This is a small Debian NSLU2 1-Wire HowTo that explains the steps needed to get some data out of those small cool devices using a DS18S20 NSLU2 1-Wire setup.
The component covered by green heat shrink in the picture below is a 1-Wire component, specifically a temperature measuring device, model DS18S20:
(18S20 wiring is shown on this page: DS18S20 Wiring )
The 1-Wire bus runs well on both telephone cable and Ethernet cable, and since the DS18S20 was already soldered onto a piece of Ethernet cable and covered in heat shrink, I chose an easy to make test setup by connecting the Ethernet cable to a piece of ordinary telephone cable, because the connector already mounted on the telephone cable fits directly into a DS9490R 1-Wire USB adapter available from hobby-boards.com. It’s the blue device in the picture below:
(See the post called Debian on NSLU2 With USB Hard Disk and Homeplug Network for more details about the rest of the system.)
Paul Alfille wrote a clever piece of software that makes it easy to handle 1-Wire units. It’s called OWFS, and the project has its own website at owfs.org, if you want to know more about how OWFS works. I chose this software to handle the units on my 1-Wire NSLU2 Debian installation, but there’s a bit of work to do to get the 1-Wire software installed and running. Instructions are available at owfs.org / Setup / Install / Download, which points to the project files on SourceForge.net.
In order to get the installation files for OWFS onto the NSLU2 I logged in via my laptop PC using ssh and use wget on NSLU2: (Replace .xx with the address of the NSLU2 on the intranet)
$ ssh thomas@192.168.1.xx $ mkdir /home/thomas/owfs_install $ cd /home/thomas/owfs_install $ wget sourceforge.net/projects/owfs/files/owfs/2.8p13/owfs-2.8p13.tar.gz/download $ mv download owfs-2.8p13.tar.gz $ tar -zxvf owfs-2.8p13.tar.gz $ cd /home/thomas/owfs_install/owfs-2.8p13
For some reason the downloaded file is named download so I use the mv command to rename it to something more precise.
When I try to install OWFS it turns out that I’m missing something on my freshly installed Debian:
$ ./configure error: no acceptable C compiler found in $PATH
The package build-essential contains the needed C compiler:
$ su # apt-get install build-essential # exit
Trying to configure one more time reveals a whole bunch of missing software required for OWFS to compile and run:
$ ./configure ... configure: WARNING: Cannot find php binary. Install php or php5 package configure: WARNING: OWPHP is disabled because php binary is not found configure: WARNING: Cannot find python include-file. Install python-devel package. configure: WARNING: OWPYTHON is disabled because python include-file is not found checking for Tcl configuration... configure: WARNING: Can't find Tcl configuration definitions configure: WARNING: OWTCL is disabled because tclConfig.sh is not found configure: WARNING: LD_EXTRALIBS= OSLIBS= configure: WARNING: Can't find fuse.h - Add the search path with --with-fuseinclude configure: WARNING: Install FUSE-2.2 or later to enable owfs - download it from http://fuse.sourceforge.net/ configure: WARNING: OWFS is disabled because fuse.h is not found. configure: WARNING: Can't find libusb configure: WARNING: libusb not found, usb will be disabled ... Compile-time options: USB is DISABLED Profiling is DISABLED Tracing memory allocation is DISABLED 1wire bus traffic reports is DISABLED ... Module configuration: owfs is DISABLED swig is DISABLED owperl is DISABLED owphp is DISABLED owpython is DISABLED owtcl is DISABLED
Fortunately most of the missing stuff is contained in these 7 packages:
$ su # apt-get install php5-cli python2.4-dev tcl-dev tk-dev libusb-dev swig libperl-dev # exit
The warning about the missing FUSE software is cleared by downloading and installing like this:
$ mkdir /home/thomas/fuse $ cd /home/thomas/fuse $ wget http://sourceforge.net/projects/fuse/files/fuse-2.X/2.8.5/fuse-2.8.5.tar.gz/download $ mv download fuse-2.8.5.tar.gz $ tar -zxvf fuse-2.8.5.tar.gz $ cd /home/thomas/fuse/fuse-2.8.5/ $ ./configure $ make $ su # make install # exit
Now only one warning is present and a few disabled functions, which is acceptable for the purpose of reading temperature from the DS18S20 IC:
$ cd /home/thomas/owfs_install/owfs-2.8p13 $ ./configure configure: WARNING: LD_EXTRALIBS= OSLIBS= Compile-time options: Profiling is DISABLED Tracing memory allocation is DISABLED 1wire bus traffic reports is DISABLED Module configuration: owlib is enabled owshell is enabled owfs is enabled owhttpd is enabled owftpd is enabled owserver is enabled ownet is enabled ownetlib is enabled owtap is enabled owmon is enabled owcapi is enabled swig is enabled owperl is enabled owphp is enabled owpython is enabled owtcl is enabled
And a final install:
$ make $ su # make install # exit
Note that $ means you are working on the CLI as a normal user, and # means you’re working as root, which should be minimized since you have total power as root which again means that you could easily cause irreversible damage to your system by accident. Therefore it’s best to do as much as you can as a normal user.
Howto access DS9490: FS in OWFS stands for File System so I created a directory for the 1-Wire devices and mounted the one-wire file system in this new directory:
$ mkdir /home/thomas/owfs $ /opt/owfs/bin/owfs -u /home/thomas/owfs DEFAULT: owlib.c:SetupSingleInboundConnection(201) Cannot open USB bus master DEFAULT: owlib.c:LibStart(54) No valid 1-wire buses found
Again, the separation between root and normal users means that as a normal user (thomas) I don’t have direct access to the USB DS9490R adapter, so I have to change to superuser root to mount OWFS:
$ su # /opt/owfs/bin/owfs -u /home/thomas/owfs DEFAULT: ow_usb_msg.c:DS9490_open(276) Opened USB DS9490 bus master at 1:4. DEFAULT: ow_usb_cycle.c:DS9490_ID_this_master(191) Set DS9490 1:4 unique id to 81 59 25 27 00 00 00 CE # exit
But still more problems related to root versus normal user permissions – the mounted directory containing the 1-Wire data is not available to normal users:
$ ls -la /home/thomas total 32 drwxr-xr-x 5 thomas thomas 4096 Sep 8 12:44 . drwxr-xr-x 3 root root 4096 Sep 2 20:20 .. -rw------- 1 thomas thomas 1338 Sep 8 12:47 .bash_history -rw-r--r-- 1 thomas thomas 220 Sep 2 20:20 .bash_logout -rw-r--r-- 1 thomas thomas 3116 Sep 2 20:20 .bashrc -rw-r--r-- 1 thomas thomas 675 Sep 2 20:20 .profile drwxr-xr-x 3 thomas thomas 4096 Sep 8 09:15 fuse d????????? ? ? ? ? ? owfs drwxr-xr-x 3 thomas thomas 4096 Sep 7 20:59 owfs_install
and can’t be listed when you’re logged in as a normal user:
$ ls -la /home/thomas/owfs ls: cannot access owfs: Permission denied
Changing to superuser using su reveals the goodies:
$ su # ls -la /home/thomas total 32 drwxr-xr-x 5 thomas thomas 4096 Sep 8 12:44 . drwxr-xr-x 3 root root 4096 Sep 2 20:20 .. -rw------- 1 thomas thomas 1338 Sep 8 12:47 .bash_history -rw-r--r-- 1 thomas thomas 220 Sep 2 20:20 .bash_logout -rw-r--r-- 1 thomas thomas 3116 Sep 2 20:20 .bashrc -rw-r--r-- 1 thomas thomas 675 Sep 2 20:20 .profile drwxr-xr-x 3 thomas thomas 4096 Sep 8 09:15 fuse drwxr-xr-x 1 root root 8 Sep 8 12:51 owfs drwxr-xr-x 3 thomas thomas 4096 Sep 7 20:59 owfs_install
My OWFS NSLU2 system is up and running, and 10.4F7… is the DS18S20 IC on the 1-Wire bus:
# ls -la /home/thomas/owfs total 4 drwxr-xr-x 1 root root 8 Sep 8 12:51 . drwxr-xr-x 5 thomas thomas 4096 Sep 8 12:44 .. drwxrwxrwx 1 root root 8 Sep 8 12:52 10.4F7494010800 drwxrwxrwx 1 root root 8 Sep 8 12:52 81.592527000000 drwxr-xr-x 1 root root 8 Sep 8 12:51 alarm drwxr-xr-x 1 root root 8 Sep 8 12:51 bus.0 drwxr-xr-x 1 root root 8 Sep 8 12:51 settings drwxrwxrwx 1 root root 8 Sep 8 12:52 simultaneous drwxr-xr-x 1 root root 8 Sep 8 12:51 statistics drwxr-xr-x 1 root root 32 Sep 8 12:51 structure drwxr-xr-x 1 root root 8 Sep 8 12:51 system drwxr-xr-x 1 root root 8 Sep 8 12:51 uncached
In order to get access to OWFS as a normal user there’s trick you can do, but first I’m rebooting to make sure OWFS is completely shutdown. (There’s probably a clever way to do this, if you know what you’re doing 
):
# reboot
Log in again from laptop to NSLU2:
$ ssh thomas@192.168.1.xx
The option --allow-other can be added when running OWFS, which allows normal users to access the 1-Wire file system without changing to superuser (the -u option means that you’re connecting via USB adapter instead of a serial connector):
$ su # /opt/owfs/bin/owfs --allow_other -u /home/thomas/owfs DEFAULT: ow_usb_msg.c:DS9490_open(276) Opened USB DS9490 bus master at 1:4. DEFAULT: ow_usb_cycle.c:DS9490_ID_this_master(191) Set DS9490 1:4 unique id to 81 59 25 27 00 00 00 CE # exit
Now there is access to the owfs directory even when you’re logged in as a normal user:
$ ls -la /home/thomas total 32 drwxr-xr-x 5 thomas thomas 4096 Sep 8 12:44 . drwxr-xr-x 3 root root 4096 Sep 2 20:20 .. -rw------- 1 thomas thomas 1452 Sep 8 12:57 .bash_history -rw-r--r-- 1 thomas thomas 220 Sep 2 20:20 .bash_logout -rw-r--r-- 1 thomas thomas 3116 Sep 2 20:20 .bashrc -rw-r--r-- 1 thomas thomas 675 Sep 2 20:20 .profile drwxr-xr-x 3 thomas thomas 4096 Sep 8 09:15 fuse drwxr-xr-x 1 root root 8 Sep 8 13:02 owfs drwxr-xr-x 3 thomas thomas 4096 Sep 7 20:59 owfs_install
$ ls -la /home/thomas/owfs total 4 drwxr-xr-x 1 root root 8 Sep 8 13:02 . drwxr-xr-x 5 thomas thomas 4096 Sep 8 12:44 .. drwxrwxrwx 1 root root 8 Sep 8 13:02 10.4F7494010800 drwxrwxrwx 1 root root 8 Sep 8 13:02 81.592527000000 drwxr-xr-x 1 root root 8 Sep 8 13:02 alarm drwxr-xr-x 1 root root 8 Sep 8 13:02 bus.0 drwxr-xr-x 1 root root 8 Sep 8 13:02 settings drwxrwxrwx 1 root root 8 Sep 8 13:02 simultaneous drwxr-xr-x 1 root root 8 Sep 8 13:02 statistics drwxr-xr-x 1 root root 32 Sep 8 13:02 structure drwxr-xr-x 1 root root 8 Sep 8 13:02 system drwxr-xr-x 1 root root 8 Sep 8 13:02 uncached
To read out the temperature from the DS18S20 IC we have to take a look at the file called temperature:
$ ls -la /home/thomas/owfs/10.4F7494010800 total 0 drwxrwxrwx 1 root root 8 Sep 8 13:03 . drwxr-xr-x 1 root root 8 Sep 8 13:02 .. -r--r--r-- 1 root root 16 Sep 8 13:02 address -rw-rw-rw- 1 root root 256 Sep 8 13:02 alias -r--r--r-- 1 root root 2 Sep 8 13:02 crc8 drwxrwxrwx 1 root root 8 Sep 8 13:03 errata -r--r--r-- 1 root root 2 Sep 8 13:02 family -r--r--r-- 1 root root 12 Sep 8 13:02 id -r--r--r-- 1 root root 16 Sep 8 13:02 locator -r--r--r-- 1 root root 1 Sep 8 13:03 power -r--r--r-- 1 root root 16 Sep 8 13:02 r_address -r--r--r-- 1 root root 12 Sep 8 13:02 r_id -r--r--r-- 1 root root 16 Sep 8 13:02 r_locator -r--r--r-- 1 root root 12 Sep 8 13:02 temperature -rw-rw-rw- 1 root root 12 Sep 8 13:03 temphigh -rw-rw-rw- 1 root root 12 Sep 8 13:03 templow -r--r--r-- 1 root root 32 Sep 8 13:02 type
All data from the 1-Wire IC are contained in different files in OWFS, and the content of files can be displayed with the cat command in Linux:
$ cat /home/thomas/owfs/10.4F7494010800/temperature 24
So this value shows that the system is running and temperature measurements are being done (24 deg. C). Information about the type of IC is contained in the type file:
$ cat /home/thomas/owfs/10.4F7494010800/type DS18S20
Just to proved that the resolution is higher than 1 deg. C I did one more readout and that showed 4 more digits after the previous value:
$ cat /home/thomas/owfs/10.4F7494010800/temperature 24.0625
The obvious next step is to build even more software on top of NSLU2 OWFS installation to make nice graphs over time to gain comprehensive information about the temperature.
The DS18S20 can of course be placed in many different locations, even outdoors if you use heat shrink to protect the IC against the weather.
(Update: Do your OWFS sensors disappear from time to time? Please join the discussion below).
