U12 Quickstart Tutorial | LabJack
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U12 Quickstart Tutorial

1. Install the appropriate LabJack driver and software bundle.

2. Connect the U12 to the computer or hub.  The status LED should immediately blink 4 times (at about 4 Hz), and then stay off while the computer enumerates (installs) the U12.  Earlier versions of Windows will bring up a hardware install window, and you should accept all defaults if prompted.  After enumeration the LED will blink twice and remain solid on.

If the U12 fails to enumerate:

  • Make sure you are running Windows OS version 4.10.2222 or higher,
  • If Win98SE, check out win98sehid.zip,
  • Try connecting the U12 to another PC,
  • Try connecting a different USB device to the same port, preferably an HID device (e.g. mouse),
  • More U12 troubleshooting info.

3.  Run LJtest.exe which was installed during step #1 above.  There should be nothing connected to the U12 besides USB, and do not select "Test Fixture Installed" or "Continuous".  Close when done.

4.  Run LJlogger.exe for basic testing and data logging.

Some basic tests:

  • Connect a jumper wire from AO0 (Analog Out 0) to AI0 (Analog In 0).  Use the control towards the upper-left of LJlogger to change AO0, and you should read back the voltage on AI0 as shown in the first row of the voltage column to the right.
  • Connect one end of a jumper wire to +5V.  Tap the other end inside the CNT terminal, and each tap will cause 10-50 counts or so on the Counter indicator.
  • Take the same +5V wire and hold the other end inside the IO0 terminal.  Element 0 of the IO State Read indicator should turn black to indicate the digital input is reading high.
  • Connect a jumper wire from IO1 to AI1.  Click (turn black) element 1 of the IO Direction control.  Now toggle element 1 of the IO State Write control and the voltage reading on AI1 should change from 0 to 5 volts.

5.  Refer to the U12 User's Guide.


Moving forward from here ...

Software Options:

  • Sample ApplicationsA great place to start, and it may be all you ever need.
  • Programming:  We have drivers/examples available for many languages. 
  • DAQFactory:  DAQFactory is measurement and automation software from AzeoTech.  The free Express version of DAQFactory works with the U12.  DAQFactory allows non-programmers to make custom applications.  It is easy to collect input data, convert to engineering units, display it, and log it to file, without any programming.  Scripting is also supported so you can do advanced applications with control and automatic setting of outputs.

Getting Support:

  • If you have a question that you think should be covered in the documentation, try going to our web page where you think it should be and post a comment there.  The U12 Datasheet is a likely location.
  • Other great options are our forum or email.




I would like to use Labjack U12 with Matlab but I have some problems. Matlab shows me this error message:
>> header='C:\Program Files (x86)\LabJack\drivers\ljackuw.h'

header =

C:\Program Files (x86)\LabJack\drivers\ljackuw.h

>> ljud_LoadDriver
Error using loadlibrary>lFullPath (line 586)
Could not find file C:\progra~1\LabJack\drivers\labjackud.h.

Error in loadlibrary (line 220)

Error in ljud_LoadDriver (line 10)


The path has changed with our new installers so needs to be modified to point to the correct location of the ljackuw.h file.  However, we are looking at doing support for newer versions of Matlab in a different way that should be much easier.  Please see this: http://forums.labjack.com/index.php?showtopic=6053&view=findpost&p=20472

Using the U12 as a single ended input, what is the maximum and minimum over voltage I can apply to the input. I know the operating range is +/- 10v , what happens when the input voltage goes outside this range. Will the A-D lock up on all channels.


The related specs are in Appendix A of the U12 User's Guide.  The limit to prevent damage is +/-40V.  The protection circuitry will handle overvoltage at least up to that level.

i want to a u12 ph board , CB 25 TERMINAL BOARD WITH CABLE ,



We do not have any CDs.  Rather you go to the U12 Support Homepage to get started.  So you just need to order a U12-PH and CB25.  Note that the DB25 cable will not connect to the pin-headers on the U12-PH, so you will have to do something for that.

See our Sales page for sales information.  The quickest way to get a quote is using the shopping cart at labjack.com.  If that does not work for you, email [email protected] and request a PDF quote.

I am trying to hook up two different U12s to DAQFactory, and the LED on both devices starts blinking if I connect them both at the same time. This is my first time working with Daqfactory, so any pointers would be most appreciated.  Thanks! 

If you connect 1 at a time does it also blink?  As I recall DAQFactory blinks the LED on the U12 when it reads from it.

Yes, they do. I think I made a rookie mistake! Thanks a lot.

I have a follow-up question- if I want to connect two different U12s, should I give them different device IDs (e.g. 0 and 1) and then use the device IDs when I set up channels and logs? 


Yes, that is how it works with our newer devices and pretty sure that is true for the original U12 also.  You can use LJconfig.exe to set the LocalID, but don't use 0 as that means first-found in DAQFactory.  See Section 2.2 of the DF-LJUD App Guide, which is for UD devices but much of it applies to the U12 also.

Thanks a lot! Both U12s are now running fine.