Temperature Sensor: Just got my self a DS18D20 and I thought it will be good to build a controller to record temperature. I am using these two websites to help me start: http://raspberrywebserver.com/cgiscripting/rpi-temperature-logger/building-an-sqlite-temperature-logger.html https://www.cl.cam.ac.uk/projects/raspberrypi/tutorials/temperature/ In the second website I understood the basic to connect a DS18B20 Then the code in python to get the readings:

!/usr/bin/env python

import os import glob import time

load the kernel modules needed to handle the sensor

os.system('modprobe w1-gpio') os.system('modprobe w1-therm')

find the path of a sensor directory that starts with 28

devicelist = glob.glob('/sys/bus/w1/devices/28*')

append the device file name to get the absolute path of the sensor

devicefile = devicelist[0] + '/w1_slave'

open the file representing the sensor.

fileobj = open(devicefile,'r') lines = fileobj.readlines() fileobj.close()

print the lines read from the sensor apart from the extra \n chars

print lines[0][:-1]

print lines[1][:-1]

Split the text with new lines (\n) and select the second line.

secondline = lines[1]

Split the line into words, referring to the spaces, and select the 10th word (counting from 0).

temperaturedata = secondline.split(" ")[9]

The first two characters are "t=", so get rid of those and convert the temperature from a string to a number.

temperature = float(temperaturedata[2:])

Put the decimal point in the right place and display it.

temperature = temperature / 1000 print temperature

Then on the other URL I started to log my entries. Here is the script:

!/usr/bin/env python

import sqlite3

import os import time import glob

global variables

speriod=(15*60)-1 dbname='/home/pi/templog.db'

store the temperature in the database

def log_temperature(temp):

conn=sqlite3.connect(dbname)
curs=conn.cursor()

curs.execute("INSERT INTO temps values(datetime('now'), (?))", (temp,))

# commit the changes
conn.commit()

conn.close()

display the contents of the database

def display_data():

conn=sqlite3.connect(dbname)
curs=conn.cursor()

for row in curs.execute("SELECT \* FROM temps"):
    print str(row\[0\])+"   "+str(row\[1\])

conn.close()

get temerature

returns None on error, or the temperature as a float

def get_temp(devicefile):

try:
    fileobj = open(devicefile,'r')
    lines = fileobj.readlines()
    fileobj.close()
except:
    return None

# get the status from the end of line 1 
status = lines\[0\]\[-4:-1\]

# is the status is ok, get the temperature from line 2
if status=="YES":
    print status
    tempstr= lines\[1\]\[-6:-1\]
    tempvalue=float(tempstr)/1000
    print tempvalue
    return tempvalue
else:
    print "There was an error."
    return None

main function

This is where the program starts

def main():

# enable kernel modules
os.system('sudo modprobe w1-gpio')
os.system('sudo modprobe w1-therm')

# search for a device file that starts with 28
devicelist = glob.glob('/sys/bus/w1/devices/28\*')
if devicelist=='':
    return None
else:
    # append /w1slave to the device file
    w1devicefile = devicelist\[0\] + '/w1\_slave'

while True:

# get the temperature from the device file
temperature = get\_temp(w1devicefile)
if temperature != None:
    print "temperature="+str(temperature)
else:
    # Sometimes reads fail on the first attempt
    # so we need to retry
    temperature = get\_temp(w1devicefile)
    print "temperature="+str(temperature)

    # Store the temperature in the database
log\_temperature(temperature)

    # display the contents of the database

display_data()

time.sleep(speriod)

if __name__=="__main__": main()

Make sure you go through the steps to create the sqlite db first. Now I have a crontab job that save my reading every 15 minutes and now I need to show those reading. I used to run my Pi as webserver (LAMP) but I always thought it was a bit too much for a RPi. So I searched the web for a python web REST service and I found this nifty website: http://webpy.org/. I have to say it work like a charm. The overhead in term of resources is way less then a LAMP and it gets the job done. Is extremely simple and quick to implement. I started with some good examples: http://www.milocreek.com/wiki/index.php/GettingStarted http://www.dreamsyssoft.com/blog/blog.php?/archives/6-Create-a-simple-REST-web-service-with-Python.html I created a rest service to broadcast reading to my web server:

!/usr/bin/env python

import web from web.template import render

db = web.database(dbn='sqlite', db='/home/pi/templog.db')

urls = (   '/', 'index',   '/(.*)','get_temp' )

app = web.application(urls, globals())

class index:     def GET(self):     temps = db.query("select * from temps where timestamp>datetime('now','-24 hours')") #select('temps')         output= ''         for temp in temps:             output += ",['"+str(temp.timestamp)+"',"+str(temp.temp)+"]"

    return output

class get_temp:     def GET(self,hours):     temps = db.query("select * from temps where timestamp>datetime('now','-%s hours')" % hours) #select('temps')         output= ''         for temp in temps:             output += ",['"+str(temp.timestamp)+"',"+str(temp.temp)+"]"

    return output

if __name__ == "__main__":     app.run()

The rest service will be broadcast on port 8080 by default. Just type http://piipaddress:8080 and you will see the data. To start the rest service when the Pi reboot just call the python code above to  crontap:

sudo crontab -e

Then add the code below to the bottom of the script.

@reboot /home/pi/rest.py

  The last step is pick the data up from my webserver (LAMP) and use Google API to present some fancy graphic. Here is the code:

 <!DOCTYPE html>

    <title>Temperature Log</title>               <script src="//code.jquery.com/jquery-1.10.2.js"></script>     <script type="text/javascript" src="https://www.google.com/jsapi"></script>     <script>         $(document).ready(function(){                                   $('#intDis').html($('#interval option:selected').text());           $('#interval').change(function () {             location.href =  'http://home.robertomignucci.co.uk?interval=' + $('#interval option:selected').val()           });         });       google.load("visualization", "1", {packages:\["corechart"\]});       google.setOnLoadCallback(drawChart);       function drawChart() {         var data = google.visualization.arrayToDataTable(\[           \['Time', 'Temperature'\]         \]);         var options = {           title: 'Temperature Log'         };         var chart = new google.visualization.LineChart                         (document.getElementById('chart\_div'));         chart.draw(data, options);       }     </script>     

Temperature Report

         

Here is the result: http://home.robertomignucci.co.uk/   I hope this will be useful to you. Have fun with it!