Interfacing, ipod, basic question

Forum 2005-2010 (read only) Hardware Interfacing
1

so I am setting up a system that can read the levels of my ipod shuffle, and translate them to light/read them into my system for minimal data understanding like maybe the tempo.

I guess my main question is about how I can interface with 2 batteries, one to power the MCU and the one built into the shuffle. As I have been taught in DC currents everybody is holding hands, and ground is ground is ground.

But I cant help being a little afraid allowing a 9v to hold hands with my shuffle. Below is a diagram of how I think it might work kind of, but I think I may need to connect the grounds (which leads me to my hesitation). I would normally try it and learn from failure but I just don't want to blow 50$.

Also another quick question, I was up for using my digital pins for the different lights, however I was wondering if anyone was aware of some kind of capacitor circuit that can enable the same effect of lights turning on with the decibel levels (like in old stereo systems with LED's, pre interface screen).

Thanks so much for your consideration,
-Chronarch

2

Key
Red Wire - Right stereo in
Green Wire - left stereo in
Black (t shape ish) wire - Ground back to shuffle
Purple - Analog Read from the left headphone
Teal - Analon Read the Right headphone

red and black from the 9v power the MCU

Generation 2 Shuffle
MCU - RBBB decamelia chip

Clicking enlarges

3

You won't have to worry about the 9V reaching your Shuffle, as long as you keep those pins as inputs.

By the looks of your diagram, I don't know if the circuit would work.

I would think the ground of the headphones should be connected the Arduino ground, and the Left+ and Right+ to your two inputs.

That way you are measuring the voltage levels of the signal, relative to the signal ground.