The document outlines the development of an Arduino-based OBD-II interface and data logger, utilizing an Atmega328 microcontroller to communicate with automotive ECU and record vehicle data. Key features include initialization of the ISO connection, data retrieval from the vehicle, and displaying results on an LCD or logging to an SD card. It emphasizes the integration of electrical engineering and computer science to harness the data generated by modern vehicles.

1. Arduino-based OBD-II
Interface and Data Logger
CS 497 Independent Study
Ryan Miller
Advisor: Prof. Douglas Comer
April 26, 2011

2. Arduino
• Italy 2005
• ATmega328 microcontroller
• 14 digital I/O pins
• 16 MHz clock speed
• 32 KB memory
• About $30 online
Arduino
Hardware
Automotive OBD
ISO Interface
Software
Data
Conclusions

3. Arduino
• Program “sketches” in
Multi-platform Java-
based IDE
• Code in C/C++
• Serial Communication
(currently USB)

4. Hardware
• Goals of this project:
• Communicate with an automotive
engine control unit (ECU) via the
Arduino
• Gather and record instantaneous
data that is reported by the vehicle
Arduino
Hardware
Automotive OBD
ISO Interface
Software
Data
Conclusions
?

5. Hardware
• Vehicles produced in
the U.S. after 1996 are
required to have an
OBD-II (on-board
diagnostic) connector

6. Hardware
• OBD-II Interface
• Very simple connection
for most applications
• Most important pins
• K-Line
• Ground
• +12V

7. Hardware
• Open-source project
called “OBDuino”
offered the interface
schematic
(which is fortunate,
because I am not an
EE major)

8. Hardware
• Open-source project
called “OBDuino”
offered the interface
schematic
(which is fortunate,
because I am not an
EE major)

9. Hardware
• Freescale MC33290 handles the tricky parts
• K-Line, Ground, and +12V go in
• Serial Tx/Rx come out

10. Hardware
OBD-II

11. Software
• A few functions to perform:
• Initialize ISO connection
• Request data from vehicle’s ECU
• Display the result on the LCD and
record the value to retrieve later
Arduino
Hardware
Automotive OBD
ISO Interface
Software
Data
Conclusions

12. Software
• Initialization:
• Starts by “bit-banging” 0x33 at 5 baud
• i.e.
0 0 1 1 0 0 1 1
200ms pause = 1.6 seconds

13. Software
• Initialization:
• Starts by “bit-banging” 0x33 at 5 baud
• Code:
byte
b
=
0x33;
for
(byte
mask
=
0x01;
mask;
mask
<<=
1)
{
if
(b
&
mask)
//
Choose
bit
digitalWrite(K_OUT,
HIGH);
//
Send
1
else
digitalWrite(K_OUT,
LOW);
//
Send
0
delay(200);
}

14. Software
• Then you can start 10.4 kbps communication and
perform these steps to finish initialization:

15. Software
• Parameter IDs (PIDs)
• SAE J1979 standard
• Examples:
PID Bytes Description Formula
0x0C 2 Engine RPM ((A*256)+B)/4
0x0D 1 Vehicle Speed (km/h) A
0x11 1 Throttle Position (%) A*100/255
0x3F 2 Catalyst Temp (B2, S2) ((A*256)+B)/10 - 40

16. Software
• Steps:
1. Request PID with hex value
2. Continuously read data from ISO until successful
checksum or timeout
3. Convert returned value with formula
4. Display / record value and repeat

17. Software
1. Request PID with hex value
Index Value Description
0 0x68 SAE J1979 standard
1 0x6A OBD-II request
2 0xF1 Off-board tool
3 0x01 Mode 1 PIDs
4 pid Hex value for PID requested
5 Checksum Computed from message
byte
message[6];
for
(int
i
=
0;
i
<
6;
i++)
iso_write_byte(message[i]);

18. Software
2. Continuously read data from ISO until successful
checksum or timeout
Byte(s) Description
0 Message Header 1
1 Message Header 2
2 Source Address
3 – 9 Data (up to 7 bytes)
Final byte Checksum
byte
buf[11];

19. Software
3. Convert returned value with formula
ie.:
PID Bytes Description Formula
0x0C 2 Engine RPM ((A*256)+B)/4
double
rpm;
rpm
=
((double)buf[0]
*
256)
+
(double)buf[1])
/
4.0;

20. Software
4. Record/display value and repeat
• Displaying on an LCD screen:
LiquidCrystal
lcd;
lcd.print(rpm);

21. Software
4. Record/display value and repeat
• Writing to an SD card:
File
log;
log.print(rpm);

22. Software
• One last note on PIDs…
• This gives you the rate of air in grams / second
PID Bytes Description Formula
0x10 2 Mass Air Flow Rate ((A*256)+B)/100

23. Software
• You can convert into
• And then use vehicle speed to convert to
or MPG
g air
s
gal gasoline
h
miles
gal gasoline

24. Data
• Scanned four PIDs over a
20-minute interval every
1-2 seconds
• Vehicle Speed
• Engine RPM
• Engine Coolant
• Calculated MPG
Arduino
Hardware
Automotive OBD
ISO Interface
Software
Data
Conclusions

25. Data
mph

26. Data
mph rpm

27. Data
°C

28. Data
mph
°C

29. Conclusions
• Embedded computing is
ubiquitous
• Massive amounts of data
generated by everyday
machines
• Elec. Engineering and CS
can come together to make
some pretty cool things
Arduino
Hardware
Automotive OBD
ISO Interface
Software
Data
Conclusions

30. Questions?