nRF5340 Audio Dev Kit Output I2S to External HW Codec (MAX98357A)

Question

Hello, 
 
 I am currently trying to connect an external hardware codec and amp (Adafruit MAX98357 I2S Class-D Mono Amp) in order to play audio via BLE Audio and I2S using two nRF5340 Audio Dev Kits (ADKs). 
 
 I have been able to properly flash the ADKs using the nRF5340 Audio code from the nRF Connect SDK in VS Code and the buildprog.py Python script. I flashed one as the gateway and one as the headset, and was successfully able to play audio through USB to the gateway and listen to it from the headset through a pair of wired headphones. 
 
 I am trying to use the I2S interface header pins (P10, specifically BCLK, FSYNC, DOUT, GND, and a power pin) on the ADK and connect them to the MAX HW codec breakout, but after probing the pins, no signal seems to be coming from them. Only the 1v8 pin seems to be outputting 2V (why 2V?). On a separate note, can you please explain what the difference is between 1V2 and 1V8 is? 
 
 I saw the post from Adarsh , but I'm not sure how to complete all of the referenced instructions. For example, I was able to complete the following 
 
 by following instructions from here . 
 
 However, I do not know how to do the following instructions:

Could you please provide some more detailed instructions on how to connect an external HW codec? 
 
 Thank you! 
 
 Best, 
 
 Louie

Elray326 · Accepted Answer

Hello Elfving, 
 I was able to successfully use the MAX98357A as an external codec for the NRF5340 Audio Dev Kit by removing any relevant code for the cs47l63, particularly by having the function cs47l63_comm_reg_conf_write() in hw_codec.c return 0. I was able to figure this out by using the debugger, setting breakpoints, and figuring out where in the code the board would fault. 
 I did not have to add the external hw codec to a dts overlay file, but I did follow the rest of your instructions. 
 Thanks for the help! 
 Best, 
 Louie