Keep Getting Pulses To LED

Projects Programming
1

New to this so a little slack please.

See following code, even with the output set to LOW, I get a brief pulse that blinks the LED on Pin 8, Output. LED stays solid when the distance is <= 20, so that works, but get the pulse on the LED each 1000 time it runs the circuit with output LOW. Thanks

#include <NewPing.h>

#define TRIGGER_PIN 11 // Arduino pin tied to trigger pin on the ultrasonic sensor.
#define ECHO_PIN 12 // Arduino pin tied to echo pin on the ultrasonic sensor.
#define MAX_DISTANCE 305 // Maximum distance we want to ping for (in centimeters). Maximum sensor distance is rated at 400-500cm. 305 is 10 feet.

NewPing sonar(TRIGGER_PIN, ECHO_PIN, MAX_DISTANCE); // NewPing setup of pins and maximum distance.

void setup() {
// put your setup code here, to run once:

pinMode (8, OUTPUT);

}

void loop() {

//Code to testing if/then on distance.
delay (1000);
digitalWrite(TRIGGER_PIN, LOW);
if (sonar.ping_cm ()<=20);
digitalWrite(8, HIGH);
if (sonar.ping_cm ()>20)
digitalWrite(8, LOW);

2 
if (sonar.ping_cm ()<=20);

The semi colon after the statement terminates the conditional, and the next line is executed.
Remove the ;

See Nick Gammon's Tips and Traps #13

3

You got it right with the second one.

4

aarg:
You got it right with the second one.

Indeed, but you omitted the code block { }.

Now I agree the language allows you to do that if there is just a single statement following the if. But many a coding standard, including many professional ones, would say that is bad style.

If you are going to allow it I would insist that the single statement is on the same line as the conditional to make it abundantly clear...

if (sonar.ping_cm ()<=20) digitalWrite(8, HIGH);
if (sonar.ping_cm ()>20) digitalWrite(8, LOW);

...far to easy to make an unintended mistake otherwise (only one of which is slapping an unintended semicolon on the end :wink: ).

Or better still use an else clause...

if (sonar.ping_cm ()<=20) {
  digitalWrite(8, HIGH);
} else {
  digitalWrite(8, LOW);
}

Or just...

digitalWrite(8, sonar.ping_cm ()<=20 ? HIGH : LOW);

And while you’re at it name your pins with constants. You’ll thank me later when you have a 1000 line program and need to remember 20 pin assignments.

5

Wow, thanks for all the great input and suggestions going forward. Will implement all, and really appreciate the help. My first post and really impressed.

6

For future issues: If you post your code as described in the how to use this forum sticky, more forum members will read it.