Power from headphone port

[lerxstrulz]

Just wondering if there is a way to power the Teensy/Audio shield through the headphone port? I am connecting it to a powered speaker (uses around 8.8V supplied by batteries) and it is sending about 4V back. Wondering if I could jump the power lead of the headphone port to the 5V in?

Thanks!

- Brent

 

[tenkai]

are you measuring it with a multimeter?

The Teensy needs 5v DC voltage to power its 3v3 LDO. If you have access to an oscilloscope, it would be good to measure it to see the waveform.

If you hooked it up, you might fry your teensy (or you might not). a $20 risk.

Nobody here knows how your powered speaker is wired, so its hard to tell you if it is a good idea. I would hazard a bet to say it is not.

 

[lerxstrulz]

Yes I did measure it with a multimeter. It's a consistent 4V. Don't have an oscilloscope. I've seen other apps where the power coming back from the speaker connection is used to power the board, but I don't know the wiring or setup of that, either. Just curious if it was a possibility.

 

[tenkai]

It might be possible! But you won't be able to get good advice without more information.

If it were possible, I wonder if you would get line noise*on your audio signal without having a separate ground.

 

[bmillier]

The headphone output from the SGTL5000 Codec on the audio shield uses the VGND pin as its common. This virtual ground is different from the digital ground ( I think it is 1/2 of the codecs power source. The manufacturer specifically warns against connecting VGND to GND. So, your speaker's 4V power would be referenced to this VGND and any current it supplied would have to flow thru VGND to GND. This wouldn't work.