Hi.

My piezo beeper & drive circuit creates a too low audio volume.
On the test bench, it is OK. But the device is handheld and will
be used in car repair shops -- background noise will be much
higher there.

I am low on pins, and can afford just 1 direct PIC pin for the
signal, and one HC595'ed pin for On/Off control.

Currently the circuit is:

                                   5V
                                    |
                                    |
3khz 50/50 duty                  | /c
port pin signal: ------ 2k2 -----|X    BC817 NPN
                                 | \e
                                    |
                                    |
                               piezo beeper
                                    |
/SPEAKER_ON                        _|
control (HC595) ----------------| |
                                | |->  BSS84 p-channel
                                | |_
                                    |
                                    |
                                   GND

I also tried to let the port pin drive the beeper directly (without
2k2 & BC817), but the audio volume was identical (as far as I could
hear).

What can I do to improve the volume?  I have heard the same beeper
in other devices generate louder beeps, so there must be room for
improvement on my side.