pylon:
Please can someone help me to setup one of the pwm output to produce a ultrasound ( form 20khz to 60khz ) wave ?
What does "wave" mean in this context? You cannot put out a sinus wave using PWM. But you can put out pulses with 60kHz. So the question is: what do you need the output for? This may influence the way to produce the output signal.
Here is the playground article: http://www.arduino.cc/playground/Code/PwmFrequency
Ultrasound transduceers are normally highly resonant, so square v. sine wave makes no difference, but the frequency has to match the
transducer.