5

I've just bought an Enviro pHAT. The temperature sensor on my pHAT reads around 31 degrees Celsius for my room

This sensor is close to the Pi, so it also gets a heatwave from the CPU

Is there a better way to approximate the actual temperature?

  • 1
    You could try a sliver of ceramic under the temp sensor. – goldilocks Feb 5 '17 at 15:14
  • @goldilocks What everyday item? – R Harrington Feb 6 '17 at 14:59
  • Orient the boards differently. If sandwiched together, orient them so air can freely flow upwards between them. Also: if there is a standard increase in temperature, you can compensate for that in your reporting. The ecobee 3 'calibrates' it's temperature -- and it just occurred to me it might be doing something like temperature compensation. – Dan Esparza Apr 22 '17 at 1:49
5

That's the main problem with the Enviro pHAT, and the SenseHAT for that matter - proximity to the Pi affecting results.

You're better off getting a Dallas 1-wire temperature sensor, preferably one with a long cable (such as, and this is just an example, the one contained in CamJam EduKit 2), or extend one without a lead by using jumper cables. This will let you get the sensor away from the Pi.

You can then use the 1-wire protocol to read the temperature. Instructions for how to do that can be found in this worksheet.

enter image description here

  • Can I put a male 40-pin header on the Enviro pHAT and use a ribbon cable to connect it to the pi? – R Harrington Feb 18 '17 at 8:14
  • Hmmm. Yeah. There's also something called a Black Hat Hackr which might be suitable. – recantha Feb 19 '17 at 20:34
3

If you really don't want to extend the temperature sensor away from the Pi, it may be possible to compensate for the effect of the CPU. This post on yaab-arduino.blogspot.co.uk outlines an attempt at this in Python, using a moving average of the readings from both the temperature and pressure sensors (the pressure sensor can also measure temperature):

import os
import time
from sense_hat import SenseHat

# get CPU temperature
def get_cpu_temp():
  res = os.popen("vcgencmd measure_temp").readline()
  t = float(res.replace("temp=","").replace("'C\n",""))
  return(t)

# use moving average to smooth readings
def get_smooth(x):
  if not hasattr(get_smooth, "t"):
    get_smooth.t = [x,x,x]
  get_smooth.t[2] = get_smooth.t[1]
  get_smooth.t[1] = get_smooth.t[0]
  get_smooth.t[0] = x
  xs = (get_smooth.t[0]+get_smooth.t[1]+get_smooth.t[2])/3
  return(xs)


sense = SenseHat()

while True:
  t1 = sense.get_temperature_from_humidity()
  t2 = sense.get_temperature_from_pressure()
  t_cpu = get_cpu_temp()
  h = sense.get_humidity()
  p = sense.get_pressure()

  # calculates the real temperature compesating CPU heating
  t = (t1+t2)/2
  t_corr = t - ((t_cpu-t)/1.5)
  t_corr = get_smooth(t_corr)

  print("t1=%.1f  t2=%.1f  t_cpu=%.1f  t_corr=%.1f  h=%d  p=%d" % (t1, t2, t_cpu, t_corr, round(h), round(p)))

  time.sleep(5)
  • Is there any way you could make that code suitable for the Enviro pHAT? – R Harrington Feb 20 '17 at 10:10

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