Hey Phil, glad you like it. I'm just being a cheapskate with the $7 JLCPCB charges for stencils. I keep making dumb mistakes on my PCBs, so I skip the stencil and assembly to save cost.
I just added details about the parts cost. The total for the project is $17.11 not including the vibration motor; I bought them several years ago and forgot how much I paid for them.
I need to add price details to my blog post. The main goal of mine was low cost. The total cost for me to produce each board is $17 where $14 of that is the SCD40 sensor.
The Dragonboard410c runs Aarch64 linaro Linux. I have one and I'm using it to test 64-bit ARM development. On the 96boards website you can download the Android or Linux disk images. It's not getting as much attention as RPI's, but it works pretty solidly and the price wasn't awful at $75 for the board (which includes wifi/bt).