How to create an echo effect in audio samples?
As hotpaw2 said, you are not going to hear an echo or delay effect unless your signal changes, so you are not hearing it because you are sending in pure, unchanging signal. You might want to try sending a burst of sine waves every second or better yet a chirp or an actual recording of music or someone speaking. It will work best if you have periods of silence in your input.

Here is an explanation of how to create a delay or echo effect in c-like pseudo-code.