Damn, I didn't think of the fact that it will use power even when the main =
core is asleep, that won't do.
I have revised the design, it will only sample the ADC when it needs to =
alarm, as the ADC value only affects the alarm tone there is no point me =
ever doing otherwise...whoops.
As for the wake-on-change I haven't ever used it before so I guess I did =
mean RB1 :-)

Thank-you everybody for your help with that.

I have got further with the piezo problem, for something with an appaling =
bandwidth it is suprisingly agile when it comes to making musical tones.
Although there is something that somebody may be able to help me with, a =
long time ago I'm sure I read of someones efforts to reproduce sounds via =
the PIC using a large RAM table with wave data in it, if anybody thinks =
they know a link it would be greatly appriciated, as melodys are extreamly =
hard to code as consecutive delays. =20



>>> Vasile Surducan <vasile@S3.ITIM-CJ.RO> 11/06/2002 11:42:28 >>>
On Mon, 10 Jun 2002, Michael Rigby-Jones wrote:

> > I'm working on a (commercial) project that involves a 16C73, most of =
the
> > other circuit functions are done but I still need to read ADC channel =
one
> > (RA0), process the value and create a signal that gets sent to a piezo
> > sounder.
> > The ADC is my main problem, I have it reading values, thanks to the
> > Piclist FAQ, but I need the PIC to sleep for as much of the time as
> > possible, it's currently sleeping while it converts then it wakes up =
and I
> > send its value to the piezo code, but I need then to put it back into
> > sleep and wait until ADC channel one or RA1 changes (circuit power use =
is
> > critical).
> > I think I can work out how to wake from sleep on RA1 changing, but I =
don't
> > even think it's possible to wake from sleep on a change in the analog
> > input?
> >
> You have a problem in both cases.  RA1 has no interrupt on change =
facility,
> unless this is a typo and you meant RB1?  There is no way to wake up =
from a
> change in analog value as you suspected, the only wakeup ascociated with =
the
> A/D converter is the end of conversion interrupt.  The ADC module itself
> raises power consumption, so depending on how often you need to sample, =
you
> might be better off using a timer interrupt to enable the ADC module  =
and
> the ADC interrupt to disable the module, the aim being to keep the ADC
> module disabled for as much time as possible.  The timer interrupt could =
be
> used to check pin RA1 as well (assuming it wasn't a typo).
>

  or to use interrupt on RB0 ( or any other interrupt on change) with a
comparator. If the analog input exceed the reference then an interrupt
will wake up the whole mess, perform the measurement and go back to sleep
again after it finished. A time delay will be necessary from the wake up
moment to measurement(s).
Vasile

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