Hi Paul
Yea I did tried to print the values, the problem is the intervals were really 500ms at the beginning when the sketch runs.
After a random period, say 10 seconds, the println started to get strange the the readings are updating in a rate like 10ms on the Serial reader.
When I try to wave in front of the ultrasonic sensor, the distance reading changes, then suddenly the println rate is back to normal.
Will the serial reader messages be held up in a queue and got blocked by something?