Hemal Chevli made this Arduino based waveform generator. He wrote a post on his blog detailing its assembly:
Finally, after sitting in the TODO list for a long time, I’ve made a basic wavefrom generator based on arduino, made using this instructable as reference. I had an enclosure laying around which has incorrect dimensions for the project in which it was supposed to be used. The instructable had the sch for Waveform generator shield, I modified it a bit so its a stand alone system. I had to carefully plan the layout as it uses too many resistors, The DAC is done using R-2R network of 10k and 20k, in place of 20K I used two 10k in series. the output of DAC network goes to LM386 audio amp. Below are some build and testing pictures. It can generate 4different types of waves, sine, pulse,sawtooth and triangle, with frequency and amplitude control, and pulse width control for the pulse wave form. For each wave the corresponding LED lights up.
Check out the video after the break.