Not exactly schematics, but [Duckman] has some Arduino pinout diagrams he made using ASCII-art. These could be useful when pasted into source code as comments, documenting the pinouts for your ...

The Arduino Wire library is a core aspect of Arduino's integrated development environment, or IDE, and is a must-have if you're using sensors or extra microcontrollers in your project.

This DIY gas leakage detector is designed for educational and basic monitoring purposes. For critical safety applications, ...

The resistor values (R1&R2) in the circuit diagram provide some over-voltage protection then measuring low voltages. Keep it in mind that any input voltage higher than about 55V could fry the Arduino.