The Ultrasonic detector is a Devantech SRF05 Ultrasonic ranger that mounts to the rear or front of the Trekker Chassis, front scanner brackets, or  bumper switches.  The ultrasonic sensor will detect obstacle and cause the robot to stop. 

The SRF05 Ultrasonic detector can detect from ~4 inches to ~13 feet.  This sensor package will plug directly into the Trekker OOPic II Expansion Board or the OOPic-R Expansion Board ultrasonic sensor headers.