Nice article on making an Arduino DDS…
My experiments with generating RTTY signals yesterday made me begin to think about generating RTTY signals with an Atmel/Arduino setup. The obvious way is to use PWM and a low pass filter to approximate a sine wave. While doing a bit of research, I found the following link which seemed to be nearly ideal: it even included an amateur radio application that uses an Arduino to generate the tones necessary to transmit WSPR. It also has a very nice lowpass filter design that can be pressed into service to smooth the PWM output. Stashed for future reference: