Posted on Sun 07 April 2019 in Home Automation,

I recently wrote a post about Raspberry Pi temperature and humidity sensors and alluded to the fact I use scripts to turn appliances on and off dependent on temperature.

Be kinda rude not to share…

I have a cron that runs every 3 minutes that probes a BME280 sensor for data and against a threshold switches a plug on or off via a 433mhz transmitter.

*/3 * * * * sudo python /home/pi/Adafruit_Python_BME280/HTC.py

If you don’t have a working 433mhz setup yet, check out this post :433Mhz

The below script is pretty easy to follow, it imports and sets up the Adafruit BME280 sensor, probes it then sends a code using 433Utils to a plug socket, switching it on or off. I'm also using the same script on another Pi, using SSH (badly) to trigger the same codes remotely. (Only one Pi has a 433mhz transmitter).

You can see from the below I've set the humidity threshold to 40%, if it drops below, it will send a 433 code to a plug socket attached to a humidifier. 3 minutes later it will check the reading again, if it's over the threshold, it will send the off command. Likewise for the temperature however it's plug socket has a large fan attached.

from Adafruit_BME280 import *
import os

sensor = BME280(t_mode=BME280_OSAMPLE_8, p_mode=BME280_OSAMPLE_8, h_mode=BME280_OSAMPLE_8)

temperature = sensor.read_temperature()
pascals = sensor.read_pressure()
hectopascals = pascals / 100
humidity = sensor.read_humidity()

if humidity is None or temperature is None:
        print('Temp={0:0.1f}*C  Humidity={1:0.1f}%'.format(temperature, humidity))

        humthresh = 40.0

        if humidity < humthresh:
                os.system ("/433Utils/RPi_utils/codesend 4543573")
                os.system ("/433Utils/RPi_utils/codesend 4543572")

        tempthresh = 25.0

        if temperature > tempthresh:

                os.system ("/433Utils/RPi_utils/codesend 4539733")
                os.system ("/433Utils/RPi_utils/codesend 4539732")

This is the remote SSH version, you (I) really should be using key files.

  humthresh = 65.0

        if humidity < humthresh:
                os.system ("sshpass -p PASSWORD ssh -o StrictHostKeyChecking=no pi@IPADDRESS 'cd /var/www/public_html && python iii.2.on.py' ")
                os.system ("sshpass -p PASSWORD ssh -o StrictHostKeyChecking=no pi@IPADDRESS 'cd /var/www/public_html && python iii.2.off.py' ")

This is example used to power a vivarium heat mat.

![PiThermostat] (images/vivpi.png "PiThermostat")

It consists of:

Raspberry Pi AWifi USB433 Tx / Rx PairDHT22 sensor1x 433Mhz plug (and remote for programming)1x Vivarium heat matJumper CablesPower

Temperature drops, heat mat on, heat ok, heat mat off. Simple. Use my 433 guide to get one working. 433Mhz