Teensy-optimized using pedvide/ADC

Optimized for Teensy 3.1+ and Teensy LC
Requires the pedvide ADC library from https://github.com/pedvide/ADC.
Up to around 1.1Msps sampling speeds are possible with reduced precision.

Use v1.0.0 for other Arduino-compatible devices.

Voltmeter mode:

Arduino Compatible, Atmega328-optimized

Uses standard Arduino code so it should work on other Arduino-compatible devices.
Optimized for Atmega328 (direct ADC control for higher sampling speeds).