Millis Ultrasonic sensor

Projects Programming
1

Hello.I have an arduino mega and an ultrasonic sensor.
I have found many codes in internet about millis AND ultrasonic sensors,but nothing worked.
I tried a code of mine ,but I get 0.00 in serial monitor
CODE:

const int Trig_pin_front = 42;
const int Echo_pin_front = 43;

long duration_front;
float distance_front;

boolean first = true;
boolean second_ = false;
unsigned long prev = 0;

void setup()
{
  Serial.begin(9600);
  pinMode(Echo_pin_front , INPUT);
  pinMode(Trig_pin_front , OUTPUT);
}

void ultrasonic_sensor_forward()           
{
  unsigned long cur = millis();
  if (first)
  {
    if (cur - prev >= 2)
    {
      digitalWrite(Trig_pin_front , HIGH);           
      first = false;
      second_ = true;
      prev = cur;
    }
  }
  if (second_)
  {
    if (cur - prev >= 2)
    {
      digitalWrite(Trig_pin_front , LOW);            
      duration_front = pulseIn(Echo_pin_front , HIGH);     
      distance_front = duration_front * 0.034 / 2;        
      Serial.println(distance_front);
      second_ = false;
      first = true;
      prev = cur;
    }
  }
}

void loop()
{
ultrasonic_sensor_forward();
}

Any advices?What wrong my code has?

Thanks...

2

250 pings per second?

About 15 times too many.

Also, a trigger pulse is normally of the order of 10 microseconds, not 2 milliseconds.

3

It didn't work.
I changed it to 20 milliseconds and after to 10 milliseconds ,but I get 0.00 distance again....

4 
void ultrasonic_sensor_forward()           
{
  static unsigned long prev;
  unsigned long cur = millis();
  if (cur - prev >= 50) // no more than 20 pings per second
  {
      digitalWrite(Trig_pin_front, HIGH);           
      delayMicrosceonds (10);
      digitalWrite(Trig_pin_front, LOW);           
      duration_front = pulseIn(Echo_pin_front , HIGH);     
      distance_front = duration_front * 0.034 / 2;       
      Serial.println(distance_front);
      prev += 50;
  }
}

Uncompiled, untested.

Better still, use the NewPing library

5

I do not want to use delay() or delayMicroseconds().
Only millis() function.
Is this possible?

6

arduiNICK:
I do not want to use delay() or delayMicroseconds().
Only millis() function.
Is this possible?

Yes, of course.
My version doesn't use delay, and pulseIn blocks longer than the delayMicroseconds I used, but hey, knock yourself out.

7

I don't understand.
Can I use ultrasonic sensor with only millis (no delay no delayMicroseconds) ?

8

Yes, I think you can - the out-going pulse train isn't sent until the falling edge of the trigger pulse (at least, that's how it should be), so I guess it shouldn't matter how long the trigger pulse is.

Can't see why you'd want to, though.

Like I said, if you're worried about blocking, then get rid of pulseIn.

9

Ok ,thank you.
Do you know how to do it or does anyone know about it?

10

Yes - use the NewPing library.

11

Thanks again .I will try