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Allows 2 digital I/O lines to each control a relay or other moderate load. The 4-pin design plugs into the standard DIO/DIO/GND/VS screw terminal block found on LabJacks such as the U3, U6, UE9, and T7. Each DIO controls a switch to ground (i.e. open-collector) that can hold off up to 50 volts and can sink up to 200 mA.

  • Connect LabJack VS terminal(5V) to the (+) of the load.

  • RelayDriver connects to the low side (-) of the load.



The LJTick-RelayDriver (LJTRD) is a signal-conditioning module that allows two digital outputs to each control up to 50 volts and 200 mA. The 4-pin design plugs into the standard DIO/DIO/GND/VS screw terminal block found on newer LabJacks such as the U3 and UE9.

In a scenario requiring multiple LJTick-RelayDrivers, consider instead the PS12DC power switching board.  It operates in a similar way, but has 12 channels, high side switching, and digital isolation. 

The pictures below show the LJTRD by itself and plugged in to a LabJack.

Figure 1: LJTick-RelayDriver (LJTRD)

Figure 2: LJTRD With U3











Extending from the back of the LJTRD are four pins. The first two pins provide +5 volt power and ground from the LabJack, although +5 volt power is not used by the LJTRD and thus is not connected to anything. The other two pins connect to digital I/O on the LabJack. The four pins plug directly into the 5.0 mm spaced screw terminals on the LabJack U3/UE9 as shown in Figure 2. The LJTRD should be plugged into a digital I/O block, as opposed to an analog I/O block.

The LJTRD has a 4-position screw-terminal providing the following connections:

RA/RB: The high side of each output switch. When IOA/IOB from the LabJack is set to output-high, the respective switch is closed. When IOA/IOB is set to output-low or input, the respective switch is open. Each switch can hold off up to 50 volts and can sink up to 200 mA.

GNDR: The low side of both output switches. Connected to LabJack GND via a 22 ohm resistor (resistor is on the LJRTD).

VR: Connect the load voltage to this terminal to bias the internal clamping diodes on each switch. If each switch has a different load voltage, the highest voltage should be connected to VR. The clamping diodes help suppress switching transients, and can be particularly important when dealing with inductive loads such as mechanical relays or solenoids. Although this connection is optional, there is usually no reason not to use it.

When connecting a relay or other type of load, there will be a voltage drop depending on current. Below is a chart which represents the voltage drops that can be expected at various currents.

If controlling at high frequencies, please note the following table.  As current through the RelayDriver increases, the cutoff frequency also increases, which means that if you encounter problems controlling at high frequencies, the load resistance should be decreased to allow more current to flow through the RelayDriver.  This behavior is almost never a problem when controlling relays, since relays typically draw 3 to 20mA, and the LabJack U3 will not output a PWM frequency exceeding 187kHz.

Following are two figures showing typical connections for the LJTRD. The first diagram shows the general connections, while the second is for the specific case where the LJTRD is controlling VS (5 volts) from the LabJack itself.

Figure 3: General Connection Diagram

Figure 4: Connection Diagram When Controlling VS from LabJack


  Product Comparison

U12 U3-LV U3-HV U6 U6-Pro UE9 UE9-Pro T7 T7-Pro
AIN Voltage ±10V 0-2.4V ±10V [1] ±10V ±10V ±5V ±5V ±10V ±10V
Analog Inputs 8 16 16 14 14 14 14 14 14
Effective Resolution [2] 12 bit 12 bit 12 bit 16 bit 22 bit 12 bit 20 bit 16 bit 22 bit
Digital I/O 20 20 16 20 20 23 23 23 23
Logic Level 5V 3.3V 3.3V 3.3V 3.3V 3.3V 3.3V 3.3V 3.3V
Analog Outputs 2 2 2 2 2 2 2 2 2
Counters 1 Up to 2 Up to 2 Up to 2 Up to 2 Up to 2 Up to 2 Up to 10 Up to 10
USB Yes Yes Yes Yes Yes Yes Yes Yes Yes
LJTick Compatible No Yes Yes Yes Yes Yes Yes Yes Yes
Internal Temp Sensor No Yes Yes Yes Yes Yes
Yes Yes
Thermocouple Ready [3] No No No Yes Yes No Yes Yes Yes
Ethernet No No No No No Yes Yes Yes Yes
Scripting No No No No No No No Yes Yes
Wireless No No No No No No No No Yes
Real-time Clock No No No No No No No No Yes
[1] Can be configured for -10V to +20V range.
[2] According to actual measured data, see related Noise and Resolution (App Note)
[3] If not thermocouple ready, can purchase an amplifier like the LJTick-InAmp, see related Thermocouples (App Note)