// ---------------------------------------------------------
    // Kijk op: https://playground.arduino.cc/Code/NewPing/
    // This example code was used to successfully communicate
    // with 15 ultrasonic sensors. You can adjust the number of
    // sensors in your project by changing SONAR_NUM and the
    // number of NewPing objects in the "sonar" array. You also
    // need to change the pins for each sensor for the NewPing
    // objects. Each sensor is pinged at 33ms intervals. So, one
    // cycle of all sensors takes 495ms (33 * 15 = 495ms). The
    // results are sent to the "oneSensorCycle" function which
    // currently just displays the distance data. Your project
    // would normally process the sensor results in this
    // function (for example, decide if a robot needs to turn
    // and call the turn function). Keep in mind this example is
    // event-driven. Your complete sketch needs to be written so
    // there's no "delay" commands and the loop() cycles at
    // faster than a 33ms rate. If other processes take longer
    // than 33ms, you'll need to increase PING_INTERVAL so it
    // doesn't get behind.
    // ---------------------------------------------------------
    #include <NewPing.h>
     
    #define SONAR_NUM     2 // Number or sensors.
    #define MAX_DISTANCE 200 // Max distance in cm.
    #define PING_INTERVAL 33 // Milliseconds between pings.
     
    unsigned long pingTimer[SONAR_NUM]; // When each pings.
    unsigned int cm[SONAR_NUM]; // Store ping distances.
    uint8_t currentSensor = 0; // Which sensor is active,
    
  //NewPing sonar(trigger_pin, echo_pin [, max_cm_distance]);
    NewPing sonar[SONAR_NUM] = { // Sensor object array.
      NewPing(4, 3, 200),
      NewPing(5, 7, 200)
    };
     
    void setup() {
      Serial.begin(57600);
      pingTimer[0] = millis() + 75; // First ping start in ms.
      for (uint8_t i = 1; i < SONAR_NUM; i++)
        pingTimer[i] = pingTimer[i - 1] + PING_INTERVAL;
    }
     
    void loop() {
      for (uint8_t i = 0; i < SONAR_NUM; i++) {
        if (millis() >= pingTimer[i]) {
          pingTimer[i] += PING_INTERVAL * SONAR_NUM;
          if (i == 0 && currentSensor == SONAR_NUM - 1)
            oneSensorCycle(); // Do something with results.
          sonar[currentSensor].timer_stop();
          currentSensor = i;
          cm[currentSensor] = 0;
          sonar[currentSensor].ping_timer(echoCheck);
        }
      }
      // The rest of your code would go here.
    }
     
    void echoCheck() { // If ping echo, set distance to array.
      if (sonar[currentSensor].check_timer())
        cm[currentSensor] = sonar[currentSensor].ping_result / US_ROUNDTRIP_CM;
    }
     
    void oneSensorCycle() { // Do something with the results.
      for (uint8_t i = 0; i < SONAR_NUM; i++) {
        Serial.print(i);
        Serial.print("=");
        Serial.print(cm[i]);
        Serial.print("cm ");
      }
      Serial.println();
    }

    // ---------------------------------------------------------
    // Kijk op: https://playground.arduino.cc/Code/NewPing/
    // This example code was used to successfully communicate
    // with 15 ultrasonic sensors. You can adjust the number of
    // sensors in your project by changing SONAR_NUM and the
    // number of NewPing objects in the "sonar" array. You also
    // need to change the pins for each sensor for the NewPing
    // objects. Each sensor is pinged at 33ms intervals. So, one
    // cycle of all sensors takes 495ms (33 * 15 = 495ms). The
    // results are sent to the "oneSensorCycle" function which
    // currently just displays the distance data. Your project
    // would normally process the sensor results in this
    // function (for example, decide if a robot needs to turn
    // and call the turn function). Keep in mind this example is
    // event-driven. Your complete sketch needs to be written so
    // there's no "delay" commands and the loop() cycles at
    // faster than a 33ms rate. If other processes take longer
    // than 33ms, you'll need to increase PING_INTERVAL so it
    // doesn't get behind.
    // ---------------------------------------------------------
    #include <NewPing.h>
     
    #define SONAR_NUM     2 // Number or sensors.
    #define MAX_DISTANCE 200 // Max distance in cm.
    #define PING_INTERVAL 33 // Milliseconds between pings.
     
    unsigned long pingTimer[SONAR_NUM]; // When each pings.
    unsigned int cm[SONAR_NUM]; // Store ping distances.
    uint8_t currentSensor = 0; // Which sensor is active,
    
  //NewPing sonar(trigger_pin, echo_pin [, max_cm_distance]);
    NewPing sonar[SONAR_NUM] = { // Sensor object array.
      NewPing(4, 3, 200),
      NewPing(5, 7, 200)
    };
     
    void setup() {
      Serial.begin(57600);
      pingTimer[0] = millis() + 75; // First ping start in ms.
      for (uint8_t i = 1; i < SONAR_NUM; i++)
        pingTimer[i] = pingTimer[i - 1] + PING_INTERVAL;
    }
     
    void loop() {
      for (uint8_t i = 0; i < SONAR_NUM; i++) {
        if (millis() >= pingTimer[i]) {
          pingTimer[i] += PING_INTERVAL * SONAR_NUM;
          if (i == 0 && currentSensor == SONAR_NUM - 1)
            oneSensorCycle(); // Do something with results.
          sonar[currentSensor].timer_stop();
          currentSensor = i;
          cm[currentSensor] = 0;
          sonar[currentSensor].ping_timer(echoCheck);
        }
      }
      // The rest of your code would go here.
    }
     
    void echoCheck() { // If ping echo, set distance to array.
      if (sonar[currentSensor].check_timer())
        cm[currentSensor] = sonar[currentSensor].ping_result / US_ROUNDTRIP_CM;
    }
     
    void oneSensorCycle() { // Do something with the results.
      for (uint8_t i = 0; i < SONAR_NUM; i++) {
        Serial.print(i);
        Serial.print("=");
        Serial.print(cm[i]);
        Serial.print("cm ");
      }
      Serial.println();
    }