LJFuse

LJFuse makes communicating with a LabJack device simple on Linux and Mac OS X. Really simple. Trivial, really.

Introduction

It’s been said (many, many, times) that everything’s a file in UNIX. LJFuse adopts that philosophy and makes the connections on a LabJack device into files on the filesystem. To do so, it uses FUSE on Linux and MacFUSE on Mac OS X.

For example, to read analog input AIN0, read a file named “AIN0”.

  
$ cat MyU6/connection/AIN0
3.300
  

To set DAC0 to 2.4V, write “2.4” to a file named “DAC0”.

  
$ echo 2.4 > MyU6/connection/DAC0
$ cat MyU6/connection/DAC0   # Read the DAC0 to verify it was set
2.400
  

To set FIO0 to digital output high, write a “1” to “FIO0”.

  
$ echo 1 > MyU6/connection/FIO0-dir  # Set the direction to output
$ echo 1 > MyU6/connection/FIO0      # Set the state to output high
$ cat MyU6/connection/FIO0           # Read the value back
1    
  

You can do this from any program that knows how read and write files. Your program doesn’t need to know about USB communication, drivers, or the LabJack API. The details are hidden by LJFuse.

Quickstart

Check the requirements (in short, a working LabJackPython installation on Linux or Mac OS X), and download the source code for LJFuse from GitHub. Click the “Download Source” button on the GitHub page to download.

Connect a LabJack and run LJFuse like this:

  
$ python ljfuse.py
  

After LJFuse starts, change to the “root-ljfuse/” directory it created and look around:

  
$ cd root-ljfuse/
$ ls
HOW_TO_UNMOUNT.txt  My U6/  README.txt
  

There are “README.txt” files in every subdirectory with context-specific help.

When done, unmount LJFuse. The file “HOW_TO_UNMOUNT.txt” has instructions.

  
$ cat HOW_TO_UNMOUNT.txt
  

Requirements

• A U3, U6, or UE9 over USB with the latest firmware. The U3 requires 1.26 or higher; the U6 requires 1.15; and the UE9 requires control firmware 2.13 and comm firmware 1.5. Check the beta folders of the firmware section if the release version doesn’t meet the requirements.
• LabJackPython
• Exodriver, the Linux and Mac OS X driver
• On Mac OS X, LJFuse requires MacFUSE. On Linux, LJFuse uses the kernel’s fuse implementation.

LJSocket is not required, but LJFuse will automatically access LabJack devices opened by LJSocket. On Mac OS X, LJSocket also has the benefit of allowing LJFuse to run in the background (instead of tying up a terminal window).

Running

Plug in a U3, U6, or UE9 and run:

  
$ python ljfuse.py
  

On Mac OS X, it will print

  
$ python ljfuse.py
Making directory root-ljfuse for LJFuse
Mounting LJFuse at root-ljfuse.
When done, eject it from the Finder or run `umount LJFuse' (without quotes).
$
  

On Linux, it will print

  
$ python ljfuse.py 
Making directory root-ljfuse for LJFuse
Mounting LJFuse at root-ljfuse.
Unmount it with `fusermount -u root-ljfuse' (without quotes).
$
  

In either case, change to the “root-ljfuse/” directory and look around. There are “README.txt” files in every subdirectory with context-specific help.

  
$ cd root-ljfuse/
$ ls
HOW_TO_UNMOUNT.txt  My U6/     README.txt
  

Example session

In this session, we have a U3-HV and U6 connected when running LJFuse:

  
$ python ljfuse.py
Making directory root-ljfuse for LJFuse
Mounting LJFuse at root-ljfuse.
When done, eject it from the Finder or run `umount LJFuse' (without quotes).
$ cd root-ljfuse/
$ ls
HOW_TO_UNMOUNT.txt  My U3-HV/           My U6/              README.txt
  

LJFuse made two directories, one for the U3-HV and one for the U6. It also made two text files with documentation.

You can rename a device by renaming its directory. The name of the device is saved in its flash memory:

  
$ mv "My U3-HV" "Marcel"
$ ls
HOW_TO_UNMOUNT.txt  Marcel/             My U6/              README.txt
$ mv "My U6" MyU6
$ ls
HOW_TO_UNMOUNT.txt  Marcel/             MyU6/               README.txt
  

Inside a device’s subdirectory, there are files relating to the device’s attributes:

  
$ cd MyU6/
$ ls
README.txt       firmwareVersion  serialNumber
connection/      modbus/
$ cat firmwareVersion 
1.15
  

The “connection/” subdirectory is the most interesting. It contains files for the different connections on the device.

  
$ cd connection/
$ ls
AIN0        DAC0        FIO1        FIO3        FIO5        FIO7
AIN1        DAC1        FIO1-dir    FIO3-dir    FIO5-dir    FIO7-dir
AIN2        FIO0        FIO2        FIO4        FIO6        README.txt
AIN3        FIO0-dir    FIO2-dir    FIO4-dir    FIO6-dir
  

Wire a jumper from DAC0 to AIN0 and run:

  
$ echo 1.5 > DAC0     # Set DAC0 to 1.5V
$ cat DAC0            # Verify that it set
1.500
$ cat AIN0            # Read AIN0
1.499
  

Connect an LED from FIO2 to GND (short side in GND) and toggle it:

  
$ cat FIO2-dir        # Check the direction of FIO2
0    
$ echo 1 > FIO2-dir   # Set FIO2 to output
$ cat FIO2-dir        # Verify the direction changed
1    
$ echo 1 > FIO2       # Set FIO2 high, turning LED on
$ echo 0 > FIO2       # Set FIO2 low, turning LED off
$ while true          # Show off a little
> do                  # Toggle the LED once per second
>   echo 1 > FIO2
>   sleep 1
>   echo 0 > FIO2
>   sleep 1
> done
^C                    # Hit Ctrl-C to quit
  

We hope these examples demonstrate how quickly and easy LJFuse makes it to communicate with your LabJack.

Shell tricks

The shell can operate on the files in the “connection/” directory to ask interesting questions. For example, which FIO connections are set to digital output?

  
$ grep 1 FIO?-dir
FIO0-dir:1    
FIO2-dir:1    
  

Answer: FIO0 and FIO2. Here’s how to set them all to digital output:

  
$ for fiodir in FIO?-dir
> do
>   echo 1 > $fiodir
> done
  

Verify that it worked:

  
$ grep 1 FIO?-dir
FIO0-dir:1    
FIO1-dir:1    
FIO2-dir:1    
FIO3-dir:1    
FIO4-dir:1    
FIO5-dir:1    
FIO6-dir:1    
FIO7-dir:1    
  

Here’s how to ask if a value is above a threshold. Carrying on with a previous example, wire a jumper connecting DAC0 to AIN0.

  
$ cat DAC0
1.500
$ cat AIN0
1.499
$ THRESHOLD=1.6
$ AIN0=$(cat AIN0)
$ if [ $(echo "$AIN0 > $THRESHOLD" | bc) -eq 1 ]
> then
>   echo "AIN0: $AIN0 above threshold $THRESHOLD"
> else
>   echo "AIN0: $AIN0 below threshold $THRESHOLD"
> fi
AIN0: 1.499 below threshold 1.6
$ echo 2.0 > DAC0
$ cat DAC0
2.000
$ cat AIN0
1.999
$ AIN0=$(cat AIN0)
$ if [ $(echo "$AIN0 > $THRESHOLD" | bc) -eq 1 ]
> then
>   echo "AIN0: $AIN0 above threshold $THRESHOLD"
> else
>   echo "AIN0: $AIN0 below threshold $THRESHOLD"
> fi
AIN0: 1.999 above threshold 1.6
  

Exiting and unmounting LJFuse

To stop LJFuse, all applications and terminal windows must exit the LJFuse “root-ljfuse/” directory and its subdirectories.

  
$ pwd
/path/to/LJFuse/root-ljfuse/MyU6/connection
$ cd ../../..
$ pwd
/path/to/LJFuse
  

On Linux run:

  
$ fusermount -u root-ljfuse
  

On Mac OS X, find the LJFuse icon in the Finder and eject it. You could also run:

  
$ umount LJFuse
  

If unmounting returns an error, double check that all applications and terminal windows have exited LJFuse directories. Since 10.6, the Mac OS X Finder will report which application is using a volume when trying to eject it.

Programming language examples

The following examples illustrate how to

1. Read AIN0 once per second and log timestamp and value
2. Toggle an LED on FIO0

in many different programming languages. The examples would not be out of place in any introductory programming book. All they do is basic file I/O.

Shell

C

Python

Ruby

PHP

Perl

Java

Scala

LabVIEW