The hardware structure is organized around a central SPI bus that connects all components,
as shown in figure 6.10. Those components are the SBC, the display and keypad
unit, the sensors and the actuator. The safety system is connected to the bus as well,
but only to listen for a heartbeat of the computer.
The SPI bus is a master-slave bus where the SBC serves as the master talking to
all other devices. Since the SBC has no direct SPI interface, an Atmel MEGA32 microcontroller15
acts as interface between the SPI bus and the parallel port of the SBC.
All sensors are connected to the SPI-bus by A/D-converters (ADC) where necessary.
The Philips UZZ9001 (UZZ) is an integrated circuit that evaluates and postprocesses
the output of the Hall sensor, and performs A/D conversion. A D/A-converter (DAC)
is connected to the bus to create the analog control signal for the pwm-amplifier that
powers the actuator. In addition to that, a display and keypad is linked to the bus to
allow simple user interaction, like starting and stopping the system and to adjust the
support ratio.