I've finished the receive part, by two C1815 and a LM339.

I have a ultrasonics sensor module(Japan). I test my receiver by receiving the output sound of the circuit board. The circuit board makes a quite "loud" noise. It has a PIC chip, output carrier with pulses.

But when I try to make the sonar work by 555, the sound is tooooo weak... I've tried some LM386 as the output driver, as well as the transistor amplifier. None of them can make a "LOUD" noise that the module can make. (sth like beep beep beep...)

(The sound is the pulses, not the 40kHz ultrasonics)

Stanley