One more suggestion: if we use an Arduino PWM pin as the common anode pin, we can power on/off the display and change its brightness. If we put in the sockets four 7-segments LED common cathode LCD ...

Wyatt]’s CPUVolt library provides a fast way to measure voltage using no external components, and no I/O pin. It only applies to certain microcontrollers, but he provides example Arduino code ...

[Thor_x86], aka [Eric], built an Arduino sketch that does just that — and he threw in the ability to send (or receive) serial messages, too. This is a neat idea — kind of a simplified Bus Pirate.

and 5V pin. Despite the massive differences in their sizes and purposes, all Arduino boards have one thing in common: a built-in USB port. This port is primarily used for connecting the board to ...