I needed to make something quick and easy for measuring voltage. I didn't want to spend a lot of money, and I wanted to leverage components I already had.

I've updated the components section to build exactly what I've built.... but I strongly suggest you consider other pieces/parts if you decide to build this.

1. Use an ESP32 Feather instead of the Cortex M0 Wifi. The ESP32 is my go-to SoC these days. I didn't use this Feather because I had two Cortex M0 Wifi feathers lying unused. 
2. Determine if you really need to save to SD; if not use a OLED screen. I only used the TFT FeatherWing because I have three sitting unused.