Simple SensorDAQ Servo Pointer

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Building a Simple SensorDAQ Servo Pointer




The instructions here are intended for adult users who are familiar with basic principles and safety procedures for DC circuits and low-power lasers. DO NOT ATTEMPT THIS PROJECT UNLESS YOU ARE QUALIFIED OR PROPERLY SUPERVISED. Even battery-powered circuits can cause fires, injury or damage.


We recommend that you use a 6-volt battery pack (such as 4 AA batteries) to power the servo motor. It MAY be possible to power the motor directly from the 5-V output on Vernier's SensorDAQ, but we've seen that overload the SensorDAQ and cause it to shut down. Note that the motor will consume current even when it is running, so it must be disconnected when not in use. You might want to add a switch. To control the servo motor, the required connections are

  1. Connect the battery pack's positive to the motor's positive (usually red)
  2. Connect the battery pack's negative to the motor's ground wire (usually black) AND to pin 5 on the SensorDAQ's Aux I/O port
  3. Connect the motor's signal line (usually white) to the high-precision counter line, pin 7, on the SensorDAQ's Aux I/O port

The software program below can also control the SensorDAQ's 4 data lines (pins 1-4) to activate a laser module, buzzers, lights and other DC devices. We much prefer to use an external 6-V power pack to power these devices and normally use a ULN2003A integrated circuit as an electronic switch. WIth a single ULN2003A, the small output currents from the SensorDAQ can control currents of 300 mA or more to each of 4 channels. See the Circuit Diagram for more details.


Zipped Servo Control software (2.0 MB, updated Sept 7, 2009) from Math Machines. Once unzipped to a convenient location on your PC computer, it should be ready to run--provided that the free runtime engines for LabVIEW 8.6.1 and NI-DAQmx 8.9 have also been installed on your computer.

Unless the full versions of LabVIEW 8.6.1 and NI-DAQmx are installed on your computer, you must download and install the runtime engines for both. They are available free from National Instruments. LabVIEW 8.6.1 Runtime is available at and NI-DAQmx 8.9 Runtime is available at


Hobby servo motors are available at a wide range of prices from many hobby shops and from many internet supplies. These motors are typically used to steer radio-controlled cars, boats and airplanes and they typically have a range of movement from roughly -90° to +90°. They have an internal potentiometer to provide feedback as to its actual orientation. Signals to these motors cause them to move to a specific position. The signals are sent in the form of square pulses, delivered about once every 20 ms. The width of the pulse (typically ranging between about 1 and 2 ms determines the position to which the motor will move.

We have generally had good success with "standard" servos, which cost around $10 each. Most often, we have used the Futaba S3003 (shown above) or Tower Hobbies STD TS-53. Both are available at




Formula Strings partial list of functions and syntax for formula strings in Servo Control

Science Laboratory Safety Manual, by Linda M. Stroud, 408 pp. Science & Safety Consulting Services, Inc. Raleigh, NC, 2008, ISBN: 9780978879617

Vernier Software and Technology. Follow this link for information about the SensorDAQ, including instruction on controlling a hobby servo motor that are written for LabVIEW programmers.

Under construction. Check back later or email with questions or suggestions.


Building Instructions