There are various forms of electronic test equipment you can build with an Arduino-based circuit - however this spectrometer by Instructables member simonfrfr takes the concept of home-made equipement to a higher level. With some simple hardware, mostly derived from an old PC optical drive, you could make this in a weekend or so.
For the curious, a spectrometer is "is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials", and for the scientifically-inclined this would be a lot of fun. For a quick explanation and demonstration, check out the following video:
If you're wanting to make your own Arduino-compatible project such as the spectrometer above, you'll need an ATmega328P MCU with Arduino Uno bootloader:
This is the same Atmel AVR ATmega328P microcontroller used in the official Arduino Uno, as well as our Eleven, EtherTen, USBDroid, and other boards. Perfect for building your own Arduino-compatible project directly on a breadboard or on a custom PCB, or for replacing the MCU in an existing board. Comes with the Arduino Uno bootloader pre-installed. Better still, it even has a special label stuck on top with details of the pinout, so you don't even need to look up the datasheet when connecting it up in your project! For more information and to order, click here!