What "triggers" the UltraSonic Sensor?

Hi,

I bought an HC-SR04 Ultrasonic Sensor and included it in a very basic laptimer. THIS ONE

My problem now is, that it works like a charm in my apartment, while when I am outside it gets false values all the time.

Conditions: it was a little windy, sun was shining and a little (very little) dust was in the air. Does any of those trigger an echo on the sensor?

I am using the "NewPing" library with the median ping (10 times). Since it works in my apartment I don't think it's code related, any ideas how I may solve that? Maybe a more reliable sensor (which)?

Thanks, any hint highly appreciated.

Cheers

PrimuS

Maybe a false echo? The datasheet recommends using a pulse repetition rate of no shorter than 60ms to prevent false echoes.

I am using 30ms, but would that explain the inside/outside difference?

primus852: I am using 30ms, but would that explain the inside/outside difference?

According to the datasheet, 30ms is not long enough.

The distance to a reflecting surface would make a difference. How far does sound travel in 30ms? About 27 feet. That is round trip, so divide that by 2. About 14 feet to the target. So if there is a reflecting surface at 16 feet, the sensor would detect it at 2 feet on a second pulse.