tekgnosis wrote:I agree that there are easier ways
For simplicity's sake, I was just wanting to tap into the wires and get away with not having to buy the cable.
You can't connect directly across from the ECU's datastream to a USB port, or indeed an RS232 port for that matter. The electrical levels are different, and the ECU uses a single line for both Tx and Rx.
You don't
have to buy the Tactrix cable but you need an interface of some description. If all you want to do is datalog, then pretty much any ISO9141-2 compatible interface design will work. both commercial and DIY. If you want to flash though you'll need that "extra 12V", and that's where the Tactrix cable has it all covered out of the box.
I'll have to dig deeper into the cable to make sure it's just converting the signal from rs232 into usb. I believe there was an extra 12V pin or something along those lines.
The OpenPort cable translates from USB to RS232, and from there to the ISO9141 K-line standard used by the ECU. Whatever you make will have to accomplish both tasks.
The "extra 12V" is the flash enable. You don't need this to datalog, but you do to flash.
Bottom line: without buying the cable and ghetto rigging it under the dash, is there a way to buy my own chip(s) and wire this myself?
Sure. Look elsewhere on the forums and you'll see a number of ways to do it. It can be as simple as two IC's plus a couple of discrete components if logging is all you want.
As the other guys have said though, trying to re-invent the wheel seems a little pointless if all you want to do is get the cable away from your legs. Easiest option is just to dismount the OBDII socket from the under-dash moulding and secure it up inside with the OpenPort permanently plugged into it.
If you want a USB port all neat in your dashboard, you can do that easily enough just by making up an extension cable and mounting the USB socket wherever in the car you want!