That circuit drives the low side of a optoisolator transmitter. The receiving side of it is connected the I/O pin of the Arduino. You can see the schematic as well as a demo clip after the break.

Olympia Circuits Teases Arduino Programmers With $60 Arno Shield. by Ray Willington — Monday, April 29, 2013, 05:50 PM EDT. Comments. Homemade gadgets seem ...