If choice of waveform type isnt essential, you can do this very nicely with a simple 555 timer in astable mode: 555 and 556 Timer Circuits Use a .01 uf capacitor, make R2 a pot.
If you need waveform selection, take a look at the website for the link you posted, with schematics and code for inspiration: http://bleeplabs.com/nebulophone/