ultrasonic-distance-module.ino

// Ultrasonic module: HC - SR04
const int US1TRIGPIN = 12;
const int US1ECHOPIN = 13;

//define sound speed in cm/uS
#define SOUND_SPEED 0.034
#define CM_TO_INCH 0.393701
#define UL unsigned long
#define SUL static unsigned long

#define sp(v) Serial.print(v)
#define spl(v) Serial.println(v)
#define spt(v) do { Serial.print(v); Serial.print("\t"); } while(0)

#define VCNT 10
double vs[VCNT];
int cv=0;

void setup() {
	Serial.begin(115200);
	delay(1000);
	pinMode(US1TRIGPIN, OUTPUT);
	pinMode(US1ECHOPIN, INPUT);
	for (cv=0; cv<VCNT; cv++) {
		vs[cv] = read_us_time_ms(US1TRIGPIN, US1ECHOPIN);
		delay(60);
	}
}

unsigned long read_us_time_ms(int trigpin, int echopin) {
	UL stread=millis(), enread;
	UL dur;
    
    /* clear trigger pin */
    digitalWrite(trigpin, LOW);
    delayMicroseconds(2);
    digitalWrite(trigpin, HIGH);
    delayMicroseconds(10);
    digitalWrite(trigpin, LOW);
    // Reads echo, returns the sound wave travel time in microseconds
    dur = pulseIn(echopin, HIGH);

    enread=millis();
    sp("readms:");
    spl(enread-stread);
    return dur;
}

double read_us_cm(int trigpin, int echopin) {
	return read_us_time_ms(trigpin, echopin) * SOUND_SPEED/2;
}

double vavg() {
	double tot=0;
	for (int i=0; i<VCNT; i++)   tot += vs[i];
	return tot/VCNT;
}

void loop() {
	static unsigned long last_read_us1_ms=0;
	unsigned long cmillis=millis();
	if (cmillis-last_read_us1_ms > 1) {
		if (++cv >= VCNT) cv=0;
		UL newv = read_us_time_ms(US1TRIGPIN, US1ECHOPIN);
		last_read_us1_ms = millis();
		if (newv > 0) { // if pulseIn() found the pulse
			vs[cv] = newv;
		}
		sp("ms:");
		spt(vs[cv]);
		sp("avg:");
		sp(vavg());
		spl("");
	}
}