VEX2 Sensors Overview

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For ROBOTC CORTEX Sensor functions, check out the CORTEX Sensor Functions page!

The VEX 2.0 Cortex is equipped with 20 sensor ports. There are 8 Analog Sensor Ports and 12 Digital Sensor Ports. Note that unlike the VEX - PIC microcontroller, all Analog sensors must be in Analog ports, while all Digital sensors must be in Digital ports. There are a variety of functions and variables used for configuring these ports and accessing their values. Configuring sensors can be complicated. ROBOTC has a built-in wizard that can be used to configure the VEX 2.0 Cortex sensors. The wizard contains a number of PC windows that allow you to set the following fields for the sensor: The variable name that you want to assign to the sensor. Using a name like “leftBumper” makes for a more readable program than 'dgtl3'! The port that the sensor is connected to. The type of sensor – touch, quadrature encoder, sonar, line follower, etc.

Analog Sensors

There are 5 main types of Analog Sensors for the VEX CORTEX:

Light The Light sensor, also known as the Reflection sensor, returns values ranging between 0 and 4095. 0 is the lightest reading and 4095 is the darkest. #pragma config(Sensor, in1, lightSensor, sensorReflection) //*!!Code automatically generated by 'ROBOTC' configuration wizard  !!*//   task main { wait1Msec(2000); // wait 2 seconds before exectuing following code bMotorReflected[port2] = true; // reflects direction of motor on port 2   while(true) // infinite loop: { clearLCDLine(0); // clear the top VEX LCD line clearLCDLine(1); // clear the bottom VEX LCD line   setLCDPosition(0,0); // set the VEX LCD cursor the first line, first space displayNextLCDString("Light Sensor:"); // display "Light Sensor:" on the top line   setLCDPosition(1,0); // set the VEX LCD cursor the second line, first space displayNextLCDNumber(SensorValue(lightSensor)); // display the reading of the lightSensor sensor   wait1Msec(50); // wait 50 milliseconds to help display properly } }

Potentiometer Returns an analog value between 0 and 4095 (although mechanical stops my limit the values to between 5 and 4092). #pragma config(Sensor, in1, potentiometer, sensorPotentiometer) //*!!Code automatically generated by 'ROBOTC' configuration wizard  !!*//   task main { wait1Msec(2000); // wait 2 seconds before exectuing following code bMotorReflected[port2] = true; // reflects direction of motor on port 2   while(true) // infinite loop: { clearLCDLine(0); // clear the top VEX LCD line clearLCDLine(1); // clear the bottom VEX LCD line   setLCDPosition(0,0); // set the VEX LCD cursor the first line, first space displayNextLCDString("Potentiometer:"); // display "Potentiometer:" on the top line   setLCDPosition(1,0); // set the VEX LCD cursor the second line, first space displayNextLCDNumber(SensorValue(potentiometer)); // display the reading of the potentiometer sensor   wait1Msec(50); // wait 50 milliseconds to help display properly } }

Line Follower Returns values ranging between 0 and 4095. 0 is the lightest reading and 4095 is the darkest. #pragma config(Sensor, in1, lineFollower, sensorLineFollower) //*!!Code automatically generated by 'ROBOTC' configuration wizard  !!*//   task main { wait1Msec(2000); // wait 2 seconds before exectuing following code bMotorReflected[port2] = true; // reflects direction of motor on port 2   while(true) // infinite loop: { if(SensorValue(lineFollower) < 950) // if the lineFollower sensor reads a value less than 950: { // turn left: motor[port2] = 50; // motor on port 2 is run at power level 50 motor[port3] = 0; // motor on port 3 is stopped at power level 0 } else // lineFollower sensor reads a value greater than or equal to 950: { motor[port2] = 0; // motor on port 2 is stopped at power level 0 motor[port3] = 50; // motor on port 3 is run at power level 50 } } }

Gyro As the Gyro is turned, the values it returns are in tenths of degrees, positive and negative. Thus, a SensorValue of 3600 equals 360 degrees, or one full rotation. When the sensor is mounted horizontally, counter-clockwise movements will return values from 0 to -3600; clockwise movements will return values from 0 to 3600. Once the gyro completes one full revolution, the sensor value will “roll-over” to 0 by default (for example: …3597, 3598, 3599, 3600, 0, 1, 2, 3,…). To change the “roll-over” point, un-comment line 33 (from the code below) and change the value of “SensorFullCount” from 3600 to the desired value (7200, 18000, ect) #pragma config(Motor, port2, rightMotor, tmotorNormal, openLoop) #pragma config(Motor, port3, leftMotor, tmotorNormal, openLoop, reversed) //*!!Code automatically generated by 'ROBOTC' configuration wizard !!*//   /*+++++++++++++++++++++++++++++++++++++++++++++| Notes |++++++++++++++++++++++++++++++++++++++++++++ Gyro Based Turns - Basic -This program instructs your robot to turn for the specified number of degrees in "degrees10". -For best sensor results, clear out the gyro and manually configure it at the begging of the code. -The Gyro is configured by default to provide values from 0 to -3600 for clockwise rotation, and 0 to 3600 for counter-clockwise rotation   Robot Model(s): Swervebot   [I/O Port] [Name] [Type] [Description] Motor Port 2 rightMotor VEX Motor Right side motor Motor Port 3 leftMotor VEX Motor Left side motor Analog Port 8 in8 VEX Gyro Top-center mounted, away from the Cortex --------------------------------------------------------------------------------------------------*/   task main() { //Completely clear out any previous sensor readings by setting the port to "sensorNone" SensorType[in8] = sensorNone; wait1Msec(1000); //Reconfigure Analog Port 8 as a Gyro sensor and allow time for ROBOTC to calibrate it SensorType[in8] = sensorGyro; wait1Msec(2000);   //Adjust SensorScale to correct the scaling for your gyro //SensorScale[in8] = 260; //Adjust SensorFullCount to set the "rollover" point. 3600 sets the rollover point to +/-3600 //SensorFullCount[in8] = 3600;   //Specify the number of degrees for the robot to turn (1 degree = 10, or 900 = 90 degrees) int degrees10 = 900;   //While the absolute value of the gyro is less than the desired rotation... while(abs(SensorValue[in8]) < degrees10) { //...continue turning motor[rightMotor] = 25; motor[leftMotor] = -25; }   //Brief brake to stop some drift motor[rightMotor] = -5; motor[leftMotor] = 5; wait1Msec(250); }

Accelerometer Returns an analog value between 0 and 4095. Each Accelerometer Sensor has 3 cables, X, Y, and Z. The ports you attach them to don't have to be in any particular order (however you WILL need to use 3 ports). #pragma config(Sensor, in1, xAxis, sensorAccelerometer) #pragma config(Sensor, in2, yAxis, sensorAccelerometer) #pragma config(Sensor, in3, zAxis, sensorAccelerometer) //*!!Code automatically generated by 'ROBOTC' configuration wizard  !!*//   task main { int nBiasValues[3];   int X_Accel; int Y_Accel; int Z_Accel;   wait1Msec(500); // bias values are being calculated   /* store the bias values in an array so that they can be * displayed in the ROBOTC global variables debug window */ nBiasValues[0] = SensorBias[xAxis]; nBiasValues[1] = SensorBias[yAxis]; nBiasValues[2] = SensorBias[zAxis];   while(true) { /* also store the actual sensor values so that they can be * easily displayed in the ROBOTC global variables debug window */ X_Accel = SensorValue[xAxis]; Y_Accel = SensorValue[yAxis]; Z_Accel = SensorValue[zAxis];   wait1Msec(100); } }