Introduction: Hack an ELM327 Cable to Make an Arduino OBD2 Scanner

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In my previous instructable i created an OBD2 Simulator so that i didn't have to test my Arduino OBD2 Reader in the car the whole time but instead in the comfort of my own home.

Stuff you need.

Arduino UNO

LCD shield

ELM327 USB cable.

What it can read

Coolant Temp,IAT Temp,Ambient Temp, Throttle %,RPM,Vehicle Speed, Air flow Rate,Barometric Pressure

I will be removing the board from the ELM327 Enclosure and then bypass the USB bridge chip and attach the Serial TX/RX pins of the arduino to the Serial TX/RX pins onto the ELM327 board, program the arduino and attach the ELM327 OBD2 connector to the OBD2 port .

Pretty Simple

Step 1: Prepare the ELM327 Board to Bypass the USB Bridge Chip

Start by removing the sticker on ELM327 Cable's Enclosure, remove the 4 screws with a smallish star screwdriver.

And then take out the board.

Tip:Borrow your Girlfrien's/Wife's cutex and make a mark on one side of the connector that runs to the OBD2 Connector, that way when you take it out you will know which side it goes because it can go in both ways, for this instructable its not needed to remove the mentioned connector though.

Solder 2 wires to the TX and RX pins on the board, in the attached photo's i have included the pin-out information of the USB Bridge chip. Be careful though I managed to de-solder some components which i could not put back, but luckily it still worked afterwards.

Tip:Program the arduino so that it writes to the serial monitor with some short delays in between, then connect a jumper cable to the TX pin of the arduino and poke around with the other end on the board to see where you get some serial activity, the surface mounted LED's wil flicker as communication happens, unfortunately this will not work for the RX side but in the pictures its easy enough to see where I soldered it onto the board.

NOTE:The USB cable is connected to the board with a 4 pin connector, i cut the middle 2 out so that the ELM327 cannot communicate with the PC whilst its connected, this way it only gets power from my PC's USB port and the serial controller on the board will not be occupied by the PC allowing the Arduino to talk to it

Once done put it back into the box, I just taped it up because In my Jeep the box is in my way and cannot drive it whilst in the driver seat, I will be using the enclosure for something else.

Step 2: Attach the Arduino LCD Shield to the Arduino

Attach the Arduino LCD Shield to the arduino and hook it up to your PC to be programmed.

Below is my Arduino Sketch, I noticed that the formatting messes with the code a bit, I have some more information available related to this build you can also view the code here.

http://techtinker.co.za/viewtopic.php?f=14&t=17

// include the library code:<br>#include 

//Declare Serial Read variables
int CmdCount=1;
byte inData;
char inChar;
String BuildINString="";
String DisplayString="";
long DisplayValue;
String SentMessage="";
int ByteCount=0;
long A;
int B;
int WorkingVal;
String WorkingString="";
//Declare Buttons
int MenuID=0;
// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(8, 9, 4, 5, 6, 7);
void setup() 
{
    // set up the LCD's number of columns and rows: 
  lcd.begin(16, 2);
  // Print a message to the LCD.
  lcd.setCursor(0, 0);
  Bootup();//Simulate Bootup process doesnt have to be here this only makes it look cool
  Retry:
  lcd.setCursor(0, 0);
  lcd.print("Connecting......    ");
  lcd.setCursor(0, 1);
  lcd.print("                    ");
  Serial.begin(38400);
  
  delay(500);
  //Send a test message to see if the ELM327 Chip is responding
  SentMessage = "ATI";
  Serial.println("ATI");delay(500);ReadData();
  if (BuildINString.substring(1,7)=="ELM327")
    {
      lcd.setCursor(0, 0);
      lcd.print("Welcome...            ");
      lcd.setCursor(0, 1);
      lcd.print("Connection OK         ");
      delay(1500);
    }
    else
    {
      lcd.setCursor(0, 0);
      lcd.print("Error             ");
      lcd.setCursor(0, 1);
      lcd.print("No Connection!         ");
      delay(1500);
      goto Retry;
    }
  
  delay(1500);
}
void loop() {
int x;
x = analogRead (0);
//Serial.println(x);
lcd.setCursor(10,1);
if (x > 800 and x < 820){lcd.print ("Select  ");}
if (x > 620 and x < 630){if (MenuID>0){MenuID--;}delay(250);}//Left
if (x > 400 and x < 415){lcd.print ("Down    ");}
if (x > 190 and x < 215){lcd.print ("Up      ");}
if (x > -10 and x < 10){if (MenuID<11){MenuID++;}delay(250);} //Right
  if (MenuID==0){lcd.setCursor(0, 0);lcd.print("01 Coolant Temp    ");lcd.setCursor(0, 1);lcd.print(DisplayString);SentMessage = "01 05";Serial.println("01 05");delay(300);ReadData();}
  if (MenuID==1){lcd.setCursor(0, 0);lcd.print("02 IAT Temp        ");lcd.setCursor(0, 1);lcd.print(DisplayString);SentMessage = "01 0F";Serial.println("01 0F");delay(300);ReadData();}
  if (MenuID==2){lcd.setCursor(0, 0);lcd.print("03 Ambient Temp    ");lcd.setCursor(0, 1);lcd.print(DisplayString);SentMessage = "01 46";Serial.println("01 46");delay(300);ReadData();}
  if (MenuID==3){lcd.setCursor(0, 0);lcd.print("04 Throttle %      ");lcd.setCursor(0, 1);lcd.print(DisplayString);SentMessage = "01 11";Serial.println("01 11");delay(300);ReadData();}
  if (MenuID==4){lcd.setCursor(0, 0);lcd.print("05 CAT 1 Temp      ");lcd.setCursor(0, 1);lcd.print("Not Implemented ");}
  if (MenuID==5){lcd.setCursor(0, 0);lcd.print("06 CAT 2 Temp      ");lcd.setCursor(0, 1);lcd.print("Not Implemented ");}
  if (MenuID==6){lcd.setCursor(0, 0);lcd.print("07 CAT 3 Temp      ");lcd.setCursor(0, 1);lcd.print("Not Implemented ");}
  if (MenuID==7){lcd.setCursor(0, 0);lcd.print("08 CAT 4 Temp      ");lcd.setCursor(0, 1);lcd.print("Not Implemented ");}
  if (MenuID==8){lcd.setCursor(0, 0);lcd.print("09 RPM             ");lcd.setCursor(0, 1);lcd.print(DisplayString);SentMessage = "01 0C";Serial.println("01 0C");delay(300);ReadData();}
  if (MenuID==9){lcd.setCursor(0, 0);lcd.print("10 Vehicle Speed   ");lcd.setCursor(0, 1);lcd.print(DisplayString);SentMessage = "01 0D";Serial.println("01 0D");delay(300);ReadData();}
  if (MenuID==10){lcd.setCursor(0, 0);lcd.print("11 Air Flow Rate  ");lcd.setCursor(0, 1);lcd.print(DisplayString);SentMessage = "01 10";Serial.println("01 10");delay(300);ReadData();}
  if (MenuID==11){lcd.setCursor(0, 0);lcd.print("12 Barometric     ");lcd.setCursor(0, 1);lcd.print(DisplayString);SentMessage = "01 33";Serial.println("01 33");delay(300);ReadData();}
}
//Read Data and act accordingly
void ReadData()
{
  BuildINString="";  
  while(Serial.available() > 0)
  {
    inData=0;
    inChar=0;
    inData = Serial.read();
    inChar=char(inData);
    BuildINString = BuildINString + inChar;
  }
  
  //if(BuildINString!=""){Serial.print(BuildINString);}
  BuildINString.replace(SentMessage,"");
  BuildINString.replace(">","");
  BuildINString.replace("OK","");
  BuildINString.replace("STOPPED","");
  BuildINString.replace("SEARCHING","");
  BuildINString.replace("NO DATA","");
  BuildINString.replace("?","");
  BuildINString.replace(",","");
  //Serial.print(BuildINString);
  
  //Check which OBD Command was sent and calculate VALUE 
  //Calculate RPM I.E Returned bytes wil be 41 0C 1B E0 
  if (SentMessage=="01 0C")
  {
    WorkingString = BuildINString.substring(7,9);
    A = strtol(WorkingString.c_str(),NULL,0);
    WorkingString = BuildINString.substring(11,13);
    B = strtol(WorkingString.c_str(),NULL,0);
   
   DisplayValue = ((A * 256)+B)/4;
   DisplayString = String(DisplayValue) + " rpm          ";
   lcd.setCursor(0, 1);
   lcd.print(DisplayString);
  }
  //Calculate Vehicle speed I.E Returned bytes wil be 41 0C 1B E0 
  if (SentMessage=="01 0D")
  {
    WorkingString = BuildINString.substring(7,9);
    A = strtol(WorkingString.c_str(),NULL,0);
   DisplayValue = A;
   DisplayString = String(DisplayValue) + " km/h          ";
   lcd.setCursor(0, 1);
   lcd.print(DisplayString); 
  }
  
  //Coolant Temp 
  if (SentMessage=="01 05")
  {
    WorkingString = BuildINString.substring(7,9);
    A = strtol(WorkingString.c_str(),NULL,0);
   DisplayValue = A;
   DisplayString = String(DisplayValue) + " C            ";
   lcd.setCursor(0, 1);
   lcd.print(DisplayString); 
  }
  
    //IAT Temp 
  if (SentMessage=="01 0F")
  {
    WorkingString = BuildINString.substring(7,9);
    A = strtol(WorkingString.c_str(),NULL,0);
   DisplayValue = A;
   DisplayString = String(DisplayValue) + " C            ";
   lcd.setCursor(0, 1);
   lcd.print(DisplayString); 
  }
  
  //Air flow Rate
  if (SentMessage=="01 10")
  {
    WorkingString = BuildINString.substring(7,9);
    A = strtol(WorkingString.c_str(),NULL,0);
    WorkingString = BuildINString.substring(11,13);
    B = strtol(WorkingString.c_str(),NULL,0);
   
   DisplayValue = ((A * 256)+B)/100;
   DisplayString = String(DisplayValue) + " g/s          ";
   lcd.setCursor(0, 1);
   lcd.print(DisplayString); 
  }
  
  //Ambient Temp 
  if (SentMessage=="01 46")
  {
    WorkingString = BuildINString.substring(7,9);
    A = strtol(WorkingString.c_str(),NULL,0);
   DisplayValue = A;
   DisplayString = String(DisplayValue) + " C            ";
   lcd.setCursor(0, 1);
   lcd.print(DisplayString); 
  }
  
  //Throttle position 
  if (SentMessage=="01 11")
  {
    WorkingString = BuildINString.substring(7,9);
    A = strtol(WorkingString.c_str(),NULL,0);
   DisplayValue = A;
   DisplayString = String(DisplayValue) + " %            ";
   lcd.setCursor(0, 1);
   lcd.print(DisplayString); 
  }
  //Barometric pressure
  if (SentMessage=="01 33")
  {
    WorkingString = BuildINString.substring(7,9);
    A = strtol(WorkingString.c_str(),NULL,0);
   DisplayValue = A;
   DisplayString = String(DisplayValue) + " kpa            ";
   lcd.setCursor(0, 1);
   lcd.print(DisplayString); 
  }  
}
void Bootup()
{
lcd.print("WisperChip V2.00 ");
     for (int i=0; i <= 5; i++)
     {
       for (int j=1; j <= 4; j++)// -/|\-
       {
        if(j==1){lcd.setCursor(0, 1);lcd.print ("-");delay(200);} 
        if(j==2){lcd.setCursor(0, 1);lcd.print ("/");delay(200);}
        if(j==3){lcd.setCursor(0, 1);lcd.print ("|");delay(200);} 
        if(j==4){lcd.setCursor(0, 1);lcd.print ("\\");delay(200);} 
       }   
     }
     
delay(1000);  
}

Step 3: Hooking It Up to Your Vehicle,

Once you have programmed the Arduino, make sure the Arduino's TX/RX pins are connected to the TX/RX pins on the ELM327 board.

The Code ensures that its able to talk to the ELM327 Chip by sending a command "ATI" the ELM327 chip will respond with ELM327, if it doesn't the LCD will print "Error, No Connection" if it worked it will welcome you wuth a welcome message on the LCD.

From there you simply press the left and right buttons to cycle through the menus currently it will only read.
Coolant Temp,IAT Temp,Ambient Temp, Throttle %,RPM,Vehicle Speed, Air flow Rate,Barometric Pressure

You can add more if you like and change the menu to your liking
See Wiki http://en.wikipedia.org/wiki/OBD-II_PIDs for more PID's that you can add there are quite a few.

You can use a cellphone cradle that you stuck agains the window to hold it and use a USB cellphone charger to power the Arduino, The ELM327 will be powered by the OBD port on Pin 16 which is positive and PIN4/5 which is negative.

If you get stuck feel free to check out on this forum http://techtinker.co.za/viewforum.php?f=14 you may also contact me if you have questions.

Please also see the youtube video.

Good Luckl!