You might be able to use PWM audio. These audio jacks usually work something like this: https://cdn.head-fi.org/a/19786.jpg Basically, pipe your signal in one wire (one each for L and R) and GND in one, and then it outputs it to the jack if plugged in, if nothing's plugged in, it'll output the signa...

-snip- thanks for the info.... can you show how you actually have it in your build/project (images would help)... thanks.... It'd be nice if you could remove the gigantic quote please. Anyways, I'll add some images of my build, but I'm afraid it won't be much help since my wiring's pretty messy.

A while ago, I added battery monitoring via an ATTiny to my pi, and this guide is for others who want to do the same. For this, you do not need an AIO board of any kind. Required parts are: - Your build with at least a pi zero, lipo battery and a charger/booster - An ATTiny25/45/85 - two resistors, ...