Maxbotix analog programming

[tuXguy15]

Does anyone have any example code of getting the distance to something and driving that distance with a macho tis range finder?

[irvingc]

What you're asking is actually not so simple! Just getting the distance reading from the sensor can be somewhat complicated, depending on the interface. Here's some code I dug up from the last time we used an ultrasonic sensor that connected to the I2C bus (this was before we switched to the command-based framework):
import edu.wpi.first.wpilibj.*;
import java.util.TimerTask;

public class NRGUltrasonic
{
public static final boolean USING_ULTRASONIC = false;
private Timer timer;
private java.util.Timer controlLoop;
private DigitalModule digMod;
private I2C i2c;
private static final int ULTRASONIC_SLOT = 4;
private static final int ULTRASONIC_ADDRESS = 0xE0;
private static final int ECHO_ADDRESS_HIGH = 2;
private static final int ECHO_ADDRESS_LOW = 3;
private int dist;
private double period;
private boolean writeFail;

private class UltrasonicTask extends TimerTask
{
private NRGUltrasonic u;

public UltrasonicTask(NRGUltrasonic ultrasonic)
{
if (ultrasonic == null)
{
throw new NullPointerException("Given Ultrasonic was null");
}
this.u = ultrasonic;
}

public void run()
{
u.setDist();
}
}

public NRGUltrasonic()
{
dist = 0;
writeFail = false;
if(USING_ULTRASONIC)
{
digMod = DigitalModule.getInstance(ULTRASONIC_SLOT);
i2c = digMod.getI2C(ULTRASONIC_ADDRESS);
timer = new Timer();
controlLoop = new java.util.Timer();
if (i2c.addressOnly())
{
NRGLCD.println4("ERR: No Ultrasonic!");
Debug.println(Debug.FATAL_EXCEPTIONS, "ERROR: Could not find Ultrasonic.");
}
//Range: Three meters.
i2c.write(0x02, 0x46);
//Analogue Gain: 317
i2c.write(0x01, 0x18);
period = .05;
setDist();
}
}

/**
* Ends the control loop.
*/
public void free()
{
controlLoop.cancel();
controlLoop = null;
}

public int getDist()
{
return dist;
}

public boolean getWriteFail()
{
return writeFail;
}

//gets distance
private void setDist()
{
byte high, low;

try
{
//setting range to centimeters
if (i2c.write(0x00, 0x51))
{
writeFail = true;
Debug.println(Debug.ULTRASONIC, "Attemted write to ultrasonic, failed.");
}
else
{
writeFail = false;
Debug.println(Debug.ULTRASONIC, "Wrote to ultrasonic, began rangefinding in centimeters.");
timer.reset();
timer.start();

try
{
boolean done = false;
Timer.delay(.065);
for (int i = 0; i < 10; i++)
{
byte[] buffer = new byte[1];
if (i2c.read(ECHO_ADDRESS_HIGH, 1, buffer))
{
//Debug.println(Debug.ULTRASONIC, "Attempted read to ultrasonic high, failed.");
}
else
{
high = buffer[0];
if (i2c.read(ECHO_ADDRESS_LOW, 1, buffer))
{
//Debug.println(Debug.ULTRASONIC, "Attempted read to ultrasonic low, failed.");
}
else
{
low = buffer[0];
dist = high * 256 + ((int) low & 0xFF);
Debug.println(Debug.ULTRASONIC, "Try: " + i + " Time: " + timer.get() + " High: " + high + " Low: " + low + " Dist: " + dist);
done = true;
}
}
if (done)
break;
//Debug.println(Debug.ULTRASONIC, "Try "+i+" failed.");
if (i == 9)
Debug.println(Debug.ULTRASONIC, "TRIED 10 TIMES!");
Timer.delay(.02);
}
}
catch (Exception e)
{
Debug.println(Debug.FATAL_EXCEPTIONS, "Attempt to read ultrasonic caused a fatal exception.");
}
}
}
catch (Exception e)
{
Debug.println(Debug.FATAL_EXCEPTIONS, "Attempt to write to ultrasonic caused a fatal exception");
}
//Schedule next loop.
controlLoop.schedule(new UltrasonicTask(this), (long) (period * 1000));

}
}

And even after you know your distance, it's really not so easy to just drive directly at it. What type of drive train are you running? If it's a tank drive - does your robot drive straight if you just feed the same power to left and right motors?