cf: https://github.com/Seeed-Studio/Grove_Ultrasonic_Ranger

UltraSonic.ino

// Grove UltraSonic Sensor

#define Sensor 7

void setup()
{
	Serial.begin(9600);
}
void loop()
{
	long RangeInCentimeters;
	
	Serial.println("The distance to obstacles in front is: ");
	
	RangeInCentimeters = UltrasonicMeasureInCentimeters(Sensor);
	Serial.print(RangeInCentimeters);//0~400cm
	Serial.println(" cm");
	delay(250);
}


// copy from https://github.com/Seeed-Studio/Grove_Ultrasonic_Ranger/blob/master/Ultrasonic.cpp

long UltrasonicMeasureInCentimeters(int _pin)
{
	pinMode(_pin, OUTPUT);
	digitalWrite(_pin, LOW);
	delayMicroseconds(2);
	digitalWrite(_pin, HIGH);
	delayMicroseconds(5);
	digitalWrite(_pin,LOW);
	pinMode(_pin,INPUT);
	long duration;
	duration = pulseIn(_pin,HIGH);
	long RangeInCentimeters;
	RangeInCentimeters = duration/29/2;
	return RangeInCentimeters;
}