Devantech SRF01 Sonar Rangefinder
The SRF01 is a single transducer ultrasonic rangefinder in a very small footprint PCB with a single pin Serial interface. The SRF01 can measure in cm or Inches. In standard mode the SRF01 measures from approx 18cm (7in) to 600cm (19ft). In Advanced mode it is possible for the SRF01 to measure range all the way down to zero.