Digital Control Unit (DCU-BTD)
Specifications and User Guide

There have been three Digital Control Unit (DCU) models over the years. The current model is black, rectangular, and has a screw terminal for each of the output lines, as well as separate pin connectors for a servo motor.

The previous models were white, square, and used a 9-pin serial connection for output. Students used a serial cable to connect the DCU to their circuits, with each wire in the cable corresponding to a different line/pin; each cable was labeled, identifying which color wire is connected to each line/pin.

The Logger Pro Digital Out feature allows you to control up to three output lines of a DCU connected to the DIG 1 or DIG 2 port of a LabQuest or LabPro. Each of the three lines can be individually controlled based on user-configured conditional statements. This allows you to develop projects that turn DC motors, lamps, LEDs, buzzers, and other DC electrical devices on and off based on sensor readings, time, or calculated columns.

To reach the Digital Out dialog box, connect the DCU and at least one other Vernier sensor to the data-collection interface. Choose Set Up Sensors from the Experiment menu and select your interface. Click the DIG/SONIC button and select Digital Out from the drop-down menu.

Note: Logger Pro version 3.8.6 or later is required to use multiple output lines on the DCU at once. Earlier versions of Logger Pro could only activate one output line at a time.

LabQuest 2 (version 2.7 or newer) and LabQuest 3 (all versions) have support for the DCU built in and you can control digital lines with needing a computer.

Note: Utilizing the servo motor output of the current DCU model is only available when controlling the DCU via LabVIEW.

Users wanting to control the DCU with Arduino can refer to the Engineering section of the Vernier website at

Users wanting to control the DCU using a LabPro with LabVIEW or with a TI graphing calculator can refer to the previous version of the DCU manual at

On the two most recent models of the DCU, there are two different ports on the DCU for connecting power supplies. A LabQuest Power Supply can be connected to the smaller port. Alternatively, a LabPro or ULI Power Supply can be connected to the larger port. A complete list of power sources that can be used with the DCU is provided below:
* LabQuest Power Supply (order code LQ-PS): 5 V DC, regulated, 1.5 A
* LabQuest 3 Power Supply (order code LQ3-PS: 5 V DC, regulated, 2.5 A
* LabPro Power Supply (order code IPS): 6 V DC, regulated, 600 mA
* ULI Power Supply (order code ULI-PS): 9 V, unregulated, 1000 mA
* Battery power supply: one lantern battery or four to eight 1.5 V cells connected in series.

Additional details can be found here: What power supplies can I use with the DCU?

The output voltage of the DCU is set by its power source. The DCU can supply 600 mA of current on each line, but no more than 1800 mA total.

1. When you connect the DCU to an interface, does the green EN LED light up? Is external power supplied to the DCU? If you are using the current model, the blue XP LED should light up.
2. Does the DCU appear in the Set Up Sensor dialog box? Some Digital Control Units are not auto-ID. If your DCU has not been identified by Logger Pro and therefore does not show up under the DIG/SONIC button, you will need to set it up manually. To do this, click on the DIG/SONIC button and select Choose Sensor ► Digital Control Unit.
3. When you test the output lines via Logger Pro, do the correct LEDs light up? In the Digital Out dialog box, you can test 3 output lines of the DCU by selecting the check box for Line 1 On, Line 2 On, and/or Line 3 On. The LEDs on the circuit board extending from the DCU will turn on when the line is on.
4. Is your circuit set up correctly? Carefully review the circuit the DCU is turning on/off. Are all the connections secure? Are the components connected correctly (e.g., current flowing in the correct direction through diodes)? Does it require more power or current than the DCU can provide? If you are using an older 9-pin serial DCU, check to make sure that you have wired the correct line into your circuit.

* In general, you can connect any electrical device that runs on DC electricity at a voltage that matches your power supply. The DCU output voltage can range from 5 to 12 V, depending on the DCU power supply. You can find thousands of different 5 to 12 V devices at most hobby and electronic stores, such as Mouser or DigiKey.
* The Digital Out feature is unable to scan all data at fast data-collection rates. This may mean that peaks or valleys that fall above or below the user-defined comparison value, but are of very short duration, might not activate or deactivate a line as configured. In such a case, LabVIEW provides higher rates and response times.

Where do I find electronic components for use with the Digital Control Unit (DCU)?
Can I use the DCU with the CBL 2 or LabPro?
When I set up my Digital Control Unit, the Digital Out option is disabled. What should I do? (Logger Pro)
When I plug the radiation monitor into LabPro it stops working. (especially if you have been using DCU).
How can I write my own programs for LabPro?
Do you have an SDK or API for your sensors?
Logger Pro crashes when using the DCU and a Photogate with a LabPro.
What power supplies can I use with the DCU?
National Instruments LabVIEW Troubleshooting and FAQs
What sensors are not compatible with Go!Link?
What are the differences between Logger Pro and Logger Lite?
How can I control AC devices with the Digital Control Unit?
Digital sensor does not automatically identify when connected to LabQuest after using the DCU.
How fast does the DCU respond to data?
Can I use Go Direct sensors with a Digital Control Unit?
DCU Power Output Pack (DCU-POP) Troubleshooting and FAQs
How do you wire a stepper motor to the DCU?

DCU Terminal Plug Kit (DCU-PLUG)
SensorDAQ (SDAQ)
LabQuest Power Supply (LQ-PS, discontinued)
Vernier AC Adapter (IPS)
Digital Control Unit Power Output Kit (DCU-POP)