Sharp IR Distance Sensor

The Sharp GP2Y0A21YK is one of the most reliable and accurate sensors in the collection. The Sharp IR has many benefits that make it one of the best sensors for a robot for distance tracking.

Electrical Characteristics

Function	Min	Nom	Max
Input Voltage	4.5VDC	5V	7VDC
Output Voltage	-0.3VDC	—	VIN + 0.3VDC
Sensing Range	10cm	—	80cm
Current	—	30mA	40mA
Operating Temperature	-10°C	—	60°C
Storage Temperature	-40°C	—	70°C

Programming the Sharp IR Sensor

Java

C++

Roscpp

//import the Analog Library
import edu.wpi.first.wpilibj.AnalogInput;

//Create the Analog Object
private AnalogInput sharp;

//Constuct a new instance
sharp = new AnalogInput(port);

//Create an accessor method
public double getDistance()
{
    return (Math.pow(sharp.getAverageVoltage(), -1.2045)) * 27.726;
}

The accessor method will output the range in cm.

Note

The valid Analog ports are 0-3

//Include the Analog and Math Library
#include "frc/AnalogInput.h"
#include <cmath>

//Constructors
frc::AnalogInput sharp{port};

//Create an accessor function
double getDistance(void)
{
    return (pow(sharp.GetAverageVoltage(), -1.2045)) * 27.726;
}

The accessor function will output the range in cm.

Note

The valid Analog ports are 0-3

//Include the Sharp Library
#include "Sharp_ros.h"


double sharp_dist;

// Returns the distance value reported by the Sharp IR sensor
void sharp_dist_callback(const std_msgs::Float32::ConstPtr& msg)
{
   sharp_dist = msg->data;
}

int main(int argc, char **argv)
{
   system("/usr/local/frc/bin/frcKillRobot.sh"); //Terminal call to kill the robot manager used for WPILib before running the executable.
   ros::init(argc, argv, "sharp_node");

   /**
    * Constructor
    * Sharp's ros threads (publishers and services) will run asynchronously in the background
    */

   ros::NodeHandle nh; //internal reference to the ROS node that the program will use to interact with the ROS system
   VMXPi vmx(true, (uint8_t)50); //realtime bool and the update rate to use for the VMXPi AHRS/IMU interface, default is 50hz within a valid range of 4-200Hz

   ros::Subscriber sharpDist_sub;

   SharpROS sharp(&nh, &vmx);
   // or can use
   SharpROS sharp(&nh, &vmx, channel);

   //Use these to directly access the data
   double dist_cm = sharp.GetIRDistance(); //converts the average voltage read, outputs the range in cm
   double voltage = sharp.GetRawVoltage(); //returns the average voltage

   // Subscribing to Sharp distance topic to access the distance data
   sharpDist_sub = nh.subscribe("channel/22/sharp_ir/dist", 1, sharp_dist_callback);

   ros::spin(); //ros::spin() will enter a loop, pumping callbacks to obtain the latest sensor data

   return 0;
}

The valid Analog channels are 22-25. These are different from the WPI Analog Input Channels.

Important

Subscribe to Sharp topics to access the data being published and write callbacks to pass messages between various processes.

Note

Calling the frcKillRobot.sh script is necessary since the VMXPi HAL uses the pigpio library, which unfortunately can only be used in one process. Thus, everything that interfaces with the VMXPi must be run on the same executable. For more information on programming with ROS, refer to: ROS Tutorials.