examples/compensated-temperature.py

   1 #!/usr/bin/env python
   2
   3 import time
   4 from bme280 import BME280
   5 from subprocess import PIPE, Popen
   6
   7 try:
   8     from smbus2 import SMBus
   9 except ImportError:
  10     from smbus import SMBus
  11
  12 import logging
  13
  14 logging.basicConfig(
  15     format='%(asctime)s.%(msecs)03d %(levelname)-8s %(message)s',
  16     level=logging.INFO,
  17     datefmt='%Y-%m-%d %H:%M:%S')
  18
  19 logging.info("""compensated-temperature.py - Use the CPU temperature
  20 to compensate temperature readings from the BME280 sensor.
  21 Method adapted from Initial State's Enviro pHAT review:
  22 https://medium.com/@InitialState/tutorial-review-enviro-phat-for-raspberry-pi-4cd6d8c63441
  23
  24 Press Ctrl+C to exit!
  25
  26 """)
  27
  28 bus = SMBus(1)
  29 bme280 = BME280(i2c_dev=bus)
  30
  31
  32 # Get the temperature of the CPU for compensation
  33 def get_cpu_temperature():
  34     process = Popen(['vcgencmd', 'measure_temp'], stdout=PIPE, universal_newlines=True)
  35     output, _error = process.communicate()
  36     return float(output[output.index('=') + 1:output.rindex("'")])
  37
  38
  39 # Tuning factor for compensation. Decrease this number to adjust the
  40 # temperature down, and increase to adjust up
  41 factor = 0.8
  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)