examples/compensated-temperature.py

   1 #!/usr/bin/env python3
   2
   3 import time
   4 from bme280 import BME280
   5
   6 try:
   7     from smbus2 import SMBus
   8 except ImportError:
   9     from smbus import SMBus
  10
  11 import logging
  12
  13 logging.basicConfig(
  14     format='%(asctime)s.%(msecs)03d %(levelname)-8s %(message)s',
  15     level=logging.INFO,
  16     datefmt='%Y-%m-%d %H:%M:%S')
  17
  18 logging.info("""compensated-temperature.py - Use the CPU temperature
  19 to compensate temperature readings from the BME280 sensor.
  20 Method adapted from Initial State's Enviro pHAT review:
  21 https://medium.com/@InitialState/tutorial-review-enviro-phat-for-raspberry-pi-4cd6d8c63441
  22
  23 Press Ctrl+C to exit!
  24
  25 """)
  26
  27 bus = SMBus(1)
  28 bme280 = BME280(i2c_dev=bus)
  29
  30
  31 # Get the temperature of the CPU for compensation
  32 def get_cpu_temperature():
  33     with open("/sys/class/thermal/thermal_zone0/temp", "r") as f:
  34         temp = f.read()
  35         temp = int(temp) / 1000.0
  36     return temp
  37
  38
  39 # Tuning factor for compensation. Decrease this number to adjust the
  40 # temperature down, and increase to adjust up
  41 factor = 2.25
  42
  43 cpu_temps = [get_cpu_temperature()] * 5
  44
  45 while True:
  46     cpu_temp = get_cpu_temperature()
  47     # Smooth out with some averaging to decrease jitter
  48     cpu_temps = cpu_temps[1:] + [cpu_temp]
  49     avg_cpu_temp = sum(cpu_temps) / float(len(cpu_temps))
  50     raw_temp = bme280.get_temperature()
  51     comp_temp = raw_temp - ((avg_cpu_temp - raw_temp) / factor)
  52     logging.info("Compensated temperature: {:05.2f} *C".format(comp_temp))
  53     time.sleep(1.0)