On Thu, 26 Jun 2008 04:37:50 -0700 (PDT), use@[EMAIL PROTECTED]
wrote:
>
>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.
---
Not really, since "optimised for switching" should have been a clue
that the comparator's output likes to live in one of two states, "ON"
or "OFF" and is designed to have as little time between those states.
Moreover, you should take everything posted in this newsgroup with a
grain of salt and then go on to definitive sources (TI, NS, ON semi,
LTC, etc., etc,) and peruse their tutorials for the final say.
>Just goes to show how careful one needs to be about info posted here.
---
Well, this _is_ USENET, where any number of idiots are free to spread
as much misinformation as they choose and your job, knowing that,
should be learning to separate the wheat from the chaff.
---
>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.
---
But so what?
There are myriad comparators _without_ internal hysteresis which don't
s****t the 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.
---
So are you finally happy?
JF
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