#define PIN_TRIG 21 // T u1
#define PIN_ECHO 22 // E u1
#define PIN_TRIG2 2 // T u2
#define PIN_ECHO2 4 // E u2

void setup() {
  Serial.begin(115200);
  pinMode(PIN_TRIG, OUTPUT);
  pinMode(PIN_ECHO, INPUT);

  pinMode(PIN_TRIG2, OUTPUT);
  pinMode(PIN_ECHO2, INPUT);
}

void loop() {
  // Start a new measurement: U1
  digitalWrite(PIN_TRIG, LOW);
  delayMicroseconds(2);
  digitalWrite(PIN_TRIG, HIGH);
  delayMicroseconds(10);
  digitalWrite(PIN_TRIG, LOW);
int duration = pulseIn(PIN_ECHO,HIGH); //U1

// Start a new measurement: U2
  digitalWrite(PIN_TRIG2, LOW);
  delayMicroseconds(2); 
  digitalWrite(PIN_TRIG2, HIGH);
  delayMicroseconds(10);
  digitalWrite(PIN_TRIG2, LOW);  
 int duration2 = pulseIn(PIN_ECHO2,HIGH); //U2

// Read the result:
  Serial.print("U1 Distance in CM: ");
  Serial.println(duration / 58);
  //Serial.print("Distance in inches: ");
  //Serial.println(duration / 148);
  Serial.print("U2 Distance in CM: ");
  Serial.println(duration2 /58);
  //Serial.print("Distance in inches: ");
  //Serial.println(duration2 / 148);}
  delay(2000);
}