Marc,

All the suggestion thus far have been excellent.

As another alternative, one can also use a series inductor if there is not a
resonant frequency.  This will raise the sound considerably.

The piezo is a capacitor at non-resonance.  At resonance it is a series RLC
paralleled by C.  Adding an appropriate inductor at your frequency of choice
works well in the non-resonance case.  It will add the cost of an inductor
of course to your project.  The electrical and mechanical Q will be low
enough that there should not be too much of a problem maintaining resonance.

David



> 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.
>