capture/repeat data ?

[Sam]

Hey DynamoBen,

"It sounds like OBDII VPW"

I'm 99% sure that it is.

Thanks alot, I just hooked my old laptop serial input to the vehicle data line and ground (RX to data line and Ground to vehicle ground). I used fogsoft serial recorder to record the unlock and that worked. It recorded a line that appears to be ASCII ???

I'll check out the links you posted. Is it possible to use the laptop to TX this recorded data back to the vehicle's data wire? (Just to see it work)

Thanks again!

[DynamoBen]

If it truly is VPW what you did shouldn't have worked. With VPW pulses are a specific width and occur on either the +7 side or 0. It alternates High Low and the length of time gives you the data bit either 0 or 1. It should not show up as ASCII, although the computer may think it is. What voltage is the line? VPW is around 7V according to the spec. If it is VPW, and I'm 99.9% sure it is, then you would need to have the serial to VPW convert chip that elm makes to transmit and receive messages.

You may also want to check out Serial Device Check, its what I use:
http://www.hackconsulting.com/download.html

[Sam]

Hi,

I really appreciate all your help here! So do you think that this http://www.scantool.net/products/pro...products_id=12 will allow me to Rx and Tx to the data wire?

And then can I use the serial data gathered in this way to program a PIC to send the serial data onto the data wire based on input events I choose ?

As for what voltage is on the data wire, I'm not sure, I used a LED with a 1k res inline and it would flash when data was sent. I also used a 4n25 opto to isolate the laptop but this would not work even though the opto was definatley working correctly, so I then connected direct from the data wire to the RX input on the db9 and that's when I got the (ASCII ???).

Thank you very much.

[DynamoBen]

There are a couple of ways to do this. If you a multiple vehicles you may want to spend the extra money and get the below item to do your project testing, plus you can use it with the Scantool software and check diagnostic code on your vehicles.

http://www.scantool.net/products/pro...70eb642cf18b25

However if you have just the one vehicle the product you selected would work great. I have all five of the receivers that Elm makes. The ELM327 mentioned above replaces the ELM320-323. It does VPW, PWM, ISO, and CAN (this is new) which is the new automotive standard. The upshot with the ELM327 is that it has a standard TTL output mode, but outputs ASCII and is large compared to the ELM322. The advantage to the ELM322 is its size and it has a “packet mode” (not ASCII) option, but the TX on the chip is inverted from and needs to be “flipped” with external hardware or via software. (see datasheet)

The beauty of the elm chips is they handle the CRC, and buss timing for you. They also have packet filtering options, so you only are presented with the packets you want to see and not those that you don't. I interface the ELM chips via the onboard UART in the pic and handle everything with interrupts. (see instant interrupts thread)

Once testing is complete, you can integrate the elm chip into your final circuit board. You should be able to Tx/Rx on the line. The hard part will be deciphering the packet and setting up the ELM chip to spoof other devices. It is really designed to act like a diagnostics tool, but it may very well work for what you’re doing. I do have many of the SAE documents that I use for deciphering; however, they are $50 each. Some creative googleing may uncover the info you are looking for. I may also be of some assistance.

I have used the ELM chips for years and love them!

[Sam]

I'm going to order the chip:http://www.scantool.net/products/pro...&products_id=8

And I'll make the pcb myself with this: ElmScan VPW Schematic/PCB 1.0/A

And then use their s/w if you think I need anything else, please advise.

I'm going to mainly use this with a 2003 Chevy Avalanche so I hope that it is the vpw that I need. I was really hoping to record the actual data from the vehicle in serial form which I think you are saying this will do it, and prog that data into the PIC and have the PIC TX it with SEROUT.Would I still need the ELM chip in the circuit in order for this to communicate with the data bus ?

The actual data I refer to is say,what is produced on the data bus only when one button is pushed. Is all this reasonable?

Thanks again!

[DynamoBen]

You will need to use the 2.0 PCB, not 1.0.
NOTE: the schematic uses a 9.1V transistor, which could be difficult to find.

http://www.scantool.net/download/elmvpw20.pdf

You can check your vehicle to find out what data type it uses with the following link:

http://www.elmelectronics.com/obdstandard.html

On the ELM322 there is a mode called "Monitor All." Launch hyperterm and turn this mode on. Then hit the buttons you are interested in; any data on the line will show up in hyperterm.

Once you have that info that should give you an idea of what a packet looks like. There are a couple of things about the packet you need to know, for example addressing scheme of the packets. (physical or functional) I can help once you have an example of a data packet.

It would be worthwhile to grab the datasheet for the ELM322, and read it through. It’s written with hobbyists in mind and talks about all the different ways the chip can be configured. Its geared toward reading the cars ECU but you can read between the lines.

Will this work? It’s hard to say for sure until you have captured a packet. I think it should work fine; it will however take some creativity on your behalf. You don't need the chip to communicate on the buss, but it will make it a lot easier. If you don't use the chip your pic will need to deal with all the timing parameters for VPW and the CRC encoding and decoding. (not fun...not easy!)

[DynamoBen]

Here is the ELM322 board that I built based on their schematic and PCB.

Two things to note:

First is that I used a DB9 instead of the DB25. (personal choice)
Second I built a DB9-->Clips adapter for testing. You may want to do the same. (all Radio Shack parts)

If you want to use it for automotive diagnostics you will need to order the cable from scantool.net when you order the chip.