Ping sensor, false data issue

Hello, I'm trying to build a wall avoiding robot. This is my first project, so your help is very much appreciated.

I am using an arduino uno, parallax ultrasonic sensor, and 2 brushless motors(on an h bridge). I serial monitor the sensor for trouble shooting. It works fine until, the sensor hits a distance in my switch...case. Then it stops returning values for the ping and just stays on that case. Any ideas? I really appreciate it.

/* The circuit: * +V connection of the PING))) attached to +5V * GND connection of the PING))) attached to ground * SIG connection of the PING))) attached to digital pin 7

*/

const int pingPin = 7; const int rL = 0; const int rH = 900; int L1 = 3; int L2 = 5; int L3 = 9; int L4 = 10; int En = 11;

void setup() { // initialize serial communication: Serial.begin(9600); pinMode(L1, OUTPUT); pinMode(L2, OUTPUT); pinMode(L3, OUTPUT); pinMode(L4, OUTPUT); pinMode(En, OUTPUT);

}

void loop() { // establish variables for duration of the ping, // and the distance result in inches and centimeters: long duration, 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(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); int range = map(duration, rL, rH, 0, 2);

Serial.print(duration); Serial.print("duration, "); Serial.print(range); Serial.print("range, "); Serial.print(inches); Serial.print("in, "); Serial.print(cm); Serial.print("cm"); Serial.println(); delay(100);

switch (range){ case 0: //turn digitalWrite(L1, LOW); digitalWrite(L2, HIGH); digitalWrite(L3, HIGH); digitalWrite(L4, LOW); analogWrite(En, 100); break; case 1: //back up digitalWrite(L1, HIGH); digitalWrite(L2, LOW); digitalWrite(L3, HIGH); digitalWrite(L4, LOW); analogWrite(En, 100); break; case 2: //forward digitalWrite(L1, LOW); digitalWrite(L2, HIGH); digitalWrite(L3, LOW); digitalWrite(L4, HIGH); analogWrite(En, 100); delay(2000); break; default: //stand still digitalWrite(L1, LOW); digitalWrite(L2, LOW); digitalWrite(L3, LOW); digitalWrite(L4, LOW); analogWrite(En, 60); break; }

}

long microsecondsToInches(long microseconds) { // According to Parallax's datasheet for the PING))), there are // 73.746 microseconds per inch (i.e. sound travels at 1130 feet per // second). This gives the distance travelled by the ping, outbound // and return, so we divide by 2 to get the distance of the obstacle. // See: http://www.parallax.com/dl/docs/prod/acc/28015-PING-v1.3.pdf return microseconds / 74 / 2; }

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; }

the sensor hits a distance in my switch...case.

Can you explain this more ?

  • at what distance does it fail
  • how about other distances

Oh, and there are libraries for the Ping sensor. Have a look at the playground, for instance: http://playground.arduino.cc/Code/NewPing http://playground.arduino.cc/Code/Ping

And a last remark: please use code tags around the code, it makes it a lot easier to read.