Troubleshooting VEX V5 Sensors

When your robot is not behaving as intended while using sensor feedback, you can follow a step-by-step troubleshooting procedure to find and fix your issues. This article will explain the steps in a troubleshooting process, and provide tips for how to use these steps.

The steps of this process are:

  1. Identify the problem
  2. Check hardware
  3. Check software
  4. Analyze and apply data

Identify the Problem

The first step to troubleshooting your sensor is to identify which sensor is causing the problem. Compare the observed robot behavior with the intended robot behavior. Is the problematic behavior caused by a sensor? If so, which sensor? If you need more information to determine which sensor may be the problem, read the article(s) below related to the sensors on your robot.

VEX V5 Sensors:

Once you have identified which sensor is causing the unintended behavior, you can move forward in the process.

Check Hardware

The second step is to check the hardware on the robot to be sure that the sensor can function as intended. Each of the following hardware considerations could be affecting the functionality of your sensor.

Check Sensor Placement


Begin by looking at where the sensor is located on your robot. Is the sensor being blocked by anything, like another part of your robot? Ensure that the sensor has the space needed to operate as intended.

As shown here, the Optical Sensor has a clear line of vision to the object it is meant to detect.

Check Sensor Connection


Test the sensor’s functionality by looking at the data reported in the Devices Screen on the VEX V5 Brain. This can help you validate that the sensor is plugged in and working. 

To access the Devices Screen, follow the steps in this article. Once the Devices Screen is open, see if the sensor is visible in the correct port location and reporting data. Here the Optical Sensor is detected in Smart Port 11.


If the sensor is not reporting data, ensure your sensors are plugged in correctly. When plugging in sensors to a Smart Port, you should hear a snap when the sensor’s locking tab is fully engaged in a port.

When plugging sensors into a 3-Wire Port, the cable should be fully inserted in the correct orientation with the white wire closest to the Brain screen. 

You can also try swapping out the sensor you are using with another to see if that resolves your issue.

If you changed something with your sensor placement or sensor connection, test your project again to see if this resolved the issue. If your sensor placement and connection did not change, move onto the next step to continue the troubleshooting process.

Check Software

Once you have identified that the sensor is placed on and connected to the robot successfully, you can look to the VEXcode EXP project next. Iterating on a project can help you to ensure that the data from the sensor is being used effectively in your project. The following strategies can help you with coding your sensor.

If you apply any of these strategies to your VEXcode V5 project, test your project again to see if this resolved the issue.

Check Firmware and Configuration


Begin by ensuring that your EXP Brain’s firmware is up to date.

See this article to learn more about updating firmware on the V5 Brain.


Now that you are sure all devices are correctly connected to the Brain, check the Device Configuration in VEXcode V5.

Check to be sure all of the sensors are present in the configuration. Then, check to be sure each one is connected to the correct port.

Change any incorrect device configurations.

Run an Example Project


Open an Example Project that uses the sensor you are troubleshooting. You can select the ‘Sensing’ category to filter example projects.

For more information about V5 Blocks Example Projects and Templates, see this article.

For more information about V5 Python Example Projects and Templates, see this article.

For more information about V5 C++ Example Projects and Templates, see this article.


Once open, read the Note to determine if the functionality in the example project aligns with what you are trying to do with the sensor.

In the example project shown here, the note indicates that the state of the Bumper Switch or Limit Switch being pressed will be printed on the Brain screen. In this case True indicates pressed and False indicates not pressed. 

Run the example project and observe the robot behavior. Then look at the project to see how the sensor data is being used in order to cause the observed behaviors. You may want to run the example project multiple times to help with this.

You may want to try to create your own simplified project to apply what you have learned from the example project to your task.

Use Other VEXcode V5 Tools

There are also tools and strategies that you can use to help you as you learn more about coding your sensor in VEXcode V5. You can learn about the blocks or commands in the Toolbox individually by using the Help. You can also view sensor data as a project is running to learn more about what the sensor is reporting.


The Help

Read the Help for the blocks or commands in the example project, or in your project to learn about the data that is used, what values the command will report, and examples of how to use the command in a project.

View this article to learn more about accessing Help in VEXcode V5 Blocks.

View this article to learn more about accessing Help in VEXcode V5 Python.

View this article to learn more about accessing Help in VEXcode V5 C++.

Printing Data

You can also print data from the sensor as the example project or your project is running, to help you better understand what the sensor is reporting in real time. This can help you determine what reported values from the sensor to use as parameters in your project. 

Note that in a Blocks project, a separate {When started} hat block can be used to keep all of the printing commands organized in their own stack.

VEXcode V5 Blocks


VEXcode V5 Python


VEXcode V5 C++


Select each image above to enlarge.

Printing to the EXP Brain is helpful when you want to see the values changing as a VEXcode V5 project is running. This can help you determine what reported values from the sensor to use as parameters in your project. These print commands can be built into the VEXcode V5 project you have already created so you can see the sensor values change at specific times while the robot is moving. 

These example projects above show how to print values from the Distance Sensor to the V5 Brain. The comments in each project explain the flow of the project and use of each command.

VEXcode V5 Blocks


VEXcode V5 Python


VEXcode V5 C++


Select each image above to enlarge.

Printing to the Print Console in VEXcode V5 is recommended for when you are running a VEXcode EXP project where the robot does NOT move. The V5 Brain must remain plugged in during the execution of the project in order to print to the Print Console. This is beneficial because you can read the values from the VEXcode V5 window rather than trying to read data from the Brain screen.

These examples show a project printing data from the Rotation Sensor to the Console in VEXcode V5. 

For more information about using the Print Console in VEXcode V5 Blocks, see this article.

Analyze and Apply Data

Next, use what you have learned in the previous steps to adjust your original project. You can continue to use tools like the Help and printing data to enable you to use the sensor effectively to accomplish your goal.

You can also ask questions about your project to help you move forward. Think about things like:

  • Are you using greater than < or less than > in your project? Is the symbol facing the right direction? If you are using equal to = try replacing it with a greater than or less than, to use a range of values.
  • Are your parameters correct? Are you using the data from the sensor to set your parameters? Did you choose the dropdown option that you need?
  • Are you checking the conditions more than once? Try adding a Forever loop to your project, so that the condition is checked repeatedly when the project is run.
  • Is your project getting stuck? Are your conditions set correctly? If you are using nested loops, try simplifying your project to isolate individual behaviors.
  • Are your environmental conditions influencing the sensor? Is it too bright or too dark? Are there objects or people in the way? Try running your project in a different location to see if that helps.
  • Are you running the most recent version of your project? Have you downloaded your updated project to the Brain? Make sure you redownload the project each time you make a change.
  • Are you detecting the correct color? Is the sensor reporting a different color than the one you have in your project? Try changing the color parameter, or using a range of hue values, to see if that helps.
  • Are you detecting an object within the sensor’s field of view? Remember that the field of view moves in conjunction with the movement of the robot.
  • Are you using a waiting block while checking a condition? Be sure to use non-waiting blocks in a project when checking for a condition. View this article to learn more about waiting vs. non-waiting blocks in VEXcode V5.
  • If you are coding in blocks, is your whole stack attached to the {When started} hat block? Blocks will only run when they are connected. You can listen for a click sound when you drag blocks and connect them together.

As you answer these questions, be sure to change one thing in your project at a time, test it, then evaluate whether that change was effective. Testing your project frequently can help you to more easily see how your code is connected to the robot’s behaviors.  You may need to repeat steps in the troubleshooting process multiple times to solve your problem, and that is ok. Each iteration will help you learn more about the sensor you are using and how to code it in VEXcode V5.

For more information, help, and tips, check out the many resources at VEX Professional Development Plus

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