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September 5, 2015

Homework Help: Electrons circuits

Posted by Jacky on Friday, April 4, 2008 at 11:26pm.

Hi everyone! I'm new in here.

Recently I bought a movement monitor which detects micro movement. If the sensor does not detect a movement in 20 seconds, the build-in speaker will beep until the sensor detects a movement. I'm using it for my project and I have a question about it. I want to intercept a wire from the speaker to a micro controller. The point is, in order to "power up" the micro controller, a 9V DC input is needed. Therefore I want to connect a wire from the speaker to the input of the micro controller.

The situation is something like this:
When the alarm is ON (speaker beeps), nearly 9V DC will go into the input of micro controller. When the alarm is OFF (no sound), there is nearly 0V DC going to the input.

As I measured the voltage across the speaker, I got roughly 0.9V to 1.5V AC. Is there any circuit i can build to satisfy this suitation?

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