Joe,

Thank you for your reply.

There is yet another consideration that I haven't mentioned until now that =
further complicates things.  On many dedicated siren tone generator chips (=
not PICs, but custom created chips for sound generation), there is what is =
called a "soft chirp" feature.  When you ground the appropriate pin on such=
 chips, the volume will be decreased by about 30%, as long as the chip is p=
owered for 200msec or less.  Such is accomplished by varying the ON time of=
 each pulse, as follows:

Normal (FULL VOLUME) Output pulse:

    --------------------
    |                  |
----|                  |----

Soft Chirp Output:

    -- -- -- -- -- -- --
    || || || || || || ||
----||-||-||-||-||-||-||----


The reasoning behind "soft chirp" is that you may want to give audio feedba=
ck to the user when a security system is armed or disarmed, yet you don't w=
ant to blast their eardrums at those times.  But when the alarm is triggere=
d, you of course want to get maximum volume from your siren (8-ohm speaker)=
.. =20

The technique used is somewhat of a blunt instrument though.  Since the 200=
ms is fixed, when you trigger the full siren blast, the first 200msec of th=
e siren is soft and then it jumps to full volume after that (no gradual ram=
p-up in volume).  Such is not a big issue, just an observation.

By the way, the reason a lot of these sound generator chips use a fixed 200=
ms is because they don't know which alarm system controller they will be at=
tached too.  Many alarms send pulses that are only 30ms or 40ms in width, w=
hile other alarm controllers may send 100ms pulses.  So to be safe, the cre=
ators of these sound-gen chips chose a fixed 200ms cut-off. =20

If you're wondering, the reason I am using a PIC instead of a dedicated sou=
nd-gen chip is so I can create my own unique sounds and add more of them, m=
aking each one fully selectable.

Creating the sweeps is challenging enough, but pulsing each pulse to drop t=
he volume is perhaps beyond what this 16F1508 can do.  What do you think an=
 effective means of decreasing output volume for short chirps?

Thank you,

James W.


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