Circuitry: Reading signal from speaker in parallel

Hello,

I need some help or some ideas with some circuitry design. I have a speaker that generates a warble tone. I want the use the Arduino to detect when the speaker is on. The speaker is activated by a push button. I am trying to detect when the signal is on without running it in series. I have tried a few things with no luck.

Any tips and suggestions are appreciated.

instead of trying to pick up if the speaker is moving or not (which sounds like a headache) it would be simpler, based on the given information, to detect when the button is pressed and then turn on the (whatever is connected to the) speaker via arduino

what does the button control, and what is preventing it from the above?

Use the input circuitry from:-
http://interface.khm.de/index.php/labor/experimente/arduino-realtime-audio-processing/

There is no need to use the software just see when the analogue in starts changing.

Oddly enough, I measured the voltage when the speaker is making sound and it's roughly 3.2 volts analog signal. So, I tapped off a line from the speaker input, before it goes into the speaker, hooked up a 100uF cap in parallel to filter it. Pulled a reading off the high side of the cap into an analog input and it was stable around 300. Problem was when I made the tone in the speaker(via push button) there was no fluctuation of the signal. Reading stayed at 300.(with cap) Without cap, the reading was all over the place.

I then tried this full wave rectifier: http://www.radioshack.com/product/index.jsp?productId=2062581

Somehow the output voltage was 42 volts. I'm a little lost here.

It also seems that the warble tone line seems to be floating with some voltage on it even when there is no tone/signal coming through(button not pushed).

I'd like to try to condition that signal input to something more discrete. I'd still rather not use a mic. I have a piezo vibration sensor, but don't feel like trying to attach that to the speaker cone to read the vibes. The settle response time seemed very slow.

Thanks all for the replies so far.

That sounds about right with the hum. I’d like to give the isolator transformer a shot. Since I’m slightly impatient, do you think something like this will work? Also, shipping cost would be much more than item cost. Or anything specific from radio shack?

Thanks

Do I wire the transformer in parallel with the speaker or in series? Intuition says series so there's load on the transformer...But I'm not sure here.

Thanks.

oops. I've wired it in series and tested it out. It does work. My thought was that since my add-on circuit was such low impedance that "path of least resistance"(the speaker) would take over and there would be no current flow in my circuit. Please school me if I'm wrong here.

I used some parts that I had lying around like the LM7805 voltage regulator. I figured it was appropriate with the 10volts from the transformer, cap, and diode.

Thanks again. Should I try the transformer parallel?

Should I try the transformer parallel?

Yes

My thought was that since my add-on circuit was such low impedance that "path of least resistance"(the speaker) would take over and there would be no current flow in my circuit.

No it just means a proportion of the current goes through the low impedance path. For a given voltage the same amount of current passes through the high impedance path whether there is a low impedance path or not. It is simply that most of the current passes through the low impedance path.