shorted or dead audio adapter

A

ajlapp

Member
I'm using the audio adapter with a teensy 4.1

I had things all working well but then suddenly had two adapters fail. They pull the Teensy down somehow once they are attached....but it doesn't kill the Teensy...Teensy comes back once not plugged into the adapters.

The failure seems to have been caused by the line out when plugged into a 12v powered speaker.

I'm still investigating but I'm curious if others have seen this same failure.

If I only attach the 5v and ground between the two boards it does not kill the teensy.

It looks like ground is now shorted to VGND.
 
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Can you show us a wiring diagram how you hooked up all parts, including powersupplies?
Detailed photos also help.

Paul
 
Here's the setup. We've got a custom board that brings in 12v and makes 5v for the Teensy. This is an established design that we've used for a good while across many projects.

Next to it is the power supply provided with the speaker. This was just for a quick test...bought here:
amazon speaker

The main board connects up to some other stuff using ethernet...everything is on the same 12v bus with a shared ground.



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image1 (5).jpeg
image0 (7).jpeg
 
ajlapp said:
The failure seems to have been caused by the line out when plugged into a 12v powered speaker.
Click to expand...
Are you using line out? I see the headphone socket plugged and that must never be connected to anything but a headphone or earbuds, or it will short out VGND
 
MarkT said:
Are you using line out? I see the headphone socket plugged and that must never be connected to anything but a headphone or earbuds, or it will short out VGND
Click to expand...
We’re using both the micL as an input with a microphone and the line out for the speaker.
 
Maybe the USB connector could be touching the underside of the audio shield?

Can you try slipping a thin piece of plastic or paper between them?

1732649094684.png
 
If you're using audio adaptor line out for the speaker, then why do we see the headphone connector as the only audio connection?
Refer back to post#5 by @MarkT.
 
BillFM said:
If you're using audio adaptor line out for the speaker, then why do we see the headphone connector as the only audio connection?
Refer back to post#5 by @MarkT.
Click to expand...
I don’t understand the question? I’m using the mini-rca jack as the audio out and it’s plugged into some 12v computer speakers.

Are we mixing terminology? I’m using the jack as the “out”…seems like normal audio stuff to me. You plug your output into some speakers, the speaker get external power, voila…sound.

This all worked until it didn’t. Now I’m trying to understand why. Did I wire something wrong? Is there a back voltage etc that I don’t understand?

I haven’t built anything audio related in a long while.
 
I suggest you take a look at the audio adaptor schematic <here>.
Yes..., wrong terminology.
There is a 3.5mm (1/8") stereo headphone jack. Only a headphone can be plugged into this jack. This jack uses a virtual ground (DC voltage) sourced by audio chip and is not to be connected to power supply ground (logic ground). You've shorted this virtual ground to power supply ground via the powered speaker input connection. Ouch!

What you should be using is the line out signal available at 2x5 thru-hole footprint (only 9 holes). At this location, line out is referenced to power supply ground.

So yes, you've mis-wired the circuit. It was a fluke that it worked at all the first time.
 
Excellent, thank you. Easy fix.

Maybe this is standard for microcontroller audio folks but I didn’t see any reference or data about the 1/8” jack being specifically for headphones only.

The schematic is also a little cryptic.

Live and learn. Thanks again.
 
I agree, the headphone jack should have a bit more description on webpage warning about not connecting this jack to ANY ground.

BTW, there's a caution note printed on audio adaptor pcb, not to connect VGND to GND, shown on webpage (for future reference).

Around page 60 of SGTL5000 datasheet, it shows how to use capacitors on headphone output signals so that GND can be used.

Looks like an interesting project. Good luck with it.
 
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You definitely want to use the proper lineout signals for an external speaker, BTW, much higher quality signal. You have to solder to the pads on the audio-adapter to use them.

The line in and line out pads are identified by the silk-screen on the PCB, have a look.
 
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