A library and example for the HCSR04 distance sensor.
#include <hcsr04.h>
#define TRIG_PIN 12
#define ECHO_PIN 13
HCSR04 hcsr04(TRIG_PIN, ECHO_PIN, 20, 4000);
void setup(){
Serial.begin(9600);
}
void loop() {
// Output the distance in mm
Serial.println(hcsr04.distanceInMillimeters());
// Output information about the device, driver, and distance in Bifrost JSON format
Serial.println(hcsr04.ToString());
delay(250);
}