I weighed up whether I should use 5v directly in or use the original nest mini power supply. I could easily go down to the shop, grab the right barrel jack size and go from there, but I do have a few 5v UBECs sitting around for exactly this sort of project.

As these were cheapies off eBay, I wanted to make sire the voltage output from 14V came down to 5V OK. I'm glad I tested the voltage first, the UBEC I grabbed had 12V out, even though it was labelled 5V. Lucky save.

After I found another that did have a clean 5.1V output, I moved onto the test phase. I knew I didn't have an amplifier and the cheap USB sound card would not be able to drive it, and I was right, test from my PC showed it was really quiet. When I did hook it up the USB chip became quite hot, I would assume the chip is not designed to drive this speaker. A quick check with the multimeter says 4 ohms.

I jumped on eBay to order a small LM386 mini amplifier, once I have that this set up should be a lot louder.

As part of this phase I soldered the UBEC straight to the back of the barrel jack PCB. Earlier investigations found no electronics or odd connections here, so it was easy enough to get power straight to the UBEC.

I wanted to make sure I also got mixed mono from the stereo output from the USB sound card. I tried a few values, but the only one I felt safe using and gave me barely enough audio was 100ohms from left and right output with mono from where they joined.

Over to the Pi, as I am running this headless, I followed this guide to get it to connect to my home WiFi and run the ssh daemon: https://www.raspberrypi.org/documentation/configuration/wireless/headless.md

I logged into the pi over the network and rand `speaker-test` as well as installing `mpg123` and streaming an online radio station. After some adjustment of the audio device it worked fine, albeit, very quiet. But it all works.

As a side note, the mic switch when showing orange is open circuit to in side of the switch, when closed shorts to ground. This could be used wired to a GPIO pin on the pi in the futue.

14v to 5v to Pi 0 W to USB Audio to speaker.