Transcript Vehicle Interface - Princeton University

Princeton University
Prospect Eleven
Vehicle Interface
Already substantial electronic information available from the
vehicle itself:
• Engine status –
temp, RPM, diagnostic codes,...
• Transmission –
what gear are we in?
4WD on/off
• Car traction control –
are wheels slipping,
are we really moving?
• Wheel speed/odometry – how far have we moved?
how fast?
All of this can be utilized with little additional effort.
• Throttle also already electronic
Nov. 17, 2005
Princeton University
Prospect Eleven
These inputs come in a variety of forms—
Digital:
•
Straight pulses, e.g. from wheel
encoders
– As wheel turns, a digital line pulses to
indicate revolution
– Tens to thousands of ticks/rev
→ Read with a counter circuit
•
Serial data: car’s onboard computer,
OBD-II
→ Read with a dedicated decoder interface
•
A bit-code: transmission position
– e.g. “0110” for park, “0111” for drive
→ Read the digital signal directly
Nov. 17, 2005
Princeton University
Prospect Eleven
Analog: a voltage level of significance
• The tension reported by a
sensor on the brake line
– Resistive load cell produces a
voltage proportional to force
→ Use an Analog-to-Digital
converter to read value directly
• The voltage sent to throttle the
car
→ Use a Digital-to-Analog
converter to create the desired
voltage
Nov. 17, 2005
Princeton University
Prospect Eleven
OBD-II Interface
10101110101...
ABS Wheel Encoders
Left
Right
Transmission position
1001 1101
1001 0101
“Data-acquisition card”
Counters
Throttle voltage
Digital inputs
DAC
Tension on the
brake pedal
101001...
ADC
101001...
100 lb
Nov. 17, 2005
Princeton University
Prospect Eleven
Other thoughts
Nov. 17, 2005