Idea

• Using python to periodically query several DS18B20 sensors
• Write results to a logfile (no SQL database)
• Webservice reads logfile to offer current data in JSON format

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Install DS18B20 Sensor

Since the Raspbian operating system was updated end of January 2015 (kernel 3.18.8 and higher) an additional line in /boot/config.txt is required.

vi /boot/config.txt
dtoverlay=w1-gpio

Now reboot

reboot

Check if the sensors are here:

ls /sys/bus/w1/devices/
28-0000056a6f05  28-00000598caf1  w1_bus_master1

Quick test if sensors are working

cat /sys/bus/w1/devices/28-0000056a6f05/w1_slave | sed -n 's/^.*\(t=[^ ]*\).*/\1/p' | sed 's/t=//' | awk '{x=$1}END{print(x/1000)}'
38.125
cat /sys/bus/w1/devices/28-00000598caf1/w1_slave | sed -n 's/^.*\(t=[^ ]*\).*/\1/p' | sed 's/t=//' | awk '{x=$1}END{print(x/1000)}'
28.937

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Install Webservice

apt-get install apache2
service apache2 restart

import time
import json

device_file = [
    {'addr':'28-0000056a6f05','pos':'heizung_in'},
    {'addr':'28-0114656186ff','pos':'heizung_out'},
    {'addr':'28-0114657d02ff','pos':'wasser_in'},
    {'addr':'28-0114653070ff','pos':'wasser_out'},
    {'addr':'28-01146537e8ff','pos':'solar_out'},
    {'addr':'28-011465624bff','pos':'solar_in'},
    {'addr':'28-011465624bff','pos':'raum'}
]

W1_PATH = '/sys/bus/w1/devices'
OUTPUT = '/var/www/html/sensorData'


def main():
    result = {}

    for i in device_file:
        with open(f"{W1_PATH}/{i['addr']}/w1_slave") as f:
            lines = f.readlines()
            f.close()

        if lines[0].strip()[-3:] == 'YES':        
            equals_pos = lines[1].find('t=')
            if equals_pos != -1:
                result[i['pos']] = float(lines[1][equals_pos+2:]) / 1000.0   
                print(f"{i['pos']} with {result[i['pos']]}°C")

    with open(OUTPUT, 'w') as f:
        f.write(json.dumps(result))

if __name__ == "__main__":
    main()