Sending bus commands

[HOYS]

Hey all, new here but trying to figure some stuff out, not 100% related to hacking the NVRAM of a Delco ECU, but somewhat related.

I'm working on controlling a GM IPC standalone without an ECU. I am trying to emulate the J1850 bus commands that are sent to the ECU over the Class 2 data line to make the instrument panel work outside of the vehicle on a test bench. This is mainly for a racing simulator so I can have I real dashboard in front of me. I have a '06 Trail Blazer SS IPC and an Arduino Uno at my disposal at the moment.

I was wondering if it is possible to just "send" hex values addressing the IPC over a generic UART line to have the IPC react. I understand a bit about how J1850 works and am trying to get some more information/documentation. (I love reading )

If you guys have any input/suggestions I would love to hear them! Thanks a bunch!

[VL400]

Thats a pretty neat project Its possible the cluster is just another OBD-II device and uses the same standard PIDs (http://en.wikipedia.org/wiki/OBD-II_PIDs). What the device ID is of the cluster will take a bit of searching, would be easier if you could listen to the bus of a complete vehicle.

Should be able to use the arduino to send commands, here is an example interface using an AVR .. http://www.mictronics.de/projects/j1850-vpw-interface/

[HOYS]

What would be the best way to listen to the bus traffic? Eventually I am trying to make this work on other GM IPCs and I have the complete cars available to check along with a slew of PCMs to bench test.

I have a basic understanding of the ECUs innerworkings (thanks to you guys!) And would really like to see this get off the ground.

[VL400]

Would need to build/buy and OBD-II interface and find a similar vehicle to connect to and get some data from.

[HOYS]

I have at my disposal HPTuners and a cheap eBay code scanner.

I was looking at using a Bus Pirate (https://www.adafruit.com/products/237) to sniff the data transmission lines.

Any suggestions for a device?

[antus]

bus pirate looks ineresting, but doesnt appear to handle high enough voltages directly. You would need to add some extra hardware in front of it, something like this project: http://www.mictronics.de/projects/j1850-vpw-interface/ or the optical isolation in this project http://www.nerdkits.com/videos/obdii/

according to this document http://shieldedpair.net/BAE5030/Lecture ... uction.pdf VPW high is typically 7v, but can be as high as 20.

An elm327 interface from ebay can talk vpw and is cheap, but I really dont like the protocol. You cant just send and receive what you want, you need to set up headers seperatly to sending the data frame, and the length of the receive packets is quite short. It would be capable of what you want though.

There is a need of a low cost vpw interface that can handle large packets (> 1kb) and can switch to vpw 4x speed for vehicle programming purposes. If you were to build your own, document it publically and/or sell it cheaply and if it could send and receive whole packets at vpw 1x and 4x it would get very interesting around here.

[HOYS]

There is a need of a low cost vpw interface that can handle large packets (> 1kb) and can switch to vpw 4x speed for vehicle programming purposes. If you were to build your own, document it publically and/or sell it cheaply and if it could send and receive whole packets at vpw 1x and 4x it would get very interesting around here.

Honestly this is the final goal of my project. Not relying on HPTuners limited support of the cars I normally work on (V6 GM engines) and high prices of one off rare combination cars (5.3L LS4 W-Bodies...300 bucks for an unlimited liscense of ONE model/year, so a 2008 Pontiac Grand Prix GXP ONLY not 07s or 09s or Montes or Impalas).

I'd easily say that we are at the point where this stuff can be done DIY.

...Back on track...

So what would my next step be? I have a bit of funding behind me from an aftermarket parts provider to get this project going ASAP. I also have access to SAE documentation through my university so within a week or so I should be able to get all the SAE books I need ...for free .

I am going to build the VPW Interface linked a few times here and see where I can go with that. Any other ideas?

[antus]

I am going to build the VPW Interface linked a few times here and see where I can go with that. Any other ideas?

That sounds good. If you can then create a better protocol for it, and add vpw 4x support we'll be laughing.

[charlay86]

I was thinking about attempting to make an interface too and was thinking that something like this http://www.freetronics.com/collections/ ... L1EFIaOwhQ might be a good candidate as the micro has built in USB support. Probably wouldn't use the arduino tools to write the code in though...

[HOYS]

Honestly I'm focused on just commanding the IPC for the moment. If that project gets off the ground I'll have a bigger green light for more complicated projects.

Also if I was to make a standalone programmer type interface in the future, I'd make a custom PCB for it. I'm really trying to stick to the AVR interface to accomplish all of this if possible because of its now widespread use in the "hacking" community. I'm looking into other processors like the MSP line from TI and ST's new line of decently priced dev kits with a few samples on the way.

A built in programmer for the processor would be great and if that was an end goal I would look into using an ARM processor...I'm just not very well versed in those.