Ultrasonic program giving me an odd error - arduino

Question

I created a program that is intended to turn a servo motor 180 degrees then back if an object is within 20cm of the ultrasonic sensor. This works fine except sometimes when the if condition is not met. In this case, the motor doesn't move at all and the distance is put into the serial monitor. This works fine sometimes, but in most cases the serial monitor just prints 0 repeatedly and I have to restart the program for it to work again. Even when I put an object within 20cm of the sensor it still prints 0. I am quite new to Arduino so this really just stumped me haha. Any tips or help would be greatly appreciated.
#include <Servo.h>
Servo servo1; // create servo object to control a servo
#define trigPin 13
#define echoPin 12
void setup()
{
Serial.begin(9600);
servo1.attach(9); // attaches the servo on pin 9 to the servo object
pinMode(trigPin, OUTPUT);
pinMode(echoPin, INPUT);
}
void loop()
{
long duration = 0, distance = 0;
digitalWrite(trigPin, LOW);
delayMicroseconds(2);
digitalWrite(trigPin, HIGH);
delayMicroseconds(10);
digitalWrite(trigPin, LOW);
delayMicroseconds(2);
duration = pulseIn(echoPin, HIGH);
distance = (duration / 2) / 29.1;
if(distance > 2 && distance < 20){
servo1.write(180);
Serial.println(distance);
delay(1000);
servo1.write(-180);
}
else{
servo1.write(0);
Serial.println(distance);
}
delay(2000);
}

Answer 1

See what happens when you try this code, as I cleaned it up a little bit:
#include <Servo.h>
#define trigPin 13
#define echoPin 12
Servo servo1; // create servo object to control a servo
void setup() {
Serial.begin (9600);
servo1.attach(9); // attaches the servo on pin 9 to the servo object
pinMode(trigPin, OUTPUT);
pinMode(echoPin, INPUT);
}
void loop() {
float duration, distance;
digitalWrite(trigPin, LOW);
delayMicroseconds(2);
digitalWrite(trigPin, HIGH);
delayMicroseconds(10);
digitalWrite(trigPin, LOW);
duration = pulseIn(echoPin, HIGH);
distance = (duration / 2) * 29.1;
if (duration) {
if (distance > 2 && distance < 20) {
servo1.write(180);
Serial.println(distance);
delay(1000);
servo1.write(-180);
}
else {
servo1.write(0);
Serial.println(distance);
}
}
delay(2000);
}
I think if you use a float it might work. However, if it doesn't work, try switching up the pin assignments to different pins on the Arduino and see if that works. If the distance measurment is off the best way to adjust it is with the multiplied value in the distance variable in the void loop ().This one works for me.