Arduino 20mhz Crystal - 40khz wave generator?

Hello all,

I am attempting to build my own version of the high powered Ultrasonic cleaner originally published by Silicon Chip - http://www.siliconchip.com.au/cms/A_112072/article.html

In their design they use a small PIC, and even though an Arduino will be severely overkill, I want to use one in the project as I dont know PICs at all and would rather stay with one platform.

With their PIC and 20mhz crystal they can achieve between 320Hz and 40khz, Which is the best way to go about this with Arduino?

I have seen a timer variant library that hacks at the PWM 10 & 11 pins - but cant find it again

Im not sure which is the best way to go to get these results, any suggestions?

Cheers John

Which is the best way to go about this with Arduino

Phase accumulator