Earbuds inline microphone bias and 3.5mm TRRS jack.

[MaverickPT]

Hello!

I'm building a DAC based on the PCM2912A, which also possesses an ADC for microphones.

Since most headphones I buy usually have a inline microphone, they all have the 4 contact (TRRS) 3.5 mm headphone jack. And for my DAC I'm planning on adding such a corresponding female socket.

Now the problem comes when it's time to bias the microphone. The PCM2912A datasheet has a seperate 3 contact 3.5 mm jack for the mike. Being those 3 contacts, ground, signal and a 2.5V bias voltage. But since the TRRS connector only has 2 contacts for the mike (Signal and a shared ground with the earbuds), how do I go about biasing the microphone?

The only solution I'm coming up with is to connect the bias voltage to the signal pin, and then take advantage of the capacitor in the microphone signal line to block the DC.

Or should it be done in another way?

Thanks in advance!

 

[PRR]

> The PCM2912A datasheet

http://www.ti.com/lit/ds/symlink/pcm2912a.pdf

Read page 24. Connections and values are shown.

 

[MaverickPT]

> The PCM2912A datasheet

http://www.ti.com/lit/ds/symlink/pcm2912a.pdf

Read page 24. Connections and values are shown.

I'm aware of the schematic. I even checked the evaluation module. The problem is that the "bias connection" is not available in the TRRS socket.

 

[PRR]

.

 

[MaverickPT]

Thank you! That's what I was thinking on doing...but needed confirmation that it wasn't something foolish!