VT ALDL to OBD2

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VT ALDL to OBD2

Postby DaBell » Fri Dec 18, 2015 7:52 pm

I'm new to this forum. I'm a retired component level electronic technician with many years experience in SCADA (Supervisory Control and Data Acquisition). In the SCADA field I did protocol analysis programing and troubleshooting.
My 1990 Buick Reatta has a very nice digital Instrument Cluster and digital Driver's Information Center (this in a complete OBD error code reader with the capability of testing various engine components and inserting values in tables), but only 165 HP and a non-electronic controlled transmission. I have obtained a salvage 2006 Chevrolet Impala SS with a 5.3 liter V8 and an electronic controlled transmission. I need to make the different control systems talk to each other.
I understand the possibly VT version ALDL runs at 8.192K using 2's complement parity, while the OBD2 system operates at 10.4K with CRC error correction and Asynchronous collision detection.
Is it possible to make a network bridge between the two systems using a single microcontroller, or a dual microcontroller? Something along the line of a bi-directional store, convert, and forward modem.
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Re: VT ALDL to OBD2

Postby Jayme » Sat Dec 19, 2015 6:50 am

definitely possible. the VT for example has a module called a PIM, which essentially reads the OBD2 PID's it needs from the ls1 PCM (such as coolant temp, Inlet air temp, Check engine light status) , and stores the values, then constructs an ALDL packet from those values and forwards it to the dash, which speaks ALDL only. I dont see why you couldnt do the same with an arduino, a ELM327 and an ALDL comms circuit. its be jsut a matter of writing the code to store, convert and forward the values. of course you would need to fully map out each byte the dash needs first.

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Re: VT ALDL to OBD2

Postby antus » Sun Dec 20, 2015 2:44 pm

As Jayme says, possible. Worth the effort? Your call. Probably base your hardware around something like this http://www.mictronics.de/projects/j1850-vpw-interface/ but with a newer and more capable cpu and use uart serial, with the diode and resistor method fof converting standard UART serial to ALDL. Once you've done that map the two protocols together and write up a control loop to pull data from one side and push out to the other. You can probably find most of the information you need about the aldl protocol and vpw (is the obd2 variant VPW?) from the adx files on this forum to figure it all out. We dont have the 1990 Buick Reatta covered though so you'll need to see if you can find any data definitions for that elsewhere.
Have you read the FAQ? For lots of information and links to significant threads see here: viewtopic.php?f=7&t=1396

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Re: VT ALDL to OBD2

Postby DaBell » Mon Dec 21, 2015 3:44 am

Jayme and Antus,
Thank you both for your suggestions. It is unexpectedly nice to find talented people on a Website like this. I've been pondering things since I learned that the 2006 Pontiac donor car I purchased was using an integrated network of both OBD2 and CAN which adds another whole level of complexity to the project. IE: OBD2 output from the Theft deterrent exciter module is required to start the car. The data is sent to the BCM and Instrument Cluster. The BCM translates it to CAN and sends it to the ECM. I didn't trace it beyond this, but I'm beginning to feel integrating OBD1 and OBD2 isn't worth the trouble. The Northstar Engine was used with OBD1, and I found an OBD1 Heads Up Display, and so I'm likely just to go that way. I'm sure far less aspirin will be involved.
Again It's a great Forum with very knowledgeable and helpful members!
DaBell

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