Steve Hardy wrote:
>
> > From: Werner Terreblanche <wterreb@plessey.co.za>
> > I'm using a PIC in a battery operated device, and amongst other the
> > PIC must output some sound on a speaker.  My question is... how do I
> > increase the sound volume without draining too much extra power.   My
> > current method is to use two I/O pins that would always reverse polarity
> > and thus give you evectively 10Vpp swing across the leads of the
> > speaker. And yes, I do have a capacitor in series to protect the I/O
> > pins!  :)
> >
> > However I find that the sound is still not loud enough.  Would it
> > help to rather use a transistor to drive the speaker?  Would internal
> > impedance mismatch with speaker have a great influence on the volume?
> > Is there any type of small amplifier that runs of the 5V supply that
> > someone can recommend?
>
> I had a similar problem for outputting DTMF tones from a small 8 ohm
> speaker.  My solution was to use a small transistor radio transformer
> (1K : 8 ohm).  I used one PIC (PWM out) pin coupled via a 1uF cap,
> however using two pins in opposition would provide a better impedance
> match, and twice the power.  Most of the loudness is obtained by
> correct baffling of the speaker.  I cut a hole in the PCB the same
> diameter as the speaker (about 40mm) and epoxied the speaker in place.
>
> If this still isn't loud enough then NSC makes some 8-pin DIP amplifiers
> that should do 200mW easily.  Check out their web page (which is one of
> the better semiconductor sites).  Then again, if you are only interested
> in square wave drive then a PNP/NPN combo with common base and common
> emitter should give about 100mW into 8 ohms.
>
> Regards,
> SJH
> Canberra, Australia

If battery life is very important, you have to use a bridge - type
driver. (Like you are using now)

--
Friendly Regards

Tjaart van der Walt
mailto:tjaart@wasp.co.za
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