Today I posted a fully documented SONAR LIBRARY for the HandyBoard on my website. It uses the Devantech SRF04 to measure distance. The system is a-synchronious what makes it very little overhead and easy to use on your own programs.

The library consists of the following files:
sonar.asm - the assembly driver (only needed for reference and change)
sonar.icb - the compiled assembly driver (goes in the IC\libs dir)
sonar.c - the IC library (goes in the IC\libs dir)
sonar.lis - the IC list file (goas in the IC\libs dir)
test_sonar.c - an IC test program
sonar_readme.txt - documentation