mgswed

Hi all, I have a 2004 Jeep Grand Cherokee. I am trying to figure out how to use the PCI Bus connection on the back of my rbk radio. Does anyone know what type of info is coming off this and/or on what protocol. I think ive heard this called OBDII. Thanks for any help. -MG

michbound

The PCI bus is essentially a superset of J1850 VPW protocol. You should be able to monitor the bus and see what info you can get from it.

If you have remote volume up down control's on the steering wheel hit those while monitoring the bus and you can identify the command that get's sent. This should help track down the "ID" for the radio module and then you can just monitor all messages for that particular ID.

Paul
www.obdpros.com

mgswed

Thanks michbound. So, I have been reading that i can convert the signal to rs232 using the elm322. I am looking at a schematic at http://pinouts.ru/Converters/obdii_cables_pinout.shtml, its the middle schematic. Do i really need that whole circuit. From the radio, I have one pin that says pci bus. Can I just power the chip with five volts and a cap between pin 1 and 8 to ground. Plus the oscillator sub circuit and then feed the signal through pin 4 and send it to where I need to go from pin 6. I dont need to write to the bus at all. Thanks for all you help. -MG

michbound

Yes you will need the entire circuit, the voltage levels on the BUS are more than 5 volts so the glue circuitry takes care of shifting levels and is required.

Depending on what your time is worth it might be cheaper for you to just buy a ready made OBD II scantool. This might sound selfserving, but by the time you obtain all the parts and verify debug the circuit you will end up spending more than the $ 85 that it would cost to get a unit that reads all the protocols. (www.obdpros.com)

You do not have to plug into the bus at the radio itself. You can directly hook up to the OBDII connector since the J1850 bus is brought out to the DLC.

Paul
www.obdpros.com

mgswed

Thank you for all your help Paul while i try to understand this stuff. I should say I am not building a car scanner. I am building a custom ipod interface to the cd changer side of the radio. On the radio (rbk unit) there is a pci bus pin. This I am assuming will give me all my signals for next and previous song, fast forward and reverse, and more to control the Ipod. I just want those signals. Now my custom circuit has the elm chip, 12 volt rails, 5 volt rails, and 3.3 volt rails. I just want to take the signal from the radio pci bus pin and send it through whatever circuit for the elm and send the output (hopefully rs232) to the pic microcontroller in my circuit. Is this possible and why do you think it would cost so much to do? What is any of the circuit can I disregard? And I am not writing anything to the PCI bus. Thanks again. -MG

michbound

Since I do not know your level of experience with electronics and your question about what part to eliminate I assumed you were relatively inexperienced with electronics.

Depending on your experience I would assume you would need anywhere from 4-16 hours to build the circuit so parts approx $ 25.00 plus if you consider your time to be worth $ 20/hr you are at $105 even in the fastest case, now if this is a learning excercise it would be fun so go nuts

As far as the part of circuit that you could eliminate, now that you mention you are interfacing to a micro you could eliminate the RS232 level shifter since you only need TTL levels to your PIC. You could also eliminate the
driver circuitry on PIN 7 that is the OBD out signal, check the ELM322 datasheet it shows what the pin functions are that will help you understand a bit better.

Paul
www.obdpros.com

mgswed

So are you saying that the signal coming out of the radio "PCI Bus" is a TTL signal. If this is true then its great. I wont need to do anything to the signal. However I dont think this is true. Sorry if im frustrating you. I dont have much experience with OBDII. I dont know if i made my intentions clear. I need to take the OBDII signal to interface it with a PIC chip. I thought the the ELM chip would convert the PCI (OBDII) to rs232 which is acceptable by the PIC chip. Is there another simple circuit that can convert to PIC language. Thanks, -MG

mgswed

Anyone have any ideas. Thanks, -MG

chewwtoy

MG,

I think this project has potential. I'm not too much into the electronics as far as the physical layer of the network, however it's very possible that the switch inputs from the radio are NOT available on the PCI bus. Double check first before you invest too much time and money that the radio switches are sent out across the vehicle's PCI bus. It's important to note that not all switches need to be sent out as signals on the bus. The only reason some of them are is because the information needs to be shared with another ECU or module on the vehicle network. So I would be surprised if the fast forward and rewind button presses are a part of the vehicle network. But I'm not familiar with this vehicle's network.

mgswed

Thanks for the info chewwtoy. The only reason why I believe the commands like fast forward and rewind etc are sent across the PCI bus is because thats the way the radio talks to the cd changer. This is the way i wish to implement (throught the changer interface). One new thing I found out is that I have to trick the radio in thinking my ipod is a cd changer. I havent had much time to work on it but, I am still gathering information. My next step is to call Jeep and see if I can get any technical assistance. -MG

underwaterdan

I am going to bring this back to life... and ask if you have had any luck with this!?

mgswed

Hi underwaterdan, I havent had time since going back to school. I am done in April so I will be back at it then, maybe sooner if I find any available time. -MG