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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