I have been looking at my options for adding sound to the device, without adding bulk, and i can of course pipe the pwm audio to the gpio, and then add in the handful of components to add the audio filter. This will then need a little bit of an amp, and a speaker, so we are suddenly racking up the component count.

I was rummaging though my parts bin, and came across some old piezo transducers that were once inside musical greetings cards. as they are designed to be as loud and annoying as possible from a tiny battery, i thought i might be on to a winner.

So i added the necessary into the /boot/config.txt (dtoverlay=pwm-2chan,pin=18,func=2,pin2=13,func2=4), forced the audio out of the 3.5mm socket inside the raspi-config, and cranked it up to 11 in alsamixer, and jabbed the wires into the relevant pin sockets, and we got sound!! sure it is a bit scratchy, and not overly loud (i think that is a bonus), but we have sound by adding just 1 more component!!

I need to do more testing to see how it copes with no audio filtering in there, but i think the low fidelity nature of the piezo transducer actually plays into my hands here!! To be continued.......