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 print("""compensated-temperature.py - Use the CPU temperature to compensate temperature
  13 readings from the BME280 sensor. Method adapted from Initial State's Enviro pHAT
  14 review: https://medium.com/@InitialState/tutorial-review-enviro-phat-for-raspberry-pi-4cd6d8c63441
  15
  16 Press Ctrl+C to exit!
  17
  18 """)
  19
  20 bus = SMBus(1)
  21 bme280 = BME280(i2c_dev=bus)
  22
  23 # Get the temperature of the CPU for compensation
  24 def get_cpu_temperature():
  25     process = Popen(['vcgencmd', 'measure_temp'], stdout=PIPE)
  26     output, _error = process.communicate()
  27     return float(output[output.index('=') + 1:output.rindex("'")])
  28
  29 # Tuning factor for compensation. Decrease this number to adjust the
  30 # temperature down, and increase to adjust up
  31 factor = 0.8
  32
  33 cpu_temps = [0] * 5
  34
  35 while True:
  36     cpu_temp = get_cpu_temperature()
  37     # Smooth out with some averaging to decrease jitter
  38     cpu_temps = cpu_temps[1:] + [cpu_temp]
  39     avg_cpu_temp = sum(cpu_temps) / float(len(cpu_temps))
  40     raw_temp = bme280.get_temperature()
  41     comp_temp = raw_temp - ((avg_cpu_temp - raw_temp) / factor)
  42     print("Compensated temperature: {:05.2f} *C".format(comp_temp))
  43     time.sleep(1.0)