Line Out on Audio Shield Rev D

R

rcon

Member
Hi, I have a sketch that can play audio from a sequencer I am working on through the headphone jack. From what I can tell is that the audio should also be sent to the line out on the Audio Shield.

When I hook a small speaker up to it, I get nothing. Do I need to enable the line out to use it? I cannot find anything about that.
 
I figured out my problem, the audio is just so much lower on the line out that I couldn't hear it!
 
Line impedances are typically 10k or 47k, not the 8 ohms of a speaker. They are purely signal, not power. In practice most line outputs have a much lower source impedance of 100 ohms or so (to avoid losing level), but still order of magnitude too high to drive a speaker.
 
Thanks for the info!

This brings up another question. I want to create my own circuit board and have the line input and headphone output on that board. The Left and Right channels have very small pins but VGND is a tiny pad on the bottom.

teensy4_audio_back.jpg

Is there a good way to do that?
 
rcon said:
Thanks for the info!

This brings up another question. I want to create my own circuit board and have the line input and headphone output on that board. The Left and Right channels have very small pins but VGND is a tiny pad on the bottom.

View attachment 31256

Is there a good way to do that?
Click to expand...

Depending upon where your preferences fall along the "ugly/functional" to "pretty/difficult" scale, you can do as I have done on some of my projects (more towards the "ugly/functional" end of the scale): solder wires to the three terminals on the topside of the headphone jack. Just something to consider . . .

Mark J Culross
KD5RXT
 
Thanks Mark, that was along the lines of what I was thinking. Remove the headphone jack and wire in from there. I will do something similar to convert the Micro USB to USB C.
 
Normally VGND is only used for headphones. If you're adding wires to use headphones or to something that is definitely known to be "floating" (no possible connection to GND), then somehow connecting to VGND would make sense.

But if you're going to connect to anything use, you probably should not use a wire to VGND. Instead you would use 2 capacitors to connect to the left and right signals passing only the AC voltage but blocking DC voltage. Then you could connect to regular GND, not VGND (which is actually a DC voltage).
 
Thanks Paul, so if I plan on connecting it to a mixer or some other device that has ground I should use GND and not VGND?

I was also thinking of adding a small amp and speakers and run that off the Line Out. Would that be a better/safer way to do it?
 
Quick update. I tried using an amps like a LM386 and a PAM8403 with limited success. The amps worked from the Line Out but there was a ton of digital noise that I just could not clean up! I tried Paul's suggestion of putting some capacitors on the left and right channels and it totally worked! While the audio isn't super loud, it is loud enough for my purposes.
 
You must log in or register to reply here.
Back
Top