OBD-2 Question

Hi all!
I've built an OBD to SERIAL decoder using the schematics found on the ELM 320 Datasheet, i will link this to a pic by the serial port, but first i have to try it with a simple pc serial connection, i've a question for you before i proceed:

It's there a way to ruin the ECU of the car, if there's something wrong in the circut?
It's there a way to ruin the ECU of the car by the OBD port?

What do i have to check and re-check again before plugging the cable in the obd, and before i'll connect the ELM320 to the PC/PIC ?

Thank you!

Luca

P.S. I don't want to burn my ECU!!!

Quote:

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Originally Posted by oslinux

Hi all!
I've built an OBD to SERIAL decoder using the schematics found on the ELM 320 Datasheet, i will link this to a pic by the serial port, but first i have to try it with a simple pc serial connection, i've a question for you before i proceed:
It's there a way to ruin the ECU of the car, if there's something wrong in the circut?
It's there a way to ruin the ECU of the car by the OBD port?
What do i have to check and re-check again before plugging the cable in the obd, and before i'll connect the ELM320 to the PC/PIC ?
Thank you!
Luca
P.S. I don't want to burn my ECU!!!

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Nobody wants to fry an ECU, and I asked myself that same question before I plugged in my ELM327 circuit to all my vehicles...
A vehicle's ECM and OBDII port and all that related circuitry are pretty robust, meaning they can handle a lot of stuff thrown at it, shorts, opens, power on a grounds, grounds on a powers, power on a signals, ground on a signal, signals shorted to other signals...etc...
As long as you don't start throwing 120VAC into anything and stay with good ol' 5v logic, I'd say that no matter what you can possibly mess up, your ECU will survive a decent screw up on your part (at least mine did with me! shorted 12v line to ground once, blew fuse, ECU lived, grounded out J1850 bus, lived, put straight 12v on a K-line, lived, haven't killed anything yet).

I have a lot of experience with OBDII, and I agree with skimask. Have fun!

ok! i'm about to fry my ECU :D

Just Joking, i hope :D

Thank you for your answers!

Luca

Quote:

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Originally Posted by oslinux

ok! i'm about to fry my ECU :D

Just Joking, i hope :D

Thank you for your answers!

Luca

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Just curious...
Are you using J1962 cable/connector or did you tap into the wiring itself?
I did it both ways; one car I clipped the wiring behind the connector and plugged in a standard DB9 connector, another one I went with a USB connector. Someday I'll decide on one method...

i used the cable, then the DB9 connector, the news are:

It works!

and well too!

Now i'm building the pic circuit, but i found it pretty easy to do, i'm planning to use the usb port of the pic (18F4550) to communicate with a pc (Using a software made by me),
Now i've just two questions:

1. where i can find codes to communicate with the car and read the sensors?
2. what software do you suggest to use with the pc connected directly to the serial port? (FreeWare is good, Open Source is better!)

Thank you!

Luca

Technically you would need the SAE standard for the codes. However there are a number of websites that will give you the basic OBDII commands.

As far as software, go to scantool.net and use their opensource software. If you look through their code you will find most of the OBDII commands.

1 - www.google.com that was my prime source
2 - self designed PCB, PIC driven, buttons, LCD, etc..., no PC required but USB downloading from datalog memory in the works...

I'm building too a controller with a pic 18F4550, LCD 4*20 White on Black, buttons to show RPM/Coolant Temp/others and an eeprom, to test it i've coded a pic16f84 to emulate the ELM, it's cool :D

in my car (Ford KA) i don't even have the RPM counter, so this will be somewhat useful for the driver.

for the pids, i found them in wikipedia, but they says that there are more modes above #9, from the vehicle manufactures, it's possible to get the additional pids for ford in the net?

Luca

Quote:

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Originally Posted by oslinux

for the pids, i found them in wikipedia, but they says that there are more modes above #9, from the vehicle manufactures, it's possible to get the additional pids for ford in the net?
Luca

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The big question is 'is it possible to get all the PIDs for all the vehicles out there without paying an arm and a leg'?
With the new CAN bus out there, you can control anything thru it apparently.