This article is taken from the following web pages, with a few modifications by me.

• Cambridge University Computer Lab
• RaspberryPi.org

The intention is to create a Raspberry monitoring station for each room in the house, each broadcasting temperature and other information back to a central server in my office.

To start with I am using DS18B20 temperature sensor, which you can get from Amazon and eBay for about 50p-£1 each.

Along with the sensor you are going to need a breadboard, ribbon cable, some wires and 4.7k resistor

breadboard-ic.png

Once you have this wired up, you need to activate the sensor

$ sudo modprobe w1-gpio
$ sudo modprobe w1-therm
$ cd /sys/bus/w1/devices
$ ls

This will give you the id of the device starting 28- and looking something like

28-xxxxxxxxxxxxxxx

Now create a shell script we can query the sensor

nano ~/temp.sh

And add the following lines

#! /bin/bash
sudo modprobe w1-gpio
sudo modprobe w1-therm
roomtemp=$(cat /sys/bus/w1/devices/28-xxxxxxxxxxxx/w1_slave | grep  -E -o ".{0,0}t=.{0,5}" | cut -c 3-)
echo "Temperature: $roomtemp"

To make it executable, give it +x permissions

chmod +x ~/temp.sh

And it will print out the temp, device / 1000 for ‘C

$ ~./temp.sh
186903

Which is 18.69′C

Now lets create a little Python script that parses the data and loops printing out the value every 10 secs

nano ~/temp.py

And add the following lines

import time
while True:
        # Open the file that we viewed earlier so that python 
        # can see what is in it. Replace the serial number as before.
        tfile = open("/sys/bus/w1/devices/28-xxxxxxxxxx/w1_slave")
        # Read all of the text in the file.
        text = tfile.read()
        # Close the file now that the text has been read.
        tfile.close()
        # Split the text with new lines (\n) and select the second line.
        secondline = text.split("\n")[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 ("%2.2f'C" % temperature)
        time.sleep(10)

To run the script, use

python temp.py

Mine is currently showing a balmy 16-19′C in my office

19.00'C
18.94'C
19.06'C
18.81'C
18.12'C
18.12'C
18.50'C
18.56'C
18.06'C
18.06'C
18.25'C
18.06'C
17.69'C
17.81'C
17.25'C
17.12'C
16.69'C
16.31'C
16.50'C
16.81'C
17.12'C
17.38'C
17.56'C
17.56'C

Loading Drivers on Startup

The following lines are taken from raspberry.znix.com

sudo nano /etc/modprobe.d/raspi-blacklist.conf and comment out the following 2 lines

blacklist spi-bcm2708
blacklist i2c-bcm2708

sudo nano /etc/modules

w1-gpio
w1-therm

Next steps

Now that we have a temperature sensor schematic and working prototype, need to build 3 or 4 more, and then hook them up to the central server. So once they are built, I need a Restful service that each of the Pi’s can call with their temperature data. The easiest way in Python is using the Flask framework backed with a Mongo DB. Watch this space for….

Building a RESTful web service using Pythong & Flask