Even though this is an old thread, it was the top result when I searched for a problem with the HC-SR04 sensor returning 0cm all the time.
I found a solution...eventually. For some reason the ECHO_PIN seems to get stuck on high. I resolved it and received accurate measurements when adding this line of code before doing the sonar.ping:
digitalWrite(ECHO_PIN, LOW);
The full sketch is:
// ---------------------------------------------------------------------------
// Example NewPing library sketch that does a ping about 20 times per second.
// ---------------------------------------------------------------------------
#include <NewPing.h>
#define TRIGGER_PIN 12 // Arduino pin tied to trigger pin on the ultrasonic sensor.
#define ECHO_PIN 11 // Arduino pin tied to echo pin on the ultrasonic sensor.
#define MAX_DISTANCE 200 // Maximum distance we want to ping for (in centimeters). Maximum sensor distance is rated at 400-500cm.
NewPing sonar(TRIGGER_PIN, ECHO_PIN, MAX_DISTANCE); // NewPing setup of pins and maximum distance.
void setup() {
Serial.begin(115200); // Open serial monitor at 115200 baud to see ping results.
}
void loop() {
delay(50); // Wait 50ms between pings (about 20 pings/sec). 29ms should be the shortest delay between pings.
digitalWrite(ECHO_PIN, LOW);
unsigned int uS = sonar.ping(); // Send ping, get ping time in microseconds (uS).
Serial.print("Ping: ");
Serial.print(uS / US_ROUNDTRIP_CM); // Convert ping time to distance in cm and print result (0 = outside set distance range)
Serial.println("cm");
}