1-Wire USB on a Long Ethernet Cable

Units on 1-Wire bus must be connected in a daisy chain, which means you’ll have a lot of different connection points along the bus cable, in my case an ordinary Ethernet cable. This has been a problem for me earlier since my cable was placed outdoors for air and soil temperature measurements, and soil moisture measurements. I actually need a connection point to the 1-Wire bus at each unit I connect to the cable, because of the daisy chain topology. In order to make these connections somewhat weatherproof I chose to solder any cable joints together and cover it with heat shrink. This has worked well and my old outdoor system collected data for almost a year, before I took it down again when I had to move to another house.

But the soldered joints also gave me problems, because it was hard to make adjustments afterwards, like moving a unit, because the cables would have a fixed length, or taking a unit indoors for repair. This can of course be solved by investing in high quality outdoor enclosures for each unit or cable joint but since this weather data collection project is a hobby there not any immediate return on this relatively large investment. However, if you are getting paid to build this, you should be aware that the system would have a much longer lifetime if you mount the units and joints in a weather proof enclosure. But let’s stick with the hobby type of project for a while.

I wanted to make it easier to modify the physical setup of the system, and one of the easiest ways to connect wires is by using terminal strips:

(There’s a DS18S20 1-Wire IC wrapped in heat shrink to the left in the picture.)

The 1-Wire bus uses only 2 wires (?…) for communication and power transfer. (I guess the name is referring to the communication part.)

A small test showed that the bus worked just fine through the terminal strip (and 17 m ~ 56 ft of Ethernet cable), which makes my life a whole lot easier, as I’m now able to modify the physical setup in many ways, without going outside with my soldering iron in the middle of the snow to replace a unit – brrr… Just bring a screwdriver.

For soil temperature measurements I have glued a DS18S20 temperature sensor onto an aluminium sheet. Note the two cables due to the daisy chain topology:

I assume that the metal sheet will give a good average temperature as is has some mass and therefore filters out high frequency temperature changes. The large area helps averaging the temperature too.

This is all of the components in the 1-Wire system so far:

  • To the left: DS18S20 temperature sensor, for air temperature measurements
  • Aluminium sheet: DS18S20 temperature sensor, for soil temperature measurements
  • In the middle: DS2760 PCB, for soil moisture measurements
  • To the right: Watermark soil moisture probe

The DS2760 PCB has been installed in my previous garden, in a cheap plastic enclosure, wrapped in a plastic bag, but the PCB survived for several months in all kinds of weather. It still looks new with no corrosion at all. The plastic enclosure has changed color due to sunlight:

I’ll also be using terminal strips for this unit and see what happens regarding corrosion.

The soil moisture sensor part of this system is a bit special because the circuit board needs 12 volts to function, which I’m injecting into the Ethernet cable using the brown wire pair, next to the 1-Wire bus carried by the blue wire pair. The extra voltage is generated by a generic mains adapter, protected by a fuse (red and black wires in the picture below):

I have mounted the sensor for air temperature measurements on a stick and covered the sensor with a small cap with tin foil on it to reflect the sun:

I also need a barrier between the soil and the soil temperature sensor (hopefully this is not a biodegradable plastic bag ;-) ):

The soil moisture sensor circuit is tied to a stick and covered with a plastic bag to provide some protection from the weather:

Again, if you want a more reliable setup you should use a weather proof enclosure, but I haven’t experienced any problems so far, although it would be an obvious upgrade to make in the future.

The NSLU2 is placed indoors to protect it against the weather, but I have to get the signals and power outside to the sensors, so I have to go through the window. Since this is a rented house I don’t want to drill large holes in the window frame, so I have removed the extra four wires in the Ethernet cable to be able to close the window without cutting any wires accidentally. Using two different sizes of heat shrink I’m able to make a pretty discreet transition from the indoor to the outdoor environment:

There was already a not so neat looking satellite coax cable going through a hole in the window frame, so adding an Ethernet cable is not big deal, although it’s beginning to look messy:

Rather discreet looking 1-Wire cable outside (the two cables in the top are existing coax cable for satellite):

I have dug a 25 cm (10″) deep hole in the ground for the Watermark soil moisture sensor and the temperature sensor on the aluminium sheet, and once I have calibrated the soil moisture sensor the hole will be filled with soil again and the system will collect data over the winter:

The air temperature sensor is also in place and ready to collect data:

Now I’m going to work on the OWFS software setup on my Debian NSLU2.

How to Read 1-Wire Temperature Using a NSLU2 With Debian

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).