I followed the installation instructions on the Ubuntu wiki but got stuck on the line where we try to get owfs to talk to the 1-wire network.  This worked for me:

sudo /opt/owfs/bin/owfs u -m /var/lib/1wire

I have a Dallas Semiconductor DS1490F 2-in-1 Fob, 1-Wire adapter.  Also, after installing, I found that the Navitron forum has a discussion on owfs.

All I want to be able to do is log temperature data to a text file.  I think I’ll write a simple C++ app to log the temperature data to a text file and then use gnuplot to plot graphs.

In Python, I found I was getting the following error:

​>>> import ow
>>> ow.init('u')
DEFAULT: ow_ds9490.c:(255) Unclear what <> means in USB specification, 
         will use first adapter.
DEFAULT: owlib.c:(201) Cannot open USB bus master
DEFAULT: owlib.c:(54) No valid 1-wire buses found
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.6/dist-packages/ow/__init__.py", line 224, in init
    raise exNoController

This turned out to be a permissions issue.  Running python as sudo fixed the problem, but this clearly isn’t a good solution.  Luckily, a kind person gave a guide on how to make the 1-wire USB adapter usable for non-root users.  I modified the file very slightly.  All you have to do is to create a file called /etc/udev/rules.d/owfs.rules which looks something like this:

SUBSYSTEM!="usb_device", ACTION!="add", GOTO="owfs_rules_end"
# DS2490 1-Wire adapter
SYSFS{idVendor}=="04fa", SYSFS{idProduct}=="2490", MODE="660", GROUP="fuse"

Unplug and plug your USB adapter back in.  If that doesn’t work then check that you’re a member of the fuse and idVendor with GROUP:="fuse".  If that still doesn’t work then try replacing SYSFS).  For more info on udev, and for a description of how I got udev to work with my Current Cost USB cable, see this blog post.

Here’s a simple little Python script for logging every temperature sensor reading once a minute:

#! /usr/bin/env python
print "running..."
import ow
import time

ow.init( 'u' )

# We're accessing the 1-wire bus directly from python but
# if you want to use owserver:
# ow.init( 'localhost:3030' ) # /opt/owfs/bin/owserver -p 3030 -u -r

sensors = ow.Sensor("/").sensorList()

# We're only interested in temperature sensors so remove
# any 1-wire devices which aren't temperature sensors
for sensor in sensors[:]:
    if sensor.type != 'DS18B20':
        sensors.remove( sensor ) 

# Print column headers
for sensor in sensors:
    print sensor.r_address + "\t",
print "\n",

# Print temperatures
while 1==1:
    print int(time.time()), "\t",
    for sensor in sensors:
        print sensor.temperature, "\t",
    print "\n",

And here are some handy links to the owfs documentation: owpython and owserver.

The next things to do are to connect up some more temperature sensors so I can see the temp drop across our UFH, and tinker with some graphing utilities like matplotlib and Google’s Chart Tools API; and tinker with sending data to pachube.

Update 24th Feb 2012

My owfs Python code (including code to send the data to Pachube) is now on github - please see github for the latest code.