NavLab11 Brake Controller
The brake controller is responsible for controlling a an actuator
coupled to the brake pedal so as to achieve a commanded hydraulic brake
pressure. It is constructed on a four-layer PCB with a ground
plane and three signal layers. Inputs are the brake pressure,
position feedback pot, quadrature encoder on motor, motor current,
motor bus voltage and servo amp status. Outputs are DC motor
drive and drive to an electromagnetic clutch which disengages the
actuator for safe power-off failure.
The controller has not yet been completed and integrated on NavLab11,
however functional testing of the various functions and driver firmware
has been successfully completed. A commercial servo
amp module will be mounted under the PCB as the output driver.
Analog input circuitry is on the lower left, the AVR controller chip is
in the middle, and digital I/O is on the right. The top half of
the board is largely devoted to protection and filter components that
insure reliable operation in the automotive environment. Every
external connection contains both surge/ESD protection and RFI
suppression.
The crucial pressure sensor input is conditioned by a slew-rate
limiting filter which is highly effective at suppressing the impulse
noise present in the under-hood environment, yet does not introduce
large amounts of phase lag which would compromise control
stability. The signal is then digitized by a 24 bit
sigma-delta ADC.