New ping and HC-SR04. Distance reading stuck at about 140cm

Other Hardware Sensors
1

Hello all,

I'm new to Arduino and have recently tried getting a HC-SR04 ultrasonic range finder to work for a school project.

I'm using a lilypad ATmega328 with Tim's newping library, and his example sketch:

#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.
  unsigned int uS = sonar.ping(); // Send ping, get ping time in microseconds (uS).
  Serial.print("Ping: ");
  Serial.print(sonar.convert_cm(uS)); // Convert ping time to distance and print result (0 = outside set distance range, no ping echo)
  Serial.println("cm");
}

Unfortunately all I seem to get in the serial monitor is:
Ping: 142cm
Ping: 0cm
Ping: 142cm
Ping: 0cm
Ping: 142cm
Ping: 0cm
Ping: 142cm
Ping: 0cm

Pretty sure its all wired up correctly, not much to mess up on that end really. If I drop any connections the range drops to a constant 0.

Any ideas as to what I'm missing?

Thanks in advance

2

Update.

I'm testing my sensor and getting a constant:

Duration is-22332
Duration is-22316
Duration is-22316
Duration is-22316
Duration is-22316
Duration is-22330

Regardless of distance, using this code:

#define trigPin 12
#define echoPin 9

void setup() {
  Serial.begin (9600);
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
}

void loop() {
  int distance;
  int duration;
  digitalWrite(trigPin, LOW);
  delayMicroseconds(50);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(50);
  digitalWrite(trigPin, LOW);
  duration = pulseIn(echoPin, HIGH);
  distance = (duration/2) / 29.1;
  Serial.print("Duration is");
  Serial.println(duration);
  delay(1000);
}
3

Try adapting the original ping example by David Mellis - I note that the delays he uses are far shorter - not clear whether that matters. After that I'd be inclined to try another HC-SR04.

4

Do you actually have a target in front of the sensor? The device has a narrow angle of view. Have you put you hand a few inches directly in front?