AD9850 wave generator
The AD9850 is a low-cost DDS signal generator module that can easily produce signals from 0Hz to 40MHz.
I built one one an Arduino expansion board and added a 2x16 character LCD module and a rotary encoder knob.
Here is the library for adding AH_AD9850.h to the project.
Unzip and place directory in the Arduino tree under C:\program files\Arduino\hardware\arduino\avr\libraries\AH_AD9850
Arduino project files (included AH_AD9850 library files):
Source for the AD9850 libraries: