The brains of Seahorse 1 are based off of commercially available parts with custom programming.  The main component of the electronics is the computer.  A single board computer running an ARM9 processor.  The SBC also has on board Ethernet, two RS-232 Serial Ports, 2 USB ports and an 8 channel, 12 bit A/D converter.  The data sheet for the SBC can be found here.  

For guidance, Seahorse 1 uses a digital compass from Ocean Servers Technology.  The compass has a built in 3-axis accelerometer and continually measures tilt and pitch of itself.  The compass then corrects for the measured tilt and pitch to continually read the correct heading.