The range of the VEX IR line sensors is not long enough to be used for obstacle avoidance. We are attempting to use our own IR sensors. Currently we have linked a BS2 to the vex unit so that we can utilize its capabilities. We understand that if you designate motor port 1 as a speaker so that you can produce a square wave frequency out. How do denote (program) a specific frequency and how do you make it read a specific input immediately after the frequency output.

There's a PlayTone command to create the output which is generated by hardware. It's a continuous square wave at the specified frequency. There is no way to synchronize this to an input signal.

For IR distance sensors you should look at the line of sensors made by Sharp. They come with various distance ranges.