Using the Object Sensor

The Object Sensor is a 3-Wire analog sensor that consists of an infrared LED and an infrared light sensor.

The 3-Wire Sensors, including the Object Sensor, are compatible with a EXP or V5 Robot Brain, and their sensor cables can be extended using a 3-Wire Extension Cable.

For the Object Sensor to function with the V5 Brain, the sensor cable must be fully inserted into a V5 Brain 3-Wire Port.

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How the Object Sensor Works

The Object Sensor functions by illuminating a surface with its infrared LED and then measuring the reflected infrared radiation with its infrared light sensor. Based on the intensity of the reflected radiation, the Object Sensor can determine how light or dark the surface is below the sensor.

Lightly colored surfaces reflect more infrared light than dark surfaces and will appear brighter to the sensor. This allows the sensor to detect a dark line on a pale surface or a pale line on a dark surface.

To use the Object Sensor effectively, it needs to be paired with a programming language such as VEXcode EXP or VEXcode V5. This enables the creation of a user program for the Brain to utilize the reflectivity value to control the robot.

What is Reflectivity?

Reflectivity is a way to measure how much light bounces off a surface. Imagine you have a flashlight and you shine it on different things. Some things, like a mirror or a white piece of paper, will bounce a lot of the light back to you. These things are very reflective. Other things, like a black sweater or a dark piece of cloth, won't bounce much light back. These things are not very reflective.

So, reflectivity is just about how well something can bounce light back to where it came from. The more light it bounces back, the higher its reflectivity.

Common Uses of the Object Sensor:

Object Sensors can be used to see differences in the CTE Workcell's conveyors. They allow the EXP Brain to determine if an object appears on the conveyor, determined by its detection threshold for reflectivity. Here, the object sensor can detect when a disk passes underneath it, because it detects a raise in reflectivity.

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Tips and Tricks

  • Placement of the Object Sensor is critical. The sensor works best when it is about 0.02” to 0.25” above the surface it is measuring, with the optimal distance being around 3 mm (about ⅛”). It should be placed as close to this distance as possible for the best sensitivity.
  • The reflectivity detected by the Object Sensor is greatly affected by the ambient light around it. To ensure consistent and reliable readings, the Object Sensor must be kept in a stable lighting environment.
  • To view the reflectivity value of the Object Sensor in real-time, use the Devices screen on the Brain.

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

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