Web Oscilloscope via Headphone Jack

Hello,

I'm trying to do Experiment 17 from Making Things Smart, which is sending data from a Pico to your computer via the headphone jack and displaying it using the Web Audio app Gordon built here.

I've tried a variety of different methods to get things connected, but regardless of the setup I cannot get my computer to recognize the input as a valid line-in.

I am on a 2017 15" Macbook pro running Catalina.

I have tried connecting with this terminal block audio plug from Adafruit, as well as cutting a pair of iPhone headphones (after the split) and identifying the mic / mic-ground wire. I have tried both of these connectors with and without this splitter from Amazon.

None of these combinations have worked. When in System Preferences > Sound > Input I never have an option to choose an external input. Also, weirdly sometimes when connecting the circuit using the terminal block connector, closing the circuit would trigger Siri to open on my computer.

I've uploaded a picture of my circuit, where the white lead goes to the mic line on the iphone headphones (or the sleeve terminal on the adafruit connector) and the black ground goes to the mic ground on the headphones (and the second ring on the adafruit connector). Both resistors are 10k ohms, white leads to B6 and black to GND.

The code running on the pico is as follows:

var t=0;
setInterval(function() { Serial1.write(t); },5)

Any ideas on how I could get this going?

Thanks!

1 Attachment