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

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.

On the right side of the circuit, consider what happens when a bunch of 
AC shows up on the open end of C4.

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html