Counter using Ultrasonic Sensor (self.arduino)

Question

I am doing a pretty simple arduino project that uses a Parallax Ping Ultrasonic Sensor to increment a counter when an object moves past the desired distance. (object leaves, counter goes up, object comes back, this loops forever). My problem is now that every time i run this.. the serial monitor just shows me Count: 1 over and over again and does not increment. Any help would be appreciated!

example of what i want the Serial Monitor to write: Count:0 Count:1 Count:2 ....

What it is currently doing: Count:0 Count:0 Count:0

const int pingPin = 7;
void setup() {
 // initialize serial communication:
 Serial.begin(9600);
}
void loop()
{
 // establish variables for duration of the ping,
 // and the distance result in inches and centimeters:
 long duration, inches, cm, count;
 // 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);
// count = 1;
 if (inches > 5)
{
 Serial.print("Count: ");
 Serial.print(count);
 Serial.print('\n');
 delay(1000);
 count++;
}
}
long microsecondsToInches(long microseconds)
{
 return microseconds / 74 / 2;
}
long microsecondsToCentimeters(long microseconds)
{
 return microseconds / 29 / 2;
}

Answer 1

Count is a local variable - it gets re-created afresh every time the loop() runs.

Either make it global, or make it static.

These two options look like this:

Global

long count = 0;
void loop()
{
 // establish variables for duration of the ping,
 // and the distance result in inches and centimeters:
 long duration, inches, cm;

Static

void loop()
{
 // establish variables for duration of the ping,
 // and the distance result in inches and centimeters:
 long duration, inches, cm;
 static long count = 0;

Both will do the same job, but the static form is preferred since it is always better to keep a variable's scope as narrow as possible. It is also important to provide a start value for the counter to begin from (0 in this case) otherwise the starting value will be unknown.

• Tamir: i did int count inside the loop and it still didn't do anything...
• Gerben: You need to place it outside the loop (i.e. global).