capture/repeat data ?

[paul borgmeier]

YES (you haven't given much detail so it is hard to answer in more detail - what are you trying to do?

[Sam]

Thanks Paul,

What I would like to do is to be able to record a part of the data sent in my GM vehicle when, for example, you press window down and be able to repeat that at any time. Such as when I press window down on the driver door, it would also make all the windows go down. This is just an example.

GM uses one data wire running to all modules, when you press passenger window down, it sends data on this wire to the module in the passenger door, this module then activates the window motor. As far as I can determine, the data is called Class II and is sent at approx. 10.4 kbs.

I've hooked my o-scope up to this wire and can see the data sent.

Thank you

[DynamoBen]

It sounds like OBDII VPW.

You may want to think about getting an OBDII to Serial converter and testing with a PC first. I have made several interfaces between these networks and pics. I find it easier to use a converter chip instead of dealing with the protocol myself.

Check out the following for more information.

This company makes the OBDII to serial chips:
www.elmelectronics.com

This company makes assembled units but also publishes pcb's and schematics for personal use:
www.scantool.net

If you want to do it yourself onboard, read the following it talks about VPW and all of its timing requirements:
http://www.circuitcellar.com/adverti...auge%20fuel%22

Let me know if you have more questions.

[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!