If your handy try a pic or avr with an on off output to run a fet. But the 555 is likely easier. If you look at the schematics avaliable on the internet and search on 555 you should come up with a circuit that has an adjustable output. The one i have is for a morse code key practice tone generator. I don't know if you could combine that with a fet. I think it runs to fast but it could be slowed down.