> Does anybody know how to produce a reasonably loud "click" from a
> 3V battery powered circuit?  I tried sending a square pulse to a
> teensy weensy miniature speaker, but it's very quiet.

Use this circuit:

                           |+V
                           |
           NPN eg. BC548 | /
                         |/
                     ----|                  /|
                     |   |\|        47uF   / |
                     |   |-\      + | |    | |
                     |      +-------| |----| |  8 ohm spkr
                     |   ||/        | |    | |
 From        180     |   |/-             --| |
  PIC -----/\/\/\/\--+---|               |  \|
                         |\              |
           PNP eg. BC558 | \             |
                            |            |
                            +------------
                            |
                            | -V

The emitter follower pair can drive the low-impedance speaker much
better than the PIC port pin. The decoupling capacitor makes sure the speaker
sees an AC signal. IF this is not enough noise, duplicate the emitter
follower, and connect to the other side of the speaker, then drive from
another port pin in anti-phase with the first pin. This will swing twice
the supply voltage across the speaker, peak-to-peak. That should get you about
6dB more noise. If you do that, the capacitor may not be required (but I'd
probably leave it there. Be sure to set both port pins high or low when no
noise is required, to avoid reverse polarizing the capacitor, in this case.)

Also, to maximise the noise from the speaker, try baffling it, or even clamping
it directly onto a hard surface - at some frequencies a small speaker will
radiate better from the back of the speaker than the front. Just sitting in
free air is bad. Also, the larger the speaker the better - small speakers
are inefficient.

On low voltages, the base-emitter voltage drop of the emitter follower is
 significant
so you might want to use some other circuit where the load is in the collector
side, but driving the transistors is harder - you can't just connect the bases
 together
as in this circuit.

I've tested the above circuit on 5V, and it makes an impressive sound from a 1"
speaker at about 1000Hz - a double-ended version on 3V should be slightly
 better.

Happy metrognoming. Where do the best gnomes go to school? The London
School of Eco-gnomics!

--
 Clyde Smith-Stubbs       | HI-TECH Software,       | Voice: +61 7 3300 5011
 clyde@hitech.com.au      | P.O. Box 103, Alderley, | Fax:   +61 7 3300 5246
http://www.hitech.com.au  | QLD, 4051, AUSTRALIA.   | BBS:   +61 7 3300 5235
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