Not exactly schematics, but [Duckman] has some Arduino pinout diagrams he made using ASCII-art. ... Yes, they’re ugly. But they clearly documented the circuit, and can still be read today.

Original Circuit Diagram: Arduino UNO R3. Now, have a look at our favorite Arduino UNO to find out the AVR chip inside. It is ATMega328P-PU, a low-power version of the traditional ATMega328-PU. The P ...

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.

Olympia, WA, April 29, 2013– Olympia Circuits introduces the Arno Shield to expand their line of products for new Arduino users. The Arno Shield contains all the components necessary to learn ...