"See" like a bat – bat goggles code

Here be code to make an Arduino, HC-SR04 Ultrasonic distance sensor and a piezo buzzer mimic sonar. I've used this to for bat goggles but you could equally hack it to control a wall avoiding robot. This was written for a series of workshops I'm delivering for MadLab.

This code is based on Suneth Attygalle's batgoggles code, and the Arduino Ping Tutorial

// declare the pins

const int trigPin = 5;
const int echoPin = 6;
const int buzzerPin = 4;

// set up constants

const long scalingfactor = 10;

// set global variables

int cm;
unsigned long time1, time2, i, duration;
unsigned long maxtime = 1000;

void setup() {
    // initialise all the pins

    pinMode(trigPin, OUTPUT);
    pinMode(echoPin, INPUT);
    pinMode(buzzerPin, OUTPUT);

    // uncomment this if you need to check why things aren't
    // working
    // Serial.begin(9600);
}

void loop() {
    // beep
    tone(buzzerPin, 262);
    // sets the note to middle c (ish)

    delay(90);
    check_distance();

    // if the sensor doesn't time out remove the time it took for
    // the sensor to be polled from the remaining delay so that
    // the beeps remain even

    if (time2-time1<30) {
        delay(60-(time2-time1));
    }

    noTone(buzzerPin);

    // delay

    i = 0;

    // resets the counter

    while (i < maxtime){ // do this until maxtime is reached

        if (i % 60 == 0){
            check_distance();
        }

        delay(1);
        ++i; // increment counter
    }
}

void check_distance(){
    // note the time before checking the sensor
    time1 = millis();

    // The sensor is triggered by a HIGH pulse of 10 or more
    // microseconds. Giving a short LOW pulse beforehand ensures a
    // clean HIGH pulse.

    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 from an object. This will time
    // out after 30ms.

    duration = pulseIn(echoPin, HIGH);

    // note the time after checking the sensor time2 = millis();
    // translate the pulse duration into centimeters
    // 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 the distance travelled.

    cm = duration / 29 / 2; maxtime = cm * scalingfactor;

    // Not sure why it's not working? Uncomment this to check that
    // your sensor is giving the correct output
    // Serial.print(duration);
    // Serial.print(" millis");
    // Serial.println();
    // Serial.print(cm);
    // Serial.print(" cm");
    // Serial.println();
}