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### Topic: Speed Sensor (Velocity Km/H) Using Ultrasonic Sensor (Ping) (Read 18820 times)previous topic - next topic

#### matt121187

#15
##### Dec 31, 2012, 02:18 pm
i'm really blur...cant solve this problem.... =(

#### PeterH

#16
##### Dec 31, 2012, 02:48 pm
In that case I suggest you pick a simpler problem.

#### PaulS

#17
##### Dec 31, 2012, 06:08 pm
Quote
cant solve this problem.

Can't or won't? What have you tried?
The art of getting good answers lies in asking good questions.

#### matt121187

#18
##### Jan 06, 2013, 11:01 pm
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

#19
##### Jan 06, 2013, 11:04 pm
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.
I speak for myself, not Arduino.

#### matt121187

#20
##### Jan 06, 2013, 11:15 pm
can u show me the example from my coding?

#### UKHeliBob

#21
##### Jan 06, 2013, 11:24 pm
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

#22
##### Jan 06, 2013, 11:35 pm

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

#23
##### Jan 07, 2013, 08:39 am
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

#24
##### Jan 07, 2013, 08:41 am
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.
I speak for myself, not Arduino.

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