The microcontroller is the core of the entire display system, and will most
likely be an expanded Motorola 6811 system. The function of the microcontroller
is to manipulate the analog sensor input signals received from the wheel rotation
sensors, engine speed sensor, and transmission gear sensor. The 6811 will then
determine and send the desired information: acceleration times, engine speed,
and engaged gear to the electroluminescent (EL) display and LEDs. The
microcontroller analog-to-digital converter will be used (if temperature
and pressure are included) to read the input voltages from the sensors in order
to compute and display the desired results.
EL Display
The display subsystem consists of three components: the display screen itself,
the driver chip for the screen, and a 64-kilobyte RAM chip for data storage.
The display screen will be a Planar EL.320.240.36-HB unit, which has a 5.83 x
4.12-inch viewable area. This screen will be used to display engine RPM,
engaged gear, and acceleration time from zero to a user defined speed. Data
from the microcontroller is sent to the display through a driver chip, which
is also interfaced with a memory chip. There are no output lines from this
subsystem to any other.
LED Indicators
Information on the engaged gear can also be displayed using a sequential LED
display. Using microcontroller input/output ports, the corresponding transmission
gear LED will be lit up. Control logic will be necessary to interface the
microcontroller to the LEDs as shown in Fig.1. The purpose of this subsystem is
to be a lightweight and easy-to-read alternative to the EL display. Using this
convention, miniature LEDs can be mounted, possibly in the driver's helmet or
other subtle places on the car. As with the EL display, there are no output lines
from this subsystem.
Keypad
A twelve-digit keypad will provide flexibility in functionality. The user will be
able to select the desired speed range over which to compute acceleration time.
For example, the user can choose to measure 0-20mph acceleration time, 0-60mph
time, or others depending on the application. The keypad is an input to the
microcontroller and there are no outputs to any other subsystem.
System Reset
A switch will be implemented to simply reset the system.
Sensors
Three sensors will be implemented as main inputs to the system: wheel rotation
sensors, an engine speed sensor, and a transmission gear sensor. The wheel
rotation sensors will be mounted on the rear wheel assembly, one on each side
of the car, to measure shaft speed. These sensors will most likely be magnetic
in nature for practical purposes. During rotation, one magnet will pass over a
hall-effect sensor, producing electronic pulses to be processed. The engine
speed sensor will measure engine RPM by taking a signal either from the engine
control computer or from the distributor itself. For the transmission gear
sensor, a mechanical unit is currently under investigation. However, if there
is no reasonable way to mechanically determine gear engaged, microcontroller
software will be used. If axle and engine speeds are known, gear ratios can
be used to determine gear engaged computationally. All three sensor systems
will provide analog inputs to the microcontroller while none accept any input
signals from any other subsystem.
Software Routines
In addition to hardware components, the display system will require
microcontroller software to implement functionality. For the Software System
Level Block Diagram, refer to Fig. 2.
Initialization Subroutine
The initialization subroutine will configure the processor and display a prompt
for user input. A loop will then be executed that will wait for the first user
input from the keypad.
Mode Select Subroutine
This subroutine will accept the input from the user and select the appropriate
subroutine, either racing mode or demo mode, based on the input. Also, this
subroutine will loop the program after the selected subroutine is executed and
repeat the process.
Racing Mode Subroutine
This subroutine will receive a signal from the keypad and each of the sensors
and prepare data to be displayed on the display screen. The microcontroller
will receive the acquired data so that acceleration time can be determined.
The data is then sent to the EL display driver through which the display is
updated. Of this data, information on transmission gear is also sent to the
LED logic driver to power the appropriate LED.
Demo Mode Subroutine
A sample screen from the racing mode subroutine will be displayed for ten
seconds after which a test screen will be displayed. A test screen could
consist of alternating black and white squares on the display like a
checkerboard. The purpose of this subroutine is for demonstration of system
operation.
