The diode, cap and resistor aside and completely disconnected from the circuit and the pin 1 of the chip, the circuit pulls that much current.

I've tested this with a few of these chips that I've got. All the same.

Thanks again for the replies.

I connected an oscilloscope to the RPM pulse wire, with the DC offset circuit (resistor, capacitor & diode) also connected and did some test with the pulse going through the DC offset circuit and the frequencies seems to be fine.

Another thing I've found is that the reason why at higher RPMs it lows lower, is that, since the chip was getting hot the accuracy was dropping, so it seemed it was reading incorrectly. So if I leave the circuit off before it's hot, and then inject 100Hz (3000RPM) to it using an Arduino, it will read the way it should. Then of course drops when the chip gets hot

Nope I don't have pins 4 & 7 connected to pin 6. Only pin 4 & 7 are connected and 5 & 6 connected together.

I've checked the current that the circuit takes and it's about 65mA. It's supposed to take less than 5mA. This is with the input signal frequency and the output voltage disconnected.

Anyone?

Hi everyone.

I have made use of a frequency to voltage converter (LM2917, 8pin version) to convert the frequency from my car's RPM tach signal wire to voltage to then read it with my Arduino and make a digital RPM readout.

Here is the circuit I have done:


The resistor, capacitor and the diode connected to the tach signal wire is to get rid of the DC offset.

There are 2 problems at the moment:-
1) The chip doesn't convert the signal properly, the higher the RPM from the car the less accurate the output voltage, hence a very off RPM compared with the RPM dial in the car. For example when car's RPM dial reads 3000 RPM the digital output reads 2400 RPM.

2) The chip itself gets very hot even if there is no signal into it and even when nothing is connected to the output voltage pin.

Has anyone got any experience with this chip at all?

Any help is appreciated.

Thanks

Thank you.

Hi Pylon,

Did you ever manage to test my code at all?

Thanks.

Here is my version of OBDuino from their code:

Code:

//This is a character buffer that will store the data from the serial port
char rxData[20];
char rxIndex=0;

//Variables to hold the speed and RPM data.
int vehicleSpeed=0;
int vehicleRPM=0;

void setup(){

  Serial1.begin(9600);
  Serial.begin(9600);   //This is for the serial debug

  //Wait for a little while before sending the reset command to the OBD-II-UART
  delay(1500);
  //Reset the OBD-II-UART
  Serial1.print("ATWS\r");
  //Wait for a bit before starting to send commands after the reset.
  delay(1000);
 
  // turn echo off
  Serial1.print("ATE0\r");
 
  // send 01 00 until we are connected
  do
  {
    Serial1.print("0100\r");
    delay(1000);
    getResponse();    //This is only called once since the schoecho has been turned off using ATE0\r
    Serial.print("0100 Response:  ");
    Serial.print(rxData[0]);Serial.print(rxData[1]);Serial.print(rxData[3]);Serial.print(rxData[4]);Serial.print(rxData[6]);Serial.print(rxData[7]); Serial.print(rxData[9]);Serial.print(rxData[10]);
    Serial.println("");
  }
  while(ELM_CHECK_RESPONSE("0100", rxData)!=0);
   
  Serial1.flush();
   
  Serial1.print("ATDPN\r");  //Shows the protocol
  getResponse();
  Serial.print("Protocol: ");Serial.print(rxData[0]);Serial.print(rxData[1]);Serial.println("");
  // str[0] should be 'A' for automatic
  // set header to talk directly to ECU#1
  if(rxData[1]=='1')  // PWM
    Serial1.print("ATSHE410F1\r");
  else if(rxData[1]=='2')  // VPW
    Serial1.print("ATSHA810F1\r");
  else if(rxData[1]=='3')  // ISO 9141
    Serial1.print("ATSH6810F1\r");
  else if(rxData[1]=='6')  // CAN 11 bits
    Serial1.print("ATSH7E0\r");
  else if(rxData[1]=='7')  // CAN 29 bits
    Serial1.print("ATSHDA10F1\r");
 
  //Delete any data that may be in the serial port before we begin.
  Serial1.flush();

}


void loop(){
  //Delete any data that may be in the serial port before we begin. 
  Serial1.flush();

  Serial1.print("010D\r");    //Query the OBD-II-UART for the Vehicle Speed

  //Get the response from the OBD-II-UART board. We get two responses
  //because the OBD-II-UART echoes the command that is sent.
  //We want the data in the second response.
  getResponse();

  //Convert the string data to an integer
  vehicleSpeed = strtol(&rxData[6],0,16);

  //Print the speed data to debug serial window
  Serial.print("SPEED: ");
  Serial.print(vehicleSpeed);
  Serial.print(" km/h");
  Serial.println(" ");
 
  delay(20);
 
  //Delete any data that may be left over in the serial port.
  Serial1.flush();

  //Query the OBD-II-UART for the Vehicle rpm
  Serial1.println("010C\r");
  //Get the response from the OBD-II-UART board
  getResponse();

  //Convert the string data to an integer
  //NOTE: RPM data is two bytes long, and delivered in 1/4 RPM from the OBD-II-UART
  vehicleRPM = ((strtol(&rxData[6],0,16)*256)+strtol(&rxData[9],0,16))/4;

  //Print the rpm data to debug serial window
  Serial.print("RPM: ");
  Serial.print(vehicleRPM);
  Serial.println(" ");

  //Give the OBD bus a rest
  delay(50);
 
}


byte ELM_CHECK_RESPONSE(const char *cmd, char *str)
{
  // cmd is something like "010D"
  // str should be "41 0D blabla"
  if(cmd[0]+4 != rxData[0]
    || cmd[1]!= rxData[1]
    || cmd[2]!= rxData[3]
    || cmd[3]!= rxData[4])
    return 1;

  return 0;  // no error
}


void getResponse(void){
  char inChar=0;
  //Keep reading characters until we get a carriage return
  while(inChar != '\r'){
    //If a character comes in on the serial port, we need to act on it.
    if(Serial1.available() > 0){
      //Start by checking if we've received the end of message character ('\r').
      if(Serial1.peek() == '\r'){
        //Clear the Serial buffer
        inChar=Serial1.read();
        //Put the end of string character on our data string
        rxData[rxIndex]='\0';
        //Reset the buffer index so that the next character goes back at the beginning of the string.
        rxIndex=0;
      }
      //If we didn't get the end of message character, just add the new character to the string.
      else{
        //Get the new character from the Serial port.
        inChar = Serial1.read();
        //Add the new character to the string, and increment the index variable.
        rxData[rxIndex++]=inChar;
      }
    }
  }
}

Your version of OBDuino.

Hi there and thanks for your time and effort testing the code, I very much appreciate it!

The protocol will be fixed for the moment as it will going on 1 particular car, but it would be good to make it "universal".

Would there be anyway of sharing your code with me at all?

Thanks.

Hi,

Any luck with the testing? Thanks man.

Here it is, much appreciated. Just gonna test RPM and speed for now.

Code:

//This is a character buffer that will store the data from the serial port
char rxData[20];
char rxIndex=0;

//Variables to hold the speed and RPM data.
int vehicleSpeed=0;
int vehicleRPM=0;

void setup(){

  Serial1.begin(9600);
  Serial.begin(9600);   //This is for the serial debug

  //Wait for a little while before sending the reset command to the OBD-II-UART
  delay(1500);
  //Reset the OBD-II-UART
  Serial1.print("ATWS\r");
  //Wait for a bit before starting to send commands after the reset.
 
  delay(1000);
 
  Serial1.print("ATDPN\r");  //Shows the protocol
  delay(1000);
 
  Serial1.print("0100\r"); 
  delay(2000);
 
  //Delete any data that may be in the serial port before we begin.
  Serial1.flush();

}


void loop(){
  //Delete any data that may be in the serial port before we begin. 
  Serial1.flush();

  Serial1.print("010D\r");    //Query the OBD-II-UART for the Vehicle Speed

  //Get the response from the OBD-II-UART board. We get two responses
  //because the OBD-II-UART echoes the command that is sent.
  //We want the data in the second response.
  getResponse();
  getResponse();

  //Convert the string data to an integer
  vehicleSpeed = strtol(&rxData[6],0,16);

  //Print the speed data to debug serial window
  Serial.print("SPEED: ");
  Serial.print(vehicleSpeed);
  Serial.print(" km/h");
  Serial.println(" ");
 
  delay(20);
 
  //Delete any data that may be left over in the serial port.
  Serial1.flush();

  //Query the OBD-II-UART for the Vehicle rpm
  Serial1.println("010C\r");
  //Get the response from the OBD-II-UART board
  getResponse();
  getResponse();
  //Convert the string data to an integer
  //NOTE: RPM data is two bytes long, and delivered in 1/4 RPM from the OBD-II-UART
  vehicleRPM = ((strtol(&rxData[6],0,16)*256)+strtol(&rxData[9],0,16))/4;

  //Print the rpm data to debug serial window
  Serial.print("RPM: ");
  Serial.print(vehicleRPM);
  Serial.println(" ");

  //Give the OBD bus a rest
  delay(50);
 
}



void getResponse(void){
  char inChar=0;
  //Keep reading characters until we get a carriage return
  while(inChar != '\r'){
    //If a character comes in on the serial port, we need to act on it.
    if(Serial1.available() > 0){
      //Start by checking if we've received the end of message character ('\r').
      if(Serial1.peek() == '\r'){
        //Clear the Serial buffer
        inChar=Serial1.read();
        //Put the end of string character on our data string
        rxData[rxIndex]='\0';
        //Reset the buffer index so that the next character goes back at the beginning of the string.
        rxIndex=0;
      }
      //If we didn't get the end of message character, just add the new character to the string.
      else{
        //Get the new character from the Serial port.
        inChar = Serial1.read();
        //Add the new character to the string, and increment the index variable.
        rxData[rxIndex++]=inChar;
      }
    }
  }
}

I won't be able to test until I find another car close to me, that's OBDII compatible.

Does the code look fine to you? Also will you be kind enough to test the code for me if you have access to the board/car? If not, don't worry.

Thanks.

This is what I tried next:

Code:

#include <LiquidCrystal.h>

LiquidCrystal lcd(26,28,30,32,34,36);

//This is a character buffer that will store the data from the serial port
char rxData[20];
char rxIndex=0;

//Variables to hold the speed and RPM data.
int vehicleSpeed=0;
int vehicleRPM=0;

void setup(){
  //Both the Serial LCD and the OBD-II-UART use 9600 bps.
  lcd.begin(4, 20);    

  Serial1.begin(9600);
//  Serial.begin(9600);
  
  //Clear the old data from the LCD.
  lcd.clear();
  
  //Put the speed header on the first row.

  lcd.print("Speed: ");

  //Put the RPM header on the second row.
  lcd.setCursor(0,1);
  lcd.print("RPM: ");

        lcd.setCursor(0,2);
        lcd.print("Coolant");
  
  //Wait for a little while before sending the reset command to the OBD-II-UART
  delay(1500);
  //Reset the OBD-II-UART
  Serial1.print("ATWS/r");
  //Wait for a bit before starting to send commands after the reset.
  delay(1000);
  
  Serial1.print("ATDPN/r");  //Shows the protocol
  delay(1000);
  
  Serial1.print("0100/r");  
  delay(2000);
  
  //Delete any data that may be in the serial port before we begin.
  Serial1.flush();
}


void loop(){
  //Delete any data that may be in the serial port before we begin.  
  Serial1.flush();
  //Set the cursor in the position where we want the speed data.

  //Clear out the old speed data, and reset the cursor position.
//  lcd.setCursor(10,0);
//  lcd.print("   ");

  //Query the OBD-II-UART for the Vehicle Speed
  Serial1.print("010D\r");
  //Get the response from the OBD-II-UART board. We get two responses
  //because the OBD-II-UART echoes the command that is sent.
  //We want the data in the second response.
  getResponse();
  getResponse();
  //Convert the string data to an integer
  vehicleSpeed = strtol(&rxData[6],0,16);
  //Print the speed data to the lcd
  lcd.setCursor(10,0);
  lcd.print(vehicleSpeed);
  

  
  lcd.setCursor(16,0);
  lcd.print("km/h");
  delay(100);
  
  //Delete any data that may be left over in the serial port.
  Serial1.flush();

  //Query the OBD-II-UART for the Vehicle rpm
  Serial1.print("010C\r");
  //Get the response from the OBD-II-UART board
  getResponse();
  getResponse();
  //Convert the string data to an integer
  //NOTE: RPM data is two bytes long, and delivered in 1/4 RPM from the OBD-II-UART
  vehicleRPM = ((strtol(&rxData[6],0,16)*256)+strtol(&rxData[9],0,16))/4;
  //Print the rpm data to the lcd
  lcd.setCursor(10,1);
  lcd.print(vehicleRPM);

  //Give the OBD bus a rest
  delay(100);

}



void getResponse(void){
  char inChar=0;
  //Keep reading characters until we get a carriage return
  while(inChar != '\r'){
    //If a character comes in on the serial port, we need to act on it.
    if(Serial1.available() > 0){
      //Start by checking if we've received the end of message character ('\r').
      if(Serial1.peek() == '\r'){
        //Clear the Serial buffer
        inChar=Serial1.read();
        //Put the end of string character on our data string
        rxData[rxIndex]='\0';
        //Reset the buffer index so that the next character goes back at the beginning of the string.
        rxIndex=0;
      }
      //If we didn't get the end of message character, just add the new character to the string.
      else{
        //Get the new character from the Serial port.
        inChar = Serial1.read();
        //Add the new character to the string, and increment the index variable.
        rxData[rxIndex++]=inChar;
      }
    }
  }
}

This is what I tested first:

Code:

#include <LiquidCrystal.h>

LiquidCrystal lcd(26,28,30,32,34,36);

//This is a character buffer that will store the data from the serial port
char rxData[20];
char rxIndex=0;

//Variables to hold the speed and RPM data.
int vehicleSpeed=0;
int vehicleRPM=0;

void setup(){
  //Both the Serial LCD and the OBD-II-UART use 9600 bps.
  lcd.begin(4, 20);   

  Serial1.begin(9600);
//  Serial.begin(9600);
 
  //Clear the old data from the LCD.
  lcd.clear();
 
  //Put the speed header on the first row.

  lcd.print("Speed: ");

  //Put the RPM header on the second row.
  lcd.setCursor(0,1);
  lcd.print("RPM: ");

  //Wait for a little while before sending the reset command to the OBD-II-UART
  delay(1500);
  //Reset the OBD-II-UART
  Serial1.print("ATZ\r");
  //Wait for a bit before starting to send commands after the reset.
 
  delay(2000);
 
  //Delete any data that may be in the serial port before we begin.
  Serial1.flush();
}


void loop(){
  //Delete any data that may be in the serial port before we begin. 
  Serial1.flush();
  //Set the cursor in the position where we want the speed data.

  //Clear out the old speed data, and reset the cursor position.
//  lcd.setCursor(10,0);
//  lcd.print("   ");

  //Query the OBD-II-UART for the Vehicle Speed
  Serial1.print("010D\r");
  //Get the response from the OBD-II-UART board. We get two responses
  //because the OBD-II-UART echoes the command that is sent.
  //We want the data in the second response.
  getResponse();
  getResponse();
  //Convert the string data to an integer
  vehicleSpeed = strtol(&rxData[6],0,16);
  //Print the speed data to the lcd
  lcd.setCursor(10,0);
  lcd.print(vehicleSpeed);
 

 
  lcd.setCursor(16,0);
  lcd.print("km/h");
  delay(100);
 
  //Delete any data that may be left over in the serial port.
  Serial1.flush();


  //Query the OBD-II-UART for the Vehicle rpm
  Serial1.print("010C\r");
  //Get the response from the OBD-II-UART board
  getResponse();
  getResponse();
  //Convert the string data to an integer
  //NOTE: RPM data is two bytes long, and delivered in 1/4 RPM from the OBD-II-UART
  vehicleRPM = ((strtol(&rxData[6],0,16)*256)+strtol(&rxData[9],0,16))/4;
  //Print the rpm data to the lcd
  lcd.setCursor(10,1);
  lcd.print(vehicleRPM);

  //Give the OBD bus a rest
  delay(100);
 

}



void getResponse(void){
  char inChar=0;
  //Keep reading characters until we get a carriage return
  while(inChar != '\r'){
    //If a character comes in on the serial port, we need to act on it.
    if(Serial1.available() > 0){
      //Start by checking if we've received the end of message character ('\r').
      if(Serial1.peek() == '\r'){
        //Clear the Serial buffer
        inChar=Serial1.read();
        //Put the end of string character on our data string
        rxData[rxIndex]='\0';
        //Reset the buffer index so that the next character goes back at the beginning of the string.
        rxIndex=0;
      }
      //If we didn't get the end of message character, just add the new character to the string.
      else{
        //Get the new character from the Serial port.
        inChar = Serial1.read();
        //Add the new character to the string, and increment the index variable.
        rxData[rxIndex++]=inChar;
      }
    }
  }
}