LabJack

Caution

This page is in notes format, and may not be of the same quality as other pages on this site.

LabJack is a company that produces data acquisition systems (DAQs).

Drivers

LabJack provides drivers for a variety of operating systems and CPU architectures. The following table shows the drivers for each LabJack model, categorized by operating system.¹

LabJack Model	Windows	Linux	macOS
U3, U6, UE9	UD library	Exodriver	Exodriver
U12	U12 Windows Installer	ljacklm	ljacklm
T4, T7	LJM library	LJM library	LJM library

ljacklm is a higher level library that requires Exodriver.

LabJack also maintains the Python library called LabJackPython. It is cross-platform and runs on Windows, Linux and macOS. It uses the UD and U12 drivers on Windows, and the Exodriver on Linux and macOS. It doesn’t support the T4 and T7 which require the LJM library. For that, use the Python_LJM library.

For documentation on the LabJackPython, it is recommended that you read the docstrings in the source code.

LabJack U3

The LabJack U3 comes in a low voltage (U3-LV) and high voltage (U3-HV) version. This refers to the analogue input voltage range. The U3-LV has a $0-2.4V$ or $0-3.6V$ analogue input voltage range, while the U3-HV has a $\pm 10V$ or $- 10 / +20V$ analogue input voltage range.²

All of the digital I/O pins on the U3 have 3 possible states: input, output-high and output-low. When configured as an input, there is always a $100k\Omega$ pull-up resistor connected to 3.3V. When configured as an output, the pin is either connected to 3.3V or GND through a small series resistor.

Tip

Because of the $100k\Omega$ pull-up resistor, it can be hard to tell the difference between a input and a high output signal (especially when the input is not being driven by an external source). One way to tell the difference when debugging is to connect another $100k\Omega$ resistor to the input pin and ground. If the pin is an input, the voltage should drop to about half of 3.3V (1.65V). If the pin is a high output, the voltage should stay at 3.3V.

Here is a Python example showing basic control of a U3 using the LabJackPython library.

import u3

# Create a U3 device object. By default, autoOpen=True which means the first U3 will be found and opened automatically.
device = u3.U3()
# Set pin high. NOTE: This also sets the pin as an output
# EIO0 is pin 8. Mapping is:
# 0 - 7   = FIO0 - FIO7
# 8 - 15  = EIO0 - EIO7
# 16 - 19 = CIO0 - CIO3
device.setDOState(8, 1)

If you want to open a specific U3, you can pass autoOpen=False to the U3() constructor and then pass in the serial number to open():

device = u3.U3(autoOpen = False)
device.open(serial = 320095789) # Open specific U3

LabJack U6

The LabJack U6 has 20 digital I/O. The pins MIO0-MIO2 are multiplexed with the CIO0-CIO2 pins³.

The following bit numbers are used to specify the digital I/O:

0-7 FIO0-FIO7
8-15 EIO0-EIO7
16-19 CIO0-CIO3
20-22 MIO0-MIO2  (Use 16-18 to operate on these)

Using pin numbers 20-22 in the API will not work. Instead, you have to use the corresponding CIOx bit numbers 16-18.

Footnotes

1. LabJack. Exodriver Downloads (for UD-series Linux and macOS support). Retrieved 2025-11-05, from https://support.labjack.com/docs/exodriver-downloads-for-ud-series-linux-and-macos-. ↩

2. LabJack. LabJack U3-HV Product Page. Retrieved 2026-03-11, from https://labjack.com/products/u3-hv. ↩

3. LabJack. Support and Documentation / Datasheets / U6 Datasheet / 2 - Hardware Description [U6 Datasheet]. Retrieved 2024-08-30, from https://support.labjack.com/docs/2-8-digital-i-o-u6-datasheet. ↩