IAN LANG ELECTRONICS
Here's a few more eclectic things that can be done by measuring voltage/logic levels at various pins:
The purpose of this section is to take building blocks of digital logic equipment and transpose them to the Arduino. These include NOT, AND, OR, XOR as well as some more eclectic applications such as latching switches and Schmitt triggers. Whilst not being projects in themselves, these are basic input applications for sensory applications which is after all what your Arduino is meant to do.
All of these building blocks can be easily incorporated into your projects.
The three above comprise the three basic logic gates. NAND (Not AND) is achieved by attaching a NOT to AND and NOR (Not OR) is done in a similar way. In Arduino terms this is done by altering the logic arguments at the output pin to reflect the desired condition.
A variation on this theme is a fourth gate, which is known as the Exclusive OR or XOR: