> > Can anyone recommend a piezo speaker/buzzer that I can
> > drive direct from a PIC I/O pin. I just need to get someones
> > attention if they walk away from a machine without
> > shuting it off.

You will probably get more output from a small speaker type transducer than
a piezo if using a single pin. With two pins driven antiphase you get twice
the voltage (arguably 4 x the power). Small electromagnetic transducers
(like mini speakers) are available.

For a one off or small volume you could consider using earpieces from the
ultra low cost in the ear headphones available everywhere.
A PIC pin is capable of a nominal 20 MA at 5V (this is actually somewhat
qualified) = 100 mW. This is about 2.5V RMS so ideal load impedance is about
V^2/Power = 6.25/0.1 =~ 60 ohms. A "speaker" with impedance in the 20 to 200
ohm range would be a good starting point.

You can also buy small self contained annunciators with a self contained
oscillator. These look after levels and impedance matching themselves and
are an easy solution - apply 5 volts and you're running.
RS 172-7627 (EuroInd EI-242-B) is one example but you'll be able to get
cheaper and/or better locally.
Similarly RS 172-7380 = Murata PKB24SPC-3601



        RM

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