Endless loop if sensor not present/broken/disconnected

[adrianrolla]

Hi Jeremy,
Many thanks for producing this library!
Found a bug, here is the explanation and the fix.

echoInMicroseconds() function has while loops that if sensor is failing / not present / disconnected will never end.

original code within echoInMicroseconds()

    while(digitalRead(_echo) == LOW);

    int pulseStart = micros();

    while(digitalRead(_echo) == HIGH);

fixed code within echoInMicroseconds()

  // sounds go at 350meters/sec, HCSR04 reach is 4mt, to be safe 10mt, at sound speed takes 28 millis 
   const long timeout=100L; // more than safe in normal conditions.
   long started = millis();
   boolean timedout = false;
   while(digitalRead(_echo) == LOW && !(timedout=(millis()-started > timeout)));
   if (timedout) return -1; // negative distance should be treated as error condition.

   int pulseStart = micros();

   started = millis();
   while(digitalRead(_echo) == HIGH && !(timedout=(millis()-started > timeout)));
   if (timedout) return -1; // negative distance should be treated as error condition.

That's all.
Regards

[jeremylindsayni]

Brilliant catch - thank you! I'll test this and update the code. I really appreciate you taking the time to identify the issue and write a fix :)