LJTick-RelayDriver Datasheet | LabJack
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LJTick-RelayDriver Datasheet

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LabJack LJTick-RelayDriver Relay Controller Accessory Compatible with LabJack USB, Ethernet, WiFi DAQ Devices

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.

Table 3. Voltage drop based on current

Current (mA) Voltage Drop (V)
200 3.29 1.05
150 2.55 0.98
100 2.17 0.91
50 1.55 0.83


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.

Table 4. Cutoff Frequency based on current

Current (mA) Cutoff Frequency
0.5 210kHz
10.5 430kHz
41.4 1.2MHz


The LJTRD uses the ULN2003AID high-current darlington transistor array.  See that datasheet for more details.

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 5: General Connection Diagram

Figure 6: Connection Diagram When Controlling VS from LabJack



Testing Basic Operation

Use the Dashboard in Kipling (T-series) or the Test panel in LJControlPanel to control the applicable DIO lines.  The DIO have 3 states (i.e. tristate digital I/O):

Output-High:  Active.  The "switch" on the LJTRD is closed.
Output-Low:  Disabled.  The "switch" on the LJTRD is open.
Input:  Disabled.  The "switch" on the LJTRD is open.

If the "switch" mentioned above was mechanical you could simply put a DMM from RA to GNDR and measure resistance, but that generally does not work with solid-state switches.  With a solid-state switch the best way to test is to connect as shown in Figure 6 but put in a resistor where it says "Relay Control".  So for example, connect one side of a 1k resistor (100 to 1,000,000 should work) to any VS terminal (~5 volts), connect the other side to RA, and connect GNDR to any GND terminal.  Now use your DMM to measure the voltage across the resistor.  When the LJTRD is disabled the voltage will be 0 as no current is flowing so no voltage is dropping.  When the LJTRD is active the voltage will be perhaps 3-5 volts (see Table 3 above).


Declaration of Conformity

Manufacturers Name: LabJack Corporation
Manufacturers Address: 3232 S Vance St STE 200, Lakewood, CO 80227 USA
Declares that the product
Product Name: LabJack Tick Relay Driver
Model Number: LJTRD
conforms to the following Product Specifications:
EMC Directive: 89/336/EEC
EN 55011 Class A
EN 61326-1: General Requirements


Useful add-on. I'd like to see the full schematic for it, however. If for no other reason than to check the specs of the components. It would also have been nice if the common point for the two switches could have floated rather than be tied to ground. As it is it can't be used as to switch +5 back into a circuit, only to pull down to ground. If you want to switch +5 into a sink, then you'll need to attach more parts.

In response to the first part, the LJTRD uses 2 channels of the ULN2003AID from TI.  INA and INB each connect directly to a channel of the chip with a 100k pull-down on each.  COM from the chip connects to VR and E on the chip connects to GNDR which goes through a 22 ohm resistor and then to GND.  (Says 10 ohms above, so we need to check that)

For the second part, because the ULN2003AID consists of NPN transistors directly driven by a LabJack digital output they really must be low-side switches.  It gets more complicated to make something that can be high- or low-side.  We are working on a 12-channel high-side output board for DB15 connectors. 

Would be nice having a clear recommendation what relay should be connected and what not. I guess the electronic relay I'm using directly on the U3 will work fine but a circuit diagram is lacking showing their usage here with the relay driver. Also when using 230V more attention is certainly needed.

For controlling relays (SSRs only in most cases) directly with the digital I/O, see Section of the U3 User's Guide.  A specific recommendation of an SSR we use often for AC loads up to 280V/40A is the #176719 from Jameco for just $20.

For the LJTick-RelayDriver, the recommendation would be any relay that takes a control voltage of 50 volts or less at a current of 200 mA or less.  That is going to be almost any relay out there.

Generally a relay that likes 5 volts for its control voltage is convenient because you can use VS from the LabJack as shown in Figure 4.  The limit on how much current you can draw from VS is typically about 450 mA (Appendix A), but if you are doing delicate analog measurements with the U3 you might not want to draw so much current from it.

Diagrams:  I feel like Figures 3 & 4 above cover the ways to connect relays, so let us know what you feel might be missing.

More attention for 230VAC:  Whatever the load is, that is on the load side, so it is isolated from the LabJack side, so the key point is just to keep it that way.  The main recommendation here would be that only qualified personnel should work with high voltages and currents and it is at your own risk.  Beyond that, let is know what you might want help with.

Unfortunately I have been running into dangerous territory. Relays are switching together jointly if they are connected via VS and situated on the same relay driver (EIO4+5 or EIO3+4) and an Omron Mosfet realy is involved (G3VM-61VY). May be this SSR is the problem requiring to pull down '-' on the switching side to common GND via resistor....



Are you saying that if you switch EIO3 the relay on EIO4 also switches?

yes and the cause (may be) is that the relay is not suited for that high load current.

I think we are going to need a lot more information to figure out what is going on. Let's continue this via email. Please send a description of your setup to [email protected]

I think I found a replacement of the problematic SSR I have (to low allowable current)


What version would be best?

They all look like they should work with LabJack devices. The DO061B works down to 1.7V, so it may operate from an IO without any additional drive.

Can the LJtick-Relay Driver be used to switch a Furman MP-15? This wants to be actuated by having a switch placed between its internal 12V power supply and its relay. I have tried hooking it up like figure 3 but that doesn't work.

The LJTRD is a low-side switch.  I can't find any wiring diagrams for the MP-15, but if it requires high-side switching the LJTRD will not work.  To continue this and discuss options, I would post on the forum and provide any more details you can gather about the control circuit for the MP-15.

I was expecting this thing to give me a set of dry contacts. That would be too easy. Instead now I have to investigate and learn all kind of info that I dont care about. I will pay you $100 for something that simply plugs into the labjack and can open and close a set of contacts, with a decent current rating e.g. [email protected] amp. I guess i need to go to radioshack and turn a 30minute project into a 6 hour learning experience. Thank You

Dry contact output is generally what you get from a mechanical relay.  The LJTick-RelayDriver is designed to drive relays, including mechanical relays, so if you use the LJTRD to drive a mechanical relay that is the lowest cost way to get dry contact output.

If you want to buy something, get the RB12 and buy one of the dry contact modules listed on the RB12 datasheet.

Is this possible to control 12V solenoid valve (NC type) w/ T7?

Please recommend if not

The LJTRD can gate up to 50V and up to 200mA, so if the solenoid draws under 200mA then yes you can use the LJTRD to gate your 12V power supply for the solenoid.  If the solenoid draws more than 200mA look at the PS12DC or RB12.

NC: Normal Close is possible (including from NOT-Powered)

ezHST's picture

I'm trying to switch a 24V relays with the LJtick relaydriver on a LabJack U3. I'm not sure how to wire DC 24V and LJtick relaydriver to the Labjack ... Of course the driver is wired to the digital IO ports.

Perhaps its possible to tell me where I have to wire the Voltage source and the relay. The driver offers 4 Ports (VR, GNDR, RA, RB)

labjack support's picture

The LJTick-RelayDriver datasheet has a couple example circuits. I think figure 5 is what you need: https://labjack.com/support/datasheets/accessories/ljtick-relaydriver

dandavis2019's picture

I'm using a ELEGOO 4 Channel DC 5V Relay Module with Optocoupler Compatible with Arduino UNO R3 MEGA 1280 DSP ARM PIC AVR STM32 Raspberry Pi. I'm trying to interface the relays with the T4.

( https://www.amazon.com/ELEGOO-Channel-Optocoupler-Arduino-Raspberry/dp/B...). 

Will the LJTick-RelayDriver work for this application.If so,. how many?

I'm moving away from the Arduino to the T4 to have a higher quality Automatic Irrigation  System

Appreciate your comments



labjack support's picture

Have you tried with the T4 DIO by themselves? There does not seem to be much info about the input circuit for the board or logic level requirements, but there is a chance the 3.3V digital outputs from the LabJack could work for control. 

Instead of the Tick-RelayDriver I would recommend our LJTick-DigitalOut5V. You would need 1 Tick per 2 digital outputs you want: