On Wed, 25 Jun 2008 06:20:43 -0700 (PDT), use@[EMAIL PROTECTED]
wrote:
>Hello
>I have the following questions, can anyone explain to me how the
>following circuit works, how does the first op-amp oscillate, and how
>does the buzzer sound?
>
>The first op-amp is configured with negative feedback,
But it's a comparitor, not an op-amp, so the output "wants" to be either
all the way high or low (insofar as a given part can reach either rail).
> which normally
>means that the negative input will try to equal the positive input,
>which is always at half vdd, therefore it is unclear why it would
>oscillate.
If the (+) terminal at Vcc/2 is more positive than the (-) terminal then
the output will rise towards Vcc. The (-) terminal will then rise
towards Vcc at a rate determined by the R3 and C2. At some point it will
be greater than the (+) terminal, at which time the output switches to
ground and the process reverses.
>Secondly, the 2nd op-amp is connected to a dc level, so how would we
>hear the piezo, which needs an ac signal to be heard?
It's AC coupled to its input. Imagine what would happen if R4 and C4
were connected together.
--
Rich Webb Norfolk, VA
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