A Motorola MPX4250AP analog pressure sensor was designed to sense absolute air pressure within the intake manifold of an automobile from 2.9 to 36.3 psi.  However, it can be used for a variety of applications, and suits our requirements for a depth sensor very well.  The pressure sensor is mounted inside an auxiliary electronics box, away from the main electronics.  A 3 op-amp conditioning circuit adjusts the output range for zero to 18 feet underwater representing 0 to 5V. The sensor is connected to external water pressure by a small rubber tube which leads out of the auxiliary electronics box.  The voltage is sent to the NetBurner 5213 leg controller for analog to digital conversion, and used for depth control.  The selected sensor range (0-18 ft) make the sensor a good choice based on the competition facility.  Additionally, the small size (approximately 2 cm2), low cost, and the relatively simple integration, work well with RAM-Boat 8’s mechanical and electrical layout.

The vehicle heading is determined by the Devantech CMPS03 digital compass, a sensor specifically created to aid robotics navigation. The compass is connected to a DMA timer line on the NetBurner 5213 leg controller and delivers headings based on a 10Hz pulse width, with 1msec to 36.99msec representing heading values from 0 to 359.9 degrees. The compass is located inside the main pressure housing, away from the thrusters.  Positioning the compass away from the thrusters minimizes any possible magnetic interference.