Go Down

Topic: Speed Sensor (Velocity Km/H) Using Ultrasonic Sensor (Ping) (Read 5 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.

Go Up