this is the code I used
int ENA=5;//connected to arduino's port 5 (output pwm)
int IN1=2;//connected to arduino's port 2
int IN2=3;//connected to arduino's port 3
int ENB=6;//connected to arduino's port 5 (output pwm)
int IN3=4;//connected to arduino's port 4
int IN4=7;//connected to arduino's port 7
const int trigPin = 13;
const int echoPin = 12;
void setup() {
// initialize serial communication:
Serial.begin(9600);
}
void loop()
{
analogWrite (ENA,200);//start driving motorA
analogWrite (ENB,200);//start driving motorB
// establish variables for duration of the ping,
// and the distance result in inches and centimeters:
long duration, inches, cm;
// The sensor is triggered by a HIGH pulse of 10 or more microseconds.
// Give a short LOW pulse beforehand to ensure a clean HIGH pulse:
pinMode(trigPin, OUTPUT);
digitalWrite(trigPin, LOW);
delayMicroseconds(2);
digitalWrite(trigPin, HIGH);
delayMicroseconds(10);
digitalWrite(trigPin, LOW);
// Read the signal from the sensor: a HIGH pulse whose
// duration is the time (in microseconds) from the sending
// of the ping to the reception of its echo off of an object.
pinMode(echoPin, INPUT);
duration = pulseIn(echoPin, HIGH);
// convert the time into a distance
inches = microsecondsToInches(duration);
cm = microsecondsToCentimeters(duration);
Serial.print(inches);
Serial.print("in, ");
Serial.print(cm);
Serial.print("cm");
Serial.println();
if ( inches < 10) {
analogWrite (ENA,255);//start driving motorA
analogWrite (ENB,1);//start driving motorB
delay (500);
}
}
long microsecondsToInches(long microseconds)
{
// According to Parallax's datasheet for the PING))), there are
// 73.746 microseconds per inch (i.e. sound travels at 1130 feet per
// second). This gives the distance travelled by the ping, outbound
// and return, so we divide by 2 to get the distance of the obstacle.
// See: http://www.parallax.com/dl/docs/prod/acc/28015-PING-v1.3.pdf
return microseconds / 74 / 2;
}
long microsecondsToCentimeters(long microseconds)
{
// The speed of sound is 340 m/s or 29 microseconds per centimeter.
// The ping travels out and back, so to find the distance of the
// object we take half of the distance travelled.
return microseconds / 29 / 2;
}