what do you mean by check porta.0 , read post2 and 4 ????? do you mean that the porta.0 is analog and I shouldn't use it for digital signals input????

anyway , I moved the echo signal to differents port.b's and port.a's and nothing changed.

I tested few portB input pins with infrared detectors ( which worked fine) but when the echo input signal, is connected to the same portb that i just tested , and the trigger signal output (connected to portb output pins that i tested with LEDs) of my srf04 are connected , nothing is working

can you tell me clearly what do you have in mind please???