretend we checked outside temp 100 seconds ago

# Equations below from
# https://www.vaisala.com/sites/default/files/documents/Humidity_Conversion_Formulas_B210973EN-F.pdf

def saturation_pressure(temp_in_c):
    A = 6.116441
    m = 7.591386
    Tn = 240.7263 # triple point temp in C
    Pws = 100 * A * 10 ** ((m * temp_in_c) / (temp_in_c + Tn))
    return Pws # in Pa (should range ~611-7377 Pa across 0-40 C, according to National Weather Service)

def vapor_pressure(temp_in_c, rh):
    Pw = saturation_pressure(temp_in_c) * (rh/100.0)
    return Pw

def absolute_humidity(temp_in_c, rh):
    C = 2.16679 # [gK/J]
    Pw = vapor_pressure(temp_in_c, rh)
    T = temp_in_c + 273.15
    A = C * (Pw / T)
    return A #  absolute_humidity(20,80) should return 13.82 [g/m3]

while(True):
    if time.time() - last_time > 10:
        r = requests.get(WEATHER_URL)
        print("Got new weather data")
        last_time = time.time()
    weather_data = json.loads(r.text)
    out_temp = 32 + 1.8 * (weather_data['main']['temp'] - 273.15) # converting from K to F
    out_rh = weather_data['main']['humidity']


    bus = smbus.SMBus(1)

    # SHT31 address, 0x44(68)
    bus.write_i2c_block_data(0x44, 0x2C, [0x06])

    time.sleep(0.5)

    # SHT31 address, 0x44(68)
    # Read data back from 0x00(00), 6 bytes
    # Temp MSB, Temp LSB, Temp CRC, Humididty MSB, Humidity LSB, Humidity CRC
    data = bus.read_i2c_block_data(0x44, 0x00, 6)

    # Convert the data
    temp = data[0] * 256 + data[1]
    in_temp = -49 + (315 * temp / 65535.0)
    in_rh = 100 * (data[3] * 256 + data[4]) / 65535.0

    # Send data to Adafruit IO
    aio.send('woodbine-temp', in_temp)
    aio.send('somerville-temp', out_temp)

    # Output data to screen
    print("Inside temp: %.2f F" % in_temp)
    print("Inside RH: %.2f %%" % in_rh)
    print("Outside temp: %.2f F" % out_temp)
    print("Outside RH: %.2f %%" % out_rh)
    print("\n")

    if in_temp > out_temp:
        GPIO.output(26, 1) # turn on the fan
        aio.send('fan-status', 75)
    else:
        GPIO.output(26, 0) # turn off the fan
        aio.send('fan-status', 25)

    time.sleep(10) # wait a few seconds before we loop