allow temperature reads to converge a bit faster

[EVA-2020-02-2.git] / examples / compensated-temperature.py

#!/usr/bin/env python

import time
from bme280 import BME280
from subprocess import PIPE, Popen

try:
    from smbus2 import SMBus
except ImportError:
    from smbus import SMBus

print("""compensated-temperature.py - Use the CPU temperature
to compensate temperature readings from the BME280 sensor.
Method adapted from Initial State's Enviro pHAT review:
https://medium.com/@InitialState/tutorial-review-enviro-phat-for-raspberry-pi-4cd6d8c63441

Press Ctrl+C to exit!

""")

bus = SMBus(1)
bme280 = BME280(i2c_dev=bus)


# Get the temperature of the CPU for compensation
def get_cpu_temperature():
    process = Popen(['vcgencmd', 'measure_temp'], stdout=PIPE, universal_newlines=True)
    output, _error = process.communicate()
    return float(output[output.index('=') + 1:output.rindex("'")])


# Tuning factor for compensation. Decrease this number to adjust the
# temperature down, and increase to adjust up
factor = 0.8

cpu_temps = [get_cpu_temperature()] * 5

while True:
    cpu_temp = get_cpu_temperature()
    # Smooth out with some averaging to decrease jitter
    cpu_temps = cpu_temps[1:] + [cpu_temp]
    avg_cpu_temp = sum(cpu_temps) / float(len(cpu_temps))
    raw_temp = bme280.get_temperature()
    comp_temp = raw_temp - ((avg_cpu_temp - raw_temp) / factor)
    print("Compensated temperature: {:05.2f} *C".format(comp_temp))
    time.sleep(1.0)