Ping controlling a LED - pls help!

Hi all,
I bought myself a PING sensor and want to use it to control a LED. I got the PING working fine as the Serial Monitor is displaying the distances correctly, so the problem lies with the code added.
Basically, what I want it to do, is when an object is within 12" from the PING it turns on the light. If the object moves further than 12' from the PING the light stays on for the Interval time, then switches off.

I have gone over the code repeatedly but I can't seem to see what I am doing wrong. I have tested the LED (it works), I have tried using a different Arduino pin for LED (no difference).

Any help would be greatly appreciated :slight_smile:

// establish variables for duration of the ping, 
  // and the distance result in inches and centimeters:
  long duration, inches, cm;
    
  long previousMillis = 0;        // will store last time LED off timing sequence was triggered
  long interval = 5000;           // interval from stepping away from machine to LED off
 
  const int pingPin = 6;           //pin for ping pulses & reading
  int LED = 12;             //pin for controlling LEDs based on ping and interval
  
 void setup()
 {
  Serial.begin(9600);
 pinMode(LED,OUTPUT);
 LED = LOW;
 delay(500);
 
 }
  
  
  void loop()
  {
  unsigned long currentMillis = millis();
  
  // The PING))) is triggered by a HIGH pulse of 2 or more microseconds.
  // Give a short LOW pulse beforehand to ensure a clean HIGH pulse:
  pinMode(pingPin, OUTPUT);
  digitalWrite(pingPin, LOW);
  delayMicroseconds(2);
  digitalWrite(pingPin, HIGH);
  delayMicroseconds(5);
  digitalWrite(pingPin, LOW);

  // The same pin is used to read the signal from the PING))): a HIGH
  // pulse whose duration is the time (in microseconds) from the sending
  // of the ping to the reception of its echo off of an object.
  pinMode(pingPin, INPUT);
  duration = pulseIn(pingPin, HIGH);

  // convert the time into a distance
  inches = microsecondsToInches(duration);
  cm = microsecondsToCentimeters(duration);
  
   
  Serial.print(inches);
  Serial.print("in, ");
  Serial.print(cm);
  Serial.print("cm");
  Serial.println();
  
  if (inches < 12)      //if an object is within 12 inches
  {
   LED = HIGH;        //turn LED on
  }
  
  else if (inches > 12)  //if object goes outside 12 inch range
  {
   previousMillis = currentMillis;    //start counting for interval
  }
  
  else if ((inches > 12)&&(currentMillis - previousMillis > interval))    //if object is out of 12 inch range and interval time has elapsed
  {
  LED = LOW;                                                            //turn off LED
  }
  }
    
  long microsecondsToInches(long microseconds)
{
  // According to Parallax's datasheet for the PING))), there are
  // 73.746 microseconds per inch (i.e. sound travels at 1130 feet per
  // second).  This gives the distance travelled by the ping, outbound
  // and return, so we divide by 2 to get the distance of the obstacle.
  // See: http://www.parallax.com/dl/docs/prod/acc/28015-PING-v1.3.pdf
  return microseconds / 74 / 2;
}

long microsecondsToCentimeters(long microseconds)
{
  // The speed of sound is 340 m/s or 29 microseconds per centimeter.
  // The ping travels out and back, so to find the distance of the
  // object we take half of the distance travelled.
  return microseconds / 29 / 2;
}

You're not writing to the LED's pin, just moving the pin from zero to one or vice versa

LED = LOW just makes the variable LED the number 0. You need to use the digitalWrite() function if you are trying to make the ouptut of pin LED LOW.

Try defining the LED variable as a const (which it should be) and your code will not compile.

I know it is not preferred style for most of the Arduino code I see, but using #define for LED will immediately highlight the problems.

Write some code to turn the LED on and off, and test it.

Write some code to perform the distance measurement, and test it.

Write a sketch which combines both your tested functions and uses the distance reading to control the LED.

Thanks everyone, n00b mistake.
I've got the LED turning on and off now, still trying to get the delay happening without using the delay() function. That will give me something to beat my head against tomorrow!