Arduino-based OBD-II Interface and Data Logger CS 497 Independent Study Ryan Miller

Advisor: Prof. Douglas Comer April 26, 2011

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

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

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

?

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

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

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

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

Hardware •  Freescale MC33290 handles the tricky parts • K-Line, Ground, and +12V go in

• Serial Tx/Rx come out

Hardware

OBD-II

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

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

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);  

}  

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

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

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

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]);  

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];  

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;  

Software 4. Record/display value and repeat •  Displaying on an LCD screen:

LiquidCrystal  lcd;    lcd.print(rpm);    

Software 4. Record/display value and repeat •  Writing to an SD card:

File  log;    log.print(rpm);    

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

Software •  You can convert into

• And then use vehicle speed to convert to

or MPG

g airs

gal gasolineh

milesgal gasoline

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

Data

mph

Data

mph rpm

Data

°C

Data

mph °C

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

Questions?