If else statement in a loop

Projects Programming
1

Hello!

I am very new to Arduino and trying to write a program that uses a Sainsmart ultrasonic sensor to detect distance and when the distance is shorter than 11 cm, then a servo will turn 180 degrees, and then back to 0 degrees after a one second delay, followed by a minute delay (or ideally, the program would shut down at that point).

I have combined code from a servo example and also from a ping example.

The inputs and outputs read fine. My problem is, if the sensor reads 11 cm or greater, I want the servo to do nothing at all, and just delay .1 seconds. If the sensor reads 10 cm or less, I want the servo to move 180 degrees and then back to the original position and stop the loop, or at least wait one minute at that point.

Here is the code I have put together so far. Any help would be appreciated.

#include <Servo.h>
// Pin number constants
const int triggerPin = 5;
const int echoPin = 6;

Servo servo1;

void setup() {
// initialize serial communication:
Serial.begin(9600);

servo1.attach(9);
}

void loop()
{
 int position; 
// establish variables for duration of the ping,
// and the distance result in inches and centimeters:
long duration, feet, inches, cm;

// 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(triggerPin, OUTPUT);
digitalWrite(triggerPin, LOW);
delayMicroseconds(2);
digitalWrite(triggerPin, HIGH);
delayMicroseconds(5);
digitalWrite(triggerPin, LOW);


pinMode(echoPin, INPUT);
duration = pulseIn(echoPin, HIGH);

// convert the time into a distance

cm = microsecondsToCentimeters(duration);

Serial.print(cm);
Serial.print("cm");
Serial.println();

delay(100);

if (cm >= 11)

delay(100);

if (cm < 11)

servo1.write(180);
delay(1000);
servo1.write(0);
delay(60000);



}

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;
}

moderator update: added code tags - # button above the smileys

2

you might need to add some {} to make a block of all the code it must do if cm < 11

if (cm < 11)
{
  servo1.write(180);
  delay(1000);
  servo1.write(0);
}
3

Some things that occurred to me

You need to have {} brackets with IF statements to get all the actions to be subject to the IF. I always use brackets even if there is only one action

if (cm >= 11) {
    delay(100);
}

if (cm < 11) {
      servo1.write(180);
     delay(1000);
     servo1.write(0);
     delay(60000);
}

Your calculation to get cm may not work perfectly because you are doing division of integer numbers. You just need to work out a few examples to satisfy yourself that the absence of decimals is not a problem. Alternatively you could use FLOATs.

You may need a long value for duration but not for feet inches and cm. Perhaps you don't need variables for feet or inches at all.

...R

4

Thank you so much to both of you! The extra set of brackets did work like a charm!

Any suggestions on how to make the program exit the loop if the cm < 11?

BTW, fortunately the distance measured is extremely accurate with this ulltrasonic sensor. In that regard, I could not have asked for a better sensor.

5

you can do

if (cm < 11) return;
loop() is a function and return exits the loop

but wait, you can't exit loop permanently, as loop() is called repeatedly from main.

you can start an endless loop with no action in it

6

Any suggestions on how to make the program exit the loop if the cm < 11?

Do you really mean you want to shut the thing down? If you leave loop(), the program ceases to execute. If so, a really ugly way I think will work is to call exit(0);

7

The return command and exiting of a loop was what I was looking for. Thank you again to everyone. This is exactly what I was looking for.