LabJack U12 User manual

LabJack U12 User’s Guide
Revision 1.00
9/21/2001
LabJack Corporation
www.labjack.com
[e-mail]

For the latest version of the user’s guide, the quickstart guide, or software, go to
www.labjack.com.
The LabJack U12 is a measurement and automation peripheral that enables the connection of a
PC to the real-world. Although the LabJack U12 has many redundant protection mechanisms, it
is possible, in the case of improper and/or unreasonable use, to damage the LabJack and even
the PC to which it is connected. LabJack Corporation will not be liable for any such damage.
LabJack U12 Warranty
The LabJack U12 comes with a 1 year limited warranty from LabJack Corporation (LC),
covering this product and parts against defects in material or workmanship. The LabJack can
be damaged by misconnection (such as connecting 120 VAC to any of the screw terminals),
and this warranty does not cover damage obviously caused by the customer. If you have a
problem, contact [e-mail] for return authorization. In the case of warranty repairs,
the customer is responsible for shipping to LC, and LC will pay for the return shipping.

Table Of Contents
1. Installation............................................................................................................................. 5
1.1 Hardware Installation ....................................................................................................... 5
1.2 Software Installation......................................................................................................... 5
2. Hardware Description............................................................................................................ 7
2.1 AI0 – AI7.......................................................................................................................... 8
2.2 AO0 & AO1.................................................................................................................... 10
2.3 IO0 – IO3....................................................................................................................... 11
2.4 D0 – D15 ....................................................................................................................... 11
2.5 CNT ............................................................................................................................... 12
2.3 CAL – STB..................................................................................................................... 12
2.4 +5V................................................................................................................................ 12
2.5 GND .............................................................................................................................. 12
3. Example Applications .......................................................................................................... 13
3.1 LJconfig ......................................................................................................................... 13
3.2 LJlogger......................................................................................................................... 14
3.3 LJscope ......................................................................................................................... 17
3.4 LJtest............................................................................................................................. 18
4. Programming Reference ..................................................................................................... 20
4.1 AISample ....................................................................................................................... 20
4.2 AIBurst........................................................................................................................... 21
4.3 AIStreamStart ................................................................................................................ 23
4.4 AIStreamRead ...............................................................................................................25
4.5 AIStreamClear ............................................................................................................... 26
4.6 AOUpdate...................................................................................................................... 26
4.7 BitsToVolts .................................................................................................................... 27
4.8 VoltsToBits .................................................................................................................... 27
4.9 Counter.......................................................................................................................... 27
4.10 DigitalIO....................................................................................................................... 28
4.11 GetDriverVersion ......................................................................................................... 28
4.12 GetErrorString.............................................................................................................. 29
4.13 GetFirmwareVersion .................................................................................................... 29
4.14 GetWinVersion.............................................................................................................29
4.15 ListAll........................................................................................................................... 30
4.16 LocalID ........................................................................................................................ 31
4.17 ReEnum....................................................................................................................... 31
4.18 Reset ........................................................................................................................... 31
4.19 Watchdog .................................................................................................................... 31
4.20 ReadMem .................................................................................................................... 32
4.21 WriteMem .................................................................................................................... 33
4.22 BuildOptionBits (ActiveX only) ..................................................................................... 33
4.23 FourPack (ActiveX only) .............................................................................................. 34
A. Specifications...................................................................................................................... 35

Table Of Figures
Figure 2-1. LabJack U12 top surface......................................................................................... 7
Figure 2-2. Single-ended measurement. ................................................................................... 8
Figure 2-3. Differential measurement. ....................................................................................... 9
Figure 2-4. Single-ended measurement with voltage divider circuit. .......................................... 9
Figure 2-5. IO used to detect the state of a switch................................................................... 11
Figure 3-1. LJconfig................................................................................................................. 13
Figure 3-2. LJconfig Change Local ID ..................................................................................... 14
Figure 3-3. LJlogger ................................................................................................................ 14
Figure 3-4. LJlogger Configuration .......................................................................................... 15
Figure 3-5. LJlogger Internet Configuration ............................................................................. 16
Figure 3-6. LJlogger HTML Configuration................................................................................ 16
Figure 3-7. LJlogger Trigger Configuration .............................................................................. 17
Figure 3-8. LJscope................................................................................................................. 18
Figure 3-9. LJtest .................................................................................................................... 19

1. Installation
The LabJack U12 requires a PC running Windows 98SE, ME, 2000, or XP. To determine your
operating system version, go to
Start => Settings => Control Panel => System => General
and make sure the version number is 4.10.2222 or higher (Win98SE=4.10.2222,
WinME=4.90.3000, Win2000=5.0.2195, WinXP=5.1.XXXX).
It doesn’t matter if the hardware or software is installed first.
1.1 Hardware Installation
With the PC on and using the included cable, connect the LabJack U12 to the USB port on the
PC or USB hub. The USB cable provides power and communication for the LabJack U12. The
status LED should immediately blink 4 times (at about 4 Hz), and then stay off while the
LabJack enumerates.
Enumeration is the process where the PC’s operating system gathers information from a USB
device that describes it and it’s capabilities. The low-level drivers for the LabJack U12 come
with Windows and enumeration will proceed automatically. The first time a device is
enumerated on a particular PC, it can take a minute or two, and Windows might prompt you
about installing drivers. Accept all the defaults at the Windows prompts, and reboot the PC if
asked to do so. Enumeration occurs whenever the USB cable is connected, and only takes a
few seconds after the first time.
When enumeration is complete, the LED will blink twice and remain on. This means Windows
has enumerated the LabJack properly.
If the LabJack fails to enumerate:
• Make sure you are running Windows OS version 4.10.2222 or higher,
• Try connecting the LabJack to another PC,
• Try connecting a different USB device to the PC,
• Contact LabJack at [e-mail].
1.2 Software Installation
Although, the low-level USB drivers for the LabJack are included with Windows, high-level
drivers are needed to send and receive data. The included LabJack CD installs the high-level
drivers, example source code, and example applications.
Close all open applications, especially LabJack related software, and insert the LabJack CD. If
autorun is enabled, the installation program should start automatically. If the installation does
not start, you will have to manually double-click on LabJackVXXX.exe.
When the LabJack installation is finished, it will start the National Instruments LabVIEW Run-
Time Engine (LVRTE) setup. The LVRTE is required for the example applications: LJconfig,
LJlogger, LJscope, and LJtest. If prompted to reboot after this installation, go ahead and do so.

To test the installation, start LJconfig by selecting
Start => Programs => LabJack => LJconfig
and make sure 1 LabJack is listed.

2. Hardware Description
The external features of the LabJack U12 are:
• USB connector,
• DB25 digital I/O connector,
• Status LED,
• 30 screw terminals.
The USB connection provides power and communication. No external power supply is needed.
The +5 volt connections available at various locations are outputs, do not connect a power
supply.
Figure 2-1. LabJack U12 top surface.
Figure 2-1 shows the top surface of the LabJack U12. Not shown is the USB and DB25
connector, which are both on the top edge. The DB25 connector provides connections for 16
digital I/O lines, called D0-D15. It also has connections for ground and +5 volts. All
connections besides D0-D15, are provided by the 30 screw terminals shown in Figure 1. Each
individual screw terminal has a label, AI0 through STB.
The status LED blinks 4 times at power-up, and then blinks once and stays on after
enumeration (recognition of the LabJack U12 by the PC operating system). The LED also
blinks during burst and stream operations, unless disabled. The LED can be enabled/disabled
through software using the functions AISample, AIBurst, or AIStreamStart. Since the LED uses
4-5 mA of current, some users might wish to disable it for power-sensitive applications.

2.1 AI0 – AI7
Hardware
The LabJack U12 has 8 screw terminals for analog input signals. These can be configured
individually and on-the-fly as 8 single-ended channels, 4 differential channels, or combinations
in between. Each input has a 12-bit resolution and an input bias current of ±90 µA.
• Single-Ended: The input range for a single-ended measurement is ±10 volts.
• Differential channels can make use of the low noise precision PGA to provide gains up
to 20, giving an effective resolution greater than 16-bits. In differential mode, the voltage
of each AI with respect to ground must be between ±10 volts, but the range of voltage
difference between the 2 AI is a function of gain (G) as follows:
G=1 ±20 volts
G=2 ±10 volts
G=4 ±5 volts
G=5 ±4 volts
G=8 ±2.5 volts
G=10 ±2 volts
G=16 ±1.25 volts
G=20 ±1 volt
The reason the range is ±20 volts at G=1 is that, for example, AI0 could be +10 volts and AI1
could be -10 volts giving a difference of +20 volts, or AI0 could be -10 volts and AI1 could be
+10 volts giving a difference of -20 volts.
Figure 2-2 shows a typical single-ended connection measuring the voltage of a battery. This
same measurement could also be performed with a differential connection to allow the use of
the PGA. In general, any single-ended measurement can be performed using a differential
channel by connecting the voltage to an even-numbered analog input, and grounding the
associated odd-numbered analog input (as shown by the dashed connection to AI1 in Figure 2-
2).
Figure 2-2. Single-ended measurement.
Figure 2-3 shows a typical differential connection measuring the voltage across a current shunt.
A differential connection is required when neither leg of the shunt is at ground potential. Make
sure that the voltage of both AI0 an AI1 with respect to ground is within ±10 volts. For instance,
if the source (Vs) shown in Figure 2-3 is 120 VAC, the difference between AI0 and AI1 might be
small, but the voltage from both AI0 and AI1 to ground will have a maximum value near 170
volts, and will seriously damage the LabJack.

Whether or not the ground (GND) connection is needed (Figure 2-3) will depend on the nature
of Vs.
Figure 2-3. Differential measurement.
Figure 2-4 shows a single-ended connection used to measure the output voltage of a typical
voltage-divider circuit. The voltage divider circuit is a simple way to convert a varying resistance
(thermistor, photoresistor, potentiometer, etc.) to a varying voltage. With nothing connected to
Va, the value of the unknown resistance, R2, can be calculated as:
R2 = Va*R1 / (Vs-Va),
where Vs is the supply voltage (+5V in Figure 2-4).
When Va is connected to AI0, as shown in Figure 2-4, the input bias current of the LabJack
affects the voltage divider circuit, and if the resistance of R1 and R2 is too large, this effect must
be accounted for or eliminated. This is true for any signal with too high of a source impedance.
All measuring devices have maximum analog input bias currents that very from picoamps to
milliamps. The input bias current of the LabJack U12’s analog inputs varies from +70 to -94
microamps (µA). This is similar to an input impedance of about 100 kΩ, but because the current
is nonzero at 0 volts, it is better to model the analog input as a current sink obeying the following
rule:
Iin = 8.181*Va – 11.67 µA
Figure 2-4. Single-ended measurement with voltage divider circuit.

Because the input bias current is known, as a function of input voltage, the simple voltage
divider equation can be modified as follows to account for input bias current:
R2 = Va / [((Vs-Va)/R1) – (8.181µ* Va) + 11.67µ]
As an alternative to the equation above, Va can be buffered by a single-supply rail-to-rail
operational amplifier, and the original simple voltage divider equation can be used. This
solution works for any single-ended signal which stays between 0 and +5 volts. Some op-amp
choices are:
• TLV2462
• LMC6482
• MAX4166
Software
Readings from the analog inputs are returned by the functions AISample, AIBurst, and
AIStreamRead.
AISample returns a single reading of 1-4 channels, and takes up to 20 ms to execute, providing
a maximum date rate of at least 50 Hz per channel. This function also controls the status LED
and sets the state of the IO pins.
AIBurst acquires multiple samples of 1-4 channels at a hardware-timed sample rate of up to
8192 Hz. The acquisition can be triggered based on the change of state of an IO pin. This
function also controls the status LED and returns the states of the IO pins (which are read every
4 samples).
Internally, the actual number of samples collected and transferred by the LabJack during an
AIBurst call is the smallest power of 2, from 64 to 4096, which is at least as big as numSamples.
The execution time of this function, in milliseconds, can be estimated as (auto or turbo mode):
30+(1000*numSamplesActual/sampleRate)+(0.4*numSamplesActual)
numSamples = numScans * numChannels
sampleRate = scanRate * numChannels
AIStreamRead is called periodically during a stream acquisition started by AIStreamStart. Each
call retrieves multiple samples of 1-4 channels from the LabJack stream buffer, along with the
states of the IO pins (read every 4 samples). Hardware-timed sample rates of up 1200 Hz are
available.
2.2 AO0 & AO1
The LabJack U12 has 2 screw terminals for analog output voltages. Each analog output can be
set to a voltage between 0 and the supply voltage (+5 volts nominal) with 10-bits of resolution.
The output voltage is ratiometric with the +5 volt supply, which is generally accurate to ±5% (see
Appendix A). If an output voltage of 5 volts is specified, the resulting output will be 100% of the
supply voltage. Similarly, specifying 2.5 volts actually gives 50% of the supply voltage.
If improved accuracy is needed, measure the +5 volt supply with an analog input channel, and
the actual output voltage can be calculated. For instance, if an analog output of 2.5 volts is

specified and a measurement of +5V returns 5.10 volts, the actual output voltage is 2.55 volts.
Alternatively, the analog output can itself be measured with an analog input.
There is a 1st order low-pass filter on each analog output with a 3dB frequency around 22 Hz.
Software
The analog outputs are set using the function AOUpdate, which takes up to 20 ms to execute,
providing a maximum update rate of at least 50 Hz per channel. This function also
controls/reads all 20 digital I/O and the counter.
2.3 IO0 – IO3
Connections to 4 of the LabJack’s 20 digital I/O are made at the screw terminals, and are
referred to as IO0-IO3. Each pin can individually be set to input, output high, or output low.
These 4 channels include a 1.5 k Ω series resistor that provides overvoltage/short-circuit
protection. Each channel also has a 10 MΩresistor connected to ground.
One common use of a digital input is for measuring the state of a switch as shown in Figure 2-5.
If the switch is open, IO0 reads FALSE. If the switch is closed, IO0 reads TRUE.
Figure 2-5. IO used to detect the state of a switch.
While providing overvoltage/short-circuit protection, the 1.5 k Ω series resistor on each IO pin
also limits the output current capability. For instance, with an output current of 1 mA, the series
resistor will drop 1.5 volts, resulting in an output voltage of about 3.5 volts.
Software
The functions AOUpdate or DigitalIO are used to set the direction, set the state, and/or read the
state, of each IO pin. Both of these functions take up to 20 ms to execute, providing a
maximum update rate of at least 50 Hz per pin.
The function AISample can set/read the state of each IO, and the function Counter reads the
state of each IO.
The functions AIBurst and AIStreamRead, take a reading of the IO states and return it with the
analog data. The states of the 4 IO are read every 4 samples, providing a data rate of up to
2048 Hz per pin.
2.4 D0 – D15
Connections to 16 of the LabJack’s 20 digital I/O are made at the DB25 connector, and are
referred to as D0-D15. These 16 lines have no overvoltage/short-circuit protection, and can
sink or source up to 25 mA each (total sink or source current of 200 mA max for all 16). This
allows the D pins to be used to directly control some relays. All digital I/O are CMOS output and

TTL input except for D13-D15, which are Schmitt trigger input. Each D pin has a 10 MΩresistor
connected to ground.
DB25 Pinouts:
1: D0 6: D5 11: +5V 16: GND 21: D11
2: D1 7: D6 12: +5V 17: GND 22: D12
3: D2 8: D7 13: +5V 18: D8 23: D13
4: D3 9: NC 14: GND 19: D9 24: D14
5: D4 10: +5V 15: GND 20: D10 25: D15
These digital I/O can detect the state of a switch using the same circuit shown in Figure 2-5.
Because the D pins have no overvoltage/short-circuit protection, the user must be
careful to avoid damage. The following are examples of things that could damage a D
pin and/or the entire LabJack:
• Shorting a high output to ground (or any potential other than +5V).
• Shorting a low output to a nonzero voltage (such as +5V).
• Exceeding the voltage limits specified in Appendix A.
Software
The functions AOUpdate or DigitalIO are used to set the direction, set the state, and/or read the
state, of each D pin. In addition, DigitalIO also returns the current state of the direction and
output registers. Both of these functions take up to 20 ms to execute, providing a maximum
update rate of at least 50 Hz per pin.
2.5 CNT
The input connection to the 32-bit counter is made at screw-terminal CNT. This input has a
Schmitt Trigger buffer, and the counter is incremented each time the voltage at CNT changes
from less than 1 volt to greater than 4 volts. Frequencies up to at least 1 MHz can be counted.
Software
The functions AOUpdate or Counter are used to reset or read the counter. If a reset is
specified, the counter is read first. Both of these functions take up to 20 ms to execute,
providing a maximum update rate of at least 50 Hz.
2.3 CAL – STB
These terminals are used during testing and calibration. The CAL terminal is a precision +2.5
volt source and can be used to provide a few milliamps.
2.4 +5V
The LabJack has a nominal +5 volt internal power supply. Power can be drawn from this power
supply by connecting to the +5V screw-terminals, or the +5V pins on the DB25 connector. The
total amount of current that can be drawn from the +5V pins, analog outputs, and digital outputs,
is 450 mA for most desktop computers and self-powered USB hubs. Some notebook
computers and bus-powered hubs will limit this available current to about 50 mA.
2.5 GND
The GND connections available at the screw-terminals and DB25 connector provide a common
ground for all LabJack functions.

3. Example Applications
The LabJack U12 CD installs 4 example applications: LJconfig, LJlogger, LJscope, and LJtest.
• LJconfig: Lists all LabJacks connected to the USB and allows the local ID to be set on
each.
• LJlogger: Saves data to disk, writes data to an HTML page on the Internet, and
performs various actions (including email) on trigger events.
• LJscope: Simulates an oscilloscope by reading data from 2 AI channels in burst mode.
• LJtest: Runs a sequence of tests on the LabJack itself.
The LabVIEW source code for LJlogger and LJscope is installed in the examples directory.
3.1 LJconfig
Every LabJack has a local ID and serial number. The local ID is a value between 0 and 255
that can be changed by the user. The serial number is a value between 256 and 2,147,483,647
that is unique among all LabJacks and cannot be changed by the user. LJconfig is used to set
the local ID of a particular LabJack.
Figure 3-1. LJconfig
Figure 3-1 shows the window that opens when LJconfig is run. Each time the “Refresh” button
is pushed, LJconfig will scan the USB for all LabJacks. To change the local ID of a particular
LabJack, push the “Change” button next to that LabJack, and the window shown in Figure 3-2
will appear.

Figure 3-2. LJconfig Change Local ID
Enter a new local ID between 0 and 255 and push the “Change” button. The new local ID will
be written and the LabJack will be forced to re-enumerate.
3.2 LJlogger
LJlogger sends and receives data in command/response mode. It is capable of saving data to
disk, writing data to an HTML page on the Internet, and performing various actions (including
email) on trigger events.
Figure 3-3. LJlogger
The main window for LJlogger is shown in Figure 3-3. The white colored items and the “SDX”
buttons are controls to be edited/selected by the user. The grey colored items are indicators

which display various information about the LabJack. Clicking the button labeled “Save Panel
Settings” will save the current values of the controls as the default values.
If SDX is activated for a given analog input, the corresponding SDX DLL will be used to
determine the scaled data. Users can make their own SDX DLLs (see the source code for more
information), to provide more complex scaling or scaling that depends on other analog inputs.
Clicking the “Configure” button shown in Figure 3-3 brings up the window shown in Figure 3-4:
• Working Directory: This is the directory where data and configuration files will be
written.
• Data File Name: Determines the name of the data file to which data will be written.
New data is appended to the end of this file.
• Data File Write Interval: Determines the interval at which a new row of data will be
written to the data file. Minimum of 0.1 seconds.
• HTML Write Interval: Determines the interval at which the HTML file is rewritten.
Figure 3-4. LJlogger Configuration
Clicking on the “Internet Setup” button in Figure 3-4 brings up the Internet configuration window
shown in Figure 3-5. Basic customization of the HTML file can be done by clicking on
“Advanced HTML Configuration” which brings up Figure 3-6.
Clicking on the “Trigger Setup” button in Figure 3-4 brings up the window shown in Figure 3-7.

Figure 3-5. LJlogger Internet Configuration
Figure 3-6. LJlogger HTML Configuration

Figure 3-7. LJlogger Trigger Configuration
Figure 3-7 shows 9 example triggers:
• Trigger #0: If the scaled data from analog input row 7 (Figure 3-3) is greater than 5,
then set AO1 to 5 volts. Once triggered, there is a 10 second delay before it can be
triggered again.
• Trigger #1: If IO3 is high, set IO2 high. Reset delay is zero so this trigger can occur
every iteration (every 0.1 seconds) if IO3 is high.
• Trigger #2: If D15 is low, set D14 low.
• Trigger #3: If the count is greater than 10,000, set IO1 to an output.
• Trigger #4: If it has been 300 seconds since LJlogger started, set D13 to an output.
• Trigger #5: When the PC’s clock is at 15 minute intervals, the status LED will be turned
off and an email will be sent.
• Trigger #6: Calls FunctionX from function1.dll. If the function returns True, reset the
counter. Users can make their own FunctionX DLLs. See the source code for more
information.
• Trigger #7: Calls FunctionX from function2.dll. If the function returns True, stop writing
data to file.
• Trigger #8: Calls FunctionX from function10.dll. If the function returns True, write 1 row
to the data file.
3.3 LJscope
LJscope simulates an oscilloscope by reading data from 2 analog input channels in burst mode.

Figure 3-8. LJscope
3.4 LJtest
LJtest runs a sequence of tests on the LabJack itself. Users will generally leave “Test Fixture
Installed” unselected and execute the tests with nothing connected to the LabJack (except the
USB of course).

Figure 3-9. LJtest

4. Programming Reference
The LabJack U12 CD installs high-level drivers (ljackuw.dll), an ActiveX interface to the high-
level drivers (ljackuwx.ocx), and LabVIEW6 VIs which call all the DLL functions. The DLL and
OCX are installed in the Windows System directory. If the installation program can determine
the LabVIEW6 directory, it copies the LabVIEW VIs into that directory (\vi.lib\addons\) so they
show up on the function palette. Otherwise, the LabVIEW drivers are copied into the LabJack
installation directory (c:\Program Files\LabJack)\drivers\labview, and can manually be
transferred to the LabVIEW directory.
There are 21 functions exported by the LabJack DLL., and matching functions in the OCX and
LabVIEW VIs. There are two additional support functions in the OCX, required due to the
limitations of ActiveX. All functions are command/response except for AIBurst and
AIStreamStart/Read/Clear.
There are 2 parameters that are used by most functions:
• errorcode – A LabJack specific numeric error code. 0 means no error and 2 means no
LabJacks were found. Use the function “GetErrorString” to get a description of the error.
• idnum – Functions with this input take either a local ID, serial number, or -1. A local ID
or serial number will specify a specific LabJack, while –1 means the first found LabJack.
Every LabJack has a local ID and serial number. The local ID is a value between 0 and
255 that can be changed by the user. The serial number is a value between 256 and
2,147,483,647 that is unique among all LabJacks and cannot be changed by the user.
4.1 AISample
Reads the voltages from 1,2, or 4 analog inputs. Also controls/reads the 4 IO ports. Execution
time for this function is 20 milliseconds or less.
Declaration:
long __cdecl AISample ( long *idnum,
long demo,
long *stateIO,
long updateIO,
long ledOn,
long numChannels,
long *channels,
long *gains,
long disableCal,
long *overVoltage,
float *voltages )
Parameter Description:
Returns: LabJack errorcodes or 0 for no error.
Inputs:
• *idnum – Local ID, serial number, or -1 for first found.
• demo – Send 0 for normal operation, >0 for demo mode. Demo mode allows
this function to be called without a LabJack.
• *stateIO – Output states for IO0-IO3.
• updateIO – If >0, state values will be written. Otherwise, just a read is
performed.
• ledOn – If >0, the LabJack LED is turned on.
• numChannels – Number of analog input channels to read (1,2, or 4).