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Arduino-based OBD-II

Interface and Data LoggerCS 497 Independent Study

Ryan Miller

Advisor: Prof. Douglas Comer

April 26, 2011

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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

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Arduino•  Program “sketches” inMulti-platform Java-based IDE

•

 

Code in C/C++•  Serial Communication(currently USB)

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Hardware

•  Goals of this project:

•  Communicate with an automotiveengine control unit (ECU) via theArduino

•  Gather and record instantaneousdata that is reported by the vehicle

Arduino

Hardware

Automotive OBD

ISO Interface

Software

Data

Conclusions

?

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Hardware•  Vehicles produced inthe U.S. after 1996 arerequired to have an

OBD-II (on-boarddiagnostic) connector

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Hardware•  OBD-II Interface

•  Very simple connectionfor most applications

• 

Most important pins•  K-Line

•  Ground

•  +12V

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Hardware•  Open-source projectcalled “OBDuino”offered the interface

schematic(which is fortunate,because I am not anEE major)

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Hardware•  Open-source projectcalled “OBDuino”offered the interface

schematic(which is fortunate,because I am not anEE major)

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Hardware•  Freescale MC33290 handles the tricky parts

•  K-Line, Ground, and +12V go in

•  Serial Tx/Rx come out

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Hardware

OBD-II

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Software

•  A few functions to perform:

•  Initialize ISO connection

•  Request data from vehicle’s ECU

• 

Display the result on the LCD andrecord the value to retrieve later

Arduino

Hardware

Automotive OBD

ISO Interface

Software

Data

Conclusions

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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

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Software•  Initialization:

•  Starts by “bit-banging” 0x33 at 5 baud

•  Code:

!"#$ " # $%&&'

()* +!"#$ ,-./ # $%$0' ,-./' ,-./ 11# 023

4( +" 5 ,-./2 66 78)).9 "4: 

;4*4:9+?@ABCD EFGE2' 66 H9I; 0 

9=.9

;4*4:9+?@ABCD JA>2' 66 H9I; $ 

;9=-K+L$$2'

M

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

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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

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Software•  Steps:

1.  Request PID with hex value

2.  Continuously read data from ISO until successfulchecksum or timeout

3.  Convert returned value with formula

4.  Display / record value and repeat

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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

!"#$ ,9..-

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Software

2. Continuously read data from ISO until successfulchecksum 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

!"#$ "S(N00P'

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Software

3. Convert returned value with formula

ie.:

PID Bytes Description Formula

0x0C 2 Engine RPM ((A*256)+B)/4

'()!*$ *T,'

*T, # ++'()!*$2"S(N$P U LVO2 Q +'()!*$2"S(N0P2 6 WX$'

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Software

4. Record/display value and repeat

•  Displaying on an LCD screen:

+%,)%'-."/#0* =Y;'

=Y;XT*4I:+*T,2'

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Software

4. Record/display value and repeat

•  Writing to an SD card:

1%*$ =)

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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

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Software

•  You can convert into

•  And then use vehicle speed to convert to

or MPG

g air 

s

gal  gasoline

h

miles

gal gasoline

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Data

• Scanned four PIDs over a20-minute interval every1-2 seconds

• Vehicle Speed

• Engine RPM

• 

Engine Coolant• Calculated MPG

Arduino

Hardware

Automotive OBD

ISO Interface

Software

Data

Conclusions

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Data

mph

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Data

mph rpm

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Data

°C

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Data

mph°C

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Conclusions

• Embedded computing isubiquitous

•

 

Massive amounts of datagenerated by everydaymachines

• 

Elec. Engineering and CScan come together to makesome pretty cool things

Arduino

Hardware

Automotive OBD

ISO Interface

Software

Data

Conclusions

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Questions?