Richard Visokey of AD7C made a DDS VFO using AD9850 and an Arduino Uno:
I built a simple VFO for a direct conversion receiver I am putting together. The VFO uses an AD9850 DDS chip to synthesis a nice 1Vp-p sinusoidal wave. I used an Arduino Uno to set the AD9850 frequency, drive an LCD display, and take input from a rotary encoder to set the output frequency.
Project info at AD7C.
Check out the video after the break.
A bit tooting my own horn, but a lot better code for this type of VFO/generator is here:
http://janoc.rd-h.com/archives/396
The original Richard’s code works, but it is not very pleasant to use and he seems to have stopped developing it in 2013.
A yet another, more full-featured VFO is from M0XPD, this one may be preferrable if you plan on using it for exclusively radio work (more radio-specific features):
http://m0xpd.blogspot.co.uk/p/kanga-uk-resources.html#VFO2
Oh, apropos, my VFO is 3.3V, because some of those DDS modules don’t work reliably at 5V – they are fitted with only a 3.3V oscillator module!