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Topic: Speed Sensor (Velocity Km/H) Using Ultrasonic Sensor (Ping) (Read 5845 times) previous topic - next topic

matt121187


PeterH

In that case I suggest you pick a simpler problem.
I only provide help via the forum - please do not contact me for private consultancy.

PaulS

Quote
cant solve this problem.

Can't or won't? What have you tried?

matt121187

how to hold the previous distance?

this is my coding right now..but the previous state still show the current distance

Code: [Select]
const int pingPin = 7;
int start = 0;

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, currentState, previousState;

  // 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

  cm = microsecondsToCentimeters(duration);
 
  currentState = cm;
 
  previousState = currentState + start ;
  previousState = currentState;
 
  Serial.print(previousState);
  Serial.print("cm, ");
  Serial.print(currentState);
  Serial.print("cm");
  Serial.println();
 
  delay(100);
}



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;
}

AWOL

Any variable declared within a function like "loop" is going to have limited use for remembering its value.
If you want a variable to maintain its value, declare it with global scope.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.


UKHeliBob

  long duration, inches, cm, currentState, previousState;
Please do not send me PMs asking for help.  Post in the forum then everyone will benefit from seeing the questions and answers.

retrolefty


Any variable declared within a function like "loop" is going to have limited use for remembering its value.
If you want a variable to maintain its value, declare it with global scope.


I thought declaring a variable static solves any 'memory' problem for variables declared within the scope of a function?

Lefty

UKHeliBob

These variables aren't declared static in the routine though
Please do not send me PMs asking for help.  Post in the forum then everyone will benefit from seeing the questions and answers.

AWOL

Quote
I thought declaring a variable static solves any 'memory' problem for variables declared within the scope of a function?

It does - I just suggested global scope because it is what most noobs are more comfortable with.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

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