38khz???????????

how to generate 38khz of frequency from arduino???

According to the arduino reference pages there's a function called "tone()".

You might also like to read the post called "How to use this forum - please read" at the top of the forum page.

i have tried that but a maximum of 20khz was generated!!

See Detecting an IR Beam Break with the Arduino IR Library

Should be able to come pretty close by setting up one of the timers to output a fixed frequency. Lots of info at: