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