Re: How this circuit works?

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, 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.
> 

http://en.wikipedia.org/wiki/Relaxation_oscillator

> 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?
> 

The output of the first op-amp will oscillate between Vdd and Gnd so 
that the final signal that arrives at the 2nd op-amp input will 
oscillate too and will make the buzzer to oscillate as long as the final 
signal is something more than Vdd/2


> The circuit is here
> 
> http://www.geocities.com/maxcotester/S5030995.jpg
> http://www.geocities.com/maxcotester/S5030996.jpg
> http://www.geocities.com/maxcotester/S5030997.jpg