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compensated-temperature.py
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compensated-temperature.py
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#!/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)
output, _error = process.communicate()
output = output.decode()
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 = [0] * 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)