Hardwire usb cable to ecu?

[tekgnosis]

rather than plug the tactrix cable in everytime i want to tune or log, is there a way that I can just splice into the ecu wires for the obdii port and have a connector under the glove box?

this option is a lot cleaner, and means I don't have to have the cable running across my lap.

i've looked at the old schematic that was posted...i'm no expert with circuits, but would it be possible to just build my own module and splice it into the ecu? it looks like the majority of the board is for converting the signal from serial to usb. can i build my own board instead of buying the tactrix cable?

i've searched up and down, but found no answer.

[Freon]

I'm not sure how much simpler the board would be if you were interfacing to a physical serial port on your PC. From what I understand it isn't just splicing wires directly to an RS232 DB9 cable.

Why not just unscrew your OBD connector, plug in your Openport cable, tape them together, and tuck the bundle up under the dash with some zip ties? This seems to be a much smarter idea. You can put it back if you want, but it is still out of the way. You can route the cable to the glove box or whatever you want.

[tekgnosis]

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.

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.

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? I just think it'd look pimp having a female/male usb plug flush mounted to the glove box. I could even make it a double USB plug so that I can connect my iPod for charging (sony deck stuff).

[richh]

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!

[Evo4Mad]

The Laptop RS232 UART Serial Port... is NOT up to the job

1) PC serial ports can only do about a handful of different baudrate speeds... none of the required baudrate speeds by the ECU
(I know I tried even 3% speed difference and it doesn't work)

2) PC serial ports operate at the Wrong voltage levels (serial: -5 +5v) car needs (0v +12v)

[tekgnosis]

Cool, thanks for the info guys.

I think I'll buy the tactrix cable, buy another OBDII male plug, wire THAT port into the existing harness, plug the tactrix into the new port, and have it run behind the dash so that I still have the fancy USB port

[richh]

There's really not a lot of point buying the second male OBDII socket and hooking it up alongside the existing one, as you can't run connect two ISO interfaces in parallel.

In other words, if you're thinking of leaving the OpenPort permanently wired and still have the original connector free when you take the car in the shop to have it serviced, you're still gonna have to fish about behind the dash to connect the OpenPort from socket #1 before socket #0 will work.

Pulling the existing connector out of the moulding and taping it up is just sooooo much easier. You can still hardwire the Tactrix cable to a USB header on your dash, that's a totally separate issue