John Fields wrote:
> On Wed, 25 Jun 2008 10:42:54 -0700 (PDT), use@[EMAIL PROTECTED]
wrote:
>
> >
> >> Right there in the text "The left side of the circuit uses a
low-power
> >> dual comparator (MAX9022) to form a relaxation oscillator..."
> >>
> >> So, (a) you've been _told_ what's going on, and (b) it's not an
op-amp,
> >> it's a comparator.
> >
> >OK, this is clear now, shame engineers use the same symbols for
> >different things...
>
> ---
> No, the shame lies with idiots like you, who have a do***ent in front
> of them which clearly states that a _comparator_ is being used as a
> relaxation oscillator and apparently don't even bother to read it.
> ---
In fact, some time ago I asked
on this very newsgroup what is the difference between an op-amp
and a comparator, and the replies that I received then where that they
are basically the same thing, that comparators are "optimised for
switching", so due to those idiots (as you put it) back then I have
been
missed informed till yesterday. Just goes to show how careful one
needs to be about info posted here. In fact, what our designer wanted
was a little hysteresis symbol inside the op-amp symbol, which is
the agreed symbol for comparators with built in hysteresis (?).
And the datasheet of this particular one, does show the
correct symbol.
>
>
> >> On the right side of the circuit, consider what happens when a bunch
of
> >> AC shows up on the open end of C4.
> >
> >This is still not understood. The text talks about 155KHz, which is
> >more
> >than the human ear can hear, so which AC are we talking about?
> >And even if we could hear 155KHz, D3 and C5 for a rectifier which
> >converts any ac to dc, so how can a dc signal vibrate the piezo?
>
> ---
> The 155kHz signal from the oscillator is being rectified and smoothed,
> and then if the resultant DC rises to Vcc/2, the output of the second
> comparator will go high and supply DC to the piezo buzzer, which has a
> built in oscillator used to drive the piezo transducer.
Yes, this has been explained above, the little + sign is the give-
away
that it is not a "bare" piezo.
>
> And bottom post.
>
> JF
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