SparkFun MiniGen

Pro Mini Signal Generator Shield - SparkFun Electronics

This is the SparkFun MiniGen Signal Generator, a small shield for the Arduino Pro Mini that is capable of generating sine, square, or triangle waves at up to 3MHz, and approximately 1Vp-p. Though the MiniGen is technically a shield it can, in fact, operate as a stand-alone board capable of the the same functionality as it would if it were placed on top of a Pro Mini.